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 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