GPS/INS Kalman filter design for spacecraft operating in the proximity of the international space station

The next generation reusable launch vehicle will operate in five flight phases: ascent, on-orbit, proximity operations, re-entry and landing. Navigation during each of these flight phases presents unique challenges. The Space Shuttle addresses these challenges by the use of a number of navigation sensors. However, an integrated GPS/INS navigation system may be able to meet the navigation requirements of all flight phases. Integrated GPS/INS systems have been built and demonstrated for the ascent, re-entry and landing phases and their performance is known. However, the same cannot be said for integrated GPS/INS systems for the on-orbit and proximity operations flight phases. Therefore, this research examines the performance of GPS/INS navigation during a rendezvous with the ISS. Error models for INS and GPS navigation sensors operating in the vicinity of the ISS have been developed. The GPS error model includes the effects of GPS signal blockage and multipath near the ISS. These error models have been used to develop an integrated GPS/INS extended Kalman filter. A simulation of the filter has been developed and the first test case shows position errors of less than 1 meter and velocity errors of less than 0.02 m/s in each axis. The second test case shows the position errors grow to approximately 47.5 meters and the velocity errors grow to 0.13 m/s during a ten minute GPS outage. Finally, the third test case shows that the GPS/INS EKF performance is not significantly degraded by GPS signal blockage due to the ISS during a simulated rendezvous with the ISS.