Autonomous orbit control for earth-observation satellites

In this paper we will discuss the concept of an autonomous orbit position controller for low Earth orbiting satellites. A high-resolution optical camera (VHRC) of the DLR is proposed as payload. The orbit accuracy requirements are specified to +/- 1km as well in flight direction as perpendicular to the orbit plane (x- and y-position) and to +/- 200m in radial direction (z-position). An ion-thruster (RIT10: 0.2mN - 20mN) shall serve as fuel-efficient propulsion system, an onboard GPS-receiver shall provide the actual position in real time. It will be shown that a relatively simple and robust state-space controller can guarantee the specified accuracy. It tolerates GPS data deteriorated with selective availability (SA) and white noise and compensates non-linear effects inherent to the proposed design (thrust only applied in flight direction and/or perpendicular to the orbital plane). This concept was derived by using the Small Satellite Simulator (KSS) developed at the Institute of Space Technology of the Universitat der Bundes wehr Munchen.