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 1 November 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Yufeng Hu, Yibin Yao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Tropospheric delay is an important error source in space geodetic techniques. It varies significantly with height and the height dependent tropospheric error remains one of the major limitations in Global Navigation Satellite System (GNSS) techniques especially in Network Real-Time Kinematic (RTK) with significant topography variations. Based on the Gaussian function and the ten-year monthly mean Zenith Tropospheric Delay (ZTD) data from ERA-Interim of European Centre for Medium-Range Weather Forecasts (ECMWF) with a horizontal resolution of 5° × 5°, a new ZTD vertical stratification model with seasonal variations called seasonal Gaussian function model is developed in this paper. Compared with the troposphere products of 259 International GNSS Service (IGS) stations in 2016, the ERA-Interim-derived ZTDs stratified by using the seasonal Gaussian function model show that the annual mean bias and Root Mean Square error (RMS) are −0.2 cm and 1.9 cm respectively, which are better than the results (bias: −0.7 cm, RMS: 2.1 cm) by using the seasonal exponential function model. The validation with 245 radiosonde stations’ data in 2016 shows that the bias and RMS of the seasonal Gaussian function model are reduced by 0.3 cm and 0.2 cm, compared with that of the seasonal exponential function model. Thus the seasonal Gaussian function model instead of the exponential function model is more suitable for accurate ZTD stratification in GNSS data analysis.〈/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 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Kyle Copeland, William Atwell〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉There is considerable speculation about the effects at aircraft altitudes resulting from extreme solar proton events. The ground level event (GLE) of 23 February 1956 (GLE 5), remains the largest solar proton event of the neutron monitor era in terms of its influence on count rates at monitors near sea level. During this GLE the count rate was increased by as much as 4760% (15-min average) at the Leeds monitor relative to the count rate from galactic cosmic radiation (GCR). Two modern models of the event cumulative solar proton spectrum for this event, a 6-parameter fit in energy and a 4-parameter Band fit in rigidity, are compared with 1-h of GCR at solar minimum. While effective doses calculated with CARI-7A for both models at low geomagnetic cutoff rigidities are indeed high when compared with GCR and can exceed recommended exposure limits, both GLE spectra exhibit a much stronger dependence on cutoff rigidity than GCR, and a larger fraction of the dose from neutrons. At locations with cutoff rigidities above 4.2 and 6.4 GV, respectively, the GLE effective doses are smaller than the GCR hourly dose. At locations with cutoff rigidities above about 4 GV, GCR was the dominant source of exposure in 10 h or less at all altitudes examined. This suggests that if a similar event occurs in the future, low- and mid-latitude flights at modern jet flight altitudes could be well-protected by Earth’s magnetic field.〈/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 21 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Yuxi Li, Wei Lu, Guangyou Fang, Bin Zhou, Shaoxiang Shen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Lunar Regolith Penetrating Array Radar (LRPR) is one main payload of the Lander for Chinese Chang’E-5 (CE-5) mission. It is used to support the drilling and sampling device and to detect lunar regolith thickness and structure of the landing site. LRPR will only work in situ under static status, so the antenna array is employed. Since the antenna array is about 90 cm high from the ground, the layout is irregular, and the metal structure of the lander seriously interferes with LRPR, these factors make it very difficult to reconstruct the image of the drilling area, so the performance verification must be carried out. We propose a set of methods to process LRPR’s data and reconstruct image. The verification experiments demonstrate that these methods are suitable for LRPR, the thickness and structure of the lunar regolith from zero to two meters can be clearly mapped, the vertical resolution is a few centimeters, and the electromagnetic properties of the subsurface can be estimated. Therefore, the performance of LRPR meets the requirements, and LRPR can successfully support drilling and sampling.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Paolo Dabove, Vincenzo Di Pietra〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The possibility to access undifferenced and uncombined Global Navigation Satellite System (GNSS) measurements on smart devices with an Android operating system allows us to manage pseudorange and carrier-phase measurements to increase the accuracy of real-time positioning. The goal is to perform real-time kinematic network positioning with smartphones, evaluating the positioning accuracy regarding an external mass-market device. The positioning of Samsung Galaxy S8+ and Huawei P10 plus smartphones was performed using a dedicated tool developed by the authors, considering a continuous operating reference station (CORS) network with a mean inter-station distance of about 50 km. The same positioning technique was also applied to an external GNSS low-cost single-frequency receiver (u-blox EVK-M8T) to compare performance between the receiver and antenna embedded in the previous smartphones and this low-cost receiver coupled with a mass-market antenna (Garmin GA38). Attention was also focused on the phase ambiguity resolution, that it is still a challenging aspect for mass-market devices: even if the two smartphones provide slightly different results, the accuracy obtainable today is greater than 60 cm with a precision of few centimetres in real-time, if a CORS network is available. For real-time applications using portable devices, decimetre-level accuracy is sufficient for many applications, such as rapid mapping and search and rescue activities: these results will open new frontiers in terms of real-time positioning with portable low-cost devices.