ESA GNC Conference Papers Repository

Kicked-off in 2012, after the conclusion of the ARGON precursor on the PRISMA mission, the AVANTI (Autonomous Vision Approach Navigation and Target Identification) experiment has been successfully conducted in October/November 2016. For the first time in space applications, AVANTI demonstrated the capability to autonomously navigate towards a noncooperative target satellite in low-Earth orbit making use of angles-only measurements from 50km to circa 50m of inter-satellite separation range. Within AVANTI, the DLR Earth-observation BIROS spacecraft autonomously performed far- to mid-range proximity operations with respect to the BEESAT-4 one-unit CubeSat (Berlin Technical University), released in orbit on the 9th of September 2016, by means of a single picosatellite launcher device. AVANTI employed the star-tracker embarked on BIROS as far-range camera to take images of portions of the sky and autonomously carried out onboard the following activities: image processing and target identification to provide the angles-measurements of the line-of-sight to the target; realtime relative navigation through an extended Kalman filter; computation of the required impulsive maneuvers' profile to perform a rendezvous in a safe, fuel efficient manner. With respect to its preliminary design, the AVANTI GNC system evolved in complexity and completeness during the progress of its integration into the BIROS flight-software. From the one hand, BIROS has been specifically designed for Earth observation and hot spot detection in the framework of the FireBird mission. From the other hand, during its weeks of activity, AVANTI transformed FireBird into a formation-flying mission, thus it had to integrate all the required competences and activities which were not originally supported by BIROS to meet its primary science objective. As a result, in addition to the aforementioned relative orbit determination and control specific functions, the AVANTI system features the selection of the best-suited attitude mode (e.g, fixed or tracking client observation mode, cool-down attitude mode, Earth-pointing or thruster firing attitude modes) and the implementation of the onboard safety monitoring and collision avoidance task. To this last point it shall be emphasized that, although BEESAT-4 embarks a Phoenix GPS receiver, this device was not yet commissioned and, therefore, not operating by the time when AVANTI took place. Therefore, differently to the formation-flying missions flown so far in low-Earth orbit, AVANTI was confronted to an incontrovertible noncooperative scenario. This paper presents the flight results achieved by the AVANTI experiment. The performances of its navigation and control systems are critically discussed, spanning over the different experiment phases and inter-satellite ranges investigated during the four weeks of its lifetime.