ALBERT

Description: 〈p〉Publication date: Available online 3 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Jingxi Liu, Bo Xu, Lei Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Gravity assist is widely applied in the deep space exploration because of its reliability and practicability. There are lots of research in the literature about the nearly coplanar situations. In this work, a three-dimensional model of gravity assist model is developed in a semi-analytical manner on the basis of the geometry relationship between the parameters of spacecraft before gravity assist and the orbital elements after gravity assist. The parameters include 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si278.svg"〉〈mrow〉〈msubsup〉〈mrow〉〈mi mathvariant="bold-italic"〉V〈/mi〉〈/mrow〉〈mrow〉〈mi〉∞〈/mi〉〈/mrow〉〈mrow〉〈mtext〉in〈/mtext〉〈/mrow〉〈/msubsup〉〈/mrow〉〈/math〉 (the hyperbolic excess velocity vector of the spacecraft before fly-by), 〈em〉H〈/em〉 (the height of fly-by) and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si279.svg"〉〈mrow〉〈mi〉θ〈/mi〉〈/mrow〉〈/math〉 (the dihedral angle between approach plane and fly-by plane). These equations can be used for analyzing the change of orbital elements in the process of gravity assist, discussing the influence of different parameters on them and deriving the condition that remains the semi-major axis unchanged. Curve fitting of the feasible region boundary of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si280.svg"〉〈mrow〉〈mi mathvariant="normal"〉Δ〈/mi〉〈mi〉i〈/mi〉〈/mrow〉〈/math〉 and contour plot of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si281.svg"〉〈mrow〉〈mi mathvariant="normal"〉Δ〈/mi〉〈mi〉i〈/mi〉〈/mrow〉〈/math〉 are utilized to analyze the pattern of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si282.svg"〉〈mrow〉〈mi mathvariant="normal"〉Δ〈/mi〉〈mi〉i〈/mi〉〈/mrow〉〈/math〉 changing with different parameters. This method is a valuable reference for designing gravity assist trajectories to high inclination targets in the Solar system.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 1 July 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): N.Y. Zaalov, E.V. Moskaleva〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper describes a study of the daily and yearly variability of one of the main characteristics of sporadic E layers (Es), the critical frequency (foEs). Our analysis is based on ionograms recorded by GIRO network ionosondes. The study estimates the spatial and temporal variability of the Es layer parameters and generates their statistics at different seasons and phases of the solar cycle. In turn, the statistics of the Es layer parameters can provide an assessment of the capability of the HF propagation forecasting. Further, maps of the distribution of Es layer critical frequency are produced. This paper implements the “cloud” model of Es layer in HF propagation model (Northern Ionosphere Model & Ray Tracing, NIM-RT) that can accurately reproduce many features observed in experimental measurements. Within this framework, a number of vertical sounding ionograms with the presence of Es layer are simulated based on the NIM-RT software.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 21 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): S.S. Rao, Monti Chakraborty, R. Pandey, A.K. Singh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this research work, we have analyzed the data of critical frequency of the F〈sub〉2〈/sub〉 region ionosphere over southern low latitude station COCO (Keeling) Island (Geog. Lat. 12.20⁰S; Geomag. Lat. 22.83⁰S; Geog. Long. 96.80⁰E) for the period 2009-2013 and result thereof have compared with the IRI-2016 model. Our analysis shows a good correlation between variations in 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 and solar flux at F10.7 cm wavelength. With concern to geomagnetic activity during the period 2009-2013, it has found that the variability in the monthly mean Ap index remained below 20 nT throughout the period 2009-2013. Concerning quiet time F〈sub〉2〈/sub〉 region variability, our results explicated the solar cycle, semiannual, and seasonal/annual variation in 〈em〉fo〈/em〉F〈sub〉2〈/sub〉. Similar oscillations in 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 have been explored using the Lomb-Scargle Periodogram technique. We have also observed the fundamental mode (27 days) and its overtones (9 and 13-day) in the geomagnetic activity parameter (Ap). Analysis of 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 showed the consistent presence of the semiannual anomaly and absence of the winter anomaly during the ascending phase of solar cycle-24. A presence of an annual component in normalized 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 has been examined using regression analysis. A comparative study of ionosonde observed 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 with IRI-2016 modeled 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 showed that the general ionospheric trends in IRI predictions are consonant with the observations for the diurnal, seasonal, and solar cycle variation. However, a deviation in the amplitude of 〈em〉fo〈/em〉F〈sub〉2〈/sub〉 up to the order of 5 MHz depending upon local time, seasons, and phases of the solar cycle has observed.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 20 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Mohammad Javad Kalaee, Yuto Katoh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We consider the equatorial region of the magnetosphere, where the magnetic field is perpendicular (or near to perpendicular) to the density gradient and mode conversion process from UH to LO-mode waves or reverse process are expected. We review and study the mode conversion from UH (upper hybrid) to LO (left hand polarized ordinary) mode waves by a spatially two dimensional plasma fluid code. Several simulations with different initial wave vectors under the same background plasma condition have been performed. We focus on the conversion efficiency from the UH-mode waves with purely perpendicular wave normal angle to the LO-mode waves, since one of the source of generation UH wave can be Bernstein mode as the purely perpendicular electrostatic waves. For this special case, the UH wave normal is kept in perpendicular direction with respect to the magnetic field, and difficult to be in matching direction for conversion to LO mode〈em〉.〈/em〉 Simulation results show that the mode conversion efficiency in this particular case is very weak, since two branches of Z-mode wave and LO mode wave in the dispersion relation are disconnected. We present a discussion to show that for this case (purely perpendicular propagation) a special angle (except 90 degrees), between the magnetic field and the density gradient is necessary for occurrence of efficient mode conversion. For the case (purely perpendicular propagation and the magnetic field perpendicular to the density gradient), the mode conversion just occurred via the tunneling effect, where a steepness of the inhomogeneity plays an essential role.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 1 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Yanguang Fu, Xinghua Zhou, Dongxu Zhou, Jie Li, Wanjun Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Sea level variability in the South China Sea (SCS) was investigated by means of satellite altimetry and tide gauge data over a 24 years period 1993–2016. The sea level anomalies (SLAs) retrieved from satellite and tide gauge data were compared. The differences between the two datasets showed a normal distribution with 87% within ±10 cm. Considering the individual time series, the results revealed that satellite and tide gauge SLAs are in good agreement, with root mean square deviations in the range 0.9–9.9 cm (average value is 2.7 cm), and correlation coefficients exceeding 0.7 for 85% of stations. Positive linear trends of sea level were estimated for both datasets, with good agreement in most cases. The averaged linear trend of SLAs in the SCS showed a rise of 4.4±0.3 mm year〈sup〉–1〈/sup〉 during 1993–2016, consistent with the nonlinear trend of satellite and tide gauge (4.3±0.3 and 3.9±0.1 mm year〈sup〉–1〈/sup〉, respectively) extracted through empirical mode decomposition.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 13 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Pascal Willis〈/p〉

Description: 〈p〉Publication date: 15 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 64, Issue 6〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: 15 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 64, Issue 6〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: Available online 7 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Kaishi Zhang, Wenhai Jiao, Liang Wang, Zishen Li, Jianwen Li, Kai Zhou〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Global Navigation Satellite System (GNSS), once dedicated to military and geodetic applications, is entering civilian life with the development of low-cost internal multi-GNSS chips in mass-market smart devices. The recently enabled Application Programming Interface (API) to GNSS raw measurement in Android Nougat operating system, make it possible to implement precise positioning technology on Android smart devices, such as Real-Time Kinematic Positioning (RTK) and Precise Point Positioning (PPP). An optimized kinematic positioning approach on Android smart devices with Doppler-Smoothed-Code (DSC) filter and Constant Acceleration (CA) model is assessed in this paper. In this optimized approach, DSC filter is used to reduce the code measurement noise, which is extremely high on smart devices and CA model is used to accurately predict the kinematic state of smart devices. The optimized approach is named Smart-RTK for its applicability to smart devices, respectively. The performance of the Smart-RTK approach is validated by two Google/HTC Nexus 9 tablets separately under stationary, walking, and vehicular condition. The numerical experiments show the significant improvement on positioning accuracy and continuity. The positioning Root Mean Square Error (RMSE) in horizontal component reaches about 0.3–0.6 m in stationary condition and 0.4–0.7 m in walking condition, improved by about 85% compared with that of chipset original solutions. In the subsequent vehicular experiment, the horizontal positioning RMSE is about 0.85 m, 50% better than that of chipset solutions.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 6 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Prabhakar Tiwari, Navin Parihar, Adarsh Dube, Rajesh Singh, S. Sripathi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this study we present the behaviour of sporadic E-layer during a total solar eclipse (TSE) which occurred during the dawn/sunrise hours over a site located in the path of totality. A Canadian Advanced Digital Ionosonde (CADI) was operated at Allahabad (25.4° N, 81.9° E), a low latitude station located near the crest of equatorial ionization anomaly (EIA) in the Indian subcontinent to study the ionospheric effects of 22 July 2009 TSE. Corresponding to the eclipse period, a gradual increase of ftEs (top frequency of Es layer) in the 4–5 MHz range was seen on the control days. On 22 July (the TSE day), correlated changes in ftEs coinciding with the TSE progression was noted – (i) sharp decrease near first and second contact of TSE, (ii) an increase after first and second contact, and (iii) wavelike fluctuations in ftEs variation during eclipse hours and beyond. Much higher ftEs values were noted during the TSE hours in comparison to that seen on usual days. Strong blanketing Es layer developed during the TSE hours and persisted for slightly longer duration than its usual occurrence time. Near the TSE totality, slight lowering of the base height of Es layer was also noted.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 19 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Jianfeng Duan, Zhaokui Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The 〈strong〉Magpie Bridge〈/strong〉 mission is a part of the Chang’E-4 mission, it is the first Chinese spacecraft carries out Earth-Moon communication mission at Earth-Moon libration points. The 〈strong〉Magpie Bridge〈/strong〉 operations team utilizes the Beijing Aerospace Control Center (BACC) Orbit Determination and Analysis Software (BODAS) to obtain the orbit, the measurements include range, Doppler and relay, relay-rate from China Deep Space Network (CDSN) and Very Long Baseline Interferometry (VLBI) system respectively. In order to effectively improve the accuracy of the orbit, we provided the solar radiation model with multiple characteristic surfaces. The new model is based on the structure and the real-time attitude of the satellite to solve the real-time solar pressure equivalent area. Compared with the cannon-ball model, it can calculate the solar pressure equivalent area of the satellite more accurately in orbit determination. By the analysis of the tracking measurement data, we found that the new solar radiation pressure model reduces the error of position and velocity compared to the cannon-ball model.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 19 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Mohammadreza Saghamanesh, Ehsan Taheri, Hexi Baoyin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉One of the fundamental tasks in space mission design is to choose a set of inter-disciplinary mission-critical parameters that are used for both sizing spacecraft sub-systems and designing optimal trajectories. Trajectory design and sub-system sizing are tightly coupled tasks and mission designers are interested in algorithms that not only improve fidelity of the underlying models, but also facilitate comprehensive trade-off studies using dependable algorithms. This paper presents a systematic-design/computationally-efficient framework that makes use of a recently developed hybrid optimization method, which is a fusion between homotopic approach and particle swarm optimization to perform a robust homotopic approach. A salient feature of this framework is the flexibility in altering the fidelity of the dynamical models to beyond the conventional two-body model by including perturbations due to: 1) other planets of the Solar System, 2) solar radiation pressure, and 3) the oblateness effects of the Earth. Moreover, a comprehensive study on the impact of using different types of thrusters, different hyperbolic excess velocity values, and different launch opportunities is conducted. Extensive numerical simulations are performed for a heliocentric rendezvous mission from Earth to Mars and the results are compared against those in the literature.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 16 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Vegard Ophaug, Kristian Breili, Ole Baltazar Andersen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The coastal mean sea surface (MSS) has applications within oceanography as well as geodesy. Together with a geoid model, it forms an important component for geodetic mapping of ocean surface currents that are in geostrophic balance. Furthermore, it forms a bridge between open ocean MSS and in situ measurements of mean sea level at or close to land, it contributes to the mapping of the geoid and the marine gravity field, and it is essential for connecting tidal nautical chart datums to physical height systems or global geodetic reference frames.〈/p〉 〈p〉In this study, we determine a coastal MSS with an associated error field for Norway. The MSS is solely based on new-generation altimetry data, i.e., SAR(In) data from Sentinel-3A and CryoSat-2, as well as Ka-band data from SARAL/AltiKa. The data sets partly overlap in time and cover the time period from 2010 to 2017 inclusive. We have chosen these altimeters because they represent evolutions of conventional altimetry, with reduced footprint sizes as a main benefit. This is especially advantageous in the coastal zone, as a smaller footprint reduces the probability of radar pulses being contaminated by energy backscattered from land areas.〈/p〉 〈p〉The satellite missions were harmonized by applying inter-mission biases determined in a regional crossover analysis. Furthermore, in a zone closer to land than 25 km, we have replaced the global ocean tide model with a regional ocean tide model provided by the Norwegian Mapping Authority (NMA). We use an optimal interpolation technique to determine a coastal MSS grid and discuss it in context of the estimated error field.〈/p〉 〈p〉We assess our coastal MSS by comparison to state-of-the-art MSS products along three sections perpendicular to the coast, as well as ellipsoidal mean sea level as observed by an array of permanent tide gauges within the study area. In addition, we assess a higher-resolution version of our MSS in the NMA testbed for vertical datums, by comparison with temporary tide gauges. We find that the coastal MSS outperforms the global MSS models directly at the coast, with standard deviations of differences of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si19.svg"〉〈mrow〉〈mo〉~〈/mo〉〈/mrow〉〈/math〉8 cm to the tide gauges, compared to 14–22 cm, obtained with the global MSS models. All MSS models largely agree along three sections perpendicular to the coast, with standard deviations of differences of 2–4 cm. The higher-resolution version of the coastal MSS performs similarly to the coastal MSS in comparison with the temporary tide gauges (standard deviation of differences of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si20.svg"〉〈mrow〉〈mo〉~〈/mo〉〈/mrow〉〈/math〉8 cm), but its formal error field also quantifies large uncertainties at the coast and in the fjords, mainly due to the lack of altimetry observations. A trustworthy error field is decisive for the combination of altimetry with other sea-level observations.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 16 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Da-wei Qi, Le-ping Yang, Yuan-wen Zhang, Wei-wei Cai〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉As a novel approach to control the relative motion of a satellite formation, electromagnetic formation flight (EMFF) has some prominent advantages, such as no propellant consumption and no plume contamination, and has a broad prospect of application in such fields as on-orbit detection and optical interferometry. The current paper investigates the optimal control for the reconfiguration of a two-satellite electromagnetic formation using the nonlinear quadratic optimal control technique. Specifically, the effects of the Earth’s magnetic field on the EMFF satellites are analyzed, and then the nonlinear translational dynamic model of a two-satellite electromagnetic formation is derived by utilizing the analytical mechanics theory. Considering the high nonlinearity and coupling in the dynamic model and the actuator saturation, a closed-loop robust suboptimal control strategy based on the indirect robust control scheme and the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si34.svg"〉〈mrow〉〈mi〉θ〈/mi〉〈mo linebreak="badbreak" linebreakstyle="after"〉-〈/mo〉〈mrow〉〈mi mathvariant="bold-italic"〉D〈/mi〉〈/mrow〉〈/mrow〉〈/math〉 technique is proposed with robust stability and optimality. To ensure a further reduction of control input, the designed suboptimal controller is modified by applying the Tracking-Differentiator. The feasibility of the derived translational dynamics and proposed control strategy for the robust reconfiguration mission is validated through theoretical analysis and numerical simulations.