AOCS DESIGN AND EM AOCS TEST CAMPAIGN FOR THE SMALL GEO TELECOM SATELLITE

摘要

The Small GEO telecommunications satellite is a new development managed by the EuropeanSpace Agency (ESA) to fill a niche in the telecom industry for small platforms weighing about 1.5tonnes and targeting payloads of 300 kg and 3 kW. The prime contractor for Small GEO is OHB-SystemAG. OHB-Sweden AB is a partner in the consortium and supplies the Attitude and Orbit Control System(AOCS) and Electric Propulsion (EP) subsystems. The first mission, operated by Hispasat, will launchinto Geostationary Transfer Orbit (GTO). The project is currently in Phase C/D and the satellite will fly in2013.The Small GEO AOCS design is characterized by a number of advances in technology beyondtraditional telecom satellite designs. It includes modern sensors, actuators, and software developmenttechniques used to improve the mission capacity for the customer. The AOCS architecture is a threeaxisstabilized system using reaction wheels for attitude control, and APS (Active Pixel Sensor) startrackers for attitude determination. Orbit control and angular momentum management rely solely uponEP in the nominal modes. In addition, a GPS sensor will be flown on-board as an experiment to preparefor future improvements of the AOCS design. The AOCS Software implementation is model-based andis entirely developed in Matlab / Simulink. The automatically generated C-code is then integrated intothe whole on-board software by OHB-System.The project is now entering its Verification and Validation phase. In parallel with the formal On-Board Software validation, the AOCS Subsystem Testing will be completed by a series of Open Loopand Closed Loop tests, with both hardware and software in the loop. While the Open Loop tests aim atverifying the correct sensor-software-actuator chains, the Closed Loop tests will verify the functionalbehaviour of the AOCS Subsystem in operational scenarios. The GPS receiver will be tested on groundin combination with a RF-simulator to get a first assessment of its usability in geostationary orbit. Thetests on the SGEO EM satellite start in March 2011 and will continue until autumn 2011.This article gives an overview of the Small GEO AOCS design, and describes the advances in thedesign that make it unique. It also presents the current AOCS activities, focusing on the EM Open Loopand Closed Loop tests on the EM satellite.