When the Apollo astronauts landed on the Moon, they brought devices with them called retroreflectors, which are essentially small arrays of mirrors. The plan was for scientists on Earth to aim lasers at them and calculate the time it took for the beams to return. This provided exceptionally precise measurements of the Moon’s orbit and shape, including how it changed slightly based on Earth’s gravitational pull.
Source:
https://phys.org/news/2020-09-mars-rover-ready-space-lasers.html