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I watched a few videos "from the boosters" of their suborbital flight with the Shuttle, and what I noticed is that after the boosters were jettisoned there was a phase of flight that was quite chaotic - and they didn't travel far apart.

I can imagine given enough bad luck to enter the atmosphere at just the right angle they could crash into each other. Was that possible or was that apparent chaos just apparent, but in fact calculated not to create such risk?

(on unrelated note, how did other multi-booster platforms fare in that respect?)

SF.
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  • Different question, but related answer: http://space.stackexchange.com/questions/12381/is-it-possible-for-the-space-shuttle-solid-rocket-boosters-srb-to-hit-the-spac – Hobbes May 11 '16 at 09:10

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There was certainly a risk that the boosters could collide with each other, once they separated they were essentially just big pieces of pipe.

The chance of it happening was extremely low though. At separation the boosters were moving at mach 4+, and as they were angled to clear the tank they were angled away from each other. The aerodynamic forces would be pushing them apart strongly at that point, and they would be pretty far apart by the time they slowed down. At some point the boosters would stop flying and start dropping, from then on random chance could conceivably have brought them together as they spun through the sky, but it would have been very unlikely for that to happen given the space they would have occupied.

GdD
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    Would anything of consequence have happened if they did collide? – corsiKa May 11 '16 at 14:42
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    Presumably the loss of two "reusable" boosters. – MSalters May 11 '16 at 15:14
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    If they did collide you'd get a rain of booster shreds over an open space of ocean and NASA buying 2 new boosters. – GdD May 11 '16 at 15:22
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    "Hi Jim, it's Ted. We've had a bit of a situation develop kind of out of the blue. Could you perhaps deliver two more of those cigar things by next week? Yeah, whatever you want to call them. We need them in time for the launch next Saturday. Great, thanks. Talk to you later, Jim." – user May 11 '16 at 18:42
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    Second this. Try playing Kerbal Space Program and you can see what happens--if you get the aerodynamics right the booster tumbles outward, air drag imparts a radial velocity, they're not likely to hit each other. (Get the aerodynamics wrong and it tumbles into the rocket, not into the other boosters.) – Loren Pechtel May 12 '16 at 18:53
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    @LorenPechtel: My experience with KSP is pretty much "a loud explosion roughly 10 seconds after separation? Eh, just the boosters colliding again." In particular, if I use angled fins to provide clean atmospheric separation, the boosters will neatly float away from the craft, then flip around and begin accelerating towards each other as they fall. – SF. Sep 02 '16 at 10:47
  • @SF. Other than for the earliest rockets I don't find fins to be needed. Normally you can fly them fine on the engine gimbals alone. Once they get big enough you'll need separator motors to ensure they come off cleanly but so long as you get the thrust right they still tumble outward. If the boosters hit that tells me to revert and fix the separator motor thrust or fuel. – Loren Pechtel Sep 02 '16 at 23:04
  • I too get booster collision after booster collision in KSP, but then again I fly eight boosters not two. – Joshua May 11 '17 at 19:17