# Doing an experiment to fire a laser to moon and back

After reading this question: I got an itch to to test out the mirrors myself (and maybe record whole process to irritate conspiracy nuts).

What equipment would I need? I assume a high powered laser that would go through Earths atmosphere on clear night, some sort of mechanism that would be able to aim it very precisely (is there something that is commercially available), and a detector that would read the laser bounced back.

How would I have to set it up? I would need to go out of the city get on some rocky place so mechanism wouldn't 'wobble' to much then point laser to the moon (not sure how would I know where to point) then place detector on the ground at short distance from laser (again not sure how I would know where to position it) and then if after ~2.6s later detector lights up - It Works.

How would I know that reflection I got is from mirrors and not some random 90 degree angled shiny Moon rock? I would assume for this I would need to calculate how much dimmer signal has to come back (not sure how to do the calculation)

Updated by request in comment: Can I just do this or will this get me into trouble with aviation authorities?

Is such an experiment possible (for an individual), would I be able to get my hands on equipment and data necessary, or I am missing something?

• Mcdonald Observatory in west Texas still does this, I think; you can research their setup. – Organic Marble Nov 11 '15 at 12:30
• I think your question is more on-scope for Astronomy. On top of McDonald Observatory that Organic Marble mentions, several other observatories would be equipped to do this at least in a demonstrative way. Precision high power laser system (like for adaptive optics), celestial tracking (core business) and ultra sensitive photon detectors (like SPD) are standard weapons of choice for many of them. – TildalWave Nov 11 '15 at 12:52
• "then if after ~1.3s later detector lights up - It Works" In that case, you can be perfectly sure that it doesn't work - round-trip time to moon is about 2.6s ;) – asdfex Nov 15 '15 at 18:01
• You also need to read this : xkcd.com/1441 – kert Nov 16 '15 at 23:21

This question was asked on Physics.SE with the question Amateur moon laser ranging. The answer is that in order to do so, you'd have to have a really precise laser beam (1 mRad divergence), along with a very accurate time measurement system (Nanosecond scale), and need a reasonably large telescope (On the order of a meter or two seems to be large enough). It's really just not practical to do, unless you are willing to drop a whole lot of change on the project (I'm guessing \$100,000 to \$1,000,000 range, roughly)

As for the false alarm, well, the best trick is to simply repeat the measurement a day later, while pointing the laser at the same spot. The moon moves enough that if a rock directly faced you one day, it wouldn't the next day.

For an individual, I'd say just settle for this video.

• MathJax busted your cost range btw – MikeTheLiar Nov 11 '15 at 16:17
• @mikeTheLiar: Thanks, I forget about that sometimes when referencing cash... – PearsonArtPhoto Nov 11 '15 at 16:31
• Another factor: You need FAA permission to do it. Your outgoing laser beam is most definitely not eye-safe, they want to make sure it goes to the moon and not to a plane. – Loren Pechtel Nov 11 '15 at 21:57