I've been watching a lot of the shuttle videos on the National Space Society website lately. I was watching one last night, and the thought occured to me - what is the plan if one or both of the SRB's fail to seperate? I'm sure they would dump the tank and abort, but is there a chance they could make it to orbit and let the SRB's go with the tank?
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The best they could probably do is an abort-once-around, but they probably have redundancies to prevent that from ever happening.
AstroBrian":1cv16kuv said:
I believe the correct term for that is "brown trousers time".
The SRBs have some residual thrust (note the discussion in the Ares 1X thread over in M&L) after official "burnout" and separation. This is a fundamental issue with solid propellants. Also, they have a separation motor (a small solid motor) mounted at the top of the booster to nudge it away from the Orbiter, to start it tumbling the right way to avoid recontacting it (Which Would Be Bad). I don't know what they do in the event of a separation failure, but I can't imagine there would be very many good options. If that separation motor fires before the charges to cleave the SRB away, would its plume damage the ET? What if it only fails to separate on one end? The separation motor would cause the SRB to pivot around the remaining strut, which gets us to a situation eerily like the Challenger. (There was more going on there, but one of the final events was the SRB pivoting around the forward attach strut and impacting the ET, possibly hastening its structural failure.)
If shuttle_guy is reading this, perhaps he can shed light. Shall I move this to the Missions & Launches forum so he's more likely to read it? He's a long-time Shuttle veteran. We have a few other real-life Shuttle experts here, but like SG, they mainly post in M&L.
AstroBrian":3l3zoywm said:
I am not sure the ET structure could withstand the aysimetrical load that only one booster seperating would cause.
if it did, I suspect the orbiter would end up in the water, if not it would be in peices, and survivibility would be poor.
that being said there are usualy doual pyros each with two initiators, so such a failure is a near zero chance.
Why does this thread continue to appear in Free Space when it should be in Missions and Launches?
I want to take this one step further. What if the SRB separation goes okay but the External Tank doesn't separate from the orbiter? Could the shuttle still make it to the ISS?
bluegrassgazer":nbfjqrgs said:
Maybe, but it wouldn't make it down without refueling. At one point the idea of using ET's in LEO for building material was proposed but never happened.
bluegrassgazer":3krx5m8y said:
On current missions, probably not. There would not be enough margin to carry the extra weight to the proper orbit. The might make it to orbit, but not the proper one. Plus, they wouldn't be able to dock or land...
drwayne":3gqy8sgx said:Maybe some moderator hasn't moved it yet?
I got sidetracked. Sorry about that, and thanks for moving, drwayne. ;-) (Had kind of a weird weekend, and not just because of Halloween.)
Regarding a failure of ET sep -- I suspect that would not be survivable. There will always be some failure modes that are not survivable, and losing the ET is pretty much mandatory.
All manned spacecraft have this same problem -- if they can't jettison the extras properly, they are in very serious trouble, because it alters the aerodynamics of the vehicle, and these vehicles are traveling so quickly that they are in an extremely tight envelope.
As an example of this, gap fillers sticking out from between tiles on the Orbiter's belly do not cause serious problems -- but even one centimeter of protrusion is enough to cause substantially increased heating on tiles downstream of the protruding gap filler, to the point where they often have to replace tiles that should've been good for several more flights, just because of this extra heating. If that tiny little thing is enough to render tiles non-reusable, what would a whole ET do?
I retired from working on the Shuttle Program in 1993. Its been a while, but resorting to memory:
The SRBs are attached to the External Tank.
The SRB's burn out and separate after about 2 minutes of burn. Each SRB has one forward and three aft attach bolts (in the struts). As noted above each of these bolts has redundant initiation. It seems that any SRB separation failure at any one of the eight attach points would result in a catastrophy similar to launch 51-L (Challenger). If the orbiter somehow survived the likely explosion they could separate and possibly return to KSC in one of the abort modes.
The liquid LN2 and LOX in the External Tank feeding the Orbiter Main engines is expended before reaching orbit. At this point the tank is jettisoned, it does not go into orbit. The orbiter then reaches orbit with its onboard propulsion system.
It is not likely that the orbiter propulsion would have enough capacity to carry the empty tank into orbit. If it did, as someone mentioned, the orbiter could not reenter and land safely with the tank still attached. .
The SRBs are attached to the External Tank.
The SRB's burn out and separate after about 2 minutes of burn. Each SRB has one forward and three aft attach bolts (in the struts). As noted above each of these bolts has redundant initiation. It seems that any SRB separation failure at any one of the eight attach points would result in a catastrophy similar to launch 51-L (Challenger). If the orbiter somehow survived the likely explosion they could separate and possibly return to KSC in one of the abort modes.