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 16 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Patrick Mungufeni, Babatunde A. Rabiu, Daniel Okoh, Edward Jurua〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study characterised the Total Electron Content (TEC) over the African region during the years 2008 - 2015. The TEC data used were the integrated electron density observed during Radio Occultation (RO) event associated with Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites. These TEC data were referred to as COSMIC TEC. The results indicate that the COSMIC TEC captures the well known features of the ionosphere such as: (i) occurrence of minimum and maximum TEC during 0:00 - 08:00 LT and 12:00 - 16:00 LT respectively, (ii) occurrence of secondary TEC enhancement (maximum) during 16:00 - 20:00 LT, (iii) lowest TEC values being observed in June solstice and highest TEC values observed in March equinox, (iv) TEC values increase as solar activity changes from low to high, (v) mid latitude TEC values are lower than those of low latitude regions, and (vi) occurrence of equatorial ionisation anomaly. In addition, we validated RO TEC observations of COSMIC satellites using Ground-based Global Navigation Satellite System (GNSS) receiver TEC observations (Ground TEC). To achieve this, we quantified the difference between Ground TEC and COSMIC TEC that were simultaneously observed within the vicinity of the ground receiver. The Upper Quartiles, UQ, of the magnitudes of the differences of coincident COSMIC and Ground TEC over southern mid-latitude regions were 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si19.svg"〉〈mrow〉〈mo〉〈〈/mo〉〈/mrow〉〈/math〉 4 TECU, while over low-latitude and northern mid-latitude regions, the values ranged from 6.17 - 11.20 TECU. The high TEC differences over low latitude regions compared to those over southern mid latitudes could have resulted from errors due to the spherical symmetry assumption during the RO retrievals. The question that remains is, why there are large TEC differences over the northern mid-latitude regions. Since COSMIC TEC captures the well known features of the ionosphere, it might in future be used for empirical modeling over African region, thus, making this study crucial.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 16 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Arunava Banerjee, Syed Muhammad Amrr, M. Nabi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper proposes an optimal integral sliding mode control (ISMC) scheme for attitude regulation of the rigid spacecraft. This control technique is capable of handling inertial matrix uncertainties as well as external disturbances. To incorporate optimality into the robust control law, the ISMC is integrated with Legendre pseudospectral method (LPSM). The minimization of the cost function and constraint handling of the spacecraft is obtained by LPSM, while the ISMC provides disturbance rejection. LPSM is chosen for its relatively high rate of convergence and its capability of solving a wide range of challenging optimal control problems. Theoretical stability analysis of closed loop system using Lyapunov theorem guarantees the convergence of attitude states. A comparative analysis between the proposed LPSM-ISMC and Chebyshev Pseudospectral Method (CPSM) based ISMC, is also presented in this paper. The effectiveness of the proposed robust-optimal control strategy is established through simulation results.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 5 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): D.V. Blagoveshchensky, M.A. Sergeeva〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Variations of ionospheric parameters Total Electron Content (TEC) by GNSS, critical frequency (foF2) by vertical sounding and electron density (Ne) by low-altitude satellite were studied at high, mid and low latitudes of the European sector during the magnetic storm of August 25-26, 2018. During the main phase of the storm the ionospheric F2-layer was under the positive disturbance at mid and low latitudes. Then the transition from the positive to negative ΔfoF2 values occurred at all latitudes. The recovery phase was characterized by negative ionospheric disturbance at all latitudes. This is due to the decrease of thermospheric O/N2 ratio during the recovery phase of the storm. The intense Es layers screened the reflections from the F2-layer on August 26〈sup〉th〈/sup〉 at high and at low latitudes but at different times. Some blackouts occurred due to the high absorption level at high latitudes. In general, foF2 and TEC data were highly correlated. The major Ne changes were at the low latitudes. In general, Ne data confirmed the ionospheric dynamics revealed with foF2 and TEC.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 5 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Jiawei Li, Pengqi Gao, Ming Shen, You Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The bistatic radar system has been one of the effective methods to detect the space debris in low earth orbit (LEO). Tianlai radio array with cylindrical-parabolic antennas is designed for dark energy detection, which has large field of view and high sensitivity, offering a fan-beam during the observation. We propose a bistatic radar system, which consists of Tianlai radio array and an incoherent scattering radar (ISR) assumed as a transmitter in the Qujing city of China, to detect space debris. In this paper, we calculate and analyze the detection capabilities of this system. The results show the bistatic radar system has the potential to detect small space debris of less than 10 cm in LEO. We provide a space debris detection method to obtain the position of the cross-beam satisfying the observation requirement with the TLE data of the space debris. The method can solve the problem of space synchronization between the radio array and ISR. We used the long-short baseline method of the radio array to locate the space target. The relationship among positioning error, the azimuth and the elevation angle are also discussed.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 5 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Jian-zhao Wang, Ying Wang, Shu-wu Dai, Chen Wang, Ji-nan Ma, Xiao-yu Jia, Yan-cun Li, Dai Tian, Jia-wen Qiu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A new solar electron event model is developed based on Virtual Timeline Method (VTM). We study events individually by analyzing the 17-year data of 3DP instrument on WIND spacecraft. This model is established in different solar cycle phases and is based on statistics of duration, fluence, and waiting time of solar electron events. The fluences follow a log-normal distribution and logarithmic durations fit well with logarithmic fluences linearly. We prove that waiting times of events significantly deviates from the Poisson process by investigating the stationary and event independence property of Poisson distribution. After a comparison study on waiting times, we choose the Lévy distribution in solar minimum and maximum years. During solar minimum, the event frequency is much lower than that of solar maximum, but the event magnitude is independent of solar cycle period. Large events also happen in solar minimum years. In different solar cycle phases, this model can output a spectrum with confidence level and mission duration by generating many series of virtual timelines composed of many pseudo-events based on Monte Carlo method. On the other hand, spectra in solar minimum years are softer than that in solar maximum years. The fluences in solar maximum years are about one order of magnitude higher than that in solar minimum years in a given mission period. We also compare this model with Interplanetary Electron Model (IEM) quantitatively and prove that this model is advanced.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 5 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Junmi Gogoi, Kalyan Bhuyan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The geomagnetic storm is an important weather issue in the earth’s ionosphere-magnetosphere system. Many linear and nonlinear systems are involved in this earth-space environment. In order to understand the nonlinearly evolving dynamical system of magnetosphere and ionosphere, Time series analysis of foF2 data, Disturbance Storm Index Dst, Geomagnetic activity Index Ap and some other parameters during various solar cycles has been carried out in this work. The hourly data of critical frequency of F2 layer (foF2) for three ionosonde stations [Townsville (TV51R) 19.7°S, 146.9°E; Canberra (CB53N) 35.3°S, 149.1°E; Juliusruh (JR055) 54.6°N, 13.4°E] have been noted for 4 solar cycles viz., Solar Cycle 20, 21, 22 and 23. Hourly time series analysis has been performed to achieve some functional approaches such as statistical, analytical and spectral approach etc. to examine for the presence of periodicities in the data. Time Series is a sequential set of data which can be measured over time, and since the data being used for this work had been recorded as a function of time under various conditions, the appearance of missing observations in time series data is a very common issue. Different series may require different approaches to estimate these missing values. As such, to vanquish the problem of missing data we have attempted to estimate the missing value of foF2 data for various stations using the technique of Singular Value Decomposition (SVD). Another important method, Lomb Scargle Periodogram (LSP) has been performed on the Empirical Orthogonal Functions (EOFs) u1 and u2 (that has been obtained by SVD) along with the solar parameters such as solar flux f10.7, sun spot number (SSN) etc. and geomagnetic indices such as Dst index, Kp index & Ap index etc. for the four solar cycles to find the correlation, if any. For all the plots after performing LSP the power has been found out at 99% confidence level to see how much significant the generated data with respect to the parameters is. The periodicity obtained after performing LSP are divided into three terms namely:– (a) short-term periodicity, in which 27 days periodicity is found to be prominent, (b) mid-term periodicity, in which 1.3 year periodicity is found to be very common and (c) long-term periodicity, in which 11 years periodicity is very regular in almost among all the parameters and in the EOFs.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 2 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Robyn M. Millan, Rudolf von Steiger, Meir Ariel, Sergey Bartalev, Maurice Borgeaud, Stefano Campagnola, Julie C. Castillo-Rogez, René Fléron, Volker Gass, Anna Gregorio, David M. Klumpar, Bhavya Lal, Malcolm Macdonald, Jong Uk Park, V. Sambasiva Rao, Klaus Schilling, Graeme Stephens, Alan M. Title, Ji Wu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This is a COSPAR roadmap to advance the frontiers of science through innovation and international collaboration using small satellites. The world of small satellites is evolving quickly and an opportunity exists to leverage these developments to make scientific progress. In particular, the increasing availability of low-cost launch and commercially available hardware provides an opportunity to reduce the overall cost of science missions. This in turn should increase flight rates and encourage scientists to propose more innovative concepts, leading to scientific breakthroughs. Moreover, new computer technologies and methods are changing the way data are acquired, managed, and processed. The large data sets enabled by small satellites will require a new paradigm for scientific data analysis. In this roadmap we provide several examples of long-term scientific visions that could be enabled by the small satellite revolution. For the purpose of this report, the term “small satellite” is somewhat arbitrarily defined as a spacecraft with an upper mass limit in the range of a few hundred kilograms. The mass limit is less important than the processes used to build and launch these satellites. The goal of this roadmap is to encourage the space science community to leverage developments in the small satellite industry in order to increase flight rates, and change the way small science satellites are built and managed. Five recommendations are made; one each to the science community, to space industry, to space agencies, to policy makers, and finally, to COSPAR.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 14 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Angelica Tarpanelli, Stefania Camici, Karina Nielsen, Luca Brocca, Tommaso Moramarco, Jérôme Benveniste〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The monitoring of rivers is not the primary objective of the Sentinel-3 mission. The first satellite of the constellation was launched in February 2016 and so far no study has investigated the joint use of altimeter, near-infrared and thermal sensors for discharge estimation. Nevertheless, similar sensors onboard other platforms have showed their ability to estimate river discharge also in scarcely gauged areas. The advantage of altimetry lies in the observation of water surface elevation, which can be proficiently used in approaches based on rating curve, empirical formulae or hydraulic modeling. Even though their use is limited, near-infrared sensors are successfully used to detect the variability of river discharge thanks to their high capacity to discriminate water from land. Thermal sensors are nearly completely unused, but the unique study that uses the difference in temperature of the river water between day and night for the estimation of water level, encourages its use for river discharge assessment as well. To improve the estimation of river discharge and foster studies that are aimed at monitoring ungauged rivers, the combination of the sensors is considered a viable path. The aim of this manuscript is to review these studies to show the limitations and the potentials of each sensor onboard the Sentinel-3 satellite and to investigate the added value of using these three sensors co-located on the same platform for river discharge monitoring.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 10 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Yekoye Asmare Tariku〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper mainly focuses on the evaluation of efficiency of the Sunspot Number (SSN) and the 10.7 cm Solar Radio Flux (F10.7) indices as a cause for the variation of the performance of the latest versions of the International Reference Ionosphere model (IRI 2016 with NeQuick, IRI01-corr and IRI2001 options for the topside electron density) and the IRI Extended to the Plasmasphere (IRI-Plas 2017) for the modeling of the Total Electron Content (TEC) over the West Pacific regions during the recent solar maximum (2012-2014) years. The Global Positioning System (GPS)-derived TEC data obtained from the dual frequency GPS receivers located at Observation Rock〈strong〉,〈/strong〉 OBSR (geog 46.90°N, 238.18°W, Geom. 52.46°N) and Husband, HUSB (44.12°N, 238.15°W, Geom. 49.73°N) have been considered for the validation of the performance of the models. The results show that both the GPS-derived TEC (GPS VTEC) and modelled (IRI 2016 and IRI-Plas 2017 VTEC) seasonal diurnal values tend to peak at 00:00 UT (16:00 LT) and 20:00 (12:00 LT) with the highest being observed mostly at 20:00 (12:00 LT); while, their minima are mostly observed at about 13:00 UT (05:00 LT). In addition, in utilizing the SSN, the best performance is generally observed in the June solstice months, especially by the IRI-Plas 2017 model. However, for the equinoctial and December solstice months, the best performance is generally observed by the IRI 2016 model with NeQuick and IRI01 options. It has also been shown that the root-mean-square deviations between the GPS-derived and modelled VTEC diurnal variation in using the F10.7 index are generally less than those of the SSN option in all months, revealing that both the IRI 2016 and IRI-Plas 2017 models generally show better performance using F10.7 index than the SSN. Hence, the F10.7 option is recommended for better TEC modeling employing the IRI 2016 and IRI-Plas 2017 models during the recent solar maximum years over the West Pacific region. In addition, both models cannot effectively estimate the geomagnetic storm time TEC variation.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 7 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Tao Chen, Zhen Zhao, Stephen R. Schwartz, Caishan Liu, Qi Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, we study the conveying dynamics in the helical groove of an auger drilling into lunar simulant. We demonstrate that the stress-coupling effect of the conveyed granules by the groove of a drill auger plays a significant role on the dynamics of conveyance. For this, a discrete element method (DEM) is adopted first to uncover the motion and the stress characteristics of conveyed granules in a working auger. Then, a simplified dynamic model following the stress characteristics of DEM is established. The simplified model can not only reflect the results by the discrete element method, but can also explain well the proportional relationship between the maximum conveying rate and the rotating speed of the auger in the experiment (Zhao et al., 2019).〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 5 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Haoye Lin, Bo Xu, Jingxi Liu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The accuracy in pulsar-based navigation system can be improved with a well-designed observation scheme. In this paper, based on the idea that minimises the size of position probability ellipsoid at each updating time, four strategies are put forward for determining observation order. As the calculation of posterior probability ellipsoid only requires a priori orbit information, the observation scheme can be designed during preliminary mission analysis. These strategies can be employed in both situations with single detector and multiple detectors. Numerical simulations show that the proposed observation strategies achieve good performance.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 5 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Adam Łyszkowicz, Anna Bernatowicz〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Sea level is a unique indicator in climate impact studies on any changes on the surface of the Earth. Traditionally, tide gauges allow observation of relative (relative to land) sea level changes at specific locations with a high resolution in time. Common method of sea level determination in XXI century is the combination of tide gauge observations with satellite observation data. So determined sea level changes are absolute changes and they are referred to the beginning of the ITRF system.〈/p〉 〈p〉Geocentric changes in the Baltic Sea level are monitored, inter alia, by the SONEL network. This network system does not include the southern coast of the Baltic Sea. The aim of this work is to fill this gap and to compute geocentric changes in the Baltic Sea at the stations: Hel, Władysławowo, Łeba, Ustka, Kołobrzeg, Świnoujście.〈/p〉 〈p〉The tide gauge data needed for the analysis were made available by the Institute of Meteorology and Water Management and the GNSS data was taken from web page Nevada Geodetic Laboratory. The analysis of the time series of tide gauge and GNSS observations was carried out using the TSAnalyzer software. We assumed that GNSS and tide gauge series have a seasonal signal (annual plus semi-annual) and a trend. First the outliers were removed from observation, then the jumps were viewing. The trend, annual and semi-annual terms were calculated for GNSS and tide gauge series.〈/p〉 〈p〉The results of the work are calculated geocentric changes in the Baltic Sea level along southern coast and they are at a level of 0.3 mm/year except Ustka where it reach value 4.68 mm/year.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 1 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Lionel Métrailler, Guillaume Bélanger, Peter Kretschmar, Erik Kuulkers, Ricardo Pérez Martínez, Jan-Uwe Ness, Pedro Rodriguez, Mauro Casale, Jorge Fauste, Timothy Finn, Celia Sanchez, Thomas Godard, Richard Southworth〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The magnetosphere sustained by the rotation of the Earth’s liquid iron core traps charged particles, mostly electrons and protons, into structures referred to as the Van Allen Belts. These radiation belts, in which the density of charged energetic particles can be very destructive for sensitive instrumentation, have to be crossed on every orbit of satellites traveling in elliptical orbits around the Earth, as is the case for ESA’s 〈em〉INTEGRAL〈/em〉 and 〈em〉XMM-Newton〈/em〉 missions. This paper presents the first working version of the 5DRBM-e model, a global, data-driven model of the radiation belts for trapped electrons. The model is based on in situ measurements of electrons by the radiation monitors on board the 〈em〉INTEGRAL〈/em〉 and 〈em〉XMM-Newton〈/em〉 satellites along their long elliptical orbits for respectively 16 and 19 years of operations. This model, in its present form, features the integral flux for trapped electrons within energies ranging from 0.7 to 1.75 MeV. Cross-validation of the 5DRBM-e with the well-known AE8min/max and AE9mean models for a low eccentricity GPS orbit shows excellent agreement, and demonstrates that the new model can be used to provide reliable predictions along widely different orbits around Earth for the purpose of designing, planning, and operating satellites with more accurate instrument safety margins. Future work will include extending the model based on electrons of different energies and proton radiation measurement data.