SpaceX Super Heavy/Starship (BFR/BFS) - Earth to Deep Space / Re: Abort options for Starship and Starship/SuperHeavy« Last post by TheRadicalModerate on 12/05/2022 10:47 pm »
If solid rockets don't work then there is no pad abort for a Starship loaded up to 1400t with fuel.
You've over-constrained the problem. You don't need 1400t of prop. You don't even need cargo. You need a ~20t crew module and just enough prop to get to LEO and do an EDL abort from orbit. Once you're in LEO, you transfer to something else (an LSS or a fully-featured crew system suitable for either lunar surface or Mars journeys). When you come back to LEO, the abort-safe crew version takes you back through EDL.
That said, 5 gee pull-away might not be adequate. There might not be a viable way to launch a Starship from a mated SuperHeavy. But even if you can get through these two problems, there are other abort modes that probably need an escape capsule.
your same arguments apply to having a crew dragon in the cargo compartment.
I don't understand what you're saying here. If the argument is that you don't need robust abort modes for most if not all flight phases, then it's a tautology. But if it's not then... you do?
Don't get too hung up on the D2. But you need some kind of escape system if it's important to meet NASA pLOC standards--or responsible corporate standards, for that matter.
So if there is no pad abort, and ascent abort works with current design, and there is no ELD abort, I'm flummoxed as to what abort system there needs to be at all.
Again, you've constructed a tautology on a false premise. It is of course true that if you need no abort contingencies, then you need no abort mechanism.
I don't see a reality where there isn't a viable pad abort. All the flight failure trees get convolved with all the Stage 0 failure trees, and then there are any number of exogenous events.
And how did you make the leap to no EDL abort? There may not be abort options through the entire hypersonic regime, but that's true for all human orbital spacecraft. And you certainly need to deal with descent, landing, and nav contingencies.
Landing abort is all that's left. "can't get to catch tower" means water abort, which works with a robust cargo compartment.
First, I don't think it necessarily works with a robust nose. It'll work if the entire ship is robust enough, but prop tanks tend to blow up if they rupture.
Second, what about "got to catch tower but catch failed"?
Failure to ignite or correctly use engines due to the remaining single points of failure (which is tank pressurization and gimbaling) happens at such a low altitude abort would be difficult. Blasting a crew dragon horizontally won't be useful, and neither will solid rockets in the base.
Are you talking about ascent or descent here? On descent, if you start the rotation high enough, there's absolutely nothing wrong with a horizontal D2 abort; it'll steer into the proper orientation for parachute opening. And if the rotation is complete, then it's aborting vertically.
On the pad, failure to ignite isn't the problem. A failure anywhere in the final launch sequence is a problem.
And a crew dragon wouldn't blast horizontally for any pad or ascent abort; it would go up vertically (or axially, after pitchover), after popping the fairing open.
I suspect gimbaling can be made redundant barring frozen parts1, so really we are just left with inadequate pressure in the header tanks as the remaining single point of failure.
If I ran a crew safety group, I'd have a jar where anybody who said the words, "Really we are just left with..." had to put $20.
Slosh causing gas ingestion into the turbines?
Eloneron failure during rotation?
Post-ignition engine explosion?
Unexpected, large, cross-wind gusts?
Chopstick malfunctions? Plain ol' catch failures?
Leg failures for uncaught landings? Rough surface landings?
Foreign object damage on landing?
That's an off-the-top-of-my-head list. I'm sure it can be made longer.