Validation of GNSS Multipath Model for Space Proximity Operations Using the Hubble Servicing Mission 4 Experiment

Abstract

In the rendezvous and docking of spacecraft, GNSS signals can reflect off the target vehicle and cause large errors in the chaser vehicle receiver at ranges below a few hundred meters. It has been proposed that these additional ray paths, or multipath, be used as a source of information about the state of the target relative to the receiver. With Hubble Servicing Mission 4 as a case study, electromagnetic ray tracing has been used to construct a model of reflected signals from known geometry. Oscillations in the prompt correlator power due to multipath, known as multipath fading, are studied as a means of model validation. Agreement between the measured and simulated multipath fading serves to confirm the presence of signals reflected off the target spacecraft that might be used for relative navigation.

A Framework of Multipath Mitigation With Joint Multipath-Doppler Diversity for RF Relative Measurement

“…It is worth noting that the Doppler and multipath can be observed in the signal received by the receiver due to the relative motion of the spacecrafts during the RF relative measurement [16], [17]. Moreover, when the projection of the relative velocity vector in the direction of the direct signal is not the same as the projection in the direction of the multipath signal, the instantaneous Doppler shift of the multipath signal received by the receiver can be significantly different from the direct signal.…”