The Laser Ranging Test facility (LRT) is a large facility in which the necessary infrastructure has been made available for the Institute of Space Systems (DLR-RY) contribution to the Laser Ranging Instrument (LRI) on board the Gravity Recovery and Climate Experiment (GRACE) Follow-On satellites.
Fig. 1: Optical construction as part of the OGSE for verifying the Laser Ranging Instruments for the GRACE Follow-On mission. With the help of the highly stable standard plate, the company Spacetech Immenstaad (STI) used the structure to test the thermal and mechanical properties of the so-called Triple Mirror Assembly.
Following the completion of GRACE Follow-On activities, the facility will provide a test infrastructure for future Laser Ranging Instruments for missions as NGGM (Next Generation Gravity Mission, a mission to measure the Earth's gravitational fields) and eLISA (Evolved Laser Interferometer Space Antenna, a gravitational wave detector based in space).
Fig.2: Dilatometry construction, which enables the thermal characterisation of highly stable materials at temperatures ranging from 150K to 350K.
The LRT contains DLR-RY contributions to Optical Ground Support Equipment (OGSE), in particular high-precision optical metrology to verify constructions that will be used for distance measuring between satellites by laser (laser interferometry, structures that can simulate laser beams from far away satellites). A test facility is also included in the LRT, which will enable the characterisation of the thermally and mechanically highly stable materials that may be used in these optical instruments, as well as their verification for utilisation. It will be possible to determine the CTE (coefficient of thermal expansion) of tubular probes with a precision in the region of 10 ppb (parts per billion) in a temperature range of 105K to 350K. In addition, the LRT infrastructure also includes the development of high-precision optical frequency standards, which can be used as a laser source for highly sensitive laser interferometry, and a demonstration of development for the necessary laser source in space for the LRIs. The latter research will be carried out in cooperation with the Centre of Applied Space Technology and Microgravity (ZARM) at Bremen University and Airbus DS in Friedrichshafen.