This paper introduces the GPS based attitude determination system (GENIUS) onboard the university small satellite Flying Laptop. The attitude determination algorithm which is based on a Kalman Filter and processes single differences of the C/A-code and carrier phase measurements is shortly described. The algorithm uses the LAMBDA-method to resolve the integer ambiguities of the double differences of the carrier phase measurements. These resolved ambiguities are then used to fix the single difference ambiguities in the filter. The results of ground based tests and numerical simulations are introduced and the accuracy of the attitude determination algorithm is assessed.

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The Flying Laptop is a micro-satellite currently under development at the Institute of Space Systems, Universität Stuttgart. The primary mission objective of the Flying Laptop is technology demonstration for the future projects of the Institute of Space Systems. Several attitude sensors, either in-house developed or from external companies with no previous flight heritage, are being used. Electronic boards and mechanical housings were designed for the GPS system, the fiber-optic gyros and the magnetic torquers. The GENIUS experiment aims to increase the GPS accuracy in orbit by using an ultra stable oscillator (USO) and includes attitude determination. The C-FORS fiber optic gyro is a commercial product developed for aviation. With the Micro Advanced Stellar Compass made by the Technical University of Denmark and the Magnetometer made by Zarm-Technik new developments, so far not flown, are integrated. All attitude sensors and actuators are connected to a field programmable gate array (FPGA). This kind of onboard computer offers a more accurate timing and parallel processing of the sensors' and actuators' signals. The paper focuses on the attitude sensors and actuators and their interfaces to the on-board computer.