Status
APOLLO has been up and working to various degrees since October 2005, with science-quality data beginning April 2006. The current (as of mid 2011) status is:
- All 5 reflectors (three Apollo and two Lunokhod) ranged routinely.
- As many as 12 photons in a single pulse (limited by detector - might have been more)
- Sustained rate of about 3 photons per pulse over several minutes. This about 65 times more photons detected than previous efforts.
- As many as 50,000 return photons detected in a single lunation (during 5 hours total operation)
As of mid 2011, the range precision (per session) appears to be about 1.8-3.3mm per reflector, while the orbit of the Moon is being determined to roughly the 15mm level. The gap between the measurements and the theory could be due to systematic errors in the ranging, insufficient modeling of various conventional effects that become important at this level, or limitations of our theory of gravity. More observations and better modeling will help decide between these alternatives, though insufficient modeling is the primary suspect, since this is known to be both complex and difficult.
The APOLLO collaboration has discovered that the optical efficiency of the lunar reflectors decreases at full moon. This effect was not present in measurements from the early 1970s, was visible but not strong in the 1980s, and is now quite significant (about 10x). The cause is unclear but one possibility is that dust on the arrays leads to temperature gradients, distorting the returned beam. Measurements during the total lunar eclipse of December 2010 have confirmed thermal effects as the cause.
In April 2010, the APOLLO team announced that with the aid of photos from the Lunar Reconnaissance Orbiter, they had found the long-lost Lunokhod 1 rover and had received returns from the laser retroreflector. By the fall of 2010, the location of the rover had been determined to about a centimeter. The location near the limb of the moon, combined with the ability to range the rover even when it is in sunlight, promises to be particularly useful for determining aspects of the Earth-Moon system.
Read more about this topic: Apache Point Observatory Lunar Laser-ranging Operation
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