The Laser Retro-Reflector (LRR) was a passive optical device, on board the ERS-1 and ERS-2 missions, designed for accurate satellite tracking from the ground to support instrument data evaluation.

It operated in the infrared, to permit ranging of the satellite by the use of Laser Tracking Stations, and therefore the accurate determination of its height. It was used extensively during the commissioning phase and regularly during the mission to verify the stability of the positioning system.

The ERS-1 mission launched in 1991 and ended in March 2000, ERS-2 was launched in 1995 and ended in 5 September 2011. No data activities were performed by this sensor. The LRR was developed by Aerospatiale (France).

LRR instrument measurements allowed:

• calibration of the Radar Altimeter altitude measurements with an error of 10 cm
• improvement of the satellite orbit determination ensuring the production of a global ephemeris accurate to better than 1-2 m for the radial component.