Laser Beams Transmitted Via Satellite

By bouncing a high-power laser beam off an orbiting satellite, observatories in Austria and Switzerland transmitted the beam to each other. Its creators hope to apply the method to space debris detection and targeting in shuttles and other devices in low-Earth orbit.

Researchers at Zimmerwald Observatory at the Astronomical Institute of the University of Bern (AIUB) and The Institute for Space Research (IMF) of the Austrian Academy of Sciences in Graz independently determined the distance to a satellite in orbit.

The laser's path from Graz to Zimmerwald via satellite. (Image: Astronomical Institute, University of Bern)

The two observatories fired a short, weak laser pulse at the satellite, which was outfitted with retroreflectors that redirected the light right back to the observatory from whence it came. Timing how long the light takes to reflect off the satellite and return to the receiver gave the researchers distances accurate to within 2 or 3 mm.

Taking the measurements a step further, researchers at the observatory at Graz borrowed a high-power laser from the German Aerospace Center (DLR) in Stuttgart and shined it on the passing Envisat satellite, but not on its retroreflector. Instead, the light was allowed to reflect diffusely off the satellite in all directions to determine whether the researchers at AIUB could detect them.

They had a microsecond time window in which to capture the photons scattering off of the satellite, requiring exacting calculations and perfect synchronicity, according to Martin Ploner of the AIUB.

Because the light is scattered diffusely, it could hop from one source to another until it reached its intended receiver. It could also be used to detect objects that do not have retroreflectors, such as space debris. Knowing the location of space debris is integral to the safety of orbiting vessels. According to Thomas Schildknecht, head of research for space debris at AIUB, the current method of finding low-orbit space debris is by radar, which is expensive. However, this laser procedure is low cost and could save a great deal of money.

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