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Vishnuu Mallik, Moriba K. Jah〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉There are many Resident Space Objects (RSOs) in the Geostationary Earth Orbit (GEO) regime, both operational and debris. The primary non-gravitational force acting on these RSOs is Solar Radiation Pressure (SRP), which is sensitive to the RSO’s area-to-mass ratio. Sparse observation data and mismodeling of non-gravitational forces has constrained the state of practice in tracking and characterizing RSOs. Accurate identification, characterization, tracking, and motion prediction of RSOs is a high priority research issue as it shall aid in assessing collision probabilities in the GEO regime, and orbital safety writ large. Previous work in characterizing RSOs has taken a preliminary step in exploiting fused astrometric and photometric data to estimate the RSO mass, shape, attitude, and size. This works, in theory, since angles data are sensitive to SRP albedo-area-to-mass ratio, and photometric data are sensitive to shape, attitude, and observed albedo-area. By fusing these two data types, mass and albedo-area both become observable parameters and can be estimated as independent quantities. However, previous work in mass and albedo-area estimation has not quantified and assessed the fundamental physical link between SRP albedo-area and observed albedo-area. The observed albedo-area is always a function of the SRP albedo-area along the line of sight of the observer. This is the physical relationship that this current research exploits. It is shown through simulation that due to this physical link, and through the fusion of astrometric and photometric data, it is possible to observe the mass of a space object when the area is not known. Results for data from 100 trajectories generated from randomly sampled initial conditions are shown. It is seen that even when the area of the object is not known, the uncertainty in mass can be lowered from an initial value of 800 kg to the range 500–700 kg for 72% of the samples, 200–500 kg for 13% of the samples, and 0–200 kg for 15% of the samples. It is further shown that although the uncertainties are large, the actual errors in mass are much lower, with the error RMS being less than 100 kg for 30% of the samples, between 100 and 200 kg for another 30%, and between 200 and 300 kg for 24% of the samples.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): G. March, E.N. Doornbos, P.N.A.M. Visser〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉During the last two decades, accelerometers on board of the CHAMP, GRACE, GOCE and Swarm satellites have provided high-resolution thermosphere density data to improve our knowledge on atmospheric dynamics and coupling processes in the thermosphere-ionosphere region. Most users of the data have focused on relative density variations. Scale differences between datasets and models have been largely neglected or removed using ad hoc scale factors. The origin of these scale differences arises from errors in the aerodynamic modelling, specifically in the modelling of the satellite outer surface geometry and of the gas-surface interactions. Therefore, the first step to remove the scale differences is to enhance the geometry modelling. This work forms the foundation for the future improvement of characterization of satellite aerodynamics and gas-surface interactions models at TU Delft, as well as for extending the use of sideways and angular accelerations in the aerodynamic analysis of accelerations and derivation of thermosphere datasets. Although work to improve geometry and aerodynamic force models by other authors has focused on CHAMP and GRACE, this paper includes the GOCE and Swarm satellites as well. In addition, it uses a density determination algorithm that is valid for arbitrary attitude orientations, enabling a validation making use of attitude manoeuvres. The results show an improvement in the consistency of density data between these four missions, and of data obtained before, during and after attitude manoeuvres of CHAMP and Swarm. The new models result in larger densities, compared to the previously used panel method. The largest average rescaling of density, by switching to the new geometry models is reached for Swarm at 32%, the smallest for GRACE at 5%. For CHAMP and GOCE, mean differences of 11% and 9% are obtained respectively. In this paper, an overview of the improvements and comparisons of data sets is provided together with an introduction to the next research phase on the gas-surface interactions.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): 〈/p〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Akihisa Hattori, Toshimichi Otsubo〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study aims to investigate solar radiation pressure acting on the spherical geodetic satellites, Ajisai, LAGEOS-1, and LAGEOS-2. The solar radiation pressure coefficients (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si10.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉) are derived in two independent ways: (a) through precise orbit determination (POD) using satellite laser ranging (SLR) data, and (b) through modeling using the optical properties of the satellite surface material. The average 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si10.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 value of Ajisai (1.039), as calculated from the time series of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si10.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 POD estimates every 15 days, is consistently smaller than those of LAGEOS-1 (1.140) and LAGEOS-2 (1.103). This difference can be explained by the fact that the surface of Ajisai is mostly covered by mirrors. The Ajisai 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si10.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 values estimated by POD show remarkable semi-annual variation, which disagrees with the results of a previous study (Sengoku et al., 1995) predicting that the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si10.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 of Ajisai varies almost annually. We attribute this semi-annual variation to two physical reasons: the non-spherical additional cross-sectional area due to the “attached fitting ring” and the low reflectivity of the surface material in the polar regions. Furthermore, the solar radiation pressure acting on Ajisai varies annually in a direction perpendicular to the sun-satellite vector. Finally, the two independent 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si10.