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Post by dinsmore on May 3, 2008 7:32:19 GMT -4
Enter apollo retroreflector in the Search box of the Astrophysics Data System www.adsabs.harvard.edu/ for a list of scientific papers relating to the subject. Most of the full papers can't be accessed without a subscription to the relevant journal, but clicking on the "A" (Abstract) links show you a summary. Some interesting points are that the distance is now being measured to 1 millimetre, and, from the 1990 paper by Faller & Dickey, "Observatories located in Texas, Hawaii, and France now regularly range the moon with an accuracy of approximately 1 inch. Ranging programs have also been carried out in Australia and the Soviet Union."
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Post by ka9q on May 12, 2008 20:45:31 GMT -4
[ In the case of Apollo 11's LRRR, the placement was interactive with the observatory testing it. No. The LRRR and ALSEP antennas were manually aligned by the astronauts to point at the earth, but this pointing did not have to be highly accurate. Both are on fixed mechanical mounts that do not track the earth, so they had to accommodate the apparent motion of the earth in the lunar sky due to libration. This is about +/-7 deg in latitude and +/- 8 deg in longitude. The ALSEPs used medium gain antennas with 27 degree beamwidths, and the LRRRs used corner reflectors that reflect an incoming photon back along the direction it came. This had the side benefit of greatly relaxing the required pointing accuracy. Built-in bubble levels and sundials were all the astronauts needed to align them. The deployable S-band dish on Apollo 12 and 14 and the high gain dish on the Apollo 15-17 rovers were another story. They needed higher gains, and they only had to work for a short time after each manual alignment. Pointing them proved rather difficult and tedious for the astronauts, but on the rover they had an uplink signal strength meter as a guide. ooh, here's a thought. The HBs like to go on about astronauts disturbing the "air" around the flags. What about the deployable S-band dishes on Apollos 12 and 14? They were evidently large, light and flimsy, so they also should have been very susceptible to small air currents. Yet they stayed put. Can we find video of an astronaut quickly passing close to a deployed S-band dish with nothing happening?
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