The increasing demand on high speed communication networks has stimulated the development of optical free space data transmission during the last years. TESAT has developed a laser communication terminal (LCT) that fulfills the need of a power efficient system whose capability has been successfully demonstrated at bidirectional space-to-space links and bidirectional space-to-ground links (SGLs) at a data rate of 5.625 GBit/s with a homodyne detection scheme and a BPSK modulation format. In comparison to a direct detection system, the homodyne detection scheme works as a bandpass filter. The transmission is immune to false light and even data transmission with the sun in the receiver field of view (FOV) is possible.
Compared to common RF transmission which is implemented on spacecrafts for data transmission, optical transmission provides not only higher transmission rates (factor 10) but also shows excellent security features since the laser beams directivity making it immune to interception.
5.625 Gbps bidirectional laser communication at 1064 nm has been demonstrated on a repeatable basis between a Tesat
coherent laser communication terminal with a 6.5 cm diameter ground aperture mounted inside the European Space
Agency Optical Ground Station dome at Izana, Tenerife and a similar space-based terminal (12.4 cm diameter aperture)
on the Near-Field InfraRed Experiment (NFIRE) low-earth-orbiting spacecraft. Both night and day bidirectional links
were demonstrated with the longest being 177 seconds in duration. Correlation with atmospheric models and preliminary
atmospheric r0 and scintillation measurements have been made for the conditions tested, suggesting that such coherent
systems can be deployed successfully at still lower altitudes without resorting to the use of adaptive optics for
compensation.
Renny Fields, Carl Lunde, Robert Wong, Josef Wicker, David Kozlowski, John Jordan, Brian Hansen, Gerd Muehlnikel, Wayne Scheel, Uwe Sterr, Ralph Kahle, Rolf Meyer
Starting in late 2007 and continuing through the present, NFIRE (Near-Field Infrared Experiment), a
Missile Defense Agency (MDA) experimental satellite and TerraSAR-X, a German commercial SAR
satellite have been conducting mutual crosslink experiments utilizing a secondary laser communication
payload built by Tesat-Spacecom. The narrow laser beam-widths and high relative inter-spacecraft
velocities for the two low-earth-orbiting satellites imply strict pointing control and dynamics aboard both
vehicles. The satellites have achieved rapid communication acquisition times and maintained
communication for hundreds of seconds before losing line of sight to the counter satellite due to earth
blockage. Through post-mission analysis and other related telemetry we will show results for pointing
accuracy, disturbance environments and pre-engagement prediction requirements that support successful
and reliable operations.
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