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉C〈/mi〉〈/mrow〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 values of Ajisai agree more when we assume a total solar irradiance of 1361 W/m〈sup〉2〈/sup〉, whereas the value 1367 W/m〈sup〉2〈/sup〉 has been commonly used in POD.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Yunfei Xiang, Jianping Yue, Kai Tang, Zhen Li〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The 2016 M〈sub〉w〈/sub〉 6.0 Italy earthquake is successfully recorded by the near-field 10 Hz GPS and 200 Hz Strong Motion (SM) stations, providing valuable data for this study. A comprehensive study of this earthquake is carried out based on GPS data, which contains coseismic deformations analysis, noise analysis, seismic wave picking, and magnitude determination. The noise of most GPS-derived displacement waveforms can be described as a combination of white noise, flicker noise, and random walk noise after the earthquake occurrence, and the spectral indices vary significantly for most stations, implying that the seismic signals have affected the noise characteristic of GPS-derived displacement waveforms. S-transform is employed to assess the GPS capability to detect the seismic arrival time. The SM station AMT and the GPS station AMAT are in good agreement in seismic wave picking, and the difference is only 1.2 s in the north component, suggesting that the outcome of seismic wave picking using GPS data is reliable. Then, a classic empirical formula is employed to determine the moment magnitude. A robust moment magnitude (Mw 5.90) can be estimated by the nine GPS stations with about 23.9 s. If four GPS stations near the epicenter is chosen to determine the magnitude, it only take 13.0 s to retrieve a reliable preliminary (Mw 5.82) magnitude, which is 5.4 s ahead of nine stations. In addition, Cross Wavelet Transform (XWT) is adopted to measuring the correlation and phase relationship between GPS and SM records. The result of XWT analysis indicates 10 Hz GPS is capable of capturing reliable and accurate coseismic dynamic deformations, as evidenced by the XWT-based semblance being close to 1 between GPS and SM records. The above results confirm the capability of 10 Hz GPS to capture coseismic dynamic deformations, detect seismic arrival time, and determine earthquake magnitude. Moreover, rapid magnitude determination based on 10 Hz GPS data can be regarded as an important supplement to Earthquake Early Warning (EEW).〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): R.N. Boroyev〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In the present paper dependences of substorm activity on the solar wind velocity and southward component (Bz) of interplanetary magnetic field (IMF) during the main phase of magnetic storms, induced by the CIR and ICME events, is studied. Strong magnetic storms with close values of Dst〈sub〉min〈/sub〉 ≈ −100 ± 10 nT are considered. For the period of 1979–2017 there are selected 26 magnetic storms induced by the CIR and ICME (MC + Ejecta) events. It is shown that for the CIR and ICME events the average value of the AE index (AE〈sub〉aver〈/sub〉) at the main phase of magnetic storm correlates with the solar wind electric field. The highest correlation coefficient (r = 0.73) is observed for the magnetic storms induced by the CIR events. It is found that the AE〈sub〉aver〈/sub〉 for magnetic storms induced by ICME events, unlike CIR events, increases with the growth of average value of the southward IMF Bz module. The analysis of dependence between the AE〈sub〉aver〈/sub〉 and average value of the solar wind velocity (Vsw〈sub〉aver〈/sub〉) during the main phase of magnetic storm shows that in the CIR events, unlike ICME, the AE〈sub〉aver〈/sub〉 correlates on the Vsw〈sub〉aver〈/sub〉.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Seong Hyeon Hong, John W. Conklin〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This paper evaluates the impact of residual acceleration noise on the estimation of the Earth’s time-varying gravity field for future low-low satellite-to-satellite tracking missions. The goal is to determine the maximum level of residual acceleration noise that does not adversely affect the estimation error. The Gravity Recovery And Climate Experiment (GRACE) has provided monthly average gravity field solutions in spherical harmonic coefficients for more than a decade. It provides information about land and ocean mass variations with a spatial resolution of ∼350 km and with an accuracy within 2 cm throughout the entire Earth. GRACE Follow-on was launched in May 2018 to advance the work of GRACE and to test a new laser ranging interferometer, which measures the range between the two satellites with higher precision than the K-Band ranging system used in GRACE. Moreover, there have been simulation studies that show, an additional pair of satellites in an inclined orbit increases the sampling frequency and reduces temporal aliasing errors. Given the fact that future missions will likely continue to use the low-low satellite-to-satellite tracking formation with laser ranging interferometry, it is expected that the residual acceleration noise will become one of the largest error contributor for the time-variable gravity field solution. We evaluate three different levels of residual acceleration noise based on demonstrated drag-free systems to find a suitable drag-free performance target for upcoming geodesy missions. We analyze both a single collinear polar pair and the optimal double collinear pair of drag-free satellites and assume the use of a laser ranging interferometer. A partitioned best linear unbiased estimator that was developed, incorporating several novel features from the ground up is used to compute the solutions in terms of spherical harmonics. It was found that the suitable residual acceleration noise level is around 2 × 10〈sup〉−12〈/sup〉 ms〈sup〉−2〈/sup〉 Hz〈sup〉−1/2〈/sup〉. Decreasing the acceleration noise below this level did not result in more accurate gravity field solutions for the chosen mission architecture.