Space Geodesy Satellite Laser Ranging System (SGSLR)

Satellite laser ranging (SLR) involves sending a burst of photons from an ultra-short laser pulse onto a target with retroreflectors (in orbit or on the Moon) and measuring how long it takes to get a return. Multiply that by the speed of light and you have the two-way range. Simple in concept; difficult to do in practice since measuring the time interval between two events (fire and return) to a few tens of picoseconds accurately is still technologically challenging. The strength of laser ranging is that it is an unambiguous measurement of the range; other techniques must estimate biases or ambiguities. Another strength of laser ranging is that it is relatively immune to the presence of water vapor in the atmosphere, and so the refraction model is relatively simple (using ground-based meteorological data) and no corrections need to be estimated as part of the data reduction. An obvious limitation, however, is that it requires relatively clear skies, so SLR stations need to be located in areas where the weather is more benign. The resulting measurements are, for the better stations, accurate to the few mm level, supporting cm-level orbit determination. SLR stations can range to satellites in the range of 300 km to 22,000 km, though the higher targets are beyond the capability of some stations, and only a small number of stations can range to the Moon.

Image credit: J. Ries, UTCSR

The system at MGO will be part of NASA’s global network of laser ranging stations to be developed as the Space Geodesy Satellite Laser Ranging System (SGSLR), which is in turn part of a international network of stations.

SGSLR at MGO with Hobby-Eberly Telescope in the background. Image credit: E. Terrazas

SGSLR Instrument Capabilities:

  • Laser ranging from 300-km to geosynchronous (26,000 km) altitudes
  • Day-Night tracking – 532 nm (green) laser
  • Single photon detection system with high repetition rate
  • Millimeter precision ranging
  • Remote operation capable

Location: Adjacent to MLRS on Mt. Fowlkes at McDonald Observatory
Foundation completed: Jan 2019
Passed inspection test: Jan 2020
Shelter/Dome installed: Feb 2019
Gimbal/Telescope to be installed: February 2023

Construction of MGO’s SGSLR Shelter

The SGSLR pad and pier
SGSLR pad and pier complete, January 2019. Image credit: NASA Space Geodesy Project

 

The MGO dome
MGO Dome Factory Acceptance Test (FAT) at Baader Observatory successfully completed, September 19, 2019. Image credit: NASA Space Geodesy Project

 

First wall of panel going into place
MGO SGSLR shelter goes up, October 15, 2019. Image credit: NASA Space Geodesy Project

 

The shelter after the dome ring wall was added
The shelter after the dome ring wall was added, October 15, 2019. Image credit: NASA Space Geodesy Project

 

MGO SGSLR shelter is built and ready to accept dome
MGO SGSLR shelter is built and ready to accept dome, November 26, 2019. Image credit: NASA Space Geodesy Project

 

Lift of the dome ring onto the dome ring wall.
MGO SGSLR dome is installed and passes Site Acceptance Testing, January 25, 2020. Lift of the dome ring onto the dome ring wall. Image credit: NASA Space Geodesy Project

 

Lift of the dome onto the dome ring.
MGO SGSLR dome is installed and passes Site Acceptance Testing, January 25, 2020. Lift of the dome onto the dome ring. Image credit: NASA Space Geodesy Project

 

The team picture after the dome installation.
MGO SGSLR dome is installed and passes Site Acceptance Testing, January 25, 2020. The team picture after the dome installation. Image credit: NASA Space Geodesy Project

 

The team after a successful Site Acceptance Testing of the dome. Image credit: NASA Space Geodesy Project.

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Last Updated: April 6, 2021