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 3〈/p〉 〈p〉Author(s): Christian Siemes, Moritz Rexer, Roger Haagmans〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We analyse the inter-boresight angles (IBA) measured by the star trackers on board the GOCE satellite and find that they exhibit small offsets of 7–9″ with respect to the ones calculated from the rotation of the star tracker reference frames to the satellite reference frame. Further, we find small variations in the offsets with a peak-to-peak amplitude of up to 8″, which correlate with variations of the star trackers’ temperatures. Motivated by these findings, we present a method for combining the attitude quaternions measured by two or more star trackers that includes an estimation of relative attitude offsets between star trackers as a linear function of temperature. The method was used to correct and combine the star tracker attitude quaternions within the reprocessing of GOCE data performed in 2018. We demonstrate that the IBA calculated from the corrected star tracker attitude quaternions show no significant offsets with respect to the reference frame information. Finally, we show that neglecting the star tracker attitude offsets in the processing would result in perturbations in the gravity gradients that are visible at frequencies below 2 mHz and have a magnitude of up to 90 mE. The presented method avoids such perturbations to a large extent.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 3〈/p〉 〈p〉Author(s): Qiang Zhang, Qile Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Spherical harmonic (SH) expansion is widely used to model the global ionosphere map (GIM) of vertical total electron content (VTEC). According to the impact of different data processing methods of the SH expansion model on the VTEC maps, we specifically performed comprehensive analysis in terms of the data sampling rate, the time resolution, the spherical harmonic degree, and the relative constraint. One month of GPS data (January in 2016) from the International GNSS (Global Navigation Satellite System) Service (IGS) network in a moderate ionospheric activity period at the descending phase of Solar Cycle 24 was processed. To improve the computational efficiency of the daily GIM generation, the data sampling rate of 5 min was recommended allowing the GIM precision loss within 0.10 TECU (total electron content unit). The global VTEC map could be better represented in temporal and spatial domains with higher time resolution and higher spherical harmonic degree, especially at low latitude bands and in the southern hemisphere. The GIM precision improvement was about 10.91% for 1-h and about 15.15% for 0.5-h compared with the commonly used 2-h time resolution. The use of spherical harmonic degree 17 or 20 instead of 15 could improve the precision by 3.19% or 6.06%. We also found that an optimal relative constraint had to be found experimentally considering both the GIM precision and the GIM root mean square (RMS) map.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 3〈/p〉 〈p〉Author(s): Xin Liu, Shubi Zhang, Qiuzhao Zhang, Nan Ding, Wei Yang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉With the Global Navigation Satellite System (GNSS) developing, the single-frequency single-epoch multiple GNSSs (multi-GNSS) relative positioning has become feasible. Since a larger number of the observed satellites make the instantaneous (single-epoch) positioning time-consuming, a proper satellite selection is necessary. Among the present methods, the satellite selection with a fixed high cut-off elevation angle (CEA) is least time-consuming. However, there is no criterion how large a fixed high CEA should be to achieve a high success rate and less time consumption. Besides, a fixed high CEA makes the number of visible satellites largely variable, which affects the success rate. Hence, a satellite selection strategy based on ambiguity dilution of precision (ADOP) is proposed. Firstly, the theoretical proof that the ADOP increases the least when removing satellites are all low-elevation-angle satellites is given, which is important to achieve the fast positioning with a high success rate. Then, the threshold 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mi〉β〈/mi〉〈/mrow〉〈/math〉 is calculated for a different number of satellites and a given ADOP. The satellites are selected based on their elevation angles from high to low until 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mi〉β〈/mi〉〈/mrow〉〈/math〉 of the selected satellites becomes smaller than the corresponding threshold; this method is called the extended floating CEA multi-GNSS (EF-multi-GNSS). The comparison of the single-frequency single-epoch positioning performance of the EF-multi-GNSS with the satellite selections based on a fixed low CEA (L-multi-GNSS) and a fixed high CEA (H-multi-GNSS) via the relative positioning experiments shows that: (1) the EF-multi-GNSS with a minimal number of satellites can achieve the fast positioning and a high success rate close to 100%. It can greatly reduce the time consumption of the L-multi-GNSS, by about 64.0%, by selecting 12.6 satellites of 23.4 satellites; (2) the floating CEA of EF-multi-GNSS eliminates the consideration how large a fixed high CEA should be, and a CEA larger than the fixed high CEA of the H-multi-GNSS makes it more suitable for different conditions.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 3〈/p〉 〈p〉Author(s): Tirthankar Basu, Swades Pal〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Darjeeling Himalaya is one of the several mountainous areas of India which is often suffered from landslide hazards. In this paper, a multi criteria evaluation is applied using 16 morphometric indicators, geology and lineaments to identify the areas vulnerable in respect to drainage and relief conditions. As both drainage and relief parameters exert strong influences on landslide intensity, both the diversity maps are integrated for final landslide susceptibility mapping. The obtained results show that 20.17 sq. km (7.61%) area within the basin is highly susceptible for landslides, where average drainage density is 3.78 km/sq. km, relative relief is greater than 408 m and slope is greater than 12°. The validation result shows that very high landslide susceptible zone is associated with very high frequency of landslide occurrence. Beside this, ROC curve also suggests good predicted rate (86.60%) for the model. So, the proposed method can be applied for predicting landslide susceptible zone.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 28 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): A. Mahmoudian, A. Senior, M. Kosch, W.A. Scales, M.T. Rietveld, B. Isham, X. Shi, M. Ruohoniemi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Electromagnetic (EM) and electrostatic (ES) emissions can be generated in the ionosphere by high-power high-frequency (HF) radio waves transmitted from the ground. The signatures of the EM emissions observed on the ground are known as Stimulated Electromagnetic Emissions (SEE) and can be employed for remote measurement of ionospheric parameters. The experimental data from recent HF heating experiments near the fourth electron gyro-frequency (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si41.gif" overflow="scroll"〉〈mrow〉〈mn〉4〈/mn〉〈msub〉〈mrow〉〈mtext〉f〈/mtext〉〈/mrow〉〈mrow〉〈mi mathvariant="italic"〉ce〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉) at EISCAT are presented. This paper compares the temporal behavior of SEE within a few Hertz up to 50 kHz of the transmission frequency to the time evolution of enhanced ion line (EHIL) in the incoherent scatter radar (ISR) spectrum. The correlation of Wideband SEE (WSEE) spectral lines within 1 kHz to 100 kHz such as the downshifted maximum (DM), downshifted peak (DP), and broad upshifted maximum (BUM), with HF enhanced ion lines (EHIL) is shown. It is shown that WSEE spectral lines can be used to reproduce the EHIL characteristics including altitude range, rise and decay time, maximum and minimum amplitude. A data reduction technique is developed to derive ionospheric parameters such as the electron density profile near the interaction altitude, magnetic field strength 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si42.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉B〈/mi〉〈/mrow〉〈mrow〉〈mn〉0〈/mn〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 as well as the altitude profile of the EHIL using the temporal evolution of WSEE spectral lines near n〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉f〈/mi〉〈/mrow〉〈mrow〉〈mi mathvariant="italic"〉ce〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 28 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): S. Veretenenko, M. Ogurtsov〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this work we continue studying possible reasons for temporal variability observed in correlation links between characteristics of the lower atmosphere and solar activity phenomena at the multi-decadal time scale. Temporal variations of correlation coefficients between troposphere pressure at extratropical latitudes and sunspot numbers are compared with the evolution of the large-scale circulation forms according to the Vangengeim-Girs classification, as well as the characteristics of the stratospheric polar vortex and global temperature anomalies. The results obtained show that temporal variability of solar activity/galactic cosmic ray (SA/GCR) effects on troposphere pressure (the development of extratropical baric systems) is characterized by a roughly 60-year periodicity and closely related to changes in the regime of large-scale circulation which accompany transitions between the different states of the polar vortex. It was suggested that the character of SA/GCR effects depends on the polar vortex strength influencing the troposphere-stratosphere coupling. It was shown that the evolution of the polar vortex may be associated with global temperature variations, with a possible reason for these variations being long-term changes of total solar irradiance.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 25 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Pouria Razzaghi, Ehab Al Khatib, Shide Bakhtiari〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Since space debris is a problem that has been continuously increasing, removal missions should be considered. Tethered space system (TSS) has wide application prospects in the future on-orbit missions such as debris removal. However, it is rather complex and difficult for TSS to realize stabilization of tumbling combinations after connecting to the debris. In this paper, the stabilization problem of this combination is studied.〈/p〉 〈p〉An adaptive sliding mode and State-Dependent Riccati Equation control methods are applied on a TSS to stabilize the system and de-orbit the space debris. The tether tension and stability of the in-plane and out-of-plane libration angles of the system are taken into account. The tether can only resist axial stretching. The thrusters, which are the sources of the system inputs are equipped on the satellite. The controllers regulate the tether to remain fully stretched and to decrease the altitude of the orbit continuously. The numerical simulation validates the proposed control schemes for de-orbiting the debris and put it in lower altitude orbit. This makes the debris retrieve to the atmosphere in less time than the actual orbit lifetime. The comparison between two control schemes is discussed.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 30 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Tao An, Xiaoyu Hong, Weimin Zheng, Shuhua Ye, Zhihan Qian, Li Fu, Quan Guo, Sumit Jaiswal, Dali Kong, Baoqiang Lao, Lei Liu, Qinghui Liu, Weijia Lü, Prashanth Mohan, Zhiqiang Shen, Guangli Wang, Fang Wu, Xiaocong Wu, Juan Zhang, Zhongli Zhang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Space Very Long Baseline Interferometry (VLBI) has unique applications in high-resolution imaging of fine structure of astronomical objects and high-precision astrometry, owing to the key long space-Earth or space-space baselines beyond the Earth’s diameter. China has been actively involved in the development of space VLBI in recent years. This paper briefly summarizes China’s research progress in space VLBI and the development plan in future.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 30 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): R Gardiner-Garden, M Cervera, R Debnam, T Harris, A Heitmann, D Holdsworth, D Netherway, B Northey, L Pederick, J Praschifka, A Quinn, M Turley, A Unewisse, B Ward, G Warne〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The Elevation sensitive Oblique Incidence Sounder Experiment (ELOISE) was an extensive experiment undertaken by the Defence Science and Technology (DST) Group that focused on collecting ionospheric sensor data from multiple overlapping ionospheric paths in the Australian region in order to improve understanding of the characteristics of ionospheric variability and its effect on HF radio propagation. The experiment ran from July to October 2015 and included a period of three weeks of increased sample density and three days of dedicated over-the-horizon (OTH) radar operations. It was anticipated that ELOISE would sample a wide range of environmental conditions and present an opportunity to characterise periods of “normal variability” and periods of “exceptional variability” in the ionosphere.〈/p〉 〈p〉This report is a general description of the aims of this experiment and the types of data collected. Particular interest focused on observing and measuring variability in ionospheric electron density gradients and their effect on oblique HF propagation. To this end, ELOISE established a pair of two dimensional HF receiver arrays to directly measure the oblique angle of arrival (AoA) on many overlapping oblique paths. ELOISE also established a dense sub-network of spatially separated quasi-vertical incidence soundings in the vicinity of Alice Springs in central Australia. This enabled a comparison of gradients observed in a dense network of vertical sounders with gradient effects observed in oblique propagation passing overhead. Several additional ionospheric observing systems were also used to give complementary pictures of the fine scale characteristics of ionospheric variability in the region.〈/p〉 〈/div〉 〈div〉 〈h6〉Plain Language Summary〈/h6〉 〈p〉This paper is an overview of the 2015 Elevation sensitive Oblique Incidence Sounder Experiment (ELOISE), an experiment designed to observe and characterise mid-latitude ionospheric disturbances in the Australian region and understand their impact on high frequency (HF) signal propagation.〈/p〉 〈p〉ELOISE involved the simultaneous operation of a large collection of ionospheric sounders enabling ionospheric variability to be characterised on a finely sampled large scale.〈/p〉 〈p〉Particular efforts were made to provide direct high fidelity measurements of the angle of arrival (AoA) on many oblique HF propagation paths. These direct AoA measurements imply horizontal electron density gradients that can be compared to ionospheric gradients estimated from conventional models of the ionosphere derived from the spatial network of sounder sites.〈/p〉 〈p〉The size and scope of the experiment are detailed in this paper and some preliminary results are presented.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Stefan Frey, Camilla Colombo, Stijn Lemmens〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Numerical integration of orbit trajectories for a large number of initial conditions and for long time spans is computationally expensive. Semi-analytical methods were developed to reduce the computational burden. An elegant and widely used method of semi-analytically integrating trajectories of objects subject to atmospheric drag was proposed by King-Hele (KH). However, the analytical KH contraction method relies on the assumption that the atmosphere density decays strictly exponentially with altitude. If the actual density profile does not satisfy the assumption of a fixed scale height, as is the case for Earth’s atmosphere, the KH method introduces potentially large errors for non-circular orbit configurations.〈/p〉 〈p〉In this work, the KH method is extended to account for such errors by using a newly introduced atmosphere model derivative. By superimposing exponentially decaying partial atmospheres, the superimposed KH method can be applied accurately while considering more complex density profiles. The KH method is further refined by deriving higher order terms during the series expansion. A variable boundary condition to choose the appropriate eccentricity regime, based on the series truncation errors, is introduced. The accuracy of the extended analytical contraction method is shown to be comparable to numerical Gauss-Legendre quadrature. Propagation using the proposed method compares well against non-averaged integration of the dynamics, while the computational load remains very low.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Hassan Aboelkhair, Mostafa Morsy, Gamal El Afandi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The climatic reanalysis datasets are one of the most important data types that could help to overcome scarce of observations. Therefore, the main objective of this study is to evaluate NASA POWER reanalysis data for surface monthly average temperatures at 2 m (maximum (T〈sub〉max〈/sub〉), minimum (T〈sub〉min〈/sub〉), mean (T〈sub〉mean〈/sub〉) and dew point (T〈sub〉d〈/sub〉), all in °C) and relative humidity (RH) in percentage compared to the observed data at 20 Egyptian weather stations. The results showed that there are a significant correlation and goodness of fit between NASA POWER reanalysis and observed data for all parameters except RH. For temperature variables, the coefficient of determination (R〈sup〉2〈/sup〉) and Willmott Index of agreement (WI) attain around 0.75 and 0.90 respectively, while the root mean square error (RMSE) reaches to less than 5 °C; and the mean bias error (MBE) ranges from −3 to +3 °C for 85% of stations. In addition, NASA POWER accuracy of temperature parameters increases gradually northward with the highest ratio at the northern coast of Egypt. Where, it is slightly overestimated (under 3 °C) T〈sub〉max〈/sub〉, T〈sub〉min〈/sub〉, and T〈sub〉mean〈/sub〉 at 80, 75 and 65% of the stations respectively. While it is slightly underestimated T〈sub〉d〈/sub〉 with 3 °C at 90% of the stations. Contrarily, NASA POWER data accuracy of RH increases southward, particularly in Aswan. Additionally, NASA POWER reanalysis has a considerable underestimation for RH data at most stations, where the dominant MBE percentage ranges from −12 to −5% for about 75% of the stations. As well as, the maximum RMSE and MBE for all elements were recorded in the Malwi station at Middle Egypt. Consequently, R〈sup〉2〈/sup〉, WI, RMSE, and MBE for temperature parameters are almost within an acceptable range for most selected Egyptian stations which are located in the area that dominated by the influence of the Mediterranean Sea (northern of 30°N) and western of 30°E with a distance between 2.5 and 14.5 km from the Sea. While, the good RH estimation is recorded at stations that are located south of the area that dominated by the influence of the Mediterranean Sea (south of 26°N). Finally, NASA POWER reanalysis datasets can be used in case of missing or scarce of observations in Egypt. Nevertheless, it still needs improvements by taking into consideration the influence of the Mediterranean Sea and the locality of (especially middle) Egypt on temperature and in particular on relative humidity estimations.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 30 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): D.V. Blagoveshchensky, M.A. Sergeeva, P. Corona-Romero〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The main feature of the geomagnetic disturbance which occurred on September 7-8, 2017, was that it consisted of two consecutive magnetic storms separated in time by ∼13 hours. It was of interest to reveal its particular features, characteristics and geomagnetic field variations during both storms and the influence they had on the ionosphere. The results are as follows. The character of the development of the first storm and its impact on the Earth’s magnetosphere and ionosphere are significantly different from the character of the development and impact of the second storm. There are prominent differences in the geomagnetic field variations at different longitudes along the same latitude sector. The asymmetry of the dayside and nightside effects was revealed. The variations of the riometer absorption level, critical frequencies of the ionosphere and Total Electron Content in each considered observation point corresponded to the variations of the magnetic field at this point.