jacobnavia writes:
Now, consider the earth moon system. We have a mirror there, that can
reflect any laser beam to the earth.

Five, actually, regularly pinged looking for deviations:

"Tests of Gravity Using Lunar Laser Ranging" (2010)
https://link.springer.com/article/10.12942/lrr-2010-7

"Lunar laser ranging: the millimeter challenge" (2013)
https://arxiv.org/abs/1309.6294

see also

https://en.wikipedia.org/wiki/Apache...ging_Operation
https://tmurphy.physics.ucsd.edu/apollo/apollo.html

The latest observations are limited by the physical characteristics
of the reflectors.

Nobody is looking however.

??

-dan

[[Mod. note -- One particularly fascinating part of the lunar-laser-ranging
story is the unexpectation degredation of the retroreflectors, apparently
due to thermal gradients caused by lunar dust coating the reflector surfaces.
I think this was first published in https://arxiv.org/abs/1003.0713
and there's a nice summary and update in section 4.2 of the 1309.6294 paper.
-- jt]]