kevin@cs.arizona.edu (Kevin Strietzel) (03/17/90)
Here's a query that's been bumping around my skull for a few years now:
What happens if one SRB ignites, but the second won't go?
Or one (or more) of the SSME's won't go?
Here are my initial thoughts:
I assume it's disaster time.
It *might* be able to leave the pad: my numbers claim it could get off the pad
(thrust > weight) with only the SRB's, but acceleration would be way down, so
it probably wouldn't get high enough to do anything useful. If only one SSME
failed, you probably couldn't make orbit, but you could probably get high and
far enough to abort and land somewhere.
Presumably the pad would melt and/or burn if it just sat there -- if that's
even possible. I can't remember if the shuttle is held down by anything
besides gravity at engine ignition time. If you could physically hold the
shuttle down, would the torque of a single SRB flip the whole pad on its side?
Seems like an SRB could separate on the pad, and it'd leave pretty quick
without a shuttle holding it down, and they're slightly steerable. But don't
they help support the orbiter on the pad? And isn't its exhaust going to make
a mess of the shuttle, despite quick departure? And I'd guess their steering
system is totally dependent on the orbiter's computers, and even if it weren't,
would it be stable solo?
Have I answered my own question?
Any comments would be useful.
Kevin
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Kevin Strietzel, CS Department, University of Arizona, Tucson, AZ
Internet: kevin@cs.arizona.edu
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It's easy to pass the buck -- especially to someone who wants it!jnixon@andrew.ATL.GE.COM (John F Nixon) (03/17/90)
kevin@cs.arizona.edu (Kevin Strietzel) writes: >What happens if one SRB ignites, but the second won't go? The orbiter/external tank/SRBs tumble over to the side due to unbalanced thrust. One enormous fireball results. >Or one (or more) of the SSME's won't go? The launch is stopped. They light the SSMEs *before* the SRBs. -- -- ---- jnixon@atl.ge.com ...steinmetz!atl.decnet!jnxion
KDA101@psuvm.psu.edu (KeithPetto Alexander) (03/17/90)
Let's see, there are explosive bolts holding down the SRBs (4 on each),
but they are designed to go off at exactly ignition so I don't think they
will hold the broken SRB down. This suggests that, since there is still
more thrust than weight, the whole thing will lift off the pad. More
problems now though, it might tip one way or the other. Assuming it clears
the tower, sideways if necessary, I would think they might have it under
enough control to get it going up. They have to go up a ways (10000 or
20000, someone correct me) before they can turn around for the Abort to
Launch Site, they do need some space. My completely un-educated guess is
that it wouldn't kill anybody, just shake the whole thing up quite a bit.
Again.
Petto :->
"You weren't like that before the beard." -- Q
Petto is still an AI program run amuck, his opinions are the result
of a deranged program from a less deranged programmer.
kda101@psuvm.bitnetucc1q@elroy.uh.edu (A JETSON News User) (03/17/90)
In article <140@caslon.cs.arizona.edu>, kevin@cs.arizona.edu (Kevin Strietzel) writes: > Here's a query that's been bumping around my skull for a few years now: > > What happens if one SRB ignites, but the second won't go? 1. You are talking about millions of pounds of thurst from a single SRB. In one seconds time you will have such a tilt to one side that the entire group of oribter/ET/SRB's will fall over sideways. I doubt that the SSME's have enough thurst at max power to prevent the tilt. Even it the SSME's do have enough thurst they can not be steered far enough to provide enough side thurst to balance enough to climb as little as one thousand feet, much less ten or twenty thousand. Remember, the French lost an all liquid fuel launcher and payload when ONE engine lost HALF its thurst. So what you get is everything trying to fly sideways, falling over and destroying pad/orbiter/ET ( remember, a FULL ET, not half? empty). 2. Enough if you can steer the SSME,s enough to balance, it has to be done QUICK. I do not believe the system can react fast enough to such a sudden imbalance of that size. 3. if you can balance fast enough you will still start flaying sideways so far so fast that you have a 50/50 change of hitting the tower. That depends on which side the failed SRB is on. Lose an SRB on the pad and everything is slag and vapor. However, NASA does know that both SRB's MUST fire and the igniters in them are massively overpowered and have many duplicate firing charges. The igniters are muliti-staged: several small igniters to light several larger ones to light the main igniter that lights the SRB proper. I do not remember the full layout on this but i have the general idea down right. i am not an expert. these are my opinions. I think the SRB's will light. If not it was sabotage. if one does not light, the crew aboard is DEAD.
henry@utzoo.uucp (Henry Spencer) (03/18/90)
In article <140@caslon.cs.arizona.edu> kevin@cs.arizona.edu (Kevin Strietzel) writes: >What happens if one SRB ignites, but the second won't go? >Or one (or more) of the SSME's won't go? An SSME problem before SRB ignition just results in a shutdown; this has happened once or twice. A single SSME failure after launch results in an emergency landing somewhere if it happens early, or continuation of the mission at least as far as one orbit if it happens late. (There has been one case of an SSME shutdown late in the climb.) Multiple SSME failures after launch can lead to continuation, emergency landing, ditching in the ocean, or death, depending on timing. But if only one SRB lights, this is known as an "unsurvivable accident". >Presumably the pad would melt and/or burn if it just sat there -- if that's >even possible. I can't remember if the shuttle is held down by anything >besides gravity at engine ignition time... They blow the hold-down bolts simultaneously with SRB ignition, so there is no option at that point. I've always thought this was a little dumb, but there may be good reasons for it. >If you could physically hold the >shuttle down, would the torque of a single SRB flip the whole pad on its side? No. The pad is *lots* heavier than the shuttle. >Seems like an SRB could separate on the pad, and it'd leave pretty quick >without a shuttle holding it down, and they're slightly steerable. But don't >they help support the orbiter on the pad? And isn't its exhaust going to make >a mess of the shuttle, despite quick departure? And I'd guess their steering >system is totally dependent on the orbiter's computers, and even if it weren't, >would it be stable solo? The orbiter and tank are entirely supported by the SRBs from stacking to launch. Departure of one SRB would almost certainly mean massive structural failure of the tank, which would mean loss of the orbiter and probably the crew. The exhaust of the departing SRB would add to the problem. And you are correct, the SRBs are controlled by the orbiter. I suspect they could fly reasonably well independently, if they had the brains to. -- MSDOS, abbrev: Maybe SomeDay | Henry Spencer at U of Toronto Zoology an Operating System. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
frazier@bgsuvax.UUCP (Paul Frazier) (03/18/90)
In article <231@puma.ge.com> jnixon@andrew.ATL.GE.COM (John F Nixon) writes: >>What happens if one SRB ignites, but the second won't go? > >The orbiter/external tank/SRBs tumble over to the side due to unbalanced >thrust. One enormous fireball results. > I thought that they could "blow the lid" off of the SRBs, and thereby reduce their thrust to zero. Is this true? If it were true, they could prevent the scenario you describe.
henry@utzoo.uucp (Henry Spencer) (03/19/90)
In article <5564@bgsuvax.UUCP> frazier@bgsuvax.UUCP (Paul Frazier) writes: >I thought that they could "blow the lid" off of the SRBs, and thereby reduce >their thrust to zero. Is this true? ... No, it's a common misconception. The destruct system on the SRBs uses a linear shaped charge running up along the side to blow the casings open like a pea pod. This is sometimes known as a "thrust termination" system, which is its purpose -- destruct systems are not meant to shred the rocket, just to make sure it follows a predictable path and doesn't run wild -- but it's not the sort of thing one would use on the pad. There is no provision for gentle, or even only mildly violent, SRB shutdown. -- MSDOS, abbrev: Maybe SomeDay | Henry Spencer at U of Toronto Zoology an Operating System. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
thomas@mvac23.UUCP (Thomas Lapp) (03/22/90)
I'm sorry. I couldn't resist.
> 1. You are talking about millions of pounds of thurst from a single SRB.
^^^^^^
That's a pretty "thursty" SRB. No wonder the pads are located near the
Atlantic ocean!
- tom
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