Gravity Gradient Earth Sensor experiment on REXUS 11

This experiment is the first test of the concept for a novel attitude determination sensor in freefall, that utilizes the Earth`s gravity gradient as a reference. Current sensors require multiple optical heads with access on all faces of a satellite that might point towards the Earth [1]. Earth sensors determine the Earth vector by sensing the position of the Earth’s horizon, detecting the Earth`s IR emission against the background of space [2]. The gravity-gradient based approach does not require optical access for the sensor, and one single, compact unit can be located anywhere inside the satellite, and provide complete 4π steradian field of view. The sensor principle is based on the use of a Micro Electro Mechanical System (MEMS) device that can measure the Gravity Gradient Torque (GGT) [3]. We describe the design of the experiment to test the MEMS GGT sensor on a REXUS flight and present the results obtained.