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We all know that the Space Shuttle Solid Rocket Boosters (SRB) were the pair of large solid rockets used by the United States' NASA Space Shuttle during the first two minutes of its powered flight. Together, they provided about 83% of liftoff thrust for the Space Shuttle.

What would have happened if the Solid Rocket Boosters didn't separate after the separation point?

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  • $\begingroup$ This case happened due to modelling bugs in the Shuttle Mission Simulator at least once. The manual sep didn't work because of the particular model that was erroneous. The software didn't proceed to the next ops mode because SRB sep didn't happen; the crew could do it manually, but it was a mess. Ended up as a loss of control case. Sadly I don't remember many details. $\endgroup$ Jun 15, 2017 at 0:57
  • $\begingroup$ You would not go to <s>space</s> orbit today. $\endgroup$
    – Vikki
    Jul 19, 2019 at 4:04

2 Answers 2

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The empty SRBs would have added an additional mass to the vessel which would need to be carried into orbit until separation of the main tank. The additional fuel needed for this would mean that it would not have been possible to reach orbit.

The standard procedure for an abort between SRB separation and main-engine cut-off was the Transoceanic Abort Landing (TAL). The orbiter would have been separated from the external tank, continue on its sub-orbital trajectory and perform a landing on the designated abort runway in Europe (for every space shuttle launch, two different airports in Europe were prepared especially for this eventuality. It never happened).

Should the separation of the orbiter from the external tank also fail... well, the orbiter was unable to glide aerodynamically and land with the tank still attached, so this failure would have been catastrophic.

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    $\begingroup$ The answer assumes both SRBs fail to separate, a benign scenario. If one fails, it's a LOC event. $\endgroup$ Sep 22, 2014 at 16:01
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    $\begingroup$ @DeerHunter LOC? $\endgroup$
    – Everyone
    Sep 22, 2014 at 17:53
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    $\begingroup$ @DavidRicherby If the non-separated SRB is still firing at that point, the vector of thrust does not go through the shuttle's center of mass and you get the same effect you get in those spinny fireworks -- the offset thrust causes the whole to start spinning very rapidly. The Shuttle's control surfaces are not built to stabilize that kind of spin (and that's even assuming we have the space age materials we'd need to stand the kind of stresses involved)... $\endgroup$
    – Shadur
    Sep 23, 2014 at 8:12
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    $\begingroup$ @Shadur The SRBs do indeed have a self-destruct, which is operated from the ground. This was used after Challenger exploded: the SRBs continued flying after the orbiter broke up and they were deliberately destroyed to prevent them hitting the ground or ocean in one big, rocket-propelled piece. $\endgroup$ Sep 23, 2014 at 8:32
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    $\begingroup$ @DeerHunter: I don't think it's that bad. SRB separation is blocked by both trust and time since launch. If we assume a single separation failed, it still means both SRB's are no longer producing significant trust. $\endgroup$
    – MSalters
    Dec 18, 2014 at 16:47
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The flight crew had a contingency procedure for this. On Panel C3 a switch allowed the crew to manually initiate the SRB separation sequence should the software fail to trigger it automatically. I don't believe this required a call up from the flight controllers.

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  • $\begingroup$ I vaguely remember someone stating that this switch doesn't do anything other than trigger the automated processes in place that should've already been triggered. It won't instantly separate the stages if the SRBs are still burning or the software deems it unsafe, so if failures occurred to that part of the software, this switch wouldn't've done much. $\endgroup$ Jul 27, 2018 at 13:30
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    $\begingroup$ Actually according to a member of the SAIL team in 1986, the SRB sep had minimal checks before passing the command to the MEC. The ET sep on the other hand had a six second delay if conditions for ET sep were not nominal. After those 6 seconds ET sep would occur regardless of conditions. This was done at the request of the Astronaut office. It was felt that the Pilot should be in command in off nominal situations not the FSW. $\endgroup$ Jul 30, 2018 at 16:52
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    $\begingroup$ If the physical element of SRB sep, the actual decoupling mechanism between the ET and the SRB, failed, then pushing the switch wouldn't be any good. It would just send another command to the flawed decoupling assembly. The thing is, in this case it's possible that only one failed. If only one fails, you're likely facing a loss of crew and vehicle scenario. $\endgroup$
    – user31448
    May 16, 2019 at 15:22

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