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  • TIGO laser ranging telescope targets satellites

Photonics Spectra
Mar 2012
Ashley N. Paddock, ashley.paddock@photonics.com

DARMSTADT, Germany – It was like a planetary-scale video game: Working from orbital predictions, a research team took the first laser measurements of Galileo operational satellites in orbit using lasers in Chile.

The Transportable Integrated Geodetic Observatory (TIGO) performed the laser ranging at an altitude of 23,230 km using a near-infrared laser beam. The TIGO team members, led by Michael Häfner and Marcos Avendaño, took aim with their laser and fired, having first calibrated it using Europe’s first test navigation satellite, GIOVE-A. The orbital predictions had been provided by the ESA’s European Space Operations Center.


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. Courtesy of ESA/TIGO – BKG/UdeC/IGM.


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 Galileo satellites – as with many modern satellites – are fitted with reflectors that bounce the laser pulse back to its original location. 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 1 cm.

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.


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


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.

Besides being widely used for precise orbit determination of satellites, laser ranging also is employed for calibrating satellite instruments, contributing to the International Terrestrial Reference Frame (Earth’s standardized geodetic coordinate system) and measuring slight ground motion resulting from tectonic plate dynamics. It also can measure the moon’s distance from Earth, thanks to laser reflectors left on the lunar surface by the US and Soviet Union.


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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