Autonomous Orbit Determination with Satellite-to-Satellite Tracking

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Satellite-to-Satellite Tracking (SST) can be used between spacecraft in halo orbits to perform orbit determination without any Earth-based tracking data. SST, for the purposes of this discussion, will mean scalar inter-satellite observations such as crosslink range or Doppler. It has never been thought that SST could be used alone for orbit determination, because it doesn't work in Keplerian, or two-body orbits. To explain why, examine the plot shown above. Imagine there are two spacecraft orbiting the Earth (top left) and generating a crosslink range measurement, as shown on the top right. If one were to change the size, shape or relative orientation of the two orbits, the SST measurements would be affected and those changes could be estimated. However, if the orbit planes of both spacecraft were rotated together so that they now appeared like the configuration showed at the lower left, their absolute orientation has changed, but that will not affect the measurements. Thus, SST can only be used to observe the size, shape, and relative orientation of the orbits of the participating spacecraft in the two-body problem.

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