U.S.-German Laser Intersatellite Link Performs Well on 2 Spacecraft

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  Space News Business

U.S.-German Laser Intersatellite Link Performs Well on 2 Spacecraft

By PETER B. de SELDING
Space News Staff Writer
posted: 18 March 2008
03:44 pm ET







PARIS
— A German company that has spent more than a decade developing laser-optical communications systems for satellites is reporting a “flawless” performance of the technology, which is being used to deliver�� data between
U.S.
and German low-orbiting satellites.

In a series of tests that began in February and will continue for at least several months, laser terminals on board
Germany
‘s TerraSAR-X radar Earth observation satellite and the U.S. Missile Defense Agency’s Near Field Infrared Experiment, or NFIRE, missile-warning spacecraft have exchanged data simultaneously at speeds of 5.5 gigabits per second, according to the company.

For Tesat-Spacecom of Backnang, the results offer the hope that, based on a U.S.-German governmental agreement and a partnership with General Dynamics of the
United States
, its gear will find its way into multiple
U.S.
government satellite programs.

The Tesat laser communications terminals�� already are being designed for use on several German and European spacecraft, but Tesat Chief Executive Berry Smutny said the big prize remains the
U.S.
government.

“The
U.S.
is our main market, that’s clear,” Smutny said in a March 13 interview. “That is the market we are doing this for, the market that has the most potential. Our impression is that we are five or six years ahead of others working in this field, and there are a number of
U.S.
programs that could use this.”

In an interview and in documentation prepared for the German government, Smutny said the Tesat terminals functioned when the two satellites were at distances ranging from 2,000 to 8,000 kilometers, including periods when the laser link had to traverse the upper atmosphere.

Tesat
said it has taken less than 25 seconds, on average, for the terminals to lock onto each other and begin transmissions. A key feature of the gear is its ability to establish and maintain a link even when the sun is directly behind the target satellite.

Continuous transmissions were maintained for as long as the satellites were within line-of- sight position of each other, or about 20 minutes. Bit-error rate, the company said, has been less than one error for every 1 billion bits transmitted.

NFIRE is not producing its own imagery to send to the German satellite. Instead, the TerraSAR-X data imagery is sent to NFIRE, and NFIRE then returns the data by laser at the same time as it receives another packet of data, establishing the two-way exchange at the same 5.5 giga bit-per-second speed, in what Tesat calls “duplex” operations.

Tesat
designed its current generation of laser terminals for a now-abandoned U.S.-based commercial telecommunications satellite constellation called Teledesic, which called for a transmission speed of 5.5 gigabits per second��� the equivalent of 400 DVDs per hour. But the electronics is qualified to provide speeds of 16 gigabits per second, according to Tesat.

The terminals weigh less than 30 kilograms and run on less than 130 watts of power.

Smutny
said future tests with NFIRE will include sending data from the satellites to ground stations in
Germany
and��
Spain
. Tesat is building similar laser terminals for
Germany
‘s future TanDem-X radar Earth observation spacecraft, and for the large Alphasat telecommunications satellite being built for European governments and for mobile satellite services provider Inmarsat of London.

Tesat also hopes to win European Space Agency (ESA) approval to place laser terminals on several of ESA’s future Earth observation satellites being built to serve both government and commercial users. In addition, ESA is weighing whether to build its own data-relay network which would feature three satellites in geostationary orbit to transfer data between low-orbiting Earth observation spacecraft and ground teams, doing away with the need for regional ground-reception stations.

The
German
Aerospace
Center
, DLR, is considering whether to build its own data-relay satellite, which eventually would be a component of the European system. The European project, envisioned as a public- private partnership with industry, will be one of several to be presented for a decision in November by European space ministers.

Intersatellite
communications, the company said, are “a pre-condition for numerous commercial and scientific missions but also for many security-sensitive applications –��� environmental monitoring, disaster management, border security, defense –��� that require uninterrupted connectivity.”

TerraSAR
-X, built with German government and industrial financing for both government and commercial data sales, was launched in June 2007 and declared fully operational in January. NFIRE was launched in April 2007.