Radio-planetary from tie from Phobos-2 VLBI data

Details Radio-planetary from tie from Phobos-2 VLBI data Radio-planetary from tie from Phobos-2 VLBI data

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994tdar.nasa...46h&link_type=abstract

In its The Telecommunications and Data Acquisition Report p 46-82 (SEE N95-17279 04-32)

Computer Science

1

Data Acquisition, Extragalactic Radio Sources, Interplanetary Navigation, Moon, Phobos, Soviet Spacecraft, Spacecraft Orbits, Spacecraft Tracking, Stability, Time Measurement, Very Long Base Interferometry, Bias, Earth Rotation, Ephemerides, Quasars, Spacecraft Trajectories

Scientific paper

In an ongoing effort to improve the knowledge of the relative orientation (the 'frame tie') of the planetary ephemeris reference frame used in deep navigation and a second reference frame that is defined by the coordinates of a set of extragalactic radio sources, VLBI observations of the Soviet Phobos-2 spacecraft and nearby (in angle) radio sources were obtained at two epochs in 1989, shortly after the spacecraft entered orbit about Mars. The frame tie is an important systematic error source affecting both interplanetary navigation and the process of improving the theory of the Earth's orientation. The data from a single Phobos-2 VLBI session measure one component of the direction vector from Earth to Mars in the frame of the extragalactic radio sources (the 'radio frame'). The radio frame has been shown to be stable and internally consistent with an accuracy of 5 nrad. The planetary ephemeris reference frame has an internal consistency of approximately 15 nrad. The planetary and radio source reference frames were aligned prior to 1989 and measurements of occulations of the radio source 3C273 by the Moon. The Phobos-2 VLBI measurements provide improvement in the accuracy of two of the three angles describing a general rotation between the planetary and radio reference frames. A complete set of measurements is not available because data acquisition was terminated prematurely by loss of spacecraft. The analysis of the two Phobos-2 VLBI data sets indicates that, in the directions of the two rotation components determined by these data, the JPL planetary ephemeris DE200 is aligned with the radio frame as adopted by the International Earth Rotation Service within an accuracy of 20-40 nrad, depending on direction. The limiting errors in the solutions for these offsets are spacecraft trajectory (20 nrad), instrumental biases (19 nrad), and dependence of quasar coordinates on observing frequency (24 nrad).

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