Flight Test Results from Real-Time Relative Global Positioning System Flight Experiment on STS-69

Abstract A real-time relative global positioning system (GPS) Kalman ftlter has been developed in support of automatedrendezvous with the International Space Station (ISS). The filter is integrated with existing Space Shuttle ren-dezvous software running on a 486 laptop computer under Windows ®. In this work we present real-time andpostflight results achieved with the filter on Space Shuttle mission STS-69. This experiment used GPS datafrom an Osborne/Jet Propulsion Laboratory (JPL) TurboRogue receiver carried on the Wake Shield Facility(WSF) free-flyer and a Rockwell Collins 3M receiver carried on the Orbiter. Real-time filter results, processedonboard the Shuttle and replayed in near-real-time on the ground, are based on single-vehicle mode operation andon 5 to 20 minute snapshots of telemetry provided by WSF for dual-vehicle mode operation. Postflight resultswere achieved by running the ftlter in a real-time mode using data recorded during the mission.Orbiter and WSF state vectors calculated using our filter compare favorably with precise reference orbits deter-mined by the University of Texas Center for Space Research. The reference orbits were generated by double-differencing GPS data flom both vehicles along with data from GPS ground stations. The lessons learned fromthis experiment will be used in conjunction with future experiments to mitigate the technology risk posed byautomated rendezvous and docking to the ISS.