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Zama T. Katamzi-Joseph, Anasuya L. Aruliah, Kjellmar Oksavik, John Bosco Habarulema, Kirsti Kauristie, Michael J. Kosch〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study reports on observations of large-scale atmospheric gravity waves/traveling ionospheric disturbances (AGWs/TIDs) using Global Positioning System (GPS) total electron content (TEC) and Fabry–Perot Interferometer’s (FPI’s) intensity of oxygen red line emission at 630 nm measurements over Svalbard on the night of 6 January 2014. TEC large-scale TIDs have primary periods ranging between 29 and 65 min and propagate at a mean horizontal velocity of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉749–761 m/s with azimuth of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉345–347〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈mi〉°〈/mi〉〈/mrow〉〈/math〉 (which corresponds to poleward propagation direction). On the other hand, FPI large-scale AGWs have larger periods of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉42–142 min. These large-scale AGWs/TIDs were linked to enhanced auroral activity identified from co-located all-sky camera and IMAGE magnetometers. Similar periods, speed and poleward propagation were found for the all-sky camera (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉60–97 min and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉823 m/s) and the IMAGE magnetometers (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉32–53 min and 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉708 m/s) observations. Joule heating or/and particle precipitation as a result of auroral energy injection were identified as likely generation mechanisms for these disturbances.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Aaron J. Rosengren, Despoina K. Skoulidou, Kleomenis Tsiganis, George Voyatzis〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉We have carried out a numerical investigation of the coupled gravitational and non-gravitational perturbations acting on Earth satellite orbits in an extensive grid, covering the whole circumterrestrial space, using an appropriately modified version of the SWIFT symplectic integrator, which is suitable for long-term (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si48.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉120 years) integrations of the non-averaged equations of motion. Hence, we characterize the long-term dynamics and the phase-space structure of the Earth-orbiter environment, starting from low altitudes (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si48.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉400 km) and going up to the GEO region and beyond. This investigation was done in the framework of the EC-funded “ReDSHIFT” project, with the purpose of enabling the definition of passive debris removal strategies, based on the use of physical mechanisms inherent in the complex dynamics of the problem (i.e., resonances). Accordingly, the complicated interactions among resonances, generated by different perturbing forces (i.e., lunisolar gravity, solar radiation pressure, tesseral harmonics in the geopotential) are accurately depicted in our results, where we can identify the regions of phase space where the motion is regular and long-term stable and regions for which eccentricity growth and even instability due to chaotic behavior can emerge. The results are presented in an “atlas” of dynamical stability maps for different orbital zones, with a particular focus on the (drag-free) range of semimajor axes, where the perturbing effects of the Earth’s oblateness and lunisolar gravity are of comparable order. In some regions, the overlapping of the predominant lunisolar secular and semi-secular resonances furnish a number of interesting disposal hatches at moderate to low eccentricity orbits. All computations were repeated for an increased area-to-mass ratio, simulating the case of a satellite equipped with an on-board, area-augmenting device. We find that this would generally promote the deorbiting process, particularly at the transition region between LEO and MEO. Although direct reentry from very low eccentricities is very unlikely in most cases of interest, we find that a modest “delta-v” (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si27.gif" overflow="scroll"〉〈mrow〉〈mi mathvariant="normal"〉Δ〈/mi〉〈mi〉V〈/mi〉〈/mrow〉〈/math〉) budget would be enough for satellites to be steered into a relatively short-lived resonance and achieve reentry into the Earth’s atmosphere within reasonable timescales (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si48.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈/mrow〉〈/math〉50 years).〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 15 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 2〈/p〉 〈p〉Author(s): Xin-Ran Li, Xin Wang, Yong-qing Xiong〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉With the combination of two evolutionary algorithms EDA and DE, a new method of initial orbit determination for satellites based on ground-based too-short-arc is established. Compared with other algorithms, the proposed method focuses on the most densely populated region in the solution space rather than the individual with best fitness value. Both the global information and local information are well fused in the search of optimum. In the method 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si62.gif" overflow="scroll"〉〈mrow〉〈mo stretchy="false"〉(〈/mo〉〈mi〉a〈/mi〉〈mo〉,〈/mo〉〈mi〉e〈/mi〉〈mo〉,〈/mo〉〈mi〉M〈/mi〉〈mo stretchy="false"〉)〈/mo〉〈/mrow〉〈/math〉 are treated as variables of the optimization, and the optimization procedure is carried out as a two-stage hierarchical optimization problem which has three variables for each stage. Kernel density estimation is applied to build the probability distribution model without any assumptions of the specified distribution, accompanied by handling semi-major axis and eccentricity as a pair of dependent variables in the construction of the probability for the correlation between them in the practice. Numerical experiments with real ground-based observations show that the proposed method is applicable to too-short-arc with even 3 s, and the result of bias in several kilometers can be achieved with 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si63.gif" overflow="scroll"〉〈mrow〉〈msup〉〈mrow〉〈mn〉5〈/mn〉〈/mrow〉〈mrow〉〈mo〉″〈/mo〉〈/mrow〉〈/msup〉〈/mrow〉〈/math〉 error added to angular measurements.