Autonomous Formation Flying RF Ranging Subsystem

Formation Flying (FF) missions are currently under study and they will take place in the next years. These FF's missions consist of a set of satellites forming an array that makes continuous measurements to maintain an existing configuration or to move to a new configuration. The implementation of a Formation Flying concept is being considered by ESA for the Darwin mission, scheduled for around 2014. The Darwin "space interferometer", a future cornerstone mission of the European Space Agency, will enable both exo-planet detection via nulling interferometry, and aperture synthesis imagery to be achieved in the thermal infra-red. It is also planned that the SMART-3 mission, scheduled for launch in 2009, will provide in-flight validation of the potential performance and limitations of the free-flying aspects of this concept. The Formation Flying RF ranging subsystem is in charge of measuring the relative distance and angles between spacecrafts with a high degree of accuracy and to process these measurements in order to obtain on board the differential attitude and position. Once these relative data are computed, the RF subsystem provides this information to other subsystems of the FF system, which generates the necessary commands to maintain the constellation in the desired configuration. This FF RF SS has to be able to allow several basic manoeuvres such as deployment, rotation, slew and contraction/expansion of the satellite constellations. Alcatel Space Industries, with the support of GMV, is studying the concept of the formation flying RF ranging subsystem under ESA/ESTEC contract, for both Darwin and SMART-3 missions. This paper presents the main results of the work and the current status of the study. The paper covers mainly the type of relative attitude and navigation algorithms, a summary of the performances analysis (using a SW simulator developed under this study) and the description of the architecture (HW and SW, including transmitters and receivers). Within the study, the formation flying RF subsystem concept will be demonstrated, not only through simulations, but also through tests performed on a breadboard. The tests conducted on this breadboard will enable real time demonstrations to be carried out: the breadboard will be based on representative hardware for receivers/transmitters and the navigation algorithms will be processed in real time.