[cstross]

Worth noting is that because Starship HLS carries astronauts, it has to be capable of abort-to-orbit -- that is, to cancel the landing at any point and return to Lunar orbit. The Apollo LEM would have done this by shutting down and dumping the descent stage then lighting the ascent motor: Starship is a single stage that should have enough fuel and oxidizer left after a successful landing to lift off and return to orbit with a minimal payload.

I expect if astronauts aboard HLS lose their altimeter they'd have to abort the landing immediately -- to proceed without it would be the height of recklessness. But Odysseus had no abort-to-orbit capability so was committed to landing.

[facialwipe]

I’m a huge space nerd. It takes up most of my free time.

I have never once read about abort-to-orbit capability as a concept, let alone a requirement for Artemis HLS.

Here’s a 4 year old video detailing past abort systems and why Starship won’t have one: https://m.youtube.com/watch?v=v6lPMFgZU5Q

[kqr]

Huh, then you're one of today's lucky ten thousand!

Apollo 14 had a piece of loose solder in the button triggering abort-to-orbit, so it occassionally triggered itself. This wasn't a problem en route to the moon, but the second the descent phase started it would have been a Poisson-timed bomb that would prevent the landing.

There was a bit of memory that could be set to ignore the state of the abort button (this bit was the reason the abort sequence wasn't triggered en route). The problem was this ignore bit was reset by the landing sequence (to allow aborting once landing started), and they did not believe the astronauts would be quick enough to set the bit again before the button shorted out and triggered the abort.

(Ignoring the abort button was fine because an abort could be triggered in the computer instead. Takes a little longer but was determined a better option than scrapping the mission.)

Don Eyles came up with a clever hack. Setting the program state to 71 ("abort in progress") happened to both allow descent to start and prevented the abort button from being effective. So this program state was keyed in just before descent.

The drawback was that it obviously put the computer in an invalid state so some things were not scheduled correctly but Eyles and colleages had figured out which things and the astronauts could start those processes manually.

Then once the computer was in a reasonable state again the ignore abort bit could be set and the program mode set correctly and it was as if nothing had happened.

[dabluecaboose]

>I have never once read about abort-to-orbit capability as a concept

ATO was an abort mode [1] on the Shuttle program and is notably the only abort mode that was successfully used in the entire program, on STS-51f [2] . Challenger suffered an engine anomaly on liftoff that resulted in a lower orbit than was intended, but otherwise the mission went off without a hitch.

[1] https://en.wikipedia.org/wiki/Space_Shuttle_abort_modes#Abor... [2] https://en.wikipedia.org/wiki/STS-51-F

[dredmorbius]

Among last-ditch options considered for the Apollo programme (specifically several planned but eliminated long-duration, two-week missions), was the ultimate LESS-is-more approach: "Lunar escape systems".

This was basically a lawn-chair rocket for two which would utilise a disabled LEM's (lunar excursion module) fuel tanks, and would be hand-piloted without any guidance computer to an intercept orbit with the Apollo Command Module, with the hope that a rendezvous and crew transfer could occur within the four-hour window of space-suit oxygen supplies. Given that the CM's orbital period was two hours, this meant at best two chances for a successful intercept.

<https://en.wikipedia.org/wiki/Lunar_escape_systems>

(I'd run across this from the recently submitted MOOSE article, "Man out of space, easiest", a strap-a-foam-mattress-to-your-ass reentry concept: <https://en.wikipedia.org/wiki/MOOSE>.)

[loa_in_]

Apollo Lunar Module had an abort-to-orbit that was also used to lift off the surface of the Moon after successfully completing the mission. It used explosive charges to throw the lander frame away and involved Apollo Guidance Computer manuevering into orbit at any point of the mission up until the landing.

[Isamu]

The video is about launch abort I believe. As opposed to aborting a lunar landing.

[MPSimmons]

Dragon 2 has abort to orbit capabilities, too. The abort zones they call out as the rocket's IIP advances up the east coast continue until Ireland, and then after that, it's abort to orbit, where the superdracos will carry the ship to orbit without the second stage.

[postexitus]

Watch "For All Mankind" - one of the huge focus areas of S1 is "abort-to-orbit" in Apollo missions. Great series in all aspects.

[lmm]

Abort-to-orbit is a confusing term since it suggests the Shuttle's specific ATO mode. I presume the requirement is "safe abort at all points during lunar descent/landing" rather than specifically to orbit (e.g. an abort mode that put them directly on a return-to-Earth trajectory would probably also be fine).

[dotnet00]

I think since then Elon has mentioned that abort via the main Starship engines may be possible through all points of a launch (putting aside the landing process for now). Probably also helped by the hot staging related changes, since IIRC the concern regarding abort modes was whether or not the engines could safely ignite and separate from the booster.

It does still leave the system without a means of aborting if the ship's main engines have trouble, although I suppose they do have a good bit of redundancy there.

[grouchomarx]

the four year old video you linked to has nothing to do with aborting a landing on the moon

[narag]

I expect if astronauts aboard HLS lose their altimeter they'd have to abort the landing immediately -- to proceed without it would be the height of recklessness.

In addition to the obvious, it should be taken into account that the absence of atmosphere makes very difficult to assess distance and scale. Videos of approach seem like a fractal browser.

[WalterBright]

You can judge height by the distance to your shadow.

[mandeepj]

> Starship is a single stage

I'm no expert, so this is a question to confirm my understanding: Starship does have a booster. So, doesn't that make it a dual stage?

https://www.zenger.news/2023/11/27/elon-musk-reveals-simple-...

[dabluecaboose]

I think GP was saying that the lander is single-stage. By the time of a presumptive lunar landing, there's no lower stage to drop as with the Apollo LEM.

[justrealist]

The part that's landing on the moon is just the second stage.

[thereisnospork]

Assuming the landing is soft enough to survive, shouldn't it be fairly trivial for the astronauts to disembark and right the lander? To the extent anything in space is trivial.

Even if it's a bit more than doable by hand a ratchet jack should make short work of it.

[cpgxiii]

The Apollo LEM, only craft that has ever taken humans to the moon's surface, weighted somewhere around 20,000 kg after landing. Since it only ever operated in space and lunar gravity, it could be built with a much higher mass fraction than a rocket launched from earth requires - greater than 30%, where a Falcon 9 in comparison has a mass fraction below 5%. Even then, the LEM structure had to be built incredibly lightly. While the LEM structure could obviously be lifted by crane and survive launch and docking stresses, those were are at designed points in the structure. Without the presence of a crane capable of lifting the whole LEM, righting an LEM that had landed on its side would have been effectively impossible. Basically all of the modern proposed manned lunar landers are considerably larger than the LEM, and thus considerably heavier.

For comparison, a craft built for earth launch mass fractions probably wouldn't survive falling over in the first place - when that happened to a Falcon 9, the whole rocket simply exploded.

[stonemetal12]

>shouldn't it be fairly trivial for the astronauts to disembark and right the lander?

I don't think that is an assumption you can make. In the worst case scenario the lander lands on the door. In which case the only way to disembark is to lift the lander.

[jethro_tell]

Assuming you have jack points in the right place based on the way it tipped over.

[ooterness]

If it's good enough for Jebediah Kerman, it's good enough for me, but maybe not NASA.

https://xkcd.com/1244/

[abledon]

are they going to send a 'test run' HLS first? like, completely computer controlled, to stick the landing?

[bryanlarsen]

Yes, that is a condition in NASA's contract with SpaceX. It is currently scheduled for 2025.