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 28 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Bijay Kumar Sharma〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Matija Cuk et.al (2016) have proposed a new model for the birth and tidal evolution of our natural satellite Moon, born from impact generated terrestrial debris in the equatorial plane of high obliquity, high angular momentum Earth. This paper examines their findings critically in the light of advanced kinematic model (AKM) which includes Earth’s obliquity(ɸ), Moon’s orbital plane inclination (α) , Moon’s obliquity (β) and lunar’s orbit eccentricity (e). For the real Earth-Moon (E-M) system, the history of evolution of ɸ, α, β, e and (length of month)/(length of day) or LOM/LOD is traced from 45R〈sub〉E〈/sub〉 to 60.33R〈sub〉E〈/sub〉 where R〈sub〉E〈/sub〉 is Earth Radius. It is shown that AKM’s valid range of application is from 45R〈sub〉E〈/sub〉 to 60.33R〈sub〉E〈/sub〉 . The evolution of α, β, e is in correspondence with the simulation results of Matija Cuk et.al (2016) but evolution of Earth’s obliquity has a break at 45R〈sub〉E〈/sub〉 . According to AKM , earlier than 45R〈sub〉E〈/sub〉 Earth should achieve 0° obliquity in order to achieve the modern value of 23.44° obliquity. Cuk et al (2016) donot explain how this can be achieved. AKM stands vindicated because Science Advances_aax0684, AKM has successfully given near-precise theoretical formalism of LOD curve for the last 1.2Gy time span opening the way for early warning and forecasting methods for Earth-quake and sudden volcanic eruptions..〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 28 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Susan W. Samwel, Esraa A. El-Aziz, Henry B. Garrett, Ahmed A. Hady, Makram Ibrahim, Magdy Y. Amin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉The trend towards the development of small satellites, or smallsats, has been increasing over the last few years. However, the harsh space radiation environment in which these smallsats operate provides a challenge to their survivability as their desired mission lengths increase from a few months to several years also. Smallsats typically use commercial off the shelf components (COTS) that are built for ground operations, not space use. Therefore, they may be more susceptible to the hazards of space radiation than traditional spacecraft which are typically designed to withstand the high radiation levels of space. The present paper provides a targeted assessment of representative COTS components using up to date models of the space radiation environment and its effects on smallsats in a polar Low Earth Orbit (LEO). This orbit will be assumed to be sunsynchronous (98.5° inclination) and at an altitude of 800km. We employed the new Solar Accumulated and Peak Proton and Heavy Ion Radiation Environment (SAPPHIRE) model which has been released recently in 2018, ISO-15390 GCR model, and AP8/AE8 models to estimate the space radiation environment for solar particles, galactic cosmic rays (GCRs), and trapped protons and electrons respectively. The basic damage effects that can be produced in materials and electronics in this orbit due to their exposure to the space radiation are evaluated. These effects are the Total Ionizing Dose (TID), Displacement Damage Dose (DDD), and Single Event Effects (SEE) as represented by Single Event Upsets (SEUs). SEU is evaluated for different COTS components which are believed to be representative of an optimum blend of capability and cost-effectiveness for the next generation of smallsats, including 20 nm Xilinx Kintex Ultra Scale FPGA Configuration RAM (XCKU040), 90-nm SRAM, and MLC NAND flash memory (MT29F128G08CBECBH6). For comparative purposes, the analyses are performed for both maximum and minimum solar activity.〈/p〉 〈p〉Based on these comparisons, we find as expected that the space radiation environment parameters vary with solar activity. The fluence of trapped electrons and solar protons at solar maximum are higher than those at solar minimum in contrast to the trapped protons and galactic cosmic rays at low altitudes. On the other hand, TID, DDD, and SEE all show higher values during maximum solar activity than during minimum solar activity.〈/p〉 〈p〉The use of shielding material for small satellites is mandatory for this orbit as observed TID, DDD, and SEES levels that can be reached are potentially of concern to designers. However, using Al shielding thickness of at least 1.5 mm can reduce the radiation effects to acceptable levels, for both maximum and minimum solar activity for missions of moderate (∼3 years) duration.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 28 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Weiwei Xu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The precise AMS data reveals distinctive properties of cosmic-ray positron and electron fluxes. The positron spectrum hardens starting from 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉20 GeV. Most importantly, the positron spectrum exhibits a sharp drop-off at 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈mn〉300〈/mn〉〈/mrow〉〈/math〉 GeV, showing the existence of an energy cutoff at highest energy. The electron spectrum is distinctly different from the positron spectrum in both the magnitude and energy dependence. The electron spectrum hardens from 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉30 GeV. Remarkably, the electron spectrum is well described by a single power law from 55 GeV to 1 TeV and does not have an energy cutoff. These experimental data show that, at high energies, the cosmic-ray positrons predominately originate either from dark matter annihilation or from a new astrophysical source, whereas the cosmic-ray electrons originate from different sources.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Russell P. Patera〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The recently developed Vector Inertia Tensor Attitude Estimation, VITAE, method is enhanced by the addition of two different preprocessing algorithms that modify the observation vectors prior to attitude estimation. The first preprocessing algorithm is for use in cases that have one observation vector that is much more accurate than the other observation vectors. Such cases suffer numerical error caused by the large relative weight of the very accurate observation vector. Use of the preprocessing algorithm eliminates large variation in vector weights and resulting numerical error. The second preprocessing algorithm enables VITAE to generate results equivalent to a very accurate suboptimal attitude determination algorithm that produces results extremely close to the optimum solution. Preprocessing algorithms eliminate the need to select observation vector weights to remove eigenvalue degeneracy and allows the weights to be based solely on optimality, thereby improving estimation accuracy. When optimum weights are used, the inertia matrix is recognized as the information matrix, which links VITAE to other attitude estimation algorithms. The preprocessing algorithms used with VITAE were able to uncover erroneous results in a few published test cases. The VITAE solutions were validated analytically, through the inertia matrix’s inverse relationship to the error covariance matrix. A loss function comparison is also included to further validate the preprocessing algorithms and related VITAE solution.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 3〈/p〉 〈p〉Author(s): Shahida Parveen, Shahzad Mahmood, Anisa Qamar, Muhammad Adnan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The interaction between two, four and six magnetoacoustic solitons in electron-positron plasmas are investigated. The extended Poincaré–Lighthill–Kuo (PLK) perturbation method is employed to derived two KdV equations for magnetoacoustic solitons moving towards each other and studied the head-on collision between them and their phase shifts. The Hirota bilinear method is used to have multi-soliton solutions of already derived two KdV equations for right and left moving solitons. The four and six magnetoacoustic solitons solutions of the two KdV equations are obtained to discuss their interaction and phase shifts. It is found that only compressive magnetoacoustic solitons structures are formed in electron-positron plasma. The present study may be useful to understand the collective phenomena related to head-on and overtaking magnetoacoustic solitons interaction in electron-positron plasmas that may occur in a pulsar magnetosphere.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 5〈/p〉 〈p〉Author(s): Qi Li, Jianping Yuan, Chong Sun〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this paper, the motion control problem of autonomous spacecraft rendezvous and docking with a tumbling target in the presence of unknown model parameters, external disturbances, actuator saturation and faults is investigated. Firstly, a nonlinear six degree-of-freedom dynamics model is established to describe the relative motion of the chaser spacecraft with respect to the tumbling target. Subsequently, a robust fault-tolerant saturated control strategy with no precise knowledge of model parameters and external disturbances is proposed by combining the sliding mode control technique with an adaptive methodology. Then, within the Lyapunov framework, it is proved that the designed robust fault-tolerant controller can guarantee the relative position and attitude errors converge into small regions containing the origin. Finally, numerical simulations are performed to demonstrate the effectiveness and robustness of the proposed control strategy.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 5〈/p〉 〈p〉Author(s): Salih Alcay, Sermet Ogutcu, Ibrahim Kalayci, Cemal Ozer Yigit〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Besides the classical geodetic methods, GPS (Global Positioning System) based positioning methods are widely used for monitoring crustal, structural, ground etc., deformations in recent years. Currently, two main GPS positioning methods are used: Relative and Precise Point Positioning (PPP) methods. It is crucial to know which amount of displacement can be detected with these two methods in order to inform their usability according to the types of deformation. Therefore, this study conducted to investigate horizontal and vertical displacement monitoring performance and capability of determining the direction of displacements of both methods using a developed displacement simulator apparatus. For this purpose, 20 simulated displacement tests were handled. Besides the 24 h data sets, 12 h, 8 h, 4 h and 2 h subsets were considered to examine the influence of short time spans. Each data sets were processed using GAMIT/GLOBK and GIPSY/OASIS scientific software for relative and PPP applications respectively and derived displacements were compared to the simulated (true) displacements. Then statistical significance test was applied. Results of the experiment show that using 24 h data sets, relative method can determine up to 6.0 mm horizontal displacement and 12.3 mm vertical displacement, while PPP method can detect 8.1 mm and 19.2 mm displacements in horizontal and vertical directions respectively. Minimum detected displacements are found to grow larger as time spans are shortened.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 5〈/p〉 〈p〉Author(s): Rajesh Vaishnav, Som Sharma, K.K. Shukla, Prashant Kumar, S. Lal〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A comprehensive statistical analysis of the cloud base height (CBH) measured by ground-based Vaisala ceilometer (CL31) has been performed to study different layers of the cloud in the lower troposphere up to 7.5 km height over Ahmedabad, western India during 2014 and 2015. The total observations (∼69%) of cloud by using ceilometer show annual cloud occurrence frequency of around 64%. Seasonal variation of CBH and cloud occurrence frequency reveal that the maximum/minimum cloud cover is found during southwest (SW) Indian summer monsoon/pre-monsoon season. Three CBHs (CBH1, CBH2, and CBH3) are presented in monsoon period due to high cloud occurrence, and two CBHs (CBH1 and CBH2) are observed in other seasons due to low cloud occurrence by ceilometer over the observational site. The CBH1 (∼100–2000 m) and CBH2 (500–3000 m) are observed during SW monsoon and summer season, respectively. The CBH3 is occurred usually in SW monsoon season. Moreover, the cloud cover during the day and night time shows that the occurrence of cloud is more frequent in daytime than nighttime during pre-monsoon and post-monsoon season. The statistical analysis of cloud with ground-based observations is also performed in this study that may be useful for the development/improvement of regional weather and climate models to reduce the uncertainty in the prediction.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 3〈/p〉 〈p〉Author(s): B. Paul, B.K. De, A. Guha〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Following Tanna et al. (2013), we computed the percentage of occurrence of S〈sub〉4〈/sub〉 index for the period of 2012–2015 using the data of the dual frequency GPS receiver at the Tripura University, Agartala station (23.76°N, 91.26°E) situated at the northern crest of the equatorial ionization anomaly (EIA) region of the Indian Subcontinent. We have observed discrepancy in the results contradicting the actual scintillation occurrence. The distinctly noticeable discrepancy is that the maximum occurrence month is shifted to April 2013 instead of March 2014. The problem arises due to the denominator term used in the percentage of occurrence ratio i.e. the total number of days of observed scintillation activity during the complete period under consideration. But the conventional percentage of occurrence methodology uses the number of days of observation (the total number of days for which data is available) during each month in the denominator. It correctly assigns the maximum occurrence to March 2014 instead of April 2013 and the obtained monthly statistics follow the solar activity during this period.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 5〈/p〉 〈p〉Author(s): Yipeng Li, Yunpeng Wang, Yongchun Xie〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper proposes a consecutive point clouds-based estimation scheme to resolve the state estimation problem for tumbling non-cooperative space target during the rendezvous phase without a prior knowledge about its structure. First, a consistent pose estimation algorithm is realized by maintaining a global structure of the target that is reconstructed upon the pose graph optimization. Then an extend Kalman filter on Lie group is adopted to estimate the motion and inertia parameters of the target using the pose measurements of the point clouds. Finally, a semi-physical experimental study is carried out to evaluate the performance of the proposed estimation scheme. The result shows that the structure, motion and the inertia parameters can be estimated, and the total computation time is approximately linear with the number of point clouds.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 2 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Xing Meng, Hanxian Fang, Libin Weng, Zhendi Liu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Through concurrently measurements by Communication/Navigation Outage Forecasting System (C/NOFS), Sanya VHF radar and GPS ionospheric scintillation receiver on 12 March 2010, five plasma bubbles were found and three of them were observed by all those instruments. Two well-developed plumes with strong backscatter echoes were measured by Sanya radar and their corresponding depletions were observed by C/NOFS in Orbit 10317, 10318 and 10319. Broad plasma depletions resulting from merging process were found in orbit of 10318. The occurrence time and geophysical positions of scintillations correlate well with observations implemented by Sanya VHF radar and C/NOFS. Observations from three types of instrument indicate that the spread F irregularities have distinct scale. There were longitudinal differences between Sanya VHF radar and C/NOFS as irregularities measured, and the eastward drift of developed bubbles are responsible for these differences.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 3 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Dmitriy Korotyshkin, Evgeny Merzlyakov, Oleg Sherstyukov, Farhat Valiullin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉New meteor radar (MR) horizontal wind data obtained during 2015–2018 at Kazan (56°N, 49°E) are presented. The measurements were carried out with a state-of-the-art SKiYMET meteor radar. Monthly mean vertical profiles of zonal and meridional components of the prevailing wind speeds, also amplitudes and phases of the components of diurnal (DT) and semidiurnal tide (SDT) winds are displayed as contour plots for a mean calendar year over the four recent years and compared with distributions of these parameters provided by the previous multiyear (1986–2002) meteor radar (MR) measurements at Kazan and by the recent HWM07 empirical model. The analysis shows that the SKiYMET zonal and meridional prevailing wind speeds are generally in good agreement, sharing the same seasonal features, with the earlier MR seasonal winds. Comparisons with the HWM07 model are not favourable: eastward solstitial cells as modelled are significantly larger, 〉30 m/s compared to 15–20 m/s. Also, reversal lines are too variable with height, and the positions of modelled cells (positive and negative) are unlike those of either MRs at Kazan or other MLT radars. Both MR systems provide the large SDT amplitudes, approximately 30 m/s and vertical wavelengths, approximately 55 km, for both components at middle latitudes in winter. They also show the well known strong SDT September feature (heights 85–100 km, the vertical wavelength ∼55–60 km), and the weak summer SDT for 80–91 km. HWM07 shows unrealistic amplitudes and phases above 90 km by height and month: minimal amplitudes in equinoxes and no September feature.〈/p〉 〈p〉The weak DT of middle to high latitudes provide similar amplitude and phase structures from both MRs, 1986–2002 and 2015–2017: largest amplitudes (10–12 or 8–10 m/s) for the evanescent meridional tide in summer, peaking in late July; weakest (0–2, 2–4 m/s) at 80 to 92–96 km, when the tide is vertically propagating (January, February, November, December) with a vertical wavelength near 40 km. Again, HWM07 differs in amplitude and phase structures: showing peak amplitudes in equinoxes: April, 15 m/s at 88 km; October, 21 m/s at 89 km.〈/p〉 〈p〉Coupling of the MR wind parameters with the ERA5 wind parameters is studied for a case in 2016. It is shown that the prevailing winds and DT amplitudes and phases of both datasets can be simply linked together, but that the ERA5 SDT amplitudes are significantly underestimated at the top model levels of the ERA5 reanalysis project.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 3 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): H.P. Gaikwad, A.K. Sharma, O.B. Gurav, G.A. Chavan, D.P. Nade, P.T. Patil, S.S. Nikte, G.P. Naniwadekar〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study presents the quasi-two-day wave (Q2DW) characteristics of the mesosphere and lower thermosphere (MLT) region obtained by taking hourly mean values of horizontal wind velocities for 4  years (August 2013–July 2017) through continuous measurements using a medium-frequency (MF) radar (operating frequency – 1.98 MHz) located at the low-latitude Indian station Kolhapur (16.8°N; 74.2°E). The MF radar located at Kolhapur was upgraded in 2013, and these results of Q2DW have been reported for the first time after upgrading. The present study investigated variability in seasonal, annual, interannual, and solar indices of Q2DWs traveling in zonal (EW) and meridional (NS) components in the MLT region. The Q2DW activity is observed to be stronger during austral summer (January–February) (EW = ∼5 m/s and NS = ∼8–10 m/s) than during boreal summer (June–July) (EW = ∼5 m/s and NS = ∼6–8 m/s). The Q2DW amplitudes are larger in the meridional component than in the zonal one. A strong semiannual oscillation (SAO) has been observed in Q2DWs, with peak during January–February and June–July. In addition, small enhancement is seen in meridional Q2DW in October (∼5–6 m/s). It is observed that the entire spectrum (40–60 h) measured between 86 and 94 km contributes to the SAO amplitudes during January–February and June–July, whereas the waves measured between 42 h and 52 h contribute to enhancement in October similar to that reported elsewhere. In general, the Q2DW amplitude shows large interannual variability. The easterlies developed in the global circulation model in Northern hemisphere during May intensify up to around summer solstice. Q2DW activity peaks during westerly shear zone and intensifies with time at a lower thermospheric altitude (above 90 km). Small positive correlations (r = 0.2 for sunspot number and r = 0.1 for 10.7 cm solar flux) have been observed between Q2DW amplitudes and solar activity.