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  • Other Sources  (9)
  • SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING  (9)
  • Atmosphere-ocean interaction
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  • 1
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    Strategies for high-precision Global Positioning System orbit determination (1987)
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    Publication Date: 2011-08-19
    Description: Various strategies for the high-precision orbit determination of the GPS satellites are explored using data from the 1985 GPS field test. Several refinements to the orbit determination strategies were found to be crucial for achieving high levels of repeatability and accuracy. These include the fine tuning of the GPS solar radiation coefficients and the ground station zenith tropospheric delays. Multiday arcs of 3-6 days provided better orbits and baselines than the 8-hr arcs from single-day passes. Highest-quality orbits and baselines were obtained with combined carrier phase and pseudorange solutions.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 12751-12
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  • 2
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    Precise orbit determination of a geosynchronous satellite with differential very-long-baseline interferometry (1986)
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    Publication Date: 2011-08-19
    Description: The use of differential VLBI (DVLBI) to determine the orbit of a U.S. geosynchronous satellite with a position accuracy of a few meters is examined. DVLBI was employed to track the geosynchronous satellite DSCS-II; two observation channels with 2 MHz bandwidth each in a 2 GHz band were used to receive the telemetry signal of the satellite and quasar radio signals. The random observation, delay, station location, and quasar position errors are discussed. The correlation processing of the quasar and satellite signals is described. The accuracy of the estimated satellite position is evaluated using a covariance analysis. It is determined that the satellite position was estimated with an accuracy of about 4 m at the center of the observation arc. It is noted that the modeling error of the solar radiation pressure factor, ionospheric correction error, and observation error need to be corrected in order to provide more accurate orbit determinations.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
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  • 3
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    Differential spacecraft tracking by interferometry (1990)
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    Publication Date: 2011-08-19
    Description: This study estimates measurement system errors for two space vehicles on the surface of Mars, and for two Mars orbiting spacecraft, which are being tracked by differential interferometry. In these examples, signals from all spacecraft lie within the same beamwidth of an earth-based radio antenna. The measurements of all spacecraft signals are made simultaneously; errors that scale with angular source separation or with temporal separation between measurement epochs are practically removed. It is shown that errors due to system thermal noise and to systematic effects within ground receiver electronics dominate, except for geometries when signals pass close to the sun, when solar plasma becomes the dominant error source. The instantaneous relative position of two orbiters may be measured to within ten meters, leading to 50-meter three-dimensional orbital accuracy.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
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  • 4
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    Precise tracking of the Magellan and Pioneer Venus orbiters by same-beam interferometry (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Results of a demonstration of same-beam interferometry, the simultaneous tracking of two spacecraft in orbit about a distant planet by widely separated earth-based radio antennas, are presented with regard to the Magellan and Pioneer 12 orbiters at Venus. Signals from both spacecraft fall within the same beamwidth of the tracking antennas. The plane-of-sky position difference between spacecraft is precisely determined by double-differenced phase measurements. This data type complements line-of-sight Doppler and improves orbital accuracy by up to an order of magnitude. The predicted error is dominated by solar plasma fluctuations, and is 15.1 psec for a 5-min integration. The rms of the residuals is less than this by about 25 percent. The shape of the spectrum computed from residuals is consistent with that derived from a model of solar plasma fluctuations. Same-beam interferometry is expected to enhance tracking accuracy and efficiency for proposed multiple missions to Mars.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AAS PAPER 91-191 , In: Spaceflight mechanics 1991; Proceedings of the 1st AAS(AIAA Annual Spaceflight Mechanics Meeting, Houston, TX, Feb. 11-13, 1991. Pt. 2 (A93-17901 05-13); p. 1269-1288.
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  • 5
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    Spacecraft-spacecraft very long baseline interferometry for planetary approach navigation (1991)
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    Publication Date: 2019-06-28
    Description: The study presents an error budget for Delta differential one-way range (Delta-DOR) measurements between two spacecraft. Such observations, made between a planetary orbiter (or lander) and another spacecraft approaching that planet, would provide a powerful target-relative angular tracking data type for approach navigation. Accuracies of about 5 nrad should be possible for a pair of X-band spacecraft incorporating 40-MHz DOR tone spacings, while accuracies approaching 1 nrad will be possible if the spacecraft incorporate Ka-band downlinks with DOR tone spacings of order 250 MHz. Operational advantages of this data type are discussed, and ground system requirements needed to enable S/C-S/C Delta-DOR observations are outlined. A covariance analysis is presented to examine the potential navigation improvement for this scenario. The results show factors of 2-3 improvement in spacecraft targeting over conventional Doppler, range, and quasar-relative VLBI, along with reduced sensitivity to ephemeris uncertainty and other systematic errors.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AAS PAPER 91-181 , In: Spaceflight mechanics 1991; Proceedings of the 1st AAS(AIAA Annual Spaceflight Mechanics Meeting, Houston, TX, Feb. 11-13, 1991. Pt. 2 (A93-17901 05-13); p. 1161-1181.
