ESA GNC Conference Papers Repository

The National Institute for Aerospace Technology (INTA) new MicroSat program (80-150 kg) started in 2006 as a further step on our Small Satellites R&D initiative after the NanoSat program (15-25 kg) success with two spacecrafts already in orbit and working operationally (the NanoSat-01 was launched the 18 Dec. 2004 and NanoSat-1B in July 2009). INTA is responsible for the system level design, integration and verification, wile some of the subsystems are developed in close collaboration with a few Spanish universities and Small & Medium Enterprises (SME). Since 2009 the Universidad Complutense de Madrid (UCM) joined the project team helping INTA in the development of the challenging AOCS for the new MicroSat & NanoSat-2 modular platforms. INTAmicroSat1 is a first R&D earth observation mission that will validate in orbit the new Service Module and units designed and manufactured by INTA, together with a set of multispectral cameras and technological payloads (TPL). Some of these instruments require a quite high pointing accuracy and stability wile in the nadir AOCS mode. For this reason we will rely on three reaction wheels in orthogonal configuration plus a redundant fourth wheel positioned in the [1, 1, 1] direction. For the fine attitude sensors we will use a Star Tracker and 3+1 gyrometers that will be in parallel with the reaction wheels’ directions. We will also have an experimental GPS receiver based on COTS components that will be used to provide autonomous on board orbital propagation. It will carry a new IR Earth Horizon microsensor (TPL) to provide a good Nadir direction knowledge when the Star tracker is not in use. Finally, a propulsion subsystem with a single 1N thruster will be incorporated to reach & keep the target orbit under control (702 km 10:30 SSO with a 9 days revisit cycle). The coarse modes are implemented using three magnetorquer coils, a hot redundant 3axis magnetometer and three hemispherical coarse sun sensors (SS) allowing a 4pi-steradian field of view. The paper explains in detail the different AOCS modes and submodes selected, together with the design rules and verification approach along the development phases of the project.