fisher@star.DEC (Burns Fisher ZKO1-1/D42 DTN 381-1466) (01/31/86)
>>Am I correct in my understanding that, >>under less catastrophic conditions, the SRBs are capable of >>independent guidance, at least to keep them clear of the orbiter >after jettisoning following burnout or during an abort? > >I would be surprised if the SRBs were capable of independent guidance. >They have no control surfaces, and I