Dual Satellite Operations in Close Formation Flight

Kurzfassung

TerraSAR-X (TSX) and TanDEM-X (TDX) are two satellites flying in low-earth orbit. Both satellites are equipped with a synthetic aperture radar (SAR) payload for Earth observation. TSX has been launched in 2007 and TDX in 2010. Both satellites are operated by the German Space Operations Center (GSOC). Since October 2010 the two spacecraft are orbiting the Earth in a close formation flight with inter-satellite distances in the order of a few hundred meters. In this configuration the two satellites fulfill the goals of two different missions: The “TerraSAR-X” mission uses the radar instrument on either TSX or TDX satellite in stand-alone mode. The “TanDEM-X” mission uses the radar instrument on both satellites simultaneously in so-called “bi-static” mode. The former application delivers two dimensional images, the latter allows a three dimensional model of the Earth’s surface to be made. During the TanDEM-X mission a digital elevation model covering the Earth’s complete land mass is generated. This paper describes several aspects of the combined missions from the control center’s point of view. The workflow of dual satellite operations includes safety measures required to minimize the risks in close formation. In particular, protection against potential collision of the two spacecraft and protection against illumination of the partner satellite during radar beam transmission must be guaranteed. Furthermore, the concept of the mission planning system which distributes the payload requests of two different missions to two satellites will be presented.