Functional and Performance Validation of the PRISMA Precise Orbit Determination Facility

The paper summarizes the activities performed in the framework of the Swedish PRISMA mission to validate its ground facility for Precise Orbit Determination (POD). PRISMA is a challenging dual spacecraft mission for the demonstration of technology related to formation flying. The mission will rely on GPS as reference for the crossvalidation of innovative formation flying sensors and as support for the spacecraft operations. As a consequence it has to be ensured that the post-facto processing of GPS spaceborne measurements is mature and provides reliable orbit products on a routine basis. In addition the expected accuracy of the resulting GPS-based precise absolute and relative positioning needs to be assessed prior to the launch. Even if experience coming from other missions can be intensively used for these investigations, dedicated tests need to be conducted to cover complex scenarios specific to the PRISMA mission, which comprise high thrust activities or frequent rotations of the spacecraft. The tests have first been conducted using the German Space Operation Center (GSOC) formation flying testbed, which offers the possibility to enable/disable various relevant error sources in order to allow for step-by-step, systematic assessment of their impact on the POD system.. A second series of tests is conducted in cooperation with the Swedish Space Corporation (SSC) using the sophisticated Satlab simulation environment. This simulator gives the possibility to define challenging and complex formation flying scenarios comprising realistic thrust and attitude profiles as well as highly realistic sensors and actuator models. Hardware-in-theloop campaigns using true GPS receivers have also been performed using these two simulation environments. Overall the validation tests were successful and promise absolute positioning performance better than 20 cm R.M.S. and relative positioning performance better than 10 mm R.M.