[Out_of_Characte]

What's really vexing to me is how spacex refuses to build a triple stage rocket. Their 'reusability' adds a significant amount of mass in terms of heatshield and in terms of fuel margins for landing. Using additional stages benefits them more than saturn V. They likely thought they could get away with two stages and have them both return to the launch site, one the short way, the other the long way around. But the exclusion of a multi stage reusable architecture means that their empty mass fraction becomes a linchpin in bringing anything into orbit.

No wonder there's a v2 and v3 with much, much larger fuel tanks and less payload.

[mr_toad]

They need something that can land on Mars and return with a crew. Or something that can put a very large payload on Mars.

A three stage rocket is something you’d use for one-way missions with smaller payloads, or for putting something in GEO. Starship just isn’t optimised for those missions.

[Out_of_Characte]

>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.

[bell-cot]

If you have a good specific https://en.wikipedia.org/wiki/Specific_impulse , and you can get decent https://en.wikipedia.org/wiki/Mass_ratio s in your lower stages, then 2 stages are definitely the way to go to LEO. Every stage over 2 adds a load of weight (more engines, structure, etc.), lots of ground system/support complexity, and a whole 'nother stage separation worth of failure modes.

[jmaestrooper]

The full and rapid reuseability is the ultimate goal.

Make rocket launches as frequent and routine as commercial plane flights. Whether they use it for Mars or Moon on Earth-to-Earth or anything in between is irrelevant, this will revolutionize entire industries.

Just look at the share of Falcon 9 comparing to all other launch providers, and that one is only half-reuseable. If they manage to get the StarShip right this will be a game changer.

[mlindner]

A triple stage rocket when you're trying to do reuse is actually a negative. The second stage needs significant heat shielding as a result which drastically eats into the size of the upper stage and your ultimate payload.

[Gravityloss]

I guess one issue with that is that the second stage will land far from the launch site. In theory if it has sea level engines for landing, it could fly back though (after refueling).

[m4rtink]

Starship has 3 sea level engines for landing + 3 vacuum optimized engines.

[Gravityloss]

Yes. My "if" could have been a "since it probably".