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NIR Lasers in Chile Measure Satellites

Photonics.com
Dec 2011
DARMSTADT, Germany, Dec. 30, 2011 — The first laser measurements of Galileo operational satellites in orbit have been made from Chile.

The Transportable Integrated Geodetic Observatory (TIGO) performed the laser ranging at an altitude of 23,230 km using a near-infrared laser beam.


TIGO performed the world's first laser ranging of the first Galileo satellite on Nov. 27, 2011. TIGO was put in place to fill gaps in various types of worldwide geodetic measurements. (Images: ESA/TIGO — BKG/UdeC/IGM)

The laser ranging was achieved on Nov. 27 at 2:45 GMT, while the second measurement happened two days later at 10:05 GMT.

TIGO is equipped for various observations — in 2006, its radio telescope monitored ESA's first moon mission, SMART-1, to determine end-of-mission impact on the lunar surface.

The laser ranging proceeded like a planetary-scale video game: Working from orbital predictions provided via the navigation office at ESA’s European Space Operations Center in Germany, the TIGO team members, led by Michael Häfner and Marcos Avendaño, took aim with their laser and fired, having first calibrated their laser using Europe's first test navigation satellite, GIOVE-A.


Satellite Laser Ranging telescope at the TIGO ground station. The laser operates at a near-infrared wavelength of 847 nm.

Similar to many modern satellites, the Galileo satellites are fitted with reflectors that bounce the laser pulse back where it came from. The time the laser takes to return to the ground is measured with an ultraprecise timer. The speed of light is fixed, so the distance to the satellite can be measured with an accuracy of better than a centimeter.

TIGO is owned by the Federal Agency for Cartography and Geodesy and has been operating jointly with the University of Concepción and the Chilean Military Geographical Institute since 2002. It was established to fill gaps in various types of worldwide geodetic measurements.


This view of the TIGO ground station shows the Satellite Laser Ranging laser telescope (bottom), the VLBI radio telescope (right) and the GNSS station (middle).

TIGO was the first station in the 40-strong International Laser Ranging Service network to range the Galileo satellites, with Herstmonceux in the UK and Matera in Italy among the next Satellite Laser Ranging stations to succeed.

As well as being widely used for precise orbit determination of satellites, laser ranging is also employed for calibrating satellite instruments, contributing to the International Terrestrial Reference Frame (Earth’s standardized geodetic coordinate system) and measuring slight ground motion due to tectonic plate dynamics.

It can also measure the distance of the moon from Earth, thanks to laser reflectors left on the lunar surface by the US and Soviet Union.

For more information, visit: www.esa.int


GLOSSARY
telescope
An afocal optical device made up of lenses or mirrors, usually with a magnification greater than unity, that renders distant objects more distinct, by enlarging their images on the retina.
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