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 24 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Abdelrazek M.K. Shaltout, Eid A. Amin, M.M. Beheary, R.H. Hamid〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We investigate on the relationship between flares and coronal mass ejections (CMEs) in which a flare started before and after the CME events which differ in their physical properties, indicating potentially different initiation mechanisms. The physical properties of two types flare-correlated CME remain an interesting and important question in space weather. We study the relationship between flares and CMEs using a different approach requiring both temporal and spatial constraints during the period from December 1, 2008 to April 30, 2017 in which the CMEs data were acquired by SOHO/LASCO (Solar and Heliospheric Observatory/Large Angle Spectrometric Coronagraph) over the solar cycle 24. The soft X-ray flare flux data, such as flare class, location, onset time and integrated flux, are collected from Geostationary Environmental satellite (GOES) and XRT Flare catalogs. We selected 307 CMEs-flares pairs applying simultaneously temporal and spatial constraints in all events for the distinguish between two associated CME-flare types. We study the correlated properties of coincident flares and CMEs during this period, specifically separating the sample into two types: flares that precede a CME and flares that follow a CME. We found an opposite correlation relationship between the acceleration and velocity of CMEs in the After- and Before-CMEs events. We found a log-log relation between the width and mass of CMEs in the two associated types. The CMEs and flares properties show that there were significant differences in all physical parameters such as (mass, angular width, kinetic energy, speed and acceleration) between two flare-associated CME types.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 24 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Jesus A. Dominguez, Jonathan Whitlow〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉As part of our research on the feasibility of producing commodities from lunar regolith by thermal-driven processes with minimal terrestrial precursors we need to characterize, reproduce, and understand thermophysical properties of the molten regolith still unforeseen under the lunar vacuum conditions at a scalable sample size. Two unanticipated phenomena, apparently caused by lunar melt’s surface tension under vacuum, have been revealed in our research work, vacuum void formation and upwards migration. In this paper we present our findings and thinkable explanation on the upwards migration phenomenon experimentally observed and consistently replicated as JSC-1A lunar regolith simulant melted at high vacuum. Upwards migration of molten lunar regolith will make future lunar ISRU’s melting processes both challenging as molten bulk material would migrate upwards along the container’s walls, and also promising on new opportunities for alternative ISRU’s sustainable processes as regolith’s upwards migration takes place in uniformed thin-film pattern. Among the potential ISRU’s processes that might use controlled thermal thin-film-based migration without the necessity of terrestrial precursors are production of feedstock for 3D printing, fractional separation of regolith’s component’s (O〈sub〉2〈/sub〉, metals, and alloys) via pyrolysis, film coating, purification of valuables solid crystals including silicon, and fabrication of key elements for microfluidic, and MEMS devices. Thermal upwards migration phenomenon on JSC-1A’s melt is formulated and explained by the authors as due to thermal Marangoni effect (also known as thermo-capillarity) in which temperature gradients within the melt’s bulk and along the crucible’s wall yield the surface tension large enough to supersede the gravitational force and yield the experimentally observed upwards thin-film migration. As far as the authors know, upwards thermal migration of molten JSC-1A (or other lunar simulant regolith) under vacuum has not been reported in the literature. A thermal mathematical model accounting for thermal Marangoni effect on molten JSC-1A agrees with what experimentally was observed, the formation of the meniscus on the melt-wall surface interface along with an incipient upwards migration in thin-film pattern along the crucible wall that, according to the model, experiences large temperature gradient, an important factor to trigger the thermal Marangoni effect along with the fact that surface tension of the molten lunar regolith material is temperature dependent.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 6〈/p〉 〈p〉Author(s): B.R. Kalita, P.K. Bhuyan, P. Nath, A. Hazarika, K. Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The deviation of the IRI estimates of the monthly mean foF2 in the low mid latitude of 95°E–130°E longitude sector is investigated using simultaneous ground measurements at four stations during 2010–2014. The stations form two conjugate pairs of the same geo-magnetic latitude at two fixed longitudes enabling direct longitudinal and hemispheric comparison. The temporal, spatial, seasonal and solar activity variations of the deviations are discussed with reference to the longitudinal density variation in the transition region between low and midlatitudes. Cases of underestimation/overestimation as well as good estimate are noted. Underestimation (overestimation) in the daytime and overestimation (underestimation) in the nighttime of 95°E (130°E) are common. The longitudinal difference in the measurements suggests negative (positive) foF2 gradient from west to east in daytime (nighttime). In contrast, the IRI predicts flatter or increasing longitudinal profiles from 95°E to 130°E. The local time and longitudinal variation of the IRI deviations can be attributed to the combined role of the longitudinal EIA structure as well as midlatitude zonal wind-magnetic declination effect. The station/season independent deviations relate the role of solar activity representation in the IRI. These deviations may be attributed to the weak IRI response to rapid solar flux fluctuations.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 6〈/p〉 〈p〉Author(s): William A. Hartman, William D. Schmidl, Ronald Mikatarian, Ivan Galkin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A “Real-Time” plasma hazard assessment process was developed to support International Space Station (ISS) Program real-time decision-making providing solar array constraint relief information for Extravehicular Activities (EVAs) planning and operations. This process incorporates real-time ionospheric conditions, ISS solar arrays’ orientation, ISS flight attitude, and where the EVA will be performed on the ISS. This assessment requires real-time data that is presently provided by the Floating Potential Measurement Unit (FPMU) which measures the ISS floating potential (FP), along with ionospheric electron number density (Ne) and electron temperature (Te), in order to determine the present ISS environment. Once the present environment conditions are correlated with International Reference Ionosphere (IRI) values, IRI is used to forecast what the environment could become in the event of a severe geomagnetic storm. If the FPMU should fail, the Space Environments team needs another source of data which is utilized to support a short-term forecast for EVAs. The IRI Real-Time Assimilative Mapping (IRTAM) model is an ionospheric model that uses real-time measurements from a large network of digisondes to produce foF2 and hmF2 global maps in 15 min cadence. The Boeing Space Environments team has used the IRI coefficients produced in IRTAM to calculate the Ne along the ISS orbital track. The results of the IRTAM model have been compared to FPMU measurements and show excellent agreement. IRTAM has been identified as the FPMU back-up system that will be used to support the ISS Program if the FPMU should fail.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 3 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Guanglin Ma, Lixin Guo, Jutao Yang, Libin Lv, Jing Chen, Tong Xu, Shuji Hao, Jian Wu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Beat wave (BW) high frequency (HF) ionospheric heating experiments were conducted to generate very low frequency (VLF) waves. The VLF waves were registered with a VLF receiver located ∼15 km east of the European Incoherent Scatter (EISCAT) heating facility in Tromsø, Norway. A fluxgate magnetometer was used to monitor auroral electrojet current, and ionospheric conditions were measured using a Dynasonde. Correlation coefficients between VLF amplitudes and the deviation of geomagnetic north–south components were calculated. Experimental results show that strong and positive correlation exists the majority of the time, but sometimes no correlation or even a negative correlation occurred. This is consistent with similar past experiments that took place with exclusively AM generation. These results therefore support the conclusion that BW generation of VLF waves is no different than with AM, likely occurring in the D or lower E ionospheric region.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 3 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Xin Wei, Desheng Wen, Zongxi Song, Jiangbo Xi, Weikang Zhang, Gang Liu, Zhixin Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A full-sky star identification algorithm based on radial and dynamic cyclic patterns is presented with the aim of solving the “lost-in-space” problem. The dynamic cyclic pattern match is applied with a maximum cumulate comparison method to identify sensor-catalog pairings in initial match, which substantially eliminates the effects of the star position noise, magnitude noise, and false stars. After initial match pairings of stars are obtained, a chain part extension technique is employed to quickly search for the longest match chain as the final result. Experimental results indicate that the proposed algorithm is highly robust to star position noise, magnitude noise and false stars. In a series of simulations, the identification rate of the algorithm is 97.50% with 2.0 pixels star position noise, 96.90% with 0.4 Mv star magnitude noise and 95.30% with four false stars respectively. Moreover, the algorithm achieves an identification rate of 58.08% when only six stars are in the field of view.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 3 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): M. Arslan Tariq, Munawar Shah, M. Hernández-Pajares, Talat Iqbal〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The dual-frequency satellite-based measurements from Global Positioning System (GPS) may provide feasible ways of studying and potentially detecting of earthquake (EQ) related anomalies in the ionosphere. In this paper, GPS based Total Electron Content (TEC) data are studied for three major M 〉 7.0 EQs in Nepal and Iran-Iraq border during 2015–2017 by implementing statistical procedures on temporal and spatial scale. Previous studies presented different time interval of pre-seismic ionospheric anomalies, however, this study showed that EQs ionospheric precursors may occur within 10 days. Furthermore, the ionospheric anomalies on the suspected day occurred during UT = 08:00–12:00 h before the main shock. The Global Ionospheric Map TEC (GIM-TEC) data retrieved over the epicenter of M7.8 (Nepal EQ) showed a significant increase of 6 TECU on April 24, 2015 (one day before the main shock), which is recorded by the ground GPS station data of Islamabad (station lies within the EQ preparation zone). Furthermore, the spatial GIM-TEC result imply significant anomalies over the epicenter during the time interval between UT = 08:00–12:00 h (LT = 13:00–17:00). For M7.3 (Nepal EQ), the TEC anomalies were detected on May 10, 2015 (2 days before the event) in the temporal data. The spatial TEC data imply the huge clouds over the epicenter at about UT = 08:00–12:00 h on May 10, 2015, that may be associated with this EQ in the quiet geomagnetic storm conditions. Similarly, temporal and spatial TEC showed anomaly on November 3, 2017, during UT = 08:00–12:00 (9 days before the Iran-Iraq border EQ) after implementing the statistical method on it. Conversely, there exists a short-term but low magnitude TEC anomaly synchronized with a geomagnetic storm on November 7–8, 2017 (4 to 5 days prior to M7.3 Iran-Iraq border EQ). The diurnal and hourly GIM-TEC and VTEC data also imply the execution of ionospheric anomalies within 10 days prior to all events. All these positive anomalies in TEC may be due to the existence of a huge energy from the epicenter during the EQ preparation period.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 2 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Byung-Kyu Choi, Junseok Hong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Hwasong-15 (H-15), an intercontinental ballistic missile developed by North Korea, was launched at approximately 18:17 UT on 28 November 2017. It was reported that the H-15 missile reached an altitude of approximately 4500 km and traveled a distance of nearly 960 km from its launch site. We use GPS/GLONASS measurements obtained from the Korean GNSS network (KGN) to observe ionospheric total electron content (TEC) disturbances to the H-15 missile launch. TEC depletion by the H-15 missile is smaller than that by the 2016 Kwangmyongsong-4 (K-4) rocket. Two different background conditions (electron densities) result in a large difference of TEC depletions between the 2017 H-15 and the 2016 K-4. The fast-traveling ionospheric disturbances towards the southwest over South Korea were also observed ∼5–10 min after the missile launch.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 26 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): E.G. Cordaro, P. Venegas-Aravena, D. Laroze〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We report the existence of rapid variations in (effective) geomagnetic cutoff rigidity (Rc) between the equatorial and Antarctic zones adjacent to the Andes Mountains, revealed by the variation rate of geomagnetic cutoff rigidity (VRc) in the period 1975–2010. Our analysis is based on empirical records and theoretical models of the variations in cosmic rays and on the structure of geomagnetic fields. These have given us a different view of variations in Rc in time and space along the 70°W meridian, where secular variations in the geomagnetic field are strongly influenced by the proximity of the South Atlantic Magnetic Anomaly (SAMA), one of the most important characteristics of the terrestrial magnetic field that affects our planet, close from the equator to the 50°S parallel and from South America to South Africa. The VRc presents rapid changes in mid-latitudes where SAMA exerts its influence despite the existence of smooth changes in the geomagnetic field. This shows that these changes occur mainly in the spatial configuration, rather than in the temporal evolution of Rc. The analysis was performed using measurements from the Chilean Network of Cosmic Rays and Geomagnetism Observatories, equipped with BF-3 and latest generation He-3 neutron monitors, Fluxgate magnetometers, geomagnetic reference field (IGRF) and Tsyganenko 2001 model (just for completeness).〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Liang Sun〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A saturated fault-tolerant attitude tracking controller for disturbed rigid spacecraft is derived using nonlinear state feedback control method. The proposed controller achieves the constraints of control inputs by directly using the bounded function instead of the traditional saturation compensator technique, and the active tolerance to the partial loss of actuator effectiveness is also achieved by directly using the known bounds of the actuator faults in the controller. Specifically, compared with the traditional saturated control methods, a continuously bounded nonlinear function in the proposed controller is used to guarantee that the actuator outputs are smoothly bounded under the prescribed constraints. Based on some properties of the attitude tracking dynamics, the proposed controller can ensure the attitude tracking errors converge to small neighborhoods of zero via stability analysis in the Lyapunov framework. Simulation results are presented to illustrate the effectiveness of the control scheme.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Elisabeth Abbe, Thomas Renger, Maciej Sznajder, Benjamin Klemmed, Elisa Sachse, René Hübner, Tilman Schüler, Yves Bärtling, Benjamin Muchow, Martin Tajmar, Tino Schmiel〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Over the last years, Carbon Nanotubes (CNT) drew interdisciplinary attention. Regarding space technologies a variety of potential applications were proposed and investigated. However, no complex data on the behaviour and degradation process of carbon nanotubes under space environment exist. Therefore, it is necessary to investigate the performance of these new materials in space environment and to revaluate the application potential of CNTs in space technologies.〈/p〉 〈p〉Hence, CiREX (Carbon Nanotubes – Resistance Experiment) was developed as a part of a student project. It is a small and compact experiment, which is designed for CubeSat class space satellites. These are a class of nanosatellites with a standardized size and shape. The CiREX design, electrical measurements and the satellites interfaces will be discussed in detail. CiREX is the first in-situ space material experiment for CNTs.〈/p〉 〈p〉To evaluate the data obtained from CiREX, ground validation tests are mandatory. As part of an extensive test series the behaviour of CNTs under solar ultra violet light (UV) and vacuum ultraviolet light (VUV) was examined. Single-walled carbon nanotubes (SWNT), multi-walled carbon nanotubes (MWNT) and MWNT/resin composite (ME) were exposed to different light sources. After the exposure, the defect density was investigated with Raman spectroscopy. There is a clear indication that UV and VUV light can increase the defect density of untreated CNTs and influence the electrical behaviour.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 February 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 4〈/p〉 〈p〉Author(s): Melinda Nagy, Alexandre Lemerle, Paul Charbonneau〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The solar dipole moment at activity minimum is a good predictor of the strength of the subsequent solar cycle. Through a systematic analysis using a state-of-the-art 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si35.gif" overflow="scroll"〉〈mrow〉〈mn〉2〈/mn〉〈mo〉×〈/mo〉〈mn〉2〈/mn〉〈/mrow〉〈/math〉D solar dynamo model, we found that bipolar magnetic regions (BMR) with atypical characteristics can modify the strength of the next cycle via their impact on the buildup of the dipole moment as a sunspot cycle unfolds. In addition to summarizing these results, we present further effects of such “rogue” BMRs. These have the ability to generate hemispheric asymmetry in the subsequent sunspot cycle, since they modify the polar cap flux asymmetry of the ongoing cycle. We found strong correlation between the polar cap flux asymmetry of cycle 〈em〉i〈/em〉 and the total pseudo sunspot number asymmetry of cycle 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si36.gif" overflow="scroll"〉〈mrow〉〈mi〉i〈/mi〉〈mo〉+〈/mo〉〈mn〉1〈/mn〉〈/mrow〉〈/math〉. Good correlation also appears in the case of the time lag of the hemispheres of cycle 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si36.gif" overflow="scroll"〉〈mrow〉〈mi〉i〈/mi〉〈mo〉+〈/mo〉〈mn〉1〈/mn〉〈/mrow〉〈/math〉.