= 27d567bc2d48d9f40e9ccc20ea370b15)
CBHacking comments on Stupid Questions May 2015 - Less Wrong
You are viewing a comment permalink. View the original post to see all comments and the full post content.
= 783df68a0f980790206b9ea87794c5b6)
Loading…= b715d02e85f7b3b4ae65ca3d3e450868)
Subscribe to RSS Feed
Powered by Reddit
= f037147d6e6c911a85753b9abdedda8d)
You are viewing a comment permalink. View the original post to see all comments and the full post content.
Comments (263)
You're also talking about fundamentally different kinds of rocket boosters. The Space Shuttle used solid fuel boosters, which are basically nothing except a tube packed full of energetically burning material, an igniter to light said material, and a nozzle for the generated gases to come out. They couldn't throttle, couldn't gimbal, couldn't shut off or restart, didn't use cryogenic fuel so didn't need insulation, didn't rely on pressurized fuel so they didn't need turbopumps... In fact, as far as I know they basically didn't have any moving parts at all!
You ever flown a model rocket, like an Estes? That little tube of solid grey gritty stuff that you use to launch the rocket is basically a miniature version of the solid fuel boosters on the Space Shuttle. The shuttle boosters were obviously bigger, and were a lot tougher (which made them unacceptably heavy for something like the Falcon 9's first stage) so they could survive the water landing, but fundamentally they were basically just cylindrical metal tubes with a nozzle at the bottom.
Despite that, reconditioning them for re-use was still so expensive that it's unclear if the cost was worth it. Now, of course, they cost a lot less to build than a Falcon 9 first stage, but every one of the Falcon 9 first stage's nine Merlin 1D engines is many times as complicated as the entire solid booster used on the Space Shuttle. Even the first stage tank is much more complicated, since it needs to take cryogenic fuels and massive internal pressurization.
This isn't all that relevant, but the Shuttle SRBs were gimbaled (Wikipedia, NASA 1, NASA 2).
(I was thinking that there is probably at least a mechanical component to arming the ignition and/or range safety systems, but research turned up this big obvious part.)
Whoops, you're right. I thought the gimbaling was just on the SSMEs (attached to the orbiter) but in retrospect it's obvious that the SRBs had to have some control of their flight path. I'm now actually rather curious about the range safety stuff for the SRBs - one of the dangers of an SRB is that there's basically no way to shut it down, and indeed they kept going for some time after Challenger blew up - but the gimbaling is indeed an obvious sign that I should have checked my memory/assumptions. Thanks.
What I've heard (no research) is that thrust termination for a solid rocket works by charges opening the top end, so that the exhaust exits from both ends and the thrust mostly cancels itself out, or perhaps by splitting along the length of the side (destroying all integrity). In any case, the fuel still burns, but you can stop it from accelerating further.
Hm. A solid rocket burns from one end, opening up the nose will do nothing to the thrust. Splitting a side, I would guess, will lead to uncontrolled acceleration with chaotic flight path, but not zero acceleration.
Apparently that's true of some model rocket motors, but the SRBs have a hollow through the entire length of the propellant, so that it burns from the center out to the casing along the entire length at the same time.
That exposes the maximum surface area for combustion, I guess (the surface area actually increases as the propellant is burned, interestingly) so blowing the top would work, yeah.