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  • SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING  (4)
  • Atmosphere-ocean interaction
  • Australia
  • Water budget
  • 1990-1994  (4)
  • 1
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    Differential spacecraft tracking by interferometry (1990)
    In:  Other Sources
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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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  • 2
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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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  • 3
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    Spacecraft-spacecraft very long baseline interferometry for planetary approach navigation (1991)
    In:  Other Sources
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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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  • 4
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    The electromagnetic environment at S- and Ku-band frequencies for the Space Station Freedom (1993)
    In:  Other Sources
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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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