Viewing a single comment thread. View all comments

ninthtale t1_j5wwnrm wrote

Reply to comment by electric_ionland in Why do sample return missions such as OSIRIS-REx use their own reentry vehicles instead of just going to the space station for pickup and return with ISS equipment? by PromptCritical725

>If you did not have atmosphere to slow you down on you way back you would need nearly as big of a rocket to land

So missions from a lunar post would still need quite a lot of braking fuel?

2

fyrstormer t1_j5xdz36 wrote

The Moon has a tiny amount of gravity compared to the Earth, so lander modules falling towards the Moon don't speed up nearly as much and don't need nearly as much fuel to slow them down before they land. The Apollo Lunar Module was a single-stage-to-land/single-stage-to-orbit aluminum box with a little rocket motor strapped to the underside; the same setup on the surface of the Earth wouldn't even be able to lift its own weight.

16

FolkSong t1_j5x2ytl wrote

A similar amount as they use for takeoff, but it's still very little compared to getting out of Earth's gravity well.

9

cjameshuff t1_j5ygqwh wrote

A landing on an airless Earth, launched from the moon? It would be a bit more efficient than the moon landing, because the spacecraft would be at its heaviest (with a full stack of stages fully loaded with propellant) in low lunar gravity and would be doing its final braking in Earth's heavy gravity after burning most of its propellant and discarding most of its stages, but gravity losses are fairly small in comparison to the overall acceleration/deceleration requirements. You'd need something of similar size, just with fewer first stage engines to get it off the moon.

1