ESA GNC Conference Papers Repository

The Alphabus development was supported by European space agency (ESA) and the French space agency (CNES). Alphabus is a joint product of Thales Alenia Space and Airbus Defence and Space teaming with wellestablished industrial partners in Europe. Alphasat, the first satellite based on the Alphabus platform has been launched in July 2013, and is now accumulating its first year of in-orbit operations. Alphasat was built for Inmarsat under the primecontractorship of Airbus Defence and Space with Thales Alenia Space providing majors subsystems. The avionics and particularly the Attitude and Orbit Control sub-system (AOCS) and plasmic propulsion subsystems were developed by Thales Alenia Space. This paper recalls the main bus features of Alphasat AOCS and presents the main AOCS performances validated in orbit. <br><br>This paper provides also a focus on the particularity of the Alphasat mission in AOCS point of view : <br><br>the plasmic propulsion: AOCS algorithms used to manage the plasmic propulsion for station keeping maneuvers in Alphabus platform were developed in the early 2000’s by Thales Alenia Space for the Spacebus platform (and in particular Stentor an Astra1k) but not tested in flight up to now (two launch vehicles failures !) <br><br>the impact of the large deployable antenna (LDR) : the use of Alphasat like antenna is a challenge not only in system and payload point of views but also in AOCS one as such antenna leads to important attitude constraints during the phase just before and during its deployment, in addition this antenna impacts the attitude control performances, <br><br>and the use of the AA-STRS: up to now Thales Alenia Space AOCS designs were based on CCD detector based star trackers. In the frame of Alphabus development, the Selex AA-STR has been developed and manufacturer by Selex-Galileo and is now used in the Alphasat closed loop attitude control (2 additional units are also operated since January 2014 on an other S/C).