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Related to the SpaceX discussion in the CWT, can someone explain Starship's place in a mars program to a guy who never played KSP (but watched some videos)?
I see the 1st stage vehicle design as optimized for heavy surface to low orbit launches. The second stage is confusing, mixing atmospheric engines and heat shields with vac engines for fairly inefficient interplanetary burns. The whole thing looks more like Tintin's Lunar Adventure than any real mission I've seen designs for.
What am I missing here? Why is this better than launching a lightweight interplanetary-dedicated ship plus a smaller lander? Is the whole mars thing just hype for what's really a STO heavy lifter?
Nah. The 1st stage vehicle design is optimized for reusability. The staging velocity is much lower than you'd want to minimize fuel use, because that way it can fly back to the launch site easily enough, and fuel is cheap but time and operations complexity is expensive.
The heat shields are what it needs for reentry, and the atmospheric engines are what it needs for controlled landing, and those are what it needs for reusability. You're using the same pointless definition that most rocket design programs have: that "efficient" means "payload divided by fuel mass". But fuel is cheap, and the most meaningful definition of "efficient" is actually "payload divided by cost". If each SLS costs $4B to launch, it could have the highest fuel-efficiency quotient of any rocket ever in history before or since and yet its true efficiency would still be too low to ever be sustainable.
A smaller lander means you need more landers. Approximately one hundred times more landers, if you compare the heaviest thing landed on Mars so far (Perserverence) with Starship payload capacity. Starship is gross overkill for putting a flag and a few footprints on Mars and then never going back, but it's about what you'd want as the minimal scale product for a large base or a small city.
Did you mean TSTO? Part of the genius of the Starship design is the realization that, if you have a reusable two-stage-to-orbit design, you've basically also got a three-stage-to-Mars design, just by refueling the second stage and then using it as the third stage too. So instead of launching your big Mars transfer vehicle via a bigger second stage and a bigger-squared first stage, you can get rid of the "squared" level of scaling and just do more launches.
NASA designs avoided going anywhere near this in part because talking about orbital refueling used to be forbidden there. I'd love to place all the blame on a few folks like the former Senator of Alabama, but really once Congress started treating space as a jobs program, the idea of cutting costs was doomed already, and infighting over which costs were the most uncuttable was just icing on the cake.
This, on the other hand, I can't entirely rule out. It would be incredibly shitty hype for investors, because "we're just going to plow our profits into a program that won't pay off in your lifetime" is an awful spiel for getting your hands on someone's retirement fund, but for employees it's been pretty effective hype, a big part of how they've been getting very talented idealistic young people to work very long hours with otherwise barely-competitive salaries.
I don't see how the math works out for a bait-and-switch at this point, though. Starship development wouldn't make sense as a purely greedy investment unless they really expect it to undercut Falcon 9 internal costs, which means a flight rate on the order of what they're pulling off today with Falcon 9, which means so much tonnage to orbit that they'll be able to continue the Mars side of the program as a loss leader. Even if Musk is secretly planning to pull an "aw, shucks, we're going to want to cash out most of those Starlink profits in our lifetimes after all", or he somehow gets pushed out by someone else who wants to change plans, they'd still want to earmark a dozen launches for Mars every so often just to keep attracting talent.
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Compared to the moon, Mars is farther away and has a deeper gravity well.
This means that the craft has to be more substantial since the astronauts will be in there for quite a while. Also the lander needs to be more substantial since it has to escape more gravity.
The lightweight ship and small lander might not cut it.
SpaceX hasn't really explained the mars plan. They might be planning to assemble something in orbit and use a Starship as the lander.
That's the thing though: re-entry, landing, and liftoff on Mars all have substantial costs, and a longer voyage multiplies the cost of hauling all the mission's mass in and out of gravity wells.
If you need 6 months of supplies each way, a monolithic design means carrying down and then re-orbiting 6 months of supplies plus the dry mass of the other 6, plus all the fuel for the interplanetary burn back to earth, plus all the extra tankage mass for the fuel for all that stuff.
Or you could just leave all that mass in orbit like Apollo did and have a dedicated starship launcher-lander.
The moon doesn't have the long flight time issue, but it's even worse in that you're landing and launching a useless heat shield, and without an atmosphere deorbiting mass from lunar orbit is surprisingly costly. I noticed the proposed SpaceX lander for Artemis doesn't have a heat shield for that reason.
On the other hand, imagine how useful starship would be as the orbital shuttle for a dedicated interplanetary stage... If the actual starships never needed to leave low orbit, with some kept on Mars.
Maybe rather than hype, he's dreaming even bigger than I thought.
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The high-level details have been there for years. No orbital assembly, just orbital refueling. Multiple Starships as the lander(s), with cargo sent in the launch window ahead of crew so they can make sure consumables are there and refueling systems are working.
I hesitate to call this a "plan" since I don't expect it to survive contact with reality unchanged, but the changes are likely to be more along the lines of "wait to send many more cargo ships first, after some break and some get departure liftoff testing on Mars etc etc" or "redesign when Raptor turns out to be too powerful to land on unprepared Martian soil", not "orbital assembly". It would be kind of cool to see them tether two Starships together for artificial gravity in-flight, but that would be hard to combine with their "put the landing fuel tanks in between the crew quarters and the sun" plans to minimize radiation shielding weight.
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My understanding was that the Mars rocket would be assembled in LEO from parts launched in Starships, and that a tanker configuration of Starship would be used to fuel it.
Nobody has this plan. The SpaceX manned-Mars plan is that the crew/cargo configurations of Starship are the Mars rockets, that will each send ~100T to Mars after refueling in LEO from a tanker filled by several reusable tanker-configuration Starship launches. The non-SpaceX Mars probe plans are the same as they've always been, to launch <4T to Mars directly via an expendable upper stage and a separate aerobraking shell. NASA's pre-SpaceX manned-Mars proposal was generally to assemble a Mars Transfer Vehicle in LEO, from parts launched on whatever heavy-lift was politically favored at the time (I see 5 Ares V launches in the 2009 study, for example), to put 80-90T on Mars ... but the cost was always in the $100B+ range and I wouldn't call any of the studies a "plan". Looks like the latest idea was to do (relatively minimal, thanks to SLS Block 2 plus some handwaving about nuclear-electric propulsion) assembly in lunar orbit instead?
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