Work Underway in Germany on Radar Satellite with 25-centimeter Resolution
BEIJING — Even as the U.S. and French governments debate whether to permit the commercial sale of optical Earth observation imagery sharper than 50 centimeters in resolution, Astrium Geo-Information Services of Germany is designing a next-generation radar satellite with a 25-centimeter ground sampling distance, an Astrium official said here Sept. 24.
The satellite, called TerraSAR-X Next Generation, would provide data continuity to users of the current two-satellite TerraSAR-X/TanDEM-X radar system that in 2014 will be complemented by the Spanish Paz radar satellite.
TerraSAR-X, TanDEM-X and Paz satellites have sensors capable of delivering images with a resolution as sharp as 1 meter, meaning they can detect objects of that diameter and above. When Paz is launched, the three satellites will be spaced 120 degrees apart in a polar low-Earth orbit of 514 kilometers to reduce the amount of time it takes for the two current satellites to revisit an area of interest.
Built by Astrium Satellites, Paz is owned by Hisdesat of Spain. The two companies have agreed to form a single sales unit with common direct-access stations for users to be able to process Paz and TerraSAR-X/TanDEM-X data seamlessly.
To reduce the revisit time over a given area of the Earth to less than 10 hours, the constellation would need to include between three and five satellites, said Thomas Schrage of Astrium.
The business case for a second-generation TerraSAR-X has been complicated by the noninvolvement of the German Aerospace Center, DLR, in its financing, and by the less-than-stellar sales of radar data. Astrium officials have said a new product, called World DEM, to be introduced next year, should clinch the business case for building the next-generation TerraSAR-X.
Astrium officials hope to use the work they are performing for the German Defense Ministry, under contract to OHB AG of Bremen, Germany, on a second-generation German military radar reconnaissance system to build TerraSAR-X NG.
In a presentation here to the 64th International Astronautical Congress, Schrage said the second-generation TerraSAR-X could be launched in 2018.
Schrage suggested that the German government has already approved, in principle, the idea of a commercial satellite distributing 25-centimeter-resolution data on a commercial basis with a specific data-sales law. Another German industry official disputed that, saying the government has reached no decision on whether it will loosen its current 50-centimeter limit on resolution.
Using aerial imagery, Schrage presented side-by-side images of what is discernible with TerraSAR-X’s 1-meter imagery and what is possible at 25 centimeters. The difference was striking.
Confirming German government policy and proving the business case to Astrium management — which has already authorized spending some $400 million on the French Spot 6 and Spot 7 satellites without any French government support or government data-sales commitments — are not the only hurdles to TerraSAR-X NG.
The satellite system would transmit data in X-band at 1,200 megahertz — frequencies that are not yet authorized for this purpose by the International Telecommunication Union (ITU), a United Nations affiliate that regulates wireless broadcast frequencies.
The ITU’s governing body is scheduled to meet in 2015, and the 1,200-megahertz spectrum’s use for Earth observation transmissions is expected to be on the agenda.