The liquid LN2 and LOX in the External Tank feeding the Orbiter Main engines is expended before reaching orbit. At this point the tank is jettisoned, it does not go into orbit. The orbiter then reaches orbit with its onboard propulsion system.
It is not likely that the orbiter propulsion would have enough capacity to carry the empty tank into orbit. If it did, as someone mentioned, the orbiter could not reenter and land safely with the tank still attached. .
There are a total of four pyrotechnic bolts holding each SRB to the external tank, one at the forward attach point and three at the aft.
http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/srb.html#srb-sep
Each bolt contains two pyrotechnic initiators. The Soyuz has had at least two failures of pyro bolts linking the descent and service modules. But US pyrotechnic separation mechanisms have been extremely reliable, not because the initiators are redundant, although this plays a role, but because their reliability is actually measured by the classical quality control method of continuous sampling and testing of a sufficient random sample of each production lot. This is a scientifically valid procedure and can achieve any desired level of accuracy. The design has, so far as I know, changed little in recent years but if a lot were found to have any defective units then the manufacturing procedure would be revised to ensure a 100% acceptance rate.
This is in striking contrast to figures such as the "reliability" of the Shuttle or Ares, which has no rigorous statistical basis. The reliability of the Ares, for example, is apparently based on the specification given in the program architecture requirements document. For that matter, the original 1 in 100,000 probabiity of failure of the Shuttle also appears to have originated in a specification rather than by actual testing of components.
Obviously the Shuttle was not as safe as predicted. However the loss-of-crew probability of the Shuttle is now given variously as somewhere between 1/77 and 1/129. Although these figures are fairly close to the historical reliability, this has little bearing on its current reliability, since 1) the failure modes which caused the loss of Challenger and Columbia were eliminated by design changes, and 2) the only consistent observation regarding launch vehicle reliability is that failure rates almost always decrease as the number of launches increase. The Launch Systems Architecture Study advocated using the SRB for the Ares on the basis of its perfect record since Challenger, completely discounting its role in the loss of 51-L itself. Yet the loss of 51-L is apparently used in the present LOC calculations for the Shuttle, as a pime rationale for killing the Shuttle program. Could these estimates be biased by the apparent desire of program management to get rid of the Shuttle? Considering the lack of statistical rigor across a wide spectrum of risk estimates, W. Edwards Deming, the father of quality control, would be aghast.
The Shuttle now has 129 launches, more than any other manned launch system, although of course the unmanned variants of the Soyuz have considerably more. If there is another failure mode that can cause the loss of a crew, it has not shown itself in 129 flights, so the best estimate of its future LOC rate is certainly less than 1/129.
Constellation supporters would likely say that the Orion is immune to staging pyro bolt failures because of the Launch Abort System, which, according to the "fail safe" philosophy, somewhat magically protects the crew against all failures. But consider this: Suppose the crew actually has time to initiate a LAS abort, and one of the pyro bolts holding the Orion to the service module fails to separate?
http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/srb.html#srb-sep
Each bolt contains two pyrotechnic initiators. The Soyuz has had at least two failures of pyro bolts linking the descent and service modules. But US pyrotechnic separation mechanisms have been extremely reliable, not because the initiators are redundant, although this plays a role, but because their reliability is actually measured by the classical quality control method of continuous sampling and testing of a sufficient random sample of each production lot. This is a scientifically valid procedure and can achieve any desired level of accuracy. The design has, so far as I know, changed little in recent years but if a lot were found to have any defective units then the manufacturing procedure would be revised to ensure a 100% acceptance rate.
This is in striking contrast to figures such as the "reliability" of the Shuttle or Ares, which has no rigorous statistical basis. The reliability of the Ares, for example, is apparently based on the specification given in the program architecture requirements document. For that matter, the original 1 in 100,000 probabiity of failure of the Shuttle also appears to have originated in a specification rather than by actual testing of components.
Obviously the Shuttle was not as safe as predicted. However the loss-of-crew probability of the Shuttle is now given variously as somewhere between 1/77 and 1/129. Although these figures are fairly close to the historical reliability, this has little bearing on its current reliability, since 1) the failure modes which caused the loss of Challenger and Columbia were eliminated by design changes, and 2) the only consistent observation regarding launch vehicle reliability is that failure rates almost always decrease as the number of launches increase. The Launch Systems Architecture Study advocated using the SRB for the Ares on the basis of its perfect record since Challenger, completely discounting its role in the loss of 51-L itself. Yet the loss of 51-L is apparently used in the present LOC calculations for the Shuttle, as a pime rationale for killing the Shuttle program. Could these estimates be biased by the apparent desire of program management to get rid of the Shuttle? Considering the lack of statistical rigor across a wide spectrum of risk estimates, W. Edwards Deming, the father of quality control, would be aghast.
