Apollo 11 Laser Ranging Retro-Reflector: Initial Measurements from the McDonald Observatory

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Science  23 Jan 1970:
Vol. 167, Issue 3917, pp. 368-370
DOI: 10.1126/science.167.3917.368


Acquisition measurements of the round-trip travel time of light, from the McDonald Observatory to the Laser Ranging Retro-Reflector deployed on the moon by the Apollo 11 astronauts, were made on 20 August and on 3, 4, and 22 September 1969. The uncertainty in the round-trip travel time was ± 15 nanoseconds, with the pulsed ruby laser and timing system used for the acquisition. The uncertainty in later measurements of a planned long-term sequence from this observatory is expected to be an order of magnitude smaller. The successful performance of the retro-reflector at several angles of solar illumination, as well as during and after a lunar night, confirms the prediction of thermal design analyses.

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