〈/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: Available online 22 December 2018〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research〈/p〉 〈p〉Author(s): Jyoti Kumari, R.S. Pandey〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Cassini radio and plasma wave surveys aim to study radio emissions, plasma waves, thermal plasma and dust near Saturn. Using the characteristic solution and dynamics method, the influence of electron beam on the loss cone and bi-Maxwellian distribution of whistler mode waves in the parallel alternating electric field and magnetic field is studied. The dispersion relation and the growth rate of Saturn's magnetic layer were deduced and calculated in detail. Parameter analysis is performed by changing the parameters of the plasma like number density, AC frequency, temperature anisotropy, etc. The influence of AC frequency on Doppler shift and the comparative study of growth rate of oblique and parallel propagating waves are analyzed using generalized distribution function. We found temperature anisotropy 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mtext〉A〈/mtext〉〈/mrow〉〈mrow〉〈mtext〉T〈/mtext〉〈/mrow〉〈/msub〉〈mo〉=〈/mo〉〈mn〉1.25〈/mn〉〈/mrow〉〈/math〉 can explain the linear spatiotemporal growth rate of whistler mode waves. It provides the majority of the observed frequency integral power. It can be seen that the effective parameters for the generation of Whistler mode waves are not only temperature anisotropy, but also the relativistic factors discussed in the results and discussion section, and the AC field frequency and width of the loss cone distribution function.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Youtao Gao, Xi Lu, Yuming Peng, Bo Xu, Tanran Zhao〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉In this study, the Earth’s Trojan asteroid 2010 TK〈sub〉7〈/sub〉 is selected as the rendezvous target. The multiple flyby sequence of asteroid exploration was proposed by optimizing the probe’s orbit. Impulsive maneuvers and low-thrust propulsion were used respectively to design the trajectories of the multiple asteroids exploration mission. Under impulsive maneuvers, gravity assist technique was adopted to reduce fuel consumption. First a reference orbit with only 2010 TK〈sub〉7〈/sub〉 as the rendezvous target was designed. Then five asteroids near the reference orbit were selected as candidates. Finally, we obtained a multiple asteroids exploration sequence of three asteroids based on gravity assist technique and genetic algorithm, and an additional velocity impulse of 0.4 km/s was required. In the subsequent section, a sixth-degree inverse polynomial shape-based method is applied to the low-thrust trajectory design of 2010 TK〈sub〉7〈/sub〉, and the exploration sequence under the action of low-thrust propulsion was provided.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): K. Wang, A. Khodabandeh, P.J.G. Teunissen〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Various studies have been performed to investigate the accuracy of troposphere zenith wet delays (ZWDs) determined from GPS. Most of these studies use dual-frequency GPS data of large-scale networks with long baselines to determine the absolute ZWDs. For small-scale networks the estimability of the absolute ZWDs deteriorates due to high correlation between the solutions of the ZWDs and satellite-specific parameters as satellite clocks. However, as relative ZWDs (rZWDs) can always be estimated, irrespective of the size of the network, it is of interest to understand how the large-scale network rZWD-performance of dual-frequency GPS using an ionosphere-float model compares to the small-scale network rZWD-performance of single-frequency GPS using an ionosphere-weighted model. In this contribution such an analysis is performed using undifferenced and uncombined network parametrization modelling. In this context we demonstrate the ionosphere weighted constraints, which allows the determination of the rZWDs independent from signals on the second frequency. Based on an analysis of both simulated and real data, it is found that under quiet ionosphere conditions, the accuracy of the single-frequency determined rZWDs in the ionosphere-weighted network is comparable to that of the large-scale dual-frequency network without ionospheric constraints. Making use of the real data from two baselines of 15 days, it was found that the absolute differences of the rZWDs applying the two strategies are within 1 cm in over 90% and 95% of the time for ambiguity-float and -fixed cases, respectively.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): S. Mondal, M. Maiti, S. Sil, P.K. Karmakar〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Millimeterwave window frequencies between the two successive absorption maxima of 60 GHz and 120 GHz respectively, play a significant role in the context of radar and communication applications. Atmospheric parameters like temperature, water vapour and oxygen play major roles for determination of window frequencies which are latitude dependent. Radiosonde data were analyzed to identify a frequency at which minimum signal attenuation occurs in the millimeterwave band, between 60 GHz and 120 GHz, at various places in India. The data are taken from British Atmospheric Data Centre (BADC, U.K). Analysis shows that water vapour plays a dominant role for determining window frequency during the monsoon season. On the other hand, temperature dominates water vapour in shifting window frequency during the winter and summer seasons. The results obtained also show that minimum attenuation occurs at 73 GHz and maximum at 83 GHz over the chosen places in India during January to December depending on the latitudinal position. Another salient result obtained from our analyses is that water vapour is mainly responsible for lowering the window frequency from its conventionally accepted value, over certain places in India. Hence, these climatological parameters play a major role in determining window frequency over certain places of choice in India throughout the year.