The German and European space agencies are scheduled to begin testing Oct. 3 on laser-optical communications links between terminals located on mountaintops 142 kilometers apart. The testing is in preparation for the 2006 launch of the hardware aboard U.S. Missile Defense Agency and German government satellites.
The two-week trial of laser communications hardware developed by Tesat-Spacecom GmbH, of Backnang, Germany, will be conducted from the Optical Ground Station, located at an elevation of 2,000 meters on Spain’s Tenerife Island and operated by the European Space Agency (ESA).
The laser communications terminal will transmit and receive signals from an identical unit installed at a similar elevation on La Palma Island.
The purpose of the tests is to assess the degradation of a laser signal sent at a speed of 5.5 gigabits per second as it traverses the atmosphere.
The hardware is identical to gear being integrated as a secondary payload on the German government’s TerraSAR-X radar Earth observation satellite and the U.S. Missile Defense Agency’s Near Field Infrared Experiment (NFIRE), both set for launch in 2006.
The laser communications packages are not related to either satellite’s prime mission. TerraSAR-X is designed as an operational Earth observation system for use by German government and commercial industry. NFIRE is intended to develop the means to distinguish the body of missiles in their boost phase from their exhaust plume.
Once in orbit, the two laser terminals will attempt to communicate with each other in the more laser-friendly environment of low Earth orbit.
Room for the laser payload on the NFIRE satellite opened up after the Missile Defense Agency removed a kill vehicle carrying an additional sensor that was designed to fly close to the target missile during testing.
However, the U.S. Senate Appropriations Committee recommended that the Pentagon restore the kill vehicle to NFIRE in its version of the 2006 defense budget legislation, and if the House of Representatives agrees to do so when members meet to sort out differences between their bills, the laser payload may need to find a new host.
The use of laser optics for communications has yet to fulfill its backers’ long-held hopes for military or commercial space applications. But several European governments, notably Germany and France, continue to invest in it, mainly for its potential to speed communications between low-orbiting satellites and their ground controllers, even when they are on opposite sides of the Earth; between satellites located in low-Earth and the higher geostationary orbit; and between unmanned vehicles or aircraft and geostationary-orbiting satellites.
Tesat-Spacecom has been developing its laser terminals for more than a decade. Since 2002, it has received about $40 million in funding from the German Aerospace Center, DLR, which is the principal owner of TerraSAR-X.
German government officials have said the laser technology is a candidate for use on the second generation of the German Defense Ministry’s five-satellite SAR-Lupe radar reconnaissance system. The first-generation satellites, which are designed to use low-speed radio-frequency intersatellite links, are scheduled for launch starting in 2006.
Tesat-Spacecom had been selected to provide laser intersatellite links for the now-abandoned U.S.-based global satellite broadband constellations.
Berry Smutny, Tesat executive vice president, said the company has abandoned, for now, its attempt to introduce the technology into the commercial telecommunications market. But the military and civil government markets, he said, continue to show promise.
“What we hope to develop here is a trans-Atlantic link in both senses of the word,” Smutny said Sept. 28.
ESA and the French space agency, CNES, were the first in Europe to use lasers in space. The Silex laser terminal built by EADS Astrium of France was launched on CNES’ Spot 4 Earth observation satellite in 1998 and has since successfully communicated with the European Space Agency’s Artemis telecommunications satellite in geostationary orbit.
Under a 1994 agreement, ESA and the Japanese space agency, JAXA , plan to use a Japanese-built version of the Silex terminal launched Aug. 23 aboard Japan’s Kirari low-orbiting satellite to communicate with Artemis.
A.G. Bird, an Artemis program manager at ESA, said the Kirari-Artemis communications experiment is scheduled to start in November. A test model of the Japanese-built terminal was used in 2003 from the Tenerife Optical Ground Station to communicate with Artemis.
The Silex terminal on Artemis and Spot 4 weighs about 190 kilograms, operates on 200 watts of power and provides 50 megabits per second of data throughput. The Tesat-Spacecom terminal weighs less than 25 kilograms, operates on 125 watts of power and is designed to provide 5.5 gigabits of throughput.
“The EADS Astrium and Tesat-Spacecom units are different technologies that are difficult to compare,” said Zoran Sodnik, manager of the Tenerife station. “The Tesat product is a second-generation system and is certainly more advanced in terms of its capability to provide high-speed intersatellite links. How well it will operate through the atmosphere is what we will find out in the tests we are about to conduct.”
The French arms procurement agency, DGA, expects to begin tests of its Lola technology demonstrator in 2006 with a new-generation Silex terminal from EADS Astrium installed on a jet aircraft to communicate with Artemis. DGA officials say ultimately the technology could be used to beam communications between unmanned aerial vehicles and ground controllers via a geostationary satellite.
The Lola experiment and the work at ESA’s Optical Ground Station ultimately should provide clues as to whether laser communications’ advantages in encryption and data throughput can overcome the signal dispersion that occurs as the signal courses through the atmosphere, especially for ground-to-space links.