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Bo Zhang, Yuanli Cai, Fei Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Hovering over an irregular-shaped asteroid is particularly challenging due to the large gravitational uncertainties and various external disturbances. An adaptive control scheme considering commanded acceleration and its change-rate saturation for hovering is developed in this paper. Taking full advantage of terminal sliding-mode control theory, first, we convert the double-saturated control problem to a new equivalent system by introducing a special bounded function, in which just control input saturation needs to be considered. Then, a continuous finite-time saturated controller is designed for the new system with the assistance of an constructed auxiliary subsystem. Additionally, an adaptive law is devised for the controller to avoid the requirement of the unknown upper bounds of the disturbances, rendering the control scheme especially suitable to asteroid hovering missions. The finite-time stability of the whole closed-loop system is proved via Lyapunov analysis. Numerical simulation studies are carried out, and the results demonstrate the design features and the desired performance.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 27 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Elena Ancona, Roman Ya. Kezerashvili〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉For extrasolar space exploration it might be very convenient to take advantage of space environmental effects such as solar radiation heating to accelerate a solar sail coated by materials that undergo thermal desorption at a particular temperature. Thermal desorption can provide additional thrust as heating liberates atoms, embedded on the surface of the solar sail. We are considering orbital dynamics of a solar sail coated with materials that undergo thermal desorption at a specific temperature, as a result of heating by solar radiation at a particular heliocentric distance, and focus on two scenarios that only differ in the way the sail approaches the Sun. For each scenario once the perihelion is reached, the sail coat undergoes thermal desorption. When the desorption process ends, the sail then escapes the Solar System having the conventional acceleration due to solar radiation pressure. We study the dependence of a cruise speed of a solar sail on perihelion of the orbit where the solar sail is deployed. The following scenarios are considered and analyzed: (1) Hohmann transfer plus thermal desorption. In this scenario the sail would be carried as a payload to the perihelion with a conventional propulsion system by a Hohmann transfer from Earth’s orbit to an orbit very close to the Sun and then be deployed. Our calculations show that the cruise speed of the solar sail varies from 173 km/s to 325 km/s that corresponds to perihelion 0.3 AU and 0.1 AU, respectively. (2) Elliptical transfer plus Slingshot plus thermal desorption. In this scenario the transfer occurs from Earth’s orbit to Jupiter’s orbit; then a Jupiter’s fly-by leads to the orbit close to the Sun, where the sail is deployed and thermal desorption comes active. In this case the cruise speed of the solar sail varies from 187 km/s to 331 km/s depending on the perihelion of the orbit. Our study analyses and compares the different scenarios in which thermal desorption comes beside traditional propulsion systems for extrasolar space exploration.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 21 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Aleix Pinardell Pons, Ron Noomen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉GTO objects can potentially collide with operative satellites in LEO and GEO protected regions. Internationally accepted debris mitigation guidelines require that these objects exit these protected regions within 25 years, e.g. by re-entering and burning up in Earth’s atmosphere. In this paper, an inventory of the GTO debris generated from Ariane 5 launches in the period 2012–2017 is provided, and it is expected that none of these objects will re-enter within 25 years. For future launches, natural perturbations can be exploited to increase compliance with mitigation guidelines without the use of extra propellant or complex de-orbiting systems, which is attractive from an economic point of view. The lifetime of GTO objects is very sensitive to initial conditions and some environmental and body-related parameters, mainly due to the effect of solar gravity on the perigee altitude. As a consequence, the lifetime of a specific GTO object cannot be predicted accurately, but its probability of re-entering in less than 25 years can be estimated with proper accuracy by following a statistical approach. By propagating the orbits of over 800,000 simulated Ariane 5 GTO objects, it was found that the launch time leading to the highest probability of compliance with debris mitigation guidelines for GEO launches from Kourou corresponds to about 2 PM local time, regardless of the date of launch, which leads to compliance rates ranging from 60 to 100%. Current practice is to launch at around 5–9 PM, so a change in procedures would be required in order to reach a higher degree of compliance with debris mitigation guidelines, which was predicted to be on average below 20% for the objects generated in the period 2012–2017.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 5〈/p〉 〈p〉Author(s): B. Premkumar, K. Chenna Reddy, G. Yellaiah, K. Kishore Kumar〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The decay times of meteor radar echoes have been used for decades to investigate characteristics of the mesosphere and lower thermosphere (MLT) region. As the meteor echo decay time depends on background atmospheric parameters, in the present communication, we examine the seasonal variation of the vertical distributions of underdense meteor echo decay times with respect to echo strength. Observations from two similar radars located at two distinct geographical locations, Thumba (8.5°N, 77°E) and Eureka (80°N, 85.8°W) were used for the present study. Here, the radar received signal power is categorized into strong and weak echoes and vertical profiles of their decay times are constructed. It has been noticed that the monthly mean decay time vertical profile turning altitude (i.e., inflection point) varies in the range of 80–87 km of altitude depending on latitude. The turning altitude is observed at relatively lower heights in the winter than in summer at both the latitudes. The present analysis shows that the meteor decay time below the mean turning altitude follows a decreasing trend with decreasing altitude, which is quite distinct to the behaviour of ambipolar diffusion. It is also observed that there is a difference in mean decay time of strong and weak echoes below 90 km of altitude, which is very prominently seen at lower altitudes. This difference shows a seasonal pattern at high latitude, but does not show any seasonal variation at low latitude. The present results are discussed in light of current understanding of the meteor decay time.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 11 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Telmo dos Santos Klipp, Adriano Petry, Jonas Rodrigues de Souza, Gabriel Sandim Falcão, Haroldo Fraga de Campos Velho, Eurico Rodrigues de Paula, Felix Antreich, Mainul Hoque, Martin Kriegel, Jens Berdermann, Norbert Jakowski, Isabel Fernandez-Gomez, Claudia Borries, Hiroatsu Sato, Volker Wilken〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This work shows a 20-month statistical evaluation of different Total Electron Content (TEC) estimators for the Central and South America regions. The TEC provided by the International GNSS Service (IGS) in the area covered around the monitoring GNSS stations are used as reference values, and they are compared to TEC estimates from the physics-based (Sheffield University Plasmasphere Ionosphere Model—PIM) and the empirical (Neustrelitz TEC Model-Global—NTCM-GL) models. The mean TEC values show strong dependence on both solar activity and seasonal variation. A clear response was noticed for a period close to 27 days due to the mean solar rotation, as seen in the solar flux measurements. Consistently, the mean TEC values present an annual variation with maxima during December solstices for southern stations with geographic latitudes greater than 25〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.svg"〉〈mrow〉〈mi〉°〈/mi〉〈/mrow〉〈/math〉 S. Semi-annual dependence has been observed in TEC for the sector between 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"〉〈mrow〉〈mo〉±〈/mo〉〈/mrow〉〈/math〉25〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.svg"〉〈mrow〉〈mi〉°〈/mi〉〈/mrow〉〈/math〉 of geographical latitude but with modulations caused by fluctuation in the solar radiation. We observed a high correlation between solar radio flux F10.7 and NTCM-GL outputs. The fast increases in F10.7 index have caused significant differences between IGS data and NTCM-GL results mainly for equatorial and low latitudes. For the initial months of the evaluated period (January–April, 2016), the errors of the physics-based model were considerably larger, mainly near the equatorial ionization anomaly. The discrepancies observed in SUPIM results are mainly due to inputs of solar EUV flux. The EUVAC model has underestimated EUV flux between January and April, 2016, when the solar activity was moderated and Solar2000 model has overestimated such flux during low solar cycle period between May and August, 2017. In relation to IGS data, the two assessed models presented smaller differences during the June solstice season of 2016.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 10 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Jan-Uwe Ness〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Super Soft X-ray Sources (SSS) are powered by nuclear burning on the surface of an accreting white dwarf, they are seen around 0.1–1 keV (thus in the soft X-ray regime), depending on effective temperature and the amount of intervening interstellar neutral hydrogen (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"〉〈mrow〉〈msub〉〈mrow〉〈mi〉N〈/mi〉〈/mrow〉〈mrow〉〈mi mathvariant="normal"〉H〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉). The most realistic model to derive physical parameters from observed SSS spectra would be an atmosphere model that simulates the radiation transport processes. However, observed SSS high-resolution grating spectra reveal highly complex details that cast doubts on the feasibility of achieving unique results from atmosphere modeling. In this article, I discuss two independent atmosphere model analyses of the same data set, leading to different results. I then show some of the details that complicate the analysis and conclude that we need to approach the interpretation of high-resolution SSS spectra differently. We need to focus more on the data than the models and to use more phenomenological approaches as is traditionally done with optical spectra.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 11 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): A.O. Afolayan, J.S. Mandeep, M. Abdullah, S.M. Buhari〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study presents an analysis of the observed north-south asymmetry of the range spread F (RSF) intensity at the low latitude region during an equinoctial month of different solar epochs (2002, 2015 and 2017). The ionospheric parameters were obtained during geomagnetic quiet days from four digisonde stations located along the Brazilian longitude, which include a dip equator station (Sao Luiz (SL: 2.33 S, 44.2 W)), conjugate stations (Campo Grande (CG: 20.5°S, 55°W) and Boa Vista (BV: 2.8°N, 60.7°W)) and another low latitude station (Cachoeira Paulista (CP: 22.7°S, 45°W)). The results highlight the competing effect of the post-sunset electric field strength and the trans-equatorial wind on the latitudinal distribution of the irregularity intensity at both hemispheres under varying background ionospheric condition. The RSF intensity was seen to reduce as the solar flux index decreased and the latitudinal peak shifted closer to the dip equator. This was dependent on the variation of the field line mapped irregularity spectrum and the density gradient. Likewise, the north-south asymmetry in the irregularity occurrence was seen to become more significant as a denser ionosphere was observed at the hemisphere with the equatorward meridional wind. This has further proven that the non-linear cascading of the plasma irregularity across the low latitude region is strongly influenced by the local electric field.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 64, Issue 8〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: Available online 10 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Liang Tang, Kebei Zhang, Xin Guan, Renjian Hao, Youyi Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Space telescope ultrahigh precision pointing control requires the spacecraft platform to provide an ultra-quiet working environment. Vibration isolator rejection control and the multi-stage integrated control method is believed to be one of the best methods to improve the space telescope attitude control performance. In this paper, the fine dynamics model of multi-stage spacecraft systems is presented and the multi-stage integrated controller design techniques are provided. Effectiveness of the multi-stage integrated control approach is demonstrated by both the numerical simulation and experiment results. An integrated design and demonstrated experimental environment is developed for high-fidelity control performance assessment. The verification experiments for the space telescope attitude control and vibration control are carried out. The results show that the pointing accuracy and stability of the line-of-sight (LOS) for space telescope are improved at least one order by the multi-stage integrated control method.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 10 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Yijun Tian, Lifen Sui, Guorui Xiao, Dongqing Zhao, Hongzhou Chai, Chunhe Liu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The overlapping carrier frequencies L1/E1, L5/E5a and B2/E5b from GPS/Galileo/BDS allow inter-system double-differencing of observations, which shows a clear advantage over differencing of the observations of each constellation independently. However, the inter-system biases destroy the integer nature of the inter-system double-differencing ambiguities. Two methods of direct rounding and parameter estimation are used to determine the ISB value. By analyzing data collected from Curtin University from 2015 to 2018, the phase and code inter-system bias (ISB) are related to the receiver type, firmware version and the selected overlapping frequency. Upgrade of receiver firmware version results in changes of ISB values. For example, the upgrade of Javad firmware in Dec, 15, 2017 causes the difference of 0.5 cycles ISB between BDS GEO and non-GEO satellites. By comparing the three dynamic models which include white noise process, random walk process, and random constant in the parameter estimation method, the ISB determined by the random constant model is consistent with the value obtained by the direct rounding method. After the calibration of ISBs, the performances of tightly combined positioning are assessed. The success rate of ambiguity resolution and accuracy of positioning for the tight combination (TC) are significantly improved in comparison with that for the loose combination (LC) over short baselines. For L5/E5a, on which only few satellites can be observed, the maximum increase in success rates of ambiguity resolution can reach 31.7%, i.e., from 54.9% of LC to larger than 86.6% of TC, and the positioning accuracies can even be increased by 0.13 m, i.e., from 0.208 of LC to 0.074 m of TC in East direction for the mix-receiver TRIMBLE NETR9-SEPT POLARX4 in 2018.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 10 September 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Samson Tilahun, Nigussie Mezgebe〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper demonstrates that real-time, dip-equatorial, daytime, vertical 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si18.svg"〉〈mrow〉〈mi mathvariant="bold"〉E〈/mi〉〈mo〉×〈/mo〉〈mi mathvariant="bold"〉B〈/mi〉〈/mrow〉〈/math〉 drift velocities can be derived from ground-based magnetometers over an understudied Eastern African longitude sector. An integrated third order periodic mean partial least square (PMPLS) technique is introduced for vertical drift estimation. The vertical drift data sets, obtained from Communication/Navigation Outage Forecasting Systems (C/NOFS) during an extended period of 2008–2013 on quiet geomagnetic storm conditions were used. The paper also characterizes the influence of daytime horizontal magnetic field perturbations for the vertical 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si19.svg"〉〈mrow〉〈mi mathvariant="bold"〉E〈/mi〉〈mo〉×〈/mo〉〈mi mathvariant="bold"〉B〈/mi〉〈/mrow〉〈/math〉 drift velocity and therefore for the evening time plasma irregularities over Addis Ababa, Ethiopia (9.03〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si20.svg"〉〈mrow〉〈mi〉°〈/mi〉〈/mrow〉〈/math〉 N, 38.7〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si21.svg"〉〈mrow〉〈mi〉°〈/mi〉〈/mrow〉〈/math〉 E, dip latitude 2.09〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si22.svg"〉〈mrow〉〈mi〉°〈/mi〉〈/mrow〉〈/math〉). Linear and non-linear coefficients of the C/NOFS 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si23.svg"〉〈mrow〉〈mi mathvariant="bold"〉E〈/mi〉〈mo〉×〈/mo〉〈mi mathvariant="bold"〉B〈/mi〉〈/mrow〉〈/math〉 drift variations were calculated in order to capture the trend of the variation on the temporal basis. Furthermore amplified (07:00–10:00 LT), saturated (10:00–16:00 LT) and linear (16:00–1900 LT) variations of vertical drift are found. Results are compared with independent vertical ion drift estimates of International Reference Ionosphere 2012 (IRI-2012) and partial least square (PLS). PMPLS performance was better in terms of capturing the daytime trends of observed C/NOFS 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si24.svg"〉〈mrow〉〈mi mathvariant="bold"〉E〈/mi〉〈mo〉×〈/mo〉〈mi mathvariant="bold"〉B〈/mi〉〈/mrow〉〈/math〉 drift. Overall, PMPLS results showed better agreement with the observation C/NOFS 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si25.svg"〉〈mrow〉〈mi mathvariant="bold"〉E〈/mi〉〈mo〉×〈/mo〉〈mi mathvariant="bold"〉B〈/mi〉〈/mrow〉〈/math〉 drift with maximum and minimum root-mean-square errors (RMSEs) of 12.67 m/s and 9.2 m/s during noontime and post noontimes respectively. Despite 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si26.svg"〉〈mrow〉〈mi mathvariant="normal"〉Δ〈/mi〉〈mi〉H〈/mi〉〈/mrow〉〈/math〉 are weaker-positive for most of our observations during prereversal enhancement (PRE) hours the strength of the daytime 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si27.svg"〉〈mrow〉〈mi mathvariant="normal"〉Δ〈/mi〉〈mi〉H〈/mi〉〈/mrow〉〈/math〉 are somewhat related to the formation of the post-sunset irregularities.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 14 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Nirmala Bai Jadala, Miriyala Sridhar, Nirvikar Dashora, Gopa Dutta〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper presents annual, seasonal and diurnal variations of integrated water vapor (IWV) derived from Global Positioning System (GPS) measurements for a tropical site, Hyderabad (17.4° N, 78.46° E). The zenith wet delay (ZWD) due to the troposphere has been computed using GPS observations and collocated meteorological data. ZWD is converted to IWV with very little added uncertainty. Mean monthly IWV values show maximum in July (~50 kg m〈sup〉−2〈/sup〉) and minimum in December (~15 kg m〈sup〉−2〈/sup〉). Fast Fourier Transform (FFT) and Harmonic analyses methods have been adopted to extract amplitudes and phases of diurnal (24 h), semi-diurnal (12 h) and ter-diurnal (8 h) oscillations which yielded comparable results. Amplitude of the 24 h component is observed to be maximum in spring whereas 12 h and 8 h components maximize in summer. A cross-correlation study between available daily IWV values and corresponding surface temperatures over one year produced a good correlation coefficient (0.44). The correlation obtained for different seasons got reduced to 0.25, 0.02, −0.39 and 0.21 for winter, spring, summer and autumn seasons respectively. The correlation between IWV and rainfall is poor. The coefficients obtained for the whole year is 0.05 and −0.13 for the rainy season.