The BIRD Satellite Mission as a Milestone Towards GPS-based Autonomous Navigation

Abstract

The paper describes the design and implementation of an on-board navigation system for the German BIRD microsatellite. BIRD is a technology and science satellite aiming at the autonomous detection and indentification of hot spots like forest fires or volcanic activities. The Onboard Navgation System (ONS) will provide the instantaneous nadir and along-track direction for Earth- fixed camera pointing as well as precise position values for real-time geocoding of the optical and infrared images and derived data. It employs a GEM-S 5 channel C/A code receiver which provides GPS position fixes with a typical accuracy of 100 m (Selective Availability on). Using an extended Kalman filter and a fidelity force model, a dynamical orbit determination and prediction is performed to povide smooth trajectory data with a nominal accuracy of 30 m during continous GPS data takes and an accuracy of better than 100 m for prediction arcs of up to 30 mins. The ONS is, furthermore, supplemented by a prototype software for the real-time estimation of SGP4 mean elements, which allows an on- board forecast of ground station contracts or eclipse times. In addition, NORAD compatible twolineelement sets can be created and downlinked to ground terminal for autonomous station operation.