ESA GNC Conference Papers Repository
Evolution of the AOCS Design for EDRS and the satellites of the Small GEO Family
The Small GEO telecommunications platform is a new development managed by the European Space Agency (ESA) to fill a niche in the telecom industry for small platforms weighing about 1.5 tons and targeting payloads of 300 kg and 3 kW. The prime contractor for the satellites is OHB System AG. OHB Sweden AB is a partner in the consortium and supplies the Attitude and Orbit Control System (AOCS) and Electric Propulsion (EP) subsystem (when applicable). The first mission, Hispasat Advanced Generation 1 (Hispasat AG1), will fly in 2015. The spacecraft will be launched into Geostationary Transfer Orbit (GTO) and perform the transfer with Chemical Propulsion. It relies solely upon EP for both orbit control and angular momentum management once on GEO. All EP thrusters (2x4 thrusters) have fixed directions and thrust levels. The second mission, the dedicated satellite for the European Data Relay System (EDRS-C), is managed by ESA and Airbus Defence & Space, Germany. The satellite will be part of a constellation of GEO satellites intended to relay information and data between satellites / spacecraft and UAVs and ground stations. The project is currently in phase C/D and will complete its satellite CDR in the summer of 2014. The system uses chemical propulsion (CP) for both GTO transfer and GEO operations. The operation of the on-board Laser Communication Terminal imposes pointing and attitude knowledge stability requirements more stringent than on typical GEO satellites. In order to fulfil these requirements, the satellite needs to include a high-precision gyro. In the case of EDRS-C, the four-axis Astrix-120 (FOG) was selected. Because of the inherent redundancy of the four-axis gyro, it was decided to also use this gyro in Safe Modes. To provide additional robustness to these modes, a consistency check towards the Sun Presence Sensors has been included to allow the isolation of one erroneous gyro measurement axis out of the four available axes. The third mission, Heinrich Hertz (H2Sat), is financed by the German Space Agency DLR and has successfully completed PDR early 2014. The satellite uses CP for GTO transfer and a mix of CP and EP for Station Keeping once in GEO. All EP thrusters (2x2 thrusters) have fixed directions and thrust levels, which requires use of CP thrusters for Angular Momentum Management under nominal operations. Finally, Electra is a satellite developed under the ESA ARTES 33 program and will be operated by SES. The project is now in phase B. The Electra satellite is the first of the Small GEO FLEX series targeting optimized payload capacity in the medium sized telecom satellite market. It will be the first full-EP telecommunication satellite developed in Europe. The EP configuration is modified in order to cope with the large ?V capability required during the GTO transfer. This paper presents the different missions from an AOCS perspective and demonstrates the commonalities and differences between the different satellites. The paper presents for the first time the AOCS technical adaptations of the SGEO platform to the EDRS-C mission needs.