@Jared Hunt
My original post was a *very* brief summary of a longer post made some time ago on another thread. This version gave just the outlines of the suggestion.
*suitably* equipped means "modified", as in not the design as it exists now but with some *relatively* minor modifications (with most of the heavier bits on the first stage. On the 2nd stage 1Kg of extra mass nearly equals a 1Kg *loss* of payload. On 1st stages it's something like removing 16Kg to get 1Kg of payload increase. You're already running control signals into the inter-stage area anyway. How heavy can a couple of low pressure valves (<3bar gauge IIRC 1 cryogenic) and some equally low pressure piping be?
"Firstly: At stage separation, the vehicle is flying nearly horizontally"
I'd hope so.
" at about mach 6"
AFAIK most 2 stage liquid fuel launchers split the delta v *evenly* between the 2 stages. it should be at least M11 to M12.
" and has next to no fuel left so there's little scope for throttling down."
I think you're confusing fuel left and the ability to to *slow* down or the ability to *throttle* down. That's a feature of the engine design. The Falcon 1st stage Merlin engines don't seem to throttle but the 2nd stage vacuum ones can do so down to 60%. shutting down, suggesting its an engine mod (I'd suspect SpaceX can turn a Merlin vacuum engine back to a 1st stage engine *almost* as quickly.
"how do you propose that a rocket going horizontally at mach 6 (almost certainly over the ocean as well) turns its arse around to face the ground"
The same way it got into that attitude in the first place. Using thrust vectoring. It was *always* doubtful you could kill the horizontal velocity it had built up. In my original post the fallback plan was to rotate it so the engines would forward on the axis of travel. It's a 3 point turn in space or a long jumper shifting from body first to legs first for the landing depending on what analogy you prefer. When even the *lowest* thrust level exceeds the total rocket mass its time to shut off the engines and continue to let the tanks drain. BTW probably the *hairiest* moment will be at the top of the 3 point turn which I estimate will be the point of maximum risk of starvation of propellant tot he engines.
" and slows itself down to a nice guided landing?"
This is *not* a landing. It's an *abort*. I guess the phrase "mother of all crumple zones" was not specific enough. It's a controlled crash.
I fully expect the *whole* of the 2 stages to concertina (remarkably evenly if they do so like the nose down crash test that Armadillo Aerospace did of their capsule some time back), absorbing the *massive* kinetic energy of the vehicle. The Falcon is a *total* write off. But the payload, IE the load that *pays* is unharmed and can be prepared for a 2nd launch, although any humans will *probably* need some new suit liners. The phrase "Express elevator to Hell, going down" would sum up my view of it pretty well.
You may still be unclear why I proposed this.
SpaceX have talked about using their main capsule motor in a special escape mode in the event of failure (otherwise it serves like the main engine on the Apollo service module) but a serious failure puts the reliability of *all* components on a vehicle that are not *already* running in doubt, like the main motor and the separation explosive bolts and the parachute deployment.
This idea only uses components that are either *already* running (admittedly in a complex and novel way), components that can be tested *repeatedly* before flight (latching solenoid rather than explosive actuated valves for example) and the physics of the operating vehicle itself.
Customers don't *give* a stuff how their payload gets *into* orbit. Only that it gets to the *right* orbit on *time*.
A provider who could say "We didn't put your payload up, but we did not destroy it and it's in good enough condition to launch at the next window" would have a *significant* advantage over one who said "Hey its a rocket, y'know. The best ones got a 1 in 50 chance of failing anyway. Better luck next time. Come see us again when the insurance coughs up or you got some more money."
Just to be clear this would not even be *tried* without massive CFD and FEA simulation.
Yes intact abort on a rocket *sounds* insane, but nothing I know absolutely *forbids* it from working, either on Falcon or any other launcher with common fueled stages (which lets out Ariane and IIRC the Indian designs but might still include some of the FSU types).
Biting the hand that feeds IT
