German Land-mapping Radar Satellites Now in Close Proximity

by

PARIS — Ground controllers have maneuvered two German radar satellites to within 350 meters of each other in low Earth orbit for the first time, setting the stage for a three-year mission to map the Earth’s entire land mass in stereo, the German Aerospace Center, DLR, announced Oct. 15.

The TerraSAR-X and TanDEM-X radar satellites previously had been separated by 20 kilometers in identical polar orbits 514 kilometers above the Earth’s surface. Maneuvering them to within 350 meters will permit the satellites to collect simultaneous images of the same areas but from slightly different viewing angles to produce three-dimensional digital elevation models.

TerraSAR-X was launched in June 2007; TanDEM-X was lofted three years later. While the two satellites both have a five-year design life, DLR officials say they are confident that TerraSAR-X will operate long enough to fulfill the tandem mission goal of three years of stereo collection.

The digital elevation data will be collected with the satellites using a mode providing a 12-meter ground resolution, meaning objects that large or larger can be distinguished. The imaging also provides images with a vertical accuracy of 2 meters. The mission is scheduled to start in January.

Both satellites also have other imaging modes with swath widths of between 10 kilometers and 100 kilometers, and spatial resolutions of between 1 meter and 16 meters.

“This is completely uncharted territory,” Manfred Zink, TanDEM-X ground segment manager for DLR, said in an Oct. 15 statement. “Never before have two satellites worked in such close formation over a period of several years.”

The satellites were financed mainly by DLR but with a contribution from the Infoterra division of Europe’s Astrium GmbH company, which has rights to market the data commercially. It is unclear how much imaging of immediate commercial use will be done while both satellites are occupied with their principal mission of mapping the Earth’s landmass.

DLR said ground teams reduced TanDEM-X’s orbital period so that it could close in on TerraSAR-X, an exercise that took three days to complete.

The global mapping mission will be managed so that one of the satellites transmits a radar signal to Earth but both spacecraft receive the reflected signal, information that is processed to create the digital elevation models. DLR said this method of operating carries a side benefit of reducing power consumption, and thus heat buildup, in the spacecraft, potentially extending the transmission time of both.