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Elyse J. Allender, Csilla Orgel, Natasha V. Almeida, John Cook, Jessica J. Ende, Oscar Kamps, Sara Mazrouei, Thomas J. Slezak, Assi-Johanna Soini, David A. Kring〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study explores the Design Reference Mission (DRM) architecture developed by Hufenbach et al. (2015) as a prelude to the release of the 2018 Global Exploration Roadmap (GER) developed by the International Space Exploration Coordination Group (ISECG). The focus of this study is the exploration of the south polar region of the Moon, a region that has not been visited by any human missions, yet exhibits a multitude of scientifically important locations – the investigation of which will address long standing questions in lunar research. This DRM architecture involves five landing sites (Malapert massif, South Pole/Shackleton crater, Schrödinger basin, Antoniadi crater, and the South Pole-Aitken basin center), to be visited in sequential years by crew, beginning in 2028. Two Lunar Electric Rovers (LER) are proposed to be tele-robotically operated between sites to rendez-vous with crew at the time of the next landing. With engineering parameters in mind we explore the feasibility of tele-robotic operation of these LERs between lunar landing sites, and identify potential high interest sampling locations en-route. Additionally, in-depth sample collection and return traverses are identified for each individual landing site across key geologic terrains that also detail crew Extra-Vehicular Activity (EVA). Exploration at and between landing sites is designed to address a suite of National Research Council (2007) scientific concepts.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Evgeny Morozov, DanLing Tang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉An algorithm for retrieval of surface waters cell concentrations (in cell/ml) for three picophytoplankton components, 〈em〉Prochlorococcus〈/em〉 (〈em〉Pro〈/em〉), 〈em〉Synechococcus〈/em〉 (〈em〉Syn〈/em〉), and picoeukaryotes (〈em〉Peuk〈/em〉) in the South China Sea (SCS), from ocean colour satellite data was developed and tested. Level 3 merged multisensor Ocean Colour Climate Change Initiative satellite data is used. Training is performed using 〈em〉in situ〈/em〉 data on abundances of the three phytoplankton components. Several predictors derived from satellite reflectance data were tested. The regression form that assures the highest accuracy of the algorithm was chosen based on cross-validation (CV). According to the CV on test data subset, the algorithm performance is characterized by the 〈em〉r〈/em〉 value 0.89, 0.72, and 0.73 and MAPD 38, 71 and 51% for 〈em〉Peuk〈/em〉, 〈em〉Pro〈/em〉, and 〈em〉Syn〈/em〉 respectively. This is one of the few studies aimed at the 〈em〉Peuk〈/em〉, 〈em〉Pro,〈/em〉 and 〈em〉Syn〈/em〉 distribution research in the northern SCS using ocean colour satellite data. This is the only research providing algorithm with accuracy estimates of the 〈em〉Peuk〈/em〉, 〈em〉Pro〈/em〉, and 〈em〉Syn〈/em〉 concentrations retrieval from the ocean colour data. Analysis of the developed algorithm allows us to conclude that both mechanisms (specific spectral features caused by pigments composition and spectrum features sensitive to general primary productivity, e.g. band ratios in 443–510 nm range and spectrum absolute values) are important for getting accurate information on the picophytoplankton composition.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: Available online 18 December 2018〈/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 discusses the improvement of performance of the International Reference Ionosphere (IRI) model in estimating the variation of the Vertical Total Electron Content (VTEC) over the mid latitude American regions during the relatively low (2008–2010) and relatively high (2012) solar activity years. This has been conducted employing the VTEC values obtained from the dual frequency ground based Global Positioning System (GPS) receivers located at Mineral Area Community College, MACC (37.85°N, 269.52°W) and Mississippi County Airport, MAIR (36.85°N, 270.64°W), and the latest versions of the IRI online model (IRI 2007, IRI 2012 and IRI 2016). The study mainly focuses to compare the trend of variability of the monthly and seasonal modeled VTEC values (IRI 2007 VTEC, IRI 2012 VTEC and IRI 2016 VTEC) with the corresponding measured VTEC values (GPS VTEC). The overall results show that the IRI VTEC values (almost in all versions of the model) are generally smaller than the GPS VTEC except after about 15:00 UT (09:00 LT) in the December solstice when the Sun shifts to the high solar activity. On the contrary, overestimations of the VTEC values by the model are observed in traversing from the low solar activity (2008) to high solar activity (2012) phase, especially after about 15:00 UT (09::00 LT) with the IRI 2016 version showing the highest. In general, the IRI 2007 and IRI 2012 versions show similar monthly and seasonal underestimations or overestimations showing that the two versions have almost similar performance. The IRI 2016 version is generally better in capturing both the diurnal and arithmetic mean GPS VTEC values with some exceptional months and seasons as compared to those of the IRI 2007 and IRI 2012 versions.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Dariusz Strugarek, Krzysztof Sośnica, Adrian Jäggi〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The Gravity field and steady-state Ocean Circulation Explorer (GOCE) was the first European Space Agency’s (ESA) Earth Explorer core mission. Through its extremely low, about 260 km above the Earth, circular, sun-synchronous orbit, the satellite gained high spatial resolution and accuracy gravity gradient, and ocean circulation data. Global Positioning System (GPS) receivers, mounted on the spacecraft, allowed the determination of reduced-dynamic and kinematic GOCE orbits, whereas Laser Retroreflector Array (LRA) dedicated to Satellite Laser Ranging (SLR) allowed an independent validation of GPS-derived orbits. In this paper, residuals between different GPS-based orbit types and SLR observations are used to investigate the sensitivity and the influence of solar, geomagnetic, and ionospheric activities on the quality of kinematic and reduced-dynamic GOCE orbits. We also analyze the quality of data provided by individual SLR sites, by detecting time biases using ascending and descending sun-synchronous GOCE orbit passes, and the residual analysis of the measurement characteristics, i.e., the dependency of SLR residuals as a function of nadir and horizontal angles. Results show a substantial vulnerability of kinematic orbit solutions to the solar F10.7 index and the ionospheric activity measured by the variations of the Total Electron Content (TEC) values. The sensitivity of kinematic orbits to the three-hour-range KP index is rather minor. The reduced-dynamic orbits are almost insensitive to indices describing ionospheric, solar, and geomagnetic activities. The investigation of individual SLR sites shows that some of them are affected by time bias errors, whereas other demonstrate systematics, such as a dependency between observation residuals and the satellite nadir angle or the horizontal azimuth angle from the SLR station to the direction of the satellite.