Catching Photons Coming from the Moon

Roland Piquepaille writes "In 'Shooting the moon,' the San Diego Union-Tribune describes how and why physicists from UCSD are using lasers to send light pulses in direction of an array of reflectors installed on our moon in 1969 by Neil Armstrong and Buzz Aldrin. One of the goals of these experiments is to check the validity of Einstein's theory of general relativity. Another one is to measure the distance between the Earth and moon with a precision of one millimeter by catching photons after their round trip to the moon. But it is amazing to realize how difficult it is to capture photons after such a trip. I also have up a summary, which contains additional details and pictures, if you just want to learn how difficult it is to capture photons back from the moon."

Comments

Keep experiments running

[MichaelSmith]

The LR^3 retroreflector featured here was part of the ALSEP station on several of the apollo missions. In the years since these missions the ALSEP stations have been shut down. The reflectors are passive devices and don't have an off switch, which is why they are still working.

In particular the seismonitors which were a part of each system could still be operating today, and delivering new scientific results.

I think this article is an example of why experiments should not be shut down before they really stop working.

Re:Mirrors? On the moon!

[megaditto]

I know you are trolling, but the real Moon-hoax tinfoilers never claimed that 'something' didn't land on the Moon, just that no humans from Apollo 11/12 landed on the Moon.

The Hatter idea is that no living thing can escape the atmosphere and survive (due to radiation or whatever reason the Hatters claim). And no, the Space Station and the sattelites are technically inside the atmosphere, well below the Van Allen belt.

The reflector delivery and the soil sample return could be done by a robotic probe, which in fact is what the Russians did with their Luna 16 mission about a year after the alleged Apollo 11.

Since the Russkies got the first sattelite (Sputnik), the first man in orbit, the first suit walk, the first docking, etc., the thinking was that we could sound-stage their glorious defeat, end the darn space-race, then go spend the money on something more profitable.

The credible conspiracy theory: Send the humans into orbit, camp in orbit while the robot fetches the samples, reunite humans with the 'bot, then land as heroes.

Quite far from difficult, can be done by almanyone

[Ancient_Hacker]

It's not all that hard to bounce photons off the Moon. The US Army Signal Corps did it in 1947, using very mediocre WWII radar sets. Radio amateurs have been doing it since around 1960, with limited equipment, skills, and very limited transmitter power.

What's difficult is doing it with nanosecond resolution. That requires very wide bandwith antennas and receivers, which also let in a lot of wide band background noise.