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  • 6
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    Precise interferometric tracking of spacecraft at low sun-earth-probe angles (1988)
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    Publication Date: 2019-06-28
    Description: When a spacecraft is at low sun-earth-probe (SEP) angle, phase perturbations induced in the spacecraft's signal by the solar plasma can impede the acquisition of meaningful spacecraft Very Long Baseline Interferometry (VLBI) measurements. This phenomenon imposes limitations on our ability to successfully acquire the spacecraft signal, and also introduces unmodeled errors into data that are successfully acquired. In this paper, an analysis of the solar plasma induced error on interferometric delay rate as a function of SEP angle is performed. In addition, the probability of correct signal phase connection as a function of SEP angle and plasma variability is calculated for 2.3 GHz and 8.4 GHz signals. In December 1986, an experiment was conducted to demonstrate VLBI navigation at low SEP angles, using the Voyager 2 spacecraft. The results of this experiment are consistent with the conclusions reached in the low SEP analysis and are also consistent with a theoretical error model for water vapor fluctuations in the earth's troposphere.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AIAA PAPER 88-0572
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  • 7
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    Precision GPS orbit determination strategies for an earth orbiter and geodetic tracking system (1988)
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    Publication Date: 2019-07-13
    Description: Data from two 1985 GPS field tests were processed and precise GPS orbits were determined. With a combined carrier phase and pseudorange, the 1314-km repeatability improves substantially to 5 parts in 10 to the 9th (0.6 cm) in the north and 2 parts in 10 to the 8th (2-3 cm) in the other components. To achieve these levels of repeatability and accuracy, it is necessary to fine-tune the GPS solar radiation coefficients and ground station zenith tropospheric delays.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AAS PAPER 87-502 , AAS/AIAA Astrodynamics Conference; Dec 06, 1987 - Dec 09, 1987; Kalispell, MT; United States
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  • 8
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    The electromagnetic environment at S- and Ku-band frequencies for the Space Station Freedom (1993)
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    Publication Date: 2019-07-13
    Description: The purpose of this paper is to quantify the electric field strength around the Space Station Assembly/Contingency Subsystem (ACS) S-band conical horn antenna and the Space-to-Ground Subsystem (SGS) Ku-band 6-ft diameter reflector antenna. The regions in which the electric fields exceed the specified maximum permitted RF exposure of the Extravehicular Mobility Unit electronics equipment and EVA astronaut are identified for the Space Station ACS S-band conical horn antenna and the SGS Ku-band 6-ft diameter reflector antenna, respectively. The scattering effects of a flat metal plate, a representative Space Station structural element, were also examined. It was shown that the reflected waves from the reflecting structure cause both destructive and constructive interference of the electric fields in the intersection region between the incident and reflected waves.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AIAA PAPER 93-0571 , AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States|; 6 p.
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  • 9
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    Relative tracking of multiple spacecraft by interferometry (1989)
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    Publication Date: 2019-07-13
    Description: An analysis is conducted of earth-based radiometric tracking of one spacecraft relative to an angularly nearby second spacecraft. Two cases are studied: relative positioning between a lander and a rover on the surface of Mars and relative tracking between a Mars lander and a Mars orbiter. All spacecraft signals are simultaneously received in the same beamwidth of an earth tracking antenna. Differential interferometric measurement errors are predicted. Errors which scale with angular separation between sources and errors which scale with temporal separation between measurement epochs are reduced virtually to zero. System thermal noise and systematic phase shifts introduced by receiver electronics typically dominate the error budget. Solar plasma delays become dominant for signal paths which pass close to the sun. Precise line-of-sight range measurements, differenced between stations, are also considered. Meter-level accuracy is obtained for lander/rover relative position by combining interferometric and precise range measurements. Either data type alone, for geometries where earth is not near zero declination as seen from Mars and Mars is not near zero declination as seen from earth, can provide accuracy at the 10-100-m level.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: AAS PAPER 89-178 , AAS/NASA Intl. Symposium on Orbital Mechanics and Mission Design; Apr 24, 1989 - Apr 27, 1989; Greenbelt, MD; United States
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