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 11 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Heather L. Roman-Stork, Bulusu Subrahmanyam, Corinne B. Trott〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In the Bay of Bengal (BoB), surface circulation is strongly influenced by the Indian Monsoon and notable local eddying that modulates the East India Coastal Current (EICC). In this study, we apply an eddy tracking algorithm to 25 years (1993–2018) of satellite altimetric observations to identify, analyze, and track mesoscale eddies in the BoB from their generation to dissipation. We compare the characteristics and trajectories of these eddies during the southwest (SW) and northeast (NE) monsoon seasons and during the pre- and post-SW monsoon periods to better understand the seasonality of the local eddy field. We find high eddy generation in the eastern BoB associated with instability induced by coastal Kelvin waves and the westward propagating Rossby waves, but we found the most robust eddies in the western BoB around the EICC. Ocean heat content (OHC) in the BoB was compared with warm-core eddies and we find that warm-core eddies drive changes in OHC. We also compared the eddy field during strong and weak SW monsoon forcing and with varying Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO) conditions, finding a statistically significant relationship with warm-core eddies and sea surface temperatures (SSTs; R〈sup〉2〈/sup〉 = 91%) and outgoing longwave radiation (OLR; R〈sup〉2〈/sup〉 = 88%) during periods of strong ENSO and IOD forcing. To understand the impact of these eddies on local atmospheric convection we found the composite surface structure of anticyclonic and cyclonic eddies of warm-core and cold-core SSTs, finding a close relationship between the eddy-composite SSTs and OLR.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 11 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): E. Becker, M. Grygalashvyly, G.R. Sonnemann〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Based on an advanced numerical model for excited hydroxyl (OH*) we simulate the effects of gravity waves (GWs) on the OH*-layer in the upper mesosphere. The OH* model takes into account 1) production by the reaction of atomic hydrogen (H) with ozone (O〈sub〉3〈/sub〉), 2) deactivation by atomic oxygen (O), molecular oxygen (O〈sub〉2〈/sub〉), and molecular nitrogen (N〈sub〉2〈/sub〉), 3) spontaneous emission, and 4) loss due to chemical reaction with O. This OH* model is part of a chemistry-transport model (CTM) which is driven by the high-resolution dynamics from the KMCM (Kühlungsborn Mechanistic general Circulation Model) which simulates mid-frequency GWs and their effects on the mean flow in the MLT explicitly. We find that the maximum number density and the height of the OH*-layer peak are strongly determined by the distribution of atomic oxygen and by the temperature. As a results, there are two ways how GWs influence the OH*-layer: 1) through the instantaneous modulation by O and T on short time scales (a few hours), and 2) through vertical mixing of O (days to weeks). The instantaneous variations of the OH*-layer peak altitude due to GWs amount to 5-10 km. Such variations would introduce significant biases in the GW parameters derived from airglow when assuming a constant pressure level of the emission height. Performing a sensitivity experiment we find that on average, the vertical mixing by GWs moves the OH*-layer down by ∼2-7 km and increases its number density by more than 50%. This effect is strongest at middle and high latitudes during winter where secondary GWs generated in the stratopause region account for large GW amplitudes.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 3 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Wei Shao, Jincheng Xie, Liang Cao, Junge Leng, Boning Wang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉In the field of visual navigation, crater is an ideal navigation landmark on planet surface, because of its universality and significance. During the descent phase of lander, crater needs to be extracted and matched. However, as the landing proceeds, images taken by the on-board camera will change, such as the variation of scale, translation, rotation, illumination which will increase the difficulty of the matching algorithm.〈/p〉 〈p〉This paper proposes a more accurate and faster crater matching algorithm based on feature descriptor. This algorithm is designed for navigation during the descending phase. It has the invariance of scaling, rotation, illumination. First, this algorithm extracts circular arc by Gaussian Pyramid and ELSD algorithm, so that this algorithm has the invariance against scale variation. Then, in order to describe the circular arc, this algorithm determine the direction of the circular arc by the direction histogram. And this algorithm constructs the circular arc band descriptors in the support region to achieve translation, rotation and illumination invariance. At last, matching criteria is the combination of the Nearest Neighbor Distance Ratio (NNDR) and the Euclidean distance constraint. The results are obtained under different image variations. The matching results show that this crater matching algorithm has high crater correct extracting and matching rate and high computationally efficient.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 2 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): W.Z. Shao, Y.Y. Hu, G. Zheng, L.N. Cai, X.Z. Yuan, J.C. Zou〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Chinese Gaofen-3 (GF-3) synthetic aperture radar (SAR) acquired in wave mode (WV) and quad-polarization stripmap (QPS) mode default operates in quad-polarization (vertical–vertical (VV), vertical-horizontal (VH), horizontal-horizontal (HH) and horizontal-vertical (HV)) modes. To date, more than GF-3 SAR vignettes following about 110 orbits acquired in WV and QPS mode have been recorded during the mission from April 2016 to December 2017. In the vignettes, ocean surface waves signatures, that are wave-look patterns, are visible in cross-polarization (basically VH). These vignettes are collocated with surface sea state parameters simulated from numerical WAVEWATCH-III (WW3) wave model using a 0.1° grid. There are 11,269 matchups available for studying the relation between sea state parameters and SAR-derived parameters in VH-polarization. A well-known empirical CWAVE model, herein renamed as CPCWAVE_GF3, is adopted for sea state parameter retrieval from GF-3 SAR vignettes with the SAR parameters in the cross-polarization channel. The method yielded a significant correlation coefficient (COR) of 0.79 for wave height (SWH) and 0.72 for second-order cross-zero mean wave period (MWP). Validation against 76 moored buoys resulted in a 0.49 m RMSE of SWH with a 0.21 m scatter index (SI) and validation against 71 moored buoys resulted in a 1.01 s RMSE of MWP with a 0.13 s SI. The comparison of SWH with 116 footprints from the altimeter of Jason-2 also shows a 0.46 m RMSE of SWH with a 0.19 m SI. Our work demonstrates the feasibility of wave retrieval from GF-3 SAR using cross-polarization channels parameters.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 2 November 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Sophie Le Gac, François Boy, Denis Blumstein, Léa Lasson, Nicolas Picot〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉In the past 25 years, radar altimeters have been designed and operated primarily for ocean observation. However, over the past decade there has been a growing interest for altimetry measurements over inland waters. Studying lakes, reservoirs and rivers water level is of prime importance for the hydrology community to assess the Earth’s global resources of fresh water.〈/p〉 〈p〉Satellite altimetry is key to providing such global and continuous datasets of water surface height. Indeed, much progress has been made in altimeters capability to acquire quality measurements over inland waters.〈/p〉 〈p〉In this paper we present an overview of major technical evolutions of the tracking function of altimeters, from Jason-2/POS3 and SARAL/AltiKa to Jason-3/POS3B and Sentinel-3/SRAL and the improvements brought by the Open-Loop Tracking Command (OLTC) to extend the altimeter observation domain to inland waters. The OLTC is an on-board feature used to set the altimeter waveforms reception window, containing a priori elevation information built from a dedicated database of hydrological targets. This paper focuses on the use of OLTC for acquiring reliable water signal rather than discussing the accuracy of the retrieved height, which constitutes a further step in the altimeter data processing chain.〈/p〉 〈p〉We show how Jason-3 and Sentinel-3 altimetry missions are currently able to observe and monitor about 70,000 hydrological targets over the globe and how it is contributing in building a global dataset of inland waters level, in preparation for future missions such as Sentinel-6 and the Surface Water Ocean Topography mission (SWOT).〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 31 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Marco Bassetto, Andrea Caruso, Alessandro A. Quarta, Giovanni Mengali〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The interaction between electromagnetic waves and matter is the working principle of a photon-propelled spacecraft, which extracts momentum from the solar radiation to obtain a propulsive acceleration. An example is offered by solar sails, which use a thin membrane to reflect the impinging photons. The solar radiation momentum may actually be transferred to matter by means of various optical phenomena, such as absorption, emission, or refraction. This paper deals with the novel concept of a refractive sail, through which the Sun’s light is refracted by crossing a film made of polymeric micro-prisms. The main feature of a refractive sail is to give a large transverse component of thrust even when the sail nominal plane is orthogonal to the Sun-spacecraft line. Starting from the recent literature results, this paper proposes a semi-analytical thrust model that estimates the characteristics of the propulsive acceleration vector as a function of the sail attitude angles. Such a mathematical model is then used to analyze a simplified Earth-Mars and Earth-Venus interplanetary transfer within an optimal framework.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 31 October 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): M. Koroglu, F. Arikan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Forcings from above and below the ionosphere can cause disturbances that need to be detected and corrected for navigation systems. Ground Based Augmentation Systems (GBAS) are used to give corrections to aircraft navigation systems while landing. These systems use regional ionosphere monitoring algorithms to detect the anomalies in the ionosphere. The aim of this study is to understand occurrence of ionosphere anomalies and their trends over Turkey. A comprehensive analysis of spatio-temporal variability of ionosphere is carried out for a midlatitude GPS network using Slant Total Electron Content (STEC). Differential Rate Of TEC (DROT), which is a measure of the amount of deviation of temporal derivative of TEC from its trend, is used to detect and classify the level of such disturbances. The GPS satellite tracks are grouped into north, east, west and over directions. The 24 h is divided into six time intervals. The percentage occurrence of each DROT category and the deviation from STEC trend in magnitude are calculated and grouped into satellite track directions and time intervals for 2010 (low solar activity), 2011 and 2012 (medium solar activity). The highest level of disturbances is observed in north and west directions, and during sunrise and sunset hours. The dominant periods of percentage occurrences are diurnal (22–25 h), semidiurnal (12–13 h) and terdiurnal (8–9 h) followed by quasi two-day and quasi 16-day periods. Disturbances corresponding to 50% 〈 DROT 〈 70% are mostly visible during low solar activity years with magnitudes from 1 to 2 TECU. Geomagnetic storms can cause aperiodic larger scale disturbances that are mostly correlated with DROT 〉 70%. In 2012, the magnitude of such disturbances can reach 5 TECU. The anisotropic and dynamic nature of midlatitude ionosphere is reflected in the spatio-temporal and spectral distributions of DROT, and their percentage occurrences. This study serves a basis for future studies about development of a regional ionosphere monitoring for Turkey.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 6 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Diogene A. Dei Tos, Mirco Rasotto, Florian Renk, Francesco Topputo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A proposed mission extension for LISA Pathfinder involved redirecting the probe to the Sun–Earth gravitational saddle point. Realistic models for both space and ground segments were used to carry out a number of analyses for trajectory design, orbit determination, and navigation cost. In this work, we present the methods that allow assessing the feasibility of flying general limited-control-authority spacecraft in highly nonlinear dynamics, and in particular of the proposed mission extension in a statistically reliable approach. Solutions for transfers from the Sun–Earth 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉L〈/mi〉〈/mrow〉〈mrow〉〈mn〉1〈/mn〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉L〈/mi〉〈/mrow〉〈mrow〉〈mn〉2〈/mn〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 to the saddle point are shown, which feature very low 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.gif" overflow="scroll"〉〈mrow〉〈mi mathvariant="normal"〉Δ〈/mi〉〈mi〉v〈/mi〉〈/mrow〉〈/math〉 consumption, from few centimeters per second to 10 m/s. The analysis is then specialized to the case of LISA Pathfinder, for which several solutions are presented. This work gives evidence that LISA Pathfinder might have been able to fly-through the saddle point, provided initial tracking errors within 10 km in each position component and 0.1 m/s in each velocity component. A critical discussion on the opportunistic mission extension is eventually made.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 11 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Fabian Schiemenz, Jens Utzmann, Hakan Kayal〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The call for realistic covariances/uncertainties in orbit determination/estimation and propagation is becoming louder. The main reason for unrealistic uncertainties is, in most cases, a disregard of force model uncertainties, i.e. the calculated covariances are based only on the measurement uncertainties. For this reason the covariances are often scaled in practice to avoid misjudgment of orbit knowledge. J. Emmert has recently shown how solar flux uncertainties can be propagated to in-track orbit position errors in the case of long-term orbit propagation. In his method, the density error resulting from solar flux errors is obtained via the underlying atmospheric model. In this paper, a universal analytic approximation of density uncertainty is presented, which is a fast, yet reliable, alternative to the case-based propagation via the atmospheric model. The major benefit of the proposed analytic estimations is that they seamlessly integrate with orbit estimation/propagation. The uncertainty estimate can directly be computed without an additional call to the atmospheric model.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 12 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Fabian Schiemenz, Jens Utzmann, Hakan Kayal〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉Density uncertainty is the major driver of unrealistic covariances for objects in low Earth orbits. The analytic propagation of uncertainties in the neutral atmospheric density to resulting uncertainties in the orbital position and velocity has only received little attention in the literature so far.〈/p〉 〈p〉The main contribution of the paper at hand is the analytic development of an orbital state-vector error variance-covariance matrix that models the propagation of uncertainties in atmospheric density to the orbital state-vector error in the Geocentric Celestial Reference Frame (GCRF). Also extensions of the classical batch weighted least squares (WLS) and the sequential batch weighted least squares algorithms, which allow to incorporate this covariance matrix as process-noise, are presented.〈/p〉 〈p〉Numerical simulations with three different semi-empirical models are provided to validate the derivations. It is shown that the extension of the WLS-algorithm in combination with the density uncertainty GCRF covariance matrix is able to consistently perform orbit and covariance estimation, which is not the case without density uncertainty consideration in a classical WLS algorithm.〈/p〉 〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 11 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): A. Shalchi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We study the random walk of magnetic field lines as well as field line separation in a magnetized plasma such as the solar wind or the interstellar medium. By doing so we focus on turbulence with small Kubo numbers. For field line random walk this allows us to employ an approach based on a Taylor expansion which is essentially an expansion in the Kubo number. Compared to previous non-linear descriptions, no assumption concerning the field line distribution or diffusivity has to be made. Based on this approach, we compute corrections to the quasi-linear formula allowing us also to test assumptions usually made in non-linear theories of field line random walk. We show that up to the considered order, the assumption of Gaussian statistics does not alter the diffusion coefficient whereas the diffusion approximation provides a correction term which is a factor two too large. We also discuss the separation of two magnetic field lines. We develop a quasi-linear theory for field line separation and introduce a fundamental scale of turbulence describing its transverse structure. Furthermore, we discuss applications of our results in the theory of energetic particle transport. Besides quasi-linear diffusion we also discuss compound sub-diffusion as well as the recovery of diffusion due to transverse complexity. Furthermore, we derive a formula for the perpendicular diffusion coefficient of energetic particles similar compared to the famous Rechester & Rosenbluth result. Applications in astrophysics are also discussed.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 8 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Rabindra A. Gangapersaud, Guangjun Liu, Anton H.J. de Ruiter〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The detumbling of a non-cooperative, tumbling target by a space robot for the purpose of performing on-orbit servicing is a challenging and risky endeavour. The formulation of a detumbling control strategy must respect end-effector force/torque limits of the space robot without prior knowledge of the target’s inertial parameters (mass, inertia tensor, location of center of mass). Prior studies have formulated detumbling strategies with the assumption of accurate knowledge of the target’s inertial parameters. However, obtaining accurate estimates of the target’s inertial parameters is difficult, and parameter uncertainty may lead to instability and violation of the end-effector’s force/torque limits. In this paper, a novel detumbling strategy is presented to detumble targets without prior knowledge of their inertial parameters. Detumbling of the target is achieved by controlling the space robot to follow a reference force/torque that is designed to detumble the target while respecting force/torque limits at the end-effector, without the use of the target’s inertial parameters. To ensure stable detumbling of the target, a robust compensator is designed based on bounds of the target’s unknown inertial parameters. Furthermore, in order to reduce the robust control gains, bounds on the target’s unknown inertial parameters are estimated in real-time once the post-grasping detumbling process starts. Stability proof of the closed-loop system has been provided. Numerical simulations have been conducted, and the results have demonstrated the effectiveness of the proposed method.