4 ms·

An abort after T-00:02 was iffy for STS. If an abort was called after T-00:02, the RS-25s kept running until T-00:00 just in case the SRBs lit anyway.

jballanc 10y ago
Makes you wonder why anyone ever thought it was a good idea to put solid boosters on a man-rated rocket...and yet NASA is repeating that "mistake" with the SLS.
- greglindahl 10y ago
  Didn't Congress order NASA to do that, this time around?
- wolf550e 10y ago
  It's a way to use NASA budget to prop up military contractor ATK.
- sand500 10y ago
  Not a problem this time because the capsule has a launch escape system
  - JshWright 10y ago
    A launch escape system which uses parachutes, which will not react well to descending through a cloud of burning solid rocket fuel...
robryk 10y ago
I can't quite imagine what failure modes were they thinking about. Those failure modes must have had a nonnegligible chance of lighting off _both_ SRBs, but a very small one of lighting off a single SRB.
- jballanc 10y ago
  IIRC, the SRBs generated enough thrust to break the hold-down bolts even in the event the frangible nuts don't fire. I'd guess the thinking is that, if both fire you might as well have the main engines running than not (since, as I noted before, the SSMEs couldn't be re-ignited in flight). True, if only one SRB fires, you're pretty much toast no matter what, but NASA loves their contingencies of contingencies of contingencies. For example, I've read that there were serious doubts that a Return-to-Launch-Site (RTLS) abort would actually, you know, be survivable, and yet it remained one of the official abort modes throughout the shuttle program.
  - dotancohen 10y ago
    In fact, there was at least one case (and maybe two, on consecutive launches), in which one of the serial SRB holddown bolts did not fire. The SRB, as designed, tore right through it. Regardig RTLS, commander Young refused to test it on STS-1. Though it was engineered and had code and procedres written for it, RTLS was never really considered a viable option.
- JshWright 10y ago
  I assume the very mechanism that ensured both lit also introduced the latency in the abort mechanism they were concerned about.

jballanc 10y ago

Makes you wonder why anyone ever thought it was a good idea to put solid boosters on a man-rated rocket...and yet NASA is repeating that "mistake" with the SLS.

greglindahl 10y ago
Didn't Congress order NASA to do that, this time around?
wolf550e 10y ago
It's a way to use NASA budget to prop up military contractor ATK.
sand500 10y ago
Not a problem this time because the capsule has a launch escape system
- JshWright 10y ago
  A launch escape system which uses parachutes, which will not react well to descending through a cloud of burning solid rocket fuel...

robryk 10y ago

I can't quite imagine what failure modes were they thinking about. Those failure modes must have had a nonnegligible chance of lighting off _both_ SRBs, but a very small one of lighting off a single SRB.

jballanc 10y ago
IIRC, the SRBs generated enough thrust to break the hold-down bolts even in the event the frangible nuts don't fire. I'd guess the thinking is that, if both fire you might as well have the main engines running than not (since, as I noted before, the SSMEs couldn't be re-ignited in flight). True, if only one SRB fires, you're pretty much toast no matter what, but NASA loves their contingencies of contingencies of contingencies. For example, I've read that there were serious doubts that a Return-to-Launch-Site (RTLS) abort would actually, you know, be survivable, and yet it remained one of the official abort modes throughout the shuttle program.
- dotancohen 10y ago
  In fact, there was at least one case (and maybe two, on consecutive launches), in which one of the serial SRB holddown bolts did not fire. The SRB, as designed, tore right through it. Regardig RTLS, commander Young refused to test it on STS-1. Though it was engineered and had code and procedres written for it, RTLS was never really considered a viable option.
JshWright 10y ago
I assume the very mechanism that ensured both lit also introduced the latency in the abort mechanism they were concerned about.