Multi-GNSS Precise Orbit Determination of the International Space Station (ISS)

Abstract

In support of the Atomic Clock Ensemble in Space (ACES), a multi-frequency, multi-GNSS receiver will be flown onboard the International Space Station (ISS) from 2016 onwards. The Javad Triumph receiver selected for this purpose is based on commercial-off-the-shelf compo-nents but has successfully passed an extensive qualifica-tion program ensuring a proper operation in the space environment. The receiver supports tracking of GPS, GLONASS, and Galileo signals in the L1/E1, L2, and L5/E5a frequency bands, which offers access to a much larger number of signals and measurements than legacy space receivers and helps to compensate the limited field of view and unfavorable antenna orientation implied by the accommodation of the ACES payload box. Following an introduction to the ACES project and a de-scription of the ACES GNSS sub-system, the paper dis-cusses a comprehensive signal simulator test that has been conducted to validate the receiver and to assess the achievable performance. The tracking performance in a GPS-only configuration is compared with a full multi-GNSS configuration. The intrinsic difficulties of multi-GNSS positioning and precise orbit determination (such as constellation-dependent clock offset parameters, inter-signal and inter-system biases) are discussed and the as-sociated changes to DLR’S GPS High Precision Orbit Determination Software Tools (GHOST) are highlighted. Analysis results based on actual GNSS measurements obtained in the signal simulator test are presented.