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 8 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Alireza Mahmoudian, Mohammad Javad Kalaee〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This work presents the study on the electromagnetic wave penetration and propagation into the ionosphere in the frequency range of 100 Hz to 3 kHz and 3 kHz to 10 kHz, corresponding to the Ultra Low Frequency (ULF) and Very Low Frequency (VLF), respectively, for various types of applications including earthquake prediction. The main idea here is to investigate the efficiency of whistler/helicon wave generation in the E-region under different ionospheric conditions by solving Maxwell’s equations and incorporating ionospheric conditions through the Hall, Pedersen, and parallel conductivities. Specifically, the effect of pulse and continuous probing of the lower ionosphere with ULF-VLF signals and the generation of secondary waves and currents due to high conductivities in the E-region is studied. The characteristics and applications of the excited Helicon ULF-VLF waves are discussed. The effect of background ionospheric parameters such as the electron density and ionospheric disturbances due to pre-earthquake conditions and other natural sources including lightning discharges on the excitation and penetration of ULF-VLF waves into the E-region is investigated. The efficiency of this technique in developing a monitoring system to detect and locate seismic activities is discussed.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 9 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Jean-Sébastien Ardaens, Gabriella Gaias〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉A practical and effective numerical method is presented, aiming at solving the problem of initial relative orbit determination using solely line-of-sight measurements. The proposed approach exploits the small discrepancies which can be observed between a linear and a more advanced relative motion model. The method consists in systematically performing a series of least-squares adjustments at varying intersatellite distances in the vicinity of a family of collinear solutions coming from the linear theory. The solution presenting the smallest fitting residuals is then selected. The investigations specifically focus on the rendezvous in low Earth near-circular orbit with a noncooperative target. The objective is to determine the relative state of the formation using only bearing observations when the spacecraft are separated by a few dozen kilometers without any a priori additional information. The method is validated with flight data coming from the ARGON (2012) and AVANTI (2016) experiments. Both cases demonstrate that an observation time span of a few maneuver-free orbits is enough to compute a solution which can compete with Two-Line Elements in terms of accuracy.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 6 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Ju Hong, Rui Tu, Yaping Gao, Rui Zhang, Lihong Fan, Pengfei Zhang, Jinhai Liu〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The impact of inter-system bias (ISB) on integrated precise point positioning (PPP) in multi-GNSS cannot be ignored. Precise orbit/clock products of Multi-GNSS Experiment (MGEX) satellites are diverse and gradually maturing. Analysing short-term and long-term variation characteristics of different types of ISB is thus helpful in understanding their error characteristics. In this study, ISB estimation models were proposed for GPS, GLONASS, BDS, and GALILEO systems with ionosphere-free (IF) combination observations. Then, the characteristics of ISB were mostly analyzed in detail with reverse and forward filtering method. Finally, according to the diurnal variation characteristics of ISB, which were estimated using precise products from several analysis centres, different processing strategies were adopted for ISBs to determine the optional solution strategies. Preliminary results are as follows: (1) The daily mean values of ISB estimated using the same analysis centre products between GPS and GLONASS as well as between GPS and BDS differed, but they were significantly correlated with receiver types. (2) Precise products of the same satellite system exhibited systematic deviations between analysis centres, although they were consistent on the weekly scale; however, the system bias of different satellite systems of the same analysis centres and system bias of different analysis centres all differed. (3) The daily and weekly stability of ISB estimated using different analytical centre products showed similar characteristics. Furthermore, the intra-week daily stability and weekly stability of the ISB of different stations showed good consistency. (4) Considering the strength of the observed model and the stability and reliability of the positioning results, Multi-GNSS PPP with precise products of CODE, GFZ, iGMAS and WHU showed the best performance under constant estimation, 20 min piecewise constant estimation, 1 h piecewise constant estimation and constant estimation strategies, respectively.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 19 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Masoud Mahdianpari, Mahdi Motagh, Vahid Akbari, Fariba Mohammadimanesh, Bahram Salehi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Synthetic Aperture Radar (SAR) data have gained interest for a variety of remote sensing applications, given the capability of SAR sensors to operate independent of solar radiation and day/night conditions. However, the radiometric quality of SAR images is hindered by speckle noise, which affects further image processing and interpretation. As such, speckle reduction is a crucial pre-processing step in many remote sensing studies based on SAR imagery. This study proposes a new adaptive de-speckling method based on a Gaussian Markov Random Field (GMRF) model. The proposed method integrates both pixel-wised and contextual information using a weighted summation technique. As a by-product of the proposed method, a de-speckled pseudo-span image, which is obtained from the least-squares analysis of the de-speckled multi-polarization channels, is also produced. Experimental results from the medium resolution, fully polarimetric L-band ALOS PALSAR data demonstrate the effectiveness of the proposed algorithm compared to other well-known de-speckling approaches. The de-speckled images produced by the proposed method maintainthe mean value of the original image in homogenous areas, while preserving the edges of features in heterogeneous regions. In particular, the equivalent number of look (ENL) achieved using the proposed method improves by about 15% and 47% compared to the NL-SAR and SARBM3D de-speckling approaches, respectively. Other evaluation indices, such as the mean and variance of the ratio image also reveal the superiority of the proposed method relative to other de-speckling approaches examined in this study.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 19 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): A. Goswami〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The properties of front side halo coronal mass ejections (CMEs) and their interplanetary counterpart (ICME) have been studied here, as well as their relative imprint on Dst index over the period of 1995 to 2015. The results confirm that most of the faster halos are ignited from limb and most of them are associated with flares. The parametric average of interplanetary halos (except velocity and temperature) are found higher in disk associated events than that of limb. The results are also showing that fast and halo CME associated ICMEs are the most promising candidate for producing strong storms if they are exploded within ±30 degree of the central meridian. About 65% of all front side halo CME associated ICMEs are geoeffective, supporting to the high rate of geoeffectiveness of halo CMEs. A larger fraction (71%) of disk halos are geoeffective. It’s observed that, 92.6% of total Dst associated DS-ICME events have been geoeffective. This value is slightly lower for Dst associated DW-ICMEs. For intermediate events, it has been seen that, 87% of IS-ICMEs are geoeffective. But in the absence of shock intermediate ICMEs are identified as nongeoeffective ICMEs (however, only one event is present in that group). For LS-ICMEs, it has found that 83% are geoeffective events. Whereas, for LW-ICMEs, 75% are identified as geoeffective. In additions, the intensity of geomagnetic storm depends strongly on Bs and Ey in accordance with threshold limits of the storm producing criteria (more frequently observed in sheath than ejecta). The average values of Bs and Ey are significantly different from moderate to strong magnetic storms.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 16 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Michael D. Koptev, Sergey P. Trofimov, Mikhail Yu. Ovchinnikov〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The problem of designing and deploying a highly elliptical orbit tetrahedral formation of one chief microsatellite and several deputy nanosatellites is examined. Such a formation can be utilized in a number of space science missions, with magnetospheric studies as a main application. To measure the quality of the geometrical configuration in the region of interest, the scalar factor is used which evaluates both the shape and the scale of the formation. To maximize the formation quality, initial orbital elements of all the satellites are optimally selected using the K-60 supercomputing cluster. Several formation deployment schemes are considered, taking into account possible orbit injection errors.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 20 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Asheesh Bhargawa, A.K. Singh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Since the Sun is the main source of energy for our planet therefore even a slight change in its output energy can make a huge difference in the climatic conditions of the terrestrial environment. The rate of energy coming from the Sun (solar irradiance) might affect our climate directly by changing the rate of solar heating of the Earth and the atmosphere and indirectly by changing the cloud forming processes. In the present paper, based on stability test of Vector Auto Regressive (VAR) model, we have used the impulse response functions and the variance decomposition method for the analysis of climate variability. We have examined the possible connections among the solar irradiance and some climate indicators, viz., the global temperature anomaly, the global mean sea level, the global sea-ice extent and the global precipitation anomaly occurred during last forty years (1978–2017). In our investigation, we have observed that the impact of solar irradiance on the global surface temperature level in next decade will increase by ∼4.7% while the global mean sea level will increase about 0.67%. In the meantime, we have noticed about 5.3% decrement in the global sea-ice extent for the next decade. In case of the global precipitation anomaly we have not observed any particular trend just because of the variable climatic conditions. We also have studied the effect of CO〈sub〉2〈/sub〉 as anthropogenic forcing where we have observed that the global temperature in the next decade will increase by 2.7%; mean sea level will increase by 6.4%. Increasing abundance in CO〈sub〉2〈/sub〉 will be responsible for about 0.43% decrease in the sea-ice extent while there will not be any change in the precipitation pattern.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 20 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): O.S. Bayandina, N.N. Shakhvorostova, A.V. Alakoz, R.A. Burns, S.E. Kurtz, I.E. Val’tts〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Water masers are well-known to be variable on a variety of time scales, but only three Galactic H〈sub〉2〈/sub〉O masers are known to flare to the level of 10〈sup〉5〈/sup〉–10〈sup〉6〈/sup〉 Jy (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si9.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mtext〉T〈/mtext〉〈/mrow〉〈mrow〉〈mtext〉B〈/mtext〉〈/mrow〉〈/msub〉〈mo〉∼〈/mo〉〈msup〉〈mrow〉〈mn〉10〈/mn〉〈/mrow〉〈mrow〉〈mn〉17〈/mn〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉 K): Orion KL, W49N, and the recently discovered G25.65+1.05. Recently detected flaring activity of H〈sub〉2〈/sub〉O maser in the massive star-forming region G25.65+1.05 gave us a unique opportunity to study the fine structure of H〈sub〉2〈/sub〉O maser emission in the bursting state with extremely high space VLBI angular resolution. Observation of the source was carried out with ∼9 Earth diameter space-ground baseline within the framework of the RadioAstron project. H〈sub〉2〈/sub〉O maser emission from two spectral features, including the bursting one, was detected in the experiment. Only ∼1% of the bursting H〈sub〉2〈/sub〉O maser emission was detected on the space-ground baselines: it indicates the presence of a very compact spatial structure with a size of ∼25 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"〉〈mrow〉〈mi mathvariant="normal"〉μ〈/mi〉〈/mrow〉〈/math〉as, which corresponds to 0.05 AU or ∼5 solar diameters at the distance to the source of 2.08 kpc, and the brightness temperature of ∼3 × 10〈sup〉16〈/sup〉 K. Analysis of the flux density as a function of the baseline length for the bursting H〈sub〉2〈/sub〉O maser feature in the source shows that most of the emission comes from an extended “halo” structure, while the core of emission is very compact and has an extreme brightness temperature. These results are in agreement with the model of interacting maser clouds considered as the likely explanation of the nature of the burst in the source. Under the assumption of such a model, the beam size of maser emission is reduced while the brightness temperatures similar to the highest observed values are produced.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 20 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Xiaoying Gong, Dingfa Huang, Shixiang Cai, Letao Zhou, Linguo Yuan, Wei Feng〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Starting in March 2015, 5 new-generation BDS satellites, including 2 satellites in IGSO and 3 satellites in MEO, have been launched with the Inter Satellite Links (ISLs) on-board and the measurements have been tested. With the ISLs, BDS can achieve Autonomous Navigation (AutoNav) without support of ground facilities. In AutoNav, for lack of the external datum, the residual constellation rotation cannot be observed. This problem will be solved with the support of ground facilities. When ground facilities are available, Combined Orbit Determination (COD) can be achieved by using measurements from the ISLs and ground facilities, which can dramatically improve the precision of orbit determination. Normally, there are two kinds of filters adopted in AutoNav, namely the Parameter Integration Filter (PIF) and the Parameter Decomposition Filter (PDF). The PIF, which is also commonly used in COD due to the one-way property of the L-band satellite-ground measurements, had been prove less efficient than the PDF in AutoNav. As an attempt of improving the solving efficiency for COD, a new PDF is presented and implemented in COD of BDS in this paper. Based on the implement of the COD with simulated observations, the performance of PDF in COD is evaluated by comparing to the PIF in regards to precision and solving efficiency. The results indicate that, given enough observations, the PDF is superior to the PIF in terms of CERR and URE, while inferior to PIF in terms of RERR and PERR. Moreover, the solving efficiency of the PDF is much higher than that of the PIF.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 19 March 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): N.V. Nunes, N. Bartel, M.F. Bietenholz, M.V. Zakhvatkin, D.A. Litvinov, V.N. Rudenko, L.I. Gurvits, G. Granato, D. Dirkx〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We report on our efforts to test the Einstein Equivalence Principle by measuring the gravitational redshift with the VLBI spacecraft RadioAstron, in an eccentric orbit around Earth with geocentric distances as small as 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉 7,000 km and up to 350,000 km. The spacecraft and its ground stations are each equipped with stable hydrogen maser frequency standards, and measurements of the redshifted downlink carrier frequencies were obtained at both 8.4 and 15 GHz between 2012 and 2017. Over the course of the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉 9 d orbit, the gravitational redshift between the spacecraft and the ground stations varies between 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si21.gif" overflow="scroll"〉〈mrow〉〈mn〉6.8〈/mn〉〈mo〉×〈/mo〉〈msup〉〈mrow〉〈mn〉10〈/mn〉〈/mrow〉〈mrow〉〈mo〉-〈/mo〉〈mn〉10〈/mn〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉 and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si22.gif" overflow="scroll"〉〈mrow〉〈mn〉0.6〈/mn〉〈mo〉×〈/mo〉〈msup〉〈mrow〉〈mn〉10〈/mn〉〈/mrow〉〈mrow〉〈mo〉-〈/mo〉〈mn〉10〈/mn〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉. Since the clock offset between the masers is not known and cannot be estimated independently of the gravitational redshift, only the variation of the gravitational redshift is considered for this analysis. We obtain a preliminary measurement of the fractional deviation of the gravitational redshift from prediction of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si23.gif" overflow="scroll"〉〈mrow〉〈mo〉-〈/mo〉〈mn〉0.016〈/mn〉〈mo〉±〈/mo〉〈msub〉〈mrow〉〈mn〉0.003〈/mn〉〈/mrow〉〈mrow〉〈mi mathvariant="normal"〉stat〈/mi〉〈/mrow〉〈/msub〉〈mo〉±〈/mo〉〈msub〉〈mrow〉〈mn〉0.030〈/mn〉〈/mrow〉〈mrow〉〈mi mathvariant="normal"〉syst〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 with the systematic uncertainty likely being dominated by unmodelled effects including the error in accounting for the non-relativistic Doppler shift. This result is consistent with zero within the uncertainties. For the first time, the gravitational redshift has been probed over such large distances in the vicinity of Earth. About three orders of magnitude more accurate measurements may be possible with RadioAstron using existing data from dedicated interleaved observations combining uplink and downlink modes of operation.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 August 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 64, Issue 3〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: Available online 21 June 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Gerald Dibarboure, Marie-Isabelle Pujol〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉In this paper we compute a new local mean sea surface (MSS) model along the Sentinel-3A ground track. This so-called hybrid mean profile (HMP) blends the content of an average of 18 months of Sentinel-3A data for wavelengths ranging from 15 to 100 km, and the CNES/CLS 2015 gridded MSS model for larger and shorter scales.〈/p〉 〈p〉The improvement observed on Sentinel-3A sea level anomalies (SLA) is significant: the residual error is 0.2 cm〈sup〉2〈/sup〉, i.e. 17% of the SLA variance between 15 and 100 km, or 57% less than the gridded MSS model error. The highest error reduction is observed for wavelengths ranging from 20 to 80 km. From a geographical point of view, the improvement is mainly located along geodetic features that are not completely resolved in the gridded MSS models. It can locally be as high as 1 cm〈sup〉2〈/sup〉, i.e. very large when compared to the variance of the small scale SLA. Similarly, in coastal regions where the gridded model is known to exhibit higher errors, the HMP exhibits a very stable behavior that is on average 4 times more accurate.〈/p〉 〈p〉To understand the implications for future datasets and mission, we also develop a simple prediction model for the leakage of noise and small scale SLA into the MSS model. The model was validated with Sentinel-3A and ENVISAT data. Using the HMP strategy on the 21-day phase of the SWOT mission would be attractive for two reasons: 1/ this methodology would reduce the small scale error of gridded MSS models thanks to SWOT’s unprecedented 2D topography coverage and noise level, and 2/ the gridded MSS models provides a more trustworthy reference for the larger temporal scales that cannot be not averaged out by SWOT alone. After 3 years of nominal mission, the residual SWOT HMP error should be less than 2% of the sea level anomaly variance. In contrast, the so-called fast-sampling (or 1-day repeat) phase of SWOT is slightly more challenging because of the temporal correlation of the SLA (1-day samples are not independent). Depending on the accuracy of the pre-launch gridded MSS (i.e. upper wavelength limit where SWOT data must be used), the decorrelation scales could range from 1 to 5 days. The resulting HMP error would ranges from 5 to 12% of the SLA variance at the end of the fast-sampling phase.〈/p〉 〈p〉These results emphasize the need to keep improving the smaller scales of gridded MSS models as they will remain a major altimetry asset, at least until 2023, when SWOT has collected enough 21-day samples to provide a very robust HMP model.〈/p〉 〈/div〉 〈/div〉