3 ms·

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 v

• 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.