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Comment by kibwen | Hacker News Reader

> Barring a major engineering challenge in in-orbit propellant transfer

We already have that challenge. Last I checked, SpaceX was claiming it would take five Starship launches to store enough fuel in the depot to perform one lunar mission (which is innately strange considering Apollo did it in one launch on a less powerful rocket, but that's not even the point here). But according to NASA, SpaceX has failed to adequately account for cryogenic boil-off in their plans, meaning that they expect it will take about twenty Starship launches per lunar mission. That's not exactly inspiring, especially given what it implies about the number of launches it would take to get to Mars and back. To solve the cryogenic boil-off issue we might need to switch to different fuels entirely, which would necessitate new engines.

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> SpaceX was claiming it would take five Starship launches to store enough fuel in the depot to perform one lunar mission (which is innately strange considering Apollo did it in one launch on a less powerful rocket, but that's not even the point here)

Apollo was disposable. Starship is not. Apollo could thus max out payload at launch, which Starship cannot do design or fuel budget wise.

The Apollo paradigm was for literal moon shots. Starship and Artemis are more about building infrastructure.

> according to NASA, SpaceX has failed to adequately account for cryogenic boil-off in their plans, meaning that they expect it will take about twenty Starship launches per lunar mission

That is not NASA's position. Folks at NASA and SpaceX disagree around the boil-off rates. Everyone thought about it. We just don't know what it is. We should have a preliminary figure next year, and a final-ish one within two or three years (after the first vehicle's boil-off characteristics are optimized).

But yes. There are major engineering challenges in-orbit propellant transfer could raise that could require going back to the drawing board. Hence why I flagged it. Given that's something humanity has never really done, it seems like a fair risk to take given the upsides.

(Note, too, that in present designs Starship must function as a launch vehicle, spacecraft and fuel tank. That's not required long term. Well-insulated orbiting fuel depots start making sense rather quickly if you have <$1000/kg launch costs.)

Please provide a reference showing that NASA thinks that Starship will lose 3/4 of the fuel, and there is no way to fix it.

“It’s in the high teens in the number of launches,” Hawkins said. That’s driven, she suggested, about concerns about boiloff, or loss of cryogenic liquid propellants, at the depot. [...] Critics of NASA’s selection of Starship for HLS have pointed to the number of launches as a weakness in the architecture. The Government Accountability Office, in its rejection of protests by Blue Origin and Dynetics of the Starship HLS award in 2021, noted that SpaceX required 16 launches overall for a Starship lunar lander mission. Elon Musk, chief executive of SpaceX, disagreed, calling the need for 16 launches “extremely unlikely” in an August 2021 social media post. He said a “max of 8” tanker launches should be needed to fuel the Starship lander, adding it could be as few as four.

https://spacenews.com/starship-lunar-lander-missions-to-requ...

Would note that’s the GAO, not NASA. 16 launches is well within possibility, though unlikely that would ever be accepted as a final solution.

The nice thing about fuel launches though is that the cargo isn't valuable.

You're not launching exquisite rovers or satellites -- you're launching a bunch of fuel.

So if a reused Starship blows up on accent*, that's not great, but it's not terrible either. Load the next one and try again.

* Obviously, you want to be much more careful on rendezvous

> if a reused Starship blows up on accent, that's not great, but it's not terrible either

You're correct. But Starship, being a multi-use spacecraft, can't capitalise on this differential.

Fuel-only launch enables high-g launch options, e.g. rail guns. It could also enable low-reliability low-cost options, but the nature of space launch hasn't opened that niche up, and--I suspect--the nature of environmental regulations ensure it never will.

I'd make the point that it can, because {cost for relaunch} = {refurb cost} + {recertification cost}.

And likewise, probability of relaunch success scales with the money and time spent on those other two.

In fact, I'd strongly argue that fuel-to-orbit is Starship's version of Falcon's "Starlink demand seeding."

It's win/win if SpaceX has a high-volume, low-payload-cost, revenue-generating demand for Starship, as it gives them a failure tolerant mission to push relaunches to failure and then use that data to improve future reuse reliability.

Of all the things SpaceX has done, getting themselves into positive-feedback flywheels has been the smartest.

The GAO is mentioned later, but the first quote is from "Lakiesha Hawkins, assistant deputy associate administrator in NASA’s Moon to Mars Program Office".

Thank you for providing a reference. Sight unseen, I'm inclined to think that SpaceX is more likely right here. In particular part of the higher figure is a lower launch cadence. But SpaceX is building their technology around very rapid turnaround times. With multiple Starships, there is good reason to believe that they will not need to wait 6 days between launches.

Of course this depends on FAA permission. Whether they get FAA permission may well depend on who wins the election. Musk has gone out of his way to place a big bet on Trump, and it is clear that Trump will happily get rid of red tape for Musk in return. My read is that part of the reason why Musk placed that bet on Trump is because the Biden/Harris administration has already decided to place lots of red tape in Musk's way. At first as a reaction to Musk's hostility towards unions and COVID restrictions on manufacturing, and then as a reaction against what Musk was doing with Twitter.

The US government is throwing money hand-over-fist at SpaceX, the idea that the Biden administration is artificially obstructing SpaceX is not based in reality. Meanwhile, Trump is publicly anti-EVs and anti-self-driving-cars, so Musk's rabid cheerleading cannot be motivated by economic reasons.

SpaceX is so strategically critical American interests that it’s implausible for either administration to kneecap it.

from https://www.youtube.com/watch?v=fjWCEFioT_Y

Conclusions:

* Standard Starship is probably good enough for HLS

* Simple coatings and/or a specific orientation makes things a lot better

> But according to NASA, SpaceX has failed to adequately account for cryogenic boil-off in their plans, meaning that they expect it will take about twenty Starship launches per lunar mission.

According to one person at NASA. There's disagreement on the point.

https://arstechnica.com/space/2023/11/what-nasa-wants-to-see...

"[Lisa Watson-Morgan, who manages NASA's Human Landing System program] suggested the range in the number of Starship tanker flights for a single Artemis mission could be in the "high single digits to the low double digits." Elon Musk, SpaceX's founder and CEO, has suggested the company is looking at expanding Starship's capacity with larger propellant tanks. This could help reduce the number of tanker flights."

There's a lot of unknowns. Falcon 9 versions saw significant performance boosts over the generations; we may see the same with Starship.

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