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Temitope Seun Oluwadare, Chinh Nguyen Thai, Andrew Oke-Ovie Akala, Stefan Heise, Mahdi Alizadeh, Harald Schuh〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉This study characterizes total electron content (TEC) measured by Global Positioning System (GPS) over African equatorial ionization anomaly (EIA) region for 2009–2016 period during both quiet geomagnetic conditions (Kp ≤ 1) and normal conditions (1 〉 Kp ≤ 4). GPS-TEC data from four equatorial/low-latitude stations, namely, Addis Ababa (ADIS: 9.04°N, 38.77°E, mag. lat: 0.2°N) [Ethiopia]; Yamoussoukro (YKRO: 6.87°N, 5.24°W, mag. lat: 2.6°S) [Ivory Coast]; Malindi (MAL2; 3.00°S, 40.19°E, mag. lat: 12.4°S) [Kenya] and Libreville (NKLG; 0.35°N, 9.67°W, mag. lat: 13.5°S) [Gabon] were used for this study. Interesting features like noontime TEC bite-out, winter anomaly during the ascending and maximum phases of solar cycle 24, diurnal and seasonal variations with solar activity have been observed and investigated in this study. The day-to-day variations exhibited ionospheric TEC asymmetry on an annual scale. TEC observed at equatorial stations (EIA-trough) and EIA-crest reach maximum values between ∼1300–1600 LT and ∼1300–1600 LT, respectively. About 76% of the high TEC values were recorded in equinoctial months while the June solstice predominantly exhibited low TEC values. Yearly, the estimated TEC values increases or decreases with solar activity, with 2014 having the highest TEC value. Solar activity dependence of TEC within the EIA zone reveals that both F10.7 cm index and EUV flux (24–36 nm) gives a stronger correlation with TEC than Sunspot Number (SSN). A slightly higher degree of dependence is on EUV flux with the mean highest correlation coefficient (R) value of 0.70, 0.83, 0.82 and 0.88 for quiet geomagnetic conditions (Kp ≤ 1) at stations ADIS, MAL2, NKLG, and YKRO, respectively. The correlation results for the entire period consequently reveals that SSN and solar flux F10.7 cm index might not be an ideal index as a proxy for EUV flux as well as to measure the variability of TEC strength within the EIA zone. The estimated TEC along the EIA crest (MAL2 and NKLG) exhibited double-hump maximum, as well as post-sunset peaks (night time enhancement of TEC) between ∼2100 and 2300 LT. EIA formation was prominent during evening/post-noon hours.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Baiwan Pan, Zhendong Yao, Minzhong Wang, Honglin Pan, Lingbing Bu, K. Raghavendra Kumar, Haiyang Gao, Xingyou Huang〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉The present study elucidates on the evaluation of two versions (V3 and V4.10) of vertical feature mask (VFM) and aerosol sub-types data derived from the Cloud-Aerosol LiDAR and Infrared Pathfinder Satellite Observations (CALIPSO), and its utilization to analyze the impact of dust aerosol on the microphysical properties of cirrus over the Tibetan Plateau (TP). In conjunction to the CALIPSO, we have also used the CloudSat data to study the same during the summer season for the years 2007–2010 over the study area 25–40°N and 75–100°E. Compared to V3 of CALIPSO, V4.10 was found to have undergone substantial changes in the code, algorithm, and data products. Intercomparison of both versions of data products in the selected grid between 30–31°N and 83–84°E within the study area during 2007–2017 revealed that the VFM and aerosol sub-types are in good agreement of ∼95.27% and ∼82.80%, respectively. Dusty cirrus is defined as the clouds mixed with dust aerosols or existing in dust aerosol conditions, while the pure cirrus is that in a dust-free environment. The obtained results illustrated that the various microphysical properties of cirrus, namely ice water content (IWC), ice water path (IWP), ice distribution width (IDW), ice effective radius (IER), and ice number concentration (INC) noticed a decrease of 17%, 18%, 4%, 19%, and 10%, respectively due to the existence of dust aerosol, consistent with the classical “Twomey effect” for liquid clouds. Moreover, the aerosol optical depth (AOD) showed moderate negative correlations between −0.4 and −0.6 with the microphysical characteristics of cirrus. As our future studies, in addition to the present work undertaken, we planned to gain knowledge and interested to explore the impact of a variety of aerosols apart from the dust aerosol on the microphysical properties of cirrus in different regions of China.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): K.D. Moloto, N.E. Engelbrecht, R.D. Strauss, D.M. Moeketsi, J.P. van den Berg〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Three-dimensional studies of the transport and modulation of cosmic ray particles in turbulent astrospheres require large-scale simulations using specialized scientific codes. Essentially, a multi-dimensional Fokker-Planck type equation (a parabolic diffusion equation) must be integrated numerically. One such approach is to convert the relevant transport equation into a set of stochastic differential equations (SDEs), with the latter much easier to handle numerically. Due to the growing demand for high performance computing resources, research into the application of effective and suitable numerical algorithms to solve such equations is needed. We present a case study of the performance of a custom-written FORTRAN SDE numerical solver on the CHPC (Centre for High Performance Computing) Lengau cluster in South Africa for a realistic test problem with different set-ups. It is shown that SDE codes can scale very well on large parallel computing platforms. Finally, we consider an extremely computationally expensive application of the SDE approach to cosmic ray modulation, studying the behaviour of galactic cosmic ray proton latitude gradients and relative amplitudes in a physics-first manner. This is done using a modulation code that employs diffusion coefficients derived from first principles, which in turn are functions of turbulence quantities in reasonable agreement with spacecraft observations and modelled using a two-component turbulence transport model (TTM). We show that this approach leads to reduced latitude gradients qualitatively in line with spacecraft observations of the same, without making 〈em〉ad hoc〈/em〉 assumptions as to anisotropic perpendicular diffusion coefficients as are often made in many cosmic ray modulation studies.