Laser Communication with Alphasat - FD Challenges and First Flight Results

Inmarsat’s geostationary satellite Alphasat, launched on July 25, 2013, is the largest European telecommunications satellite ever built with a weight of 6.6 tons. For technology demonstration it is carrying different payloads, hereunder the laser communication terminal (LCT) built by Tesat-Spacecom and operated by DLR/GSOC. Its purpose is to establish bidirectional data links with data rates of up to 1.8 Gbit/s. Links can be either within space, so called inter-satellite links (ISL) to counter terminals in low Earth orbit (LEO), or from the geostationary satellite to terminals mounted on ground stations on the Earth’s surface, space-toground links (SGL). This paper gives an overview about the LCT operations aboard Alphasat and its counter terminals. The corresponding work flow from visibility computations over link scheduling until command generation is described. Furthermore, it provides a deeper insight into the flight dynamics tasks that comes along with the operations of an LCT, such as visibility calculations and pointing performance analysis. The results of the first successfully performed links are presented.