> If that happens, you touch down and anywhere from 20 to 35 minutes later a rock you kicked up comes right back at you from the other direction! It is not sim

> If that happens, you touch down and anywhere from 20 to 35 minutes later a rock you kicked up comes right back at you from the other direction! It is not simple as that, it is actually more interesting:) On a spherical ideal body it is impossible for the rock to do this. That is because the only orbit that does not intersect the ground must be exactly parallel to the ground at the landing site. So not only it can't hit the landing pad, it can't even hit the rocket sticking way above the ground. Now, there is couple of interesting reasons I can figure out why this is at all possible on Moon, but I am too lazy or in some cases incapable to estimate which ones are significant. 1. Moon rotates. If the landing happened anywhere but the poles, by the time the projectile completes orbit the surface has shifted (but just a tiny bit since Moon rotates so slowly). If the projectile was shot parallel to the ground in the right direction, it does not need to complete entire orbit to hit the landing pad or the rocket. 2. Moon has lumpy gravity. It is not an ideal spherical body and it is known to have huge gravitational anomalies. The anomaly is so large that satellites around Moon need regular boosts because otherwise their orbit would degrade. 3. Moon has atmosphere. It is as good as vacuum in most circumstances but it might possibly be significant for particles of dust traveling at thousands of meters per second. For those interested, the entire atmosphere of Moon is estimated to weigh around 10t. So don't count on using it Watney-style for anything practical. 4. Solar wind. Very small particles may be significantly shifted in their orbit due to interaction with energetic particles traveling in particular direction (like solar wind). 5. Particles skipping off of Lunar surface? I think it could maybe be possible for a particle being close to complete its orbit to hit something at really extremely small cross section that rather than vaporize it would just deflect it by couple arc seconds and hit the rocket. Of course this is just thought experiment. Dust flooding other structures on the Moon, satellites, orbits around Moon and Earth is reason enough to try to find a solution.