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.
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.
>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.
Thanks! I’d seen about the bailout capability mentioned in passing, but had always wondered what it would be in practice (spoiler: a pole!). Also, I didn’t realize a second engine almost shut down on STS-51-F .
Per the links:
“A particularly significant enhancement was bailout capability. Unlike the ejection seat in a fighter plane, the shuttle had an inflight crew escape system[12] (ICES). The vehicle was put in a stable glide on autopilot, the hatch was blown, and the crew slid out a pole to clear the orbiter's left wing. They would then parachute to earth or the sea. […] Before the Challenger disaster, this almost happened on STS-51-F, when a single SSME failed at about T+345 seconds. […] A second SSME almost failed because of a spurious temperature reading; however, the engine shutdown was inhibited by a quick-thinking flight controller. If the second SSME had failed within about 69 seconds of the first, there would have been insufficient energy to cross the Atlantic. Without bailout capability, the entire crew would have been killed.“
It's doubly confusing that STS-51-F, with the Challenger, is the only exercised launch abort; while STS-51-L is the famous launch disaster for which Challenger is most well known.
> “As a result of the changes in systems, flights under different numbering systems could have the same number with one having a letter appended, e.g. flight STS-51 (a mission carried out by Discovery in 1993) was many years after STS-51-A (Discovery's second flight in 1984).[6] It wasn't until STS-127 in 2009 where the flight numbering system returned to a standard and consistent order.”
Ouch, shortly after they get standardized and consistent flight numbers, the shuttle program gets cancelled. I guess computer science doesn’t have a monopoly over the difficulty of naming things.
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.
(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>.)
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.
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.
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).
Sure. I meant more generally, presumably NASA's requirement is "has an acceptable plan to safely return them to Earth after abort" rather than specifying particular orbits.
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.
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.
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.
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.
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.
>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.
Yup, jack points in the right place, jacking equipment with sufficient range of motion, AND solid lunar soil in the right place under the jack points.
Plus, you've got to get the whole jacking operation done without damaging any of your main or control thruster rockets, and without tipping past the upright point over to the other side, or just effectively rolling onto an adjacent side.
I wouldn't want to go on a craft where [jacking it back upright] was in the top ten on the list of recovery options to get home.
All the extra mass budget would likely be better spent on a more robust attitude control system to avoid flopping over in the first place. Unless you need it for something else anyway.
>I wouldn't want to go on a craft where [jacking it back upright] was in the top ten on the list of recovery options to get home.
For a counter, I wouldn't want to be on a lander so fragile[0] that being manipulated upright is infeasible. Something will go wrong, maybe not on that lander, but when it does go wrong it'll have to get duct taped together.
[0]Not just mechanically, but in terms of operation scope. Planning that everything must go perfectly or people die is a recipe for the latter.
I deliberately did not say I wanted jacking to be infeasible — but I DO want it quite far down on the options list, as in there's >10 better things to try first.
(And yes, I've done a fair amount of wrangling vehicles, gear, etc. in snow, dirt, mud, & rocks, and eventually it can often be gotten out. But on a different planet/moon, it really should be not be anything close to a primary option. OTOH, if it's got a set of 6+ pop-out lever-legs to upright itself, tested, etc., that's a different solution)
agree - which is probably why Elon Musk is so obsessive about increasing the efficiency and thrust of the merlin and raptor rocket engines, a huge amount of downstream capability can be achieved by increasing that number (all other things being equal)
So if the lander falls over because two of the feet land on regolith, odds are good you don't have a solid point on that side of the craft to put the jack...
Astronauts must be nervous stepping onto the first manned flight of a new craft that has a 100% success rate in the sole previous flight, but might have only a 50% success rate by the end of their mission...
With both Crew Dragon and Starship, there will have been _many_ successful missions involving un-crewed variants of the spacecraft (Falcon 9 and Cargo Dragon were both well-proven systems before crew was a possibility).
Well at least they would have no one else to blame but themselves. As far as I remember it was the pilots that insisted on the shuttle to be not be 100% automated, so they had to do it this way. The soviets just made the whole shuttle automated so it could be tested without risk to crew.
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.