Re:NASA’s bet on Starship for the Moon
by simonh on Friday April 23, 2021 @03:17PM
(#26918137)
The Lunar Starship has enough dV to land on the moon and return to orbit, about 3.44 km/s but boosting from the moon to Earth and braking into Low Earth Orbit actually takes more dV than that, about 3.94 km/s. Unless they build in extra 0.5 km/s capacity or about an extra 20%, it flat out won't be able to do it.
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Here's where I got the idea and some different calculations: https://caseyhandmer.wordpress.com/2021/03/26/lunar-starship...
The diagrams say "Crew transfer in LEO or direct entry of Starship" as if they're interchangeable options, but these are not equivalent. Returning from the Moon and braking into LEO takes just as much dV as transferring from LEO up to Lunar orbit. Per the diagram that's 3.94 km/s as I said.
Conversely landing on the moon and returning to Lunar orbit takes 1.72 km/s twice, which is again consistent with my numbers if we assume the payload mass is constant. That may not be the case of course but any cargo taken from the Lunar surface to Lunar orbit will also need to be brought back to Earth somehow.