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Instrument: GRACE LRR : Laser Retro-Reflector
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[Source: GFZ/Potsdam, ]

The GRACE laser retro reflector (LRR) will be provided by GFZ and is identical with the CHAMP LRR. It is a simple passive payload instrument consisting of 4 prisms manufactured from high-grade fused glass, glued into fixing rings mounted within an aluminium-alloy structure. The LLR is used to reflect short laser pulses of visible or near-infrared wavelengths transmitted by dedicated Laser ground stations. The direct distance can be measured with an accuracy of 1 - 2 cm (depending on the technological status of the ground station). The LRR data will be used for

- precise orbit determination in combination with GPS tracking data for gravity field recovery

- calibration of the on-board GPS Space Receiver,

- technological experiments such as two-colour ranging

The idea of the two-colour ranging principle is to demonstrate the possibility of differential ranging with a few mm single-shot precision and thus to verify existing tropospheric correction models as well. This is accomplished by a novel design with only 4 prisms in a dense package. Only one single prism will be visible for the laser ground station most of the time. The effective reflection plane is defined with very high accuracy and minimizes the optical depth of the reflector.

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Instrument Owner: USA/NASA