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Baolin Tan〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉Is Solar Cycle 24 anomalous? How do we predict the main features of a forthcoming cycle? In order to reply such questions, this work partitions quantitatively each cycle into valley, ascend, peak, and descend phases, statistically investigate the correlations between valley phase and the forthcoming cycle. We find that the preceding valley phase may dominate and can be predictor of the forthcoming cycle: (1) The growth rate in ascend phase strongly negatively correlates to valley length and strongly positively correlates to cycle maximum. (2) The cycle maximum strongly negatively correlates to valley length, and strongly positively correlates to cycle minimum. (3) The cycle period strongly negatively correlates to the valley variation. Based on these correlations, we conclude that the solar cycle 24 is a relatively weak and long cycle which is obviously weaker than Cycle 23. The similarity analysis also presents the similar result. The Cycle 25 is also inferred possibly to be a weak cycle. These results can help us understanding the physical processes of solar cycles.〈/p〉〈/div〉 〈/div〉

Description: 〈p〉Publication date: 1 January 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Advances in Space Research, Volume 63, Issue 1〈/p〉 〈p〉Author(s): Alberto Buzzoni, Giuseppe Altavilla, Siwei Fan, Carolin Frueh, Italo Foppiani, Marco Micheli, Jaime Nomen, Noelia Sánchez-Ortiz〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉 〈p〉We report on extensive 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si41.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi mathvariant="italic"〉BVR〈/mi〉〈/mrow〉〈mrow〉〈mi〉c〈/mi〉〈/mrow〉〈/msub〉〈msub〉〈mrow〉〈mi〉I〈/mi〉〈/mrow〉〈mrow〉〈mi〉c〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 photometry and low-resolution (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si42.gif" overflow="scroll"〉〈mrow〉〈mi〉λ〈/mi〉〈mo〉/〈/mo〉〈mi mathvariant="normal"〉Δ〈/mi〉〈mi〉λ〈/mi〉〈mo〉∼〈/mo〉〈mn〉250〈/mn〉〈/mrow〉〈/math〉) spectroscopy of the deep-space debris WT1190F, which impacted Earth offshore from Sri Lanka, on 2015 November 13. In spite of its likely artificial origin (as a relic of some past lunar mission), the case offered important points of discussion for its suggestive connection with the envisaged scenario for a (potentially far more dangerous) natural impactor, like an asteroid or a comet.〈/p〉 〈p〉Our observations indicate for WT1190F an absolute magnitude 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si43.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉R〈/mi〉〈/mrow〉〈mrow〉〈mi〉c〈/mi〉〈/mrow〉〈/msub〉〈mo〉=〈/mo〉〈msub〉〈mrow〉〈mn〉32.45〈/mn〉〈/mrow〉〈mrow〉〈mo〉±〈/mo〉〈mn〉0.31〈/mn〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉, with a flat dependence of reflectance on the phase angle, such as 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si44.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi mathvariant="italic"〉dR〈/mi〉〈/mrow〉〈mrow〉〈mi〉c〈/mi〉〈/mrow〉〈/msub〉〈mo〉/〈/mo〉〈mi〉d〈/mi〉〈mi〉ϕ〈/mi〉〈mo〉∼〈/mo〉〈msub〉〈mrow〉〈mn〉0.007〈/mn〉〈/mrow〉〈mrow〉〈mo〉±〈/mo〉〈mn〉2〈/mn〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 mag deg〈sup〉−1〈/sup〉. The detected short-timescale variability suggests that the body was likely spinning with a period twice the nominal figure of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si45.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi〉P〈/mi〉〈/mrow〉〈mrow〉〈mi mathvariant="normal"〉flash〈/mi〉〈/mrow〉〈/msub〉〈mo〉=〈/mo〉〈msub〉〈mrow〉〈mn〉1.4547〈/mn〉〈/mrow〉〈mrow〉〈mo〉±〈/mo〉〈mn〉0.0005〈/mn〉〈/mrow〉〈/msub〉〈mspace width="0.25em"〉〈/mspace〉〈mi mathvariant="normal"〉s〈/mi〉〈/mrow〉〈/math〉, as from the observed lightcurve. In the 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si41.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mi mathvariant="italic"〉BVR〈/mi〉〈/mrow〉〈mrow〉〈mi〉c〈/mi〉〈/mrow〉〈/msub〉〈msub〉〈mrow〉〈mi〉I〈/mi〉〈/mrow〉〈mrow〉〈mi〉c〈/mi〉〈/mrow〉〈/msub〉〈/mrow〉〈/math〉 color domain, WT1190F closely resembled the Planck deep-space probe. This match, together with a depressed reflectance around 4000 and 8500 Å may be suggestive of a “grey” (aluminized) surface texture.〈/p〉 〈p〉The spinning pattern remained in place also along the object fiery entry in the atmosphere, a feature that may have partly shielded the body along its fireball phase perhaps leading a large fraction of its mass to survive intact, now lying underwater along a tight (〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si47.gif" overflow="scroll"〉〈mrow〉〈mo〉∼〈/mo〉〈mn〉1〈/mn〉〈mo〉×〈/mo〉〈mn〉80〈/mn〉〈/mrow〉〈/math〉 km) strip of sea, at a depth of 1500 m or less.〈/p〉 〈p〉Under the assumption of Lambertian scatter, an inferred size of 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si48.gif" overflow="scroll"〉〈mrow〉〈msub〉〈mrow〉〈mn〉216〈/mn〉〈/mrow〉〈mrow〉〈mo〉±〈/mo〉〈mn〉30〈/mn〉〈/mrow〉〈/msub〉〈mo〉/〈/mo〉〈msqrt〉〈mrow〉〈mi〉α〈/mi〉〈mo〉/〈/mo〉〈mn〉0.1〈/mn〉〈/mrow〉〈/msqrt〉〈/mrow〉〈/math〉 cm is obtained for WT1190F. By accounting for non-gravitational dynamical perturbations, the Area-to-Mass ratio of the body was in the range 〈math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si49.gif" overflow="scroll"〉〈mrow〉〈mo stretchy="false"〉(〈/mo〉〈mn〉0.006〈/mn〉〈mo〉⩽〈/mo〉〈mi mathvariant="italic"〉AMR〈/mi〉〈mo〉⩽〈/mo〉〈mn〉0.011〈/mn〉〈mo stretchy="false"〉)〈/mo〉〈/mrow〉〈/math〉 m〈sup〉2〈/sup〉 kg〈sup〉−1〈/sup〉.〈/p〉 〈p〉Both these figures resulted compatible with the two prevailing candidates to WT1190F’s identity, namely the Athena II Trans-Lunar Injection Stage of the Lunar Prospector mission, and the ascent stage of the Apollo 10 lunar module, callsign “Snoopy”. Both candidates have been analyzed in some detail here through accurate 3D CAD design mockup modelling and BRDF reflectance rendering to derive the inherent photometric properties to be compared with the observations.〈/p〉 〈/div〉 〈/div〉