The Shuttle now has 129 launches, more than any other manned launch system, although of course the unmanned variants of the Soyuz have considerably more. If there is another failure mode that can cause the loss of a crew, it has not shown itself in 129 flights, so the best estimate of its future LOC rate is certainly less than 1/129.
Constellation supporters would likely say that the Orion is immune to staging pyro bolt failures because of the Launch Abort System, which, according to the "fail safe" philosophy, somewhat magically protects the crew against all failures. But consider this: Suppose the crew actually has time to initiate a LAS abort, and one of the pyro bolts holding the Orion to the service module fails to separate?
Two things - I don't think that LAS is initiated by the crew. It is initiated automatically, otherwise it would be almost meaningless (but I guess that crew will also have the ability to initiate it?). And a kind of failure that doomed Challenger, should not result in LOC on Orion, since it was ET that exploded, not SRB.
I don't know specifically about Shuttle (which has complicated abort scenarios), but on other vehicles, there are typically three entities who can initiate an abort: the crew, mission control, and the on-board computers. In general, all three ought to be on the same page, though, in order to achieve the best results.
I wonder if a Soyuz crew can initiate an abort nowdays? They didn't used to have that ability -- aborts were initiated by either the onboard computers or by mission controllers. (And there *were* two operational aborts.)
I wonder if a Soyuz crew can initiate an abort nowdays? They didn't used to have that ability -- aborts were initiated by either the onboard computers or by mission controllers. (And there *were* two operational aborts.)
I believe the Air Force RSO (Range Safety Officer) also has that power.
IIRC, the Air Force operates the Eastern Range and is responsible for range safety involving all launches out of Cape Canaveral, KSC and Wallops Island.
I was kinda lumping them in under the rubric of "mission control". But yeah, and you're right -- they really operate under a separate chain of command from mission control.
CalliArcale":ezyti0pi said:
I can clear up some mis-understandings. There are 3 ET sep bolts one forward and one on each of the 2 aft attach points. The third strut in the aft does not connect to the Orbiter; it is just a diagonal strut between the 2 main aft struts.
If The SRBs failed to sep the Orbiter could not make it to any contingency landing site. They would have to shutdown the main engines and sep the ET with SRBs attached then bail out. If the SRBs did sep. but the ET did not sep (when comanded after the main engines cut off) the Orbiter could take itself to orbit and get to the ISS. They could then dock with the ISS and later set up the Orbiter for an unmanned un-docking and destructive re-entry with the ET attached.
The ET weight nearly empty unburned propellant weight is about 70,000 pounds. That weight is about 28% of the weight of the Orbiter and it's payload. By using the OMS engine propellant reserves and the propellant that was to be used for the re-entry burn they have enough prop. to get to the ISS. The reserve RCS and OMS prop temaining might be be enough to de-orbit the ET and the Orbiter combination. If not there would be enough prop to get it clear of the ISS.
The Shuttle crew on the ISS would be picked up by the Shuttle which has been processed as the Launch On Need (LON) Shuttle which has been the way we operate since the loss of Columbia.
EarthlingX":3ezg0djb said:Shuttle can bring empty ET to ISS ? Thought it couldn't .. Interesting
Do note that it would cost an Orbiter to do so; shuttle_guy indicated that it would require consuming the OMS propellant normally reserved for a safe deorbit. Rather an expensive way to bring an ET to the ISS, really.
EarthlingX":js7d072t said:
You can always reduce the amount of payload in payload bay if you want to bring ET to ISS and have enough fuel for safe deorbit. But what's the point? Empty ET won't be very useful for ISS and full shuttle payload capasity is very useful...
Not as it is, but if it were different, it might be useful. How different, how much different, is probably not this thread topic, but i guess, with some changes it could be used as, let say, extra fuel storage, or something else.Zipi":1y3h65q6 said:
It's a big thing and it is in orbit, it could be brought to ISS, if shuttle had de-orbit fuel, that is all.
I'm not suggesting to do it, as it is.
EarthlingX":20y9hdw3 said:
Two huge draw backs are the size, due to solar heating and the insulation flaking off creating a cloud of debris.
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