[19870213]

From what I understand, when they plan to land on the Moon or Mars, they won't have a flame trench setup (on the Moon/Mars), so it needs to be able to land and take off from the ground.

[nunuvit]

Yeah but there's a huge difference between fully loaded in earth's gravity and (a smaller stage) partially empty in less gravity.

[ilyagr]

Moon or Mars would only get the second stage of the starship, with 9 engines (was it?), not the super-heavy with dozens. So, it's okay to only have the flame trench on Earth.