Revolution in satellite-to-earth communication: Data transfer via Laser
Todays earth observation satellite missions face one big problem: It takes quite some time until the recorded data can be sent from space to ground. It is not unusual to wait for several hours after a data take until the satellite is visible by a ground station and the data can be downloaded. Even then, it might happen that the complete data set is too large to be downloaded at once. Sometimes it is of highest importance to receive the data on ground as soon as possible, e.g. in case of observations of disasters like forest fires or floods.
One possible solution to this problem is the the data transfer via laser. A Laser Communication Terminal (LCT) does not send the data directly from the observation satellite in Low Earth orbit to the ground, but takes a detour via a high flying communications satellite. Not only is that satellite always in contact with the ground station, it is much more often reachable for the low flying satellite. The laser technology makes this concept possible, since it permits data transmission at a very high rate (up to 1.8 Gigabit per second), even at large distances.
TDP-1 is an ESA program with the goal to test this concept. In the past years, more than 2000 laser links have been performed using the gestationary satellite Alphasat, operated by Inmarsat and the satellites Sentinel 1a, 1b, 2a, 2b or an optical Ground Station on Tenerife. The data submitted via laser can be transferred via radio from Alphasat to the ground station at the German Remote Sensing Data Center (DFD) in Oberpfaffenhofen. The planning of the laser links is done by the German Space Operations Center (GSOC), also located in Oberpfaffenhofen. The technology for this groundbreaking data link originates in Germany as well. The laser communication terminal is facilitated by the DLR Space Administration, it is funded by the Federal Ministry for Economics and Energy (Bundesministerium für Wirtschaft und Energie), and is developed by TESAT Spacecom GmbH.
TDP-1 is also a pioneering testbed for the European Data Relay System (EDRS). This system is already in operation utilizing the satellite EDRS-A (EDRS-C is coming soon) and serves ESA's satellites of the Sentinel Program.
There is still large interest in performing laser links for test purposes. TDP-1 is going to continue to support this aim. The planning system is being further developed to provide a greater range of possible tests and to improve flexibility.