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>They need something that can land on Mars and return with a crew >A three stage rocket is something you’d use for one-way missions with smaller payloads

The only succesfull human spacecraft that landed on another body and taken off again used a three stage rocket to deliver a three stage lander,

The Command and Service Module(CSM) which brought the two stages into low lunar orbit The Lunar Lander (LM) contained a descent stage and an ascent stage, the descent stage was used as a platform for the ascent stage.

To say that three stage rockets are just for one way missions is silly, especially considering that more stages enable larger payloads. We've yet to see whether SpaceX's two stage solution will actually be any good. I also do not expect a single stage to the surface of the moon and back to Low Lunar Orbit to be very usefull. Any mars mission will likely follow the exact apollo staging plan.

m4rtink
Depending on your mission profile, there are more ways how to get to the Moon and possibly back - the Surveyor space probes did direct ascent without entering lunar orbit & massive burn with an embedded solid rocket engine just before landing.

The soviet plan (if they actually managed to get the N1 to work) was to take the upper stage of that rocket all they way to the Moon (fueled by kerolox BTW) and use it for the final braking burn of the LK lander[1], before eecting the stage to crash on the surface while the lander used its engine for soft landing.

And then the lander would launch directly to lunar orbit using the same (or backup) engine, not dropping any stages, just the landing legs. This was forced by the much lower carrying capacity of the N1. There was just one cosmonaut landing as a result, with another one in the "lunar Souyuz" staying in lunar orbit. So just 2 people versus 3 in Apollo. And there was not even a hatch between the two modules & the cosmonaut was supposed to spacewalk (!) between the two before landing and after meeting back with the Soyuz spacecraft.

So if you can realistically do a single stage to landing & orbit on a body, I'm sure it will be the preferred option going forward, it has a significant benefits.

[1] https://en.wikipedia.org/wiki/LK_(spacecraft) [2] https://en.wikipedia.org/wiki/Soyuz_7K-LOK

rtkwe
The more fuel economic way long term is break the mission into parts and reuse vehicles; single ship from surface to Lunar orbit, dock and transfer to a staged lander at a station and take the up and down. Taking Starship all the way to the surface wastes a tremendous amount of fuel hauling around the mass to get back home and through to landing safely.
m4rtink
Long term definitely like this! BTW, this exact sequence can be seen at the start of the Space Odyssey movie, with the main character traveling from Earth to Moon.
rtkwe
That's the long term NASA plan under the Gateway name. A little lunar orbit permanent station to replace the ISS.
mr_toad
A third stage with the current Starship design would have to be under 100 tonnes and the payload would be small. It would have to do all the work of injecting into a transfer orbit, landing on Mars, and returning. It’s hard to imagine such a small craft getting all the way to Mars, with a crew, and returning them.

Starship is just not a good design for pushing a third stage into a transfer orbit by itself. It’s totally dependent on the idea of in-orbit refuelling and refuelling on Mars. Once you refuel it, the game changes completely.

It’s also not a workable solution for landing on the Moon without refuelling for the same reasons. In some ways the Moon is more problematic because you can’t manufacture methalox on the Moon.

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