Effects of multipath and signal blockage on GPS navigation in the vicinity of the International Space Station (ISS)

Previous studies examining GPS relative navigation for spacecraft performing rendezvous with the International Space Station (ISS) have not accounted for degradation in GPS navigation performance due to multipath or blockage of GPS signals by the ISS. This study analyzes these effects on GPS navigation in the vicinity of the ISS. A simulation of a spacecraft GPS receiver operating near the ISS has been developed. This simulation includes orbit models for the GPS constellation, the ISS, and the spacecraft, as well as models for GPS signal blockage and multipath. The blockage simulation shows that aiding of GPS is required when the spacecraft approaches within 60 m of the ISS. The multipath simulation shows the expected trends in range errors as a function of GPS satellite elevation angle, distance from the ISS, number of multipath rays, and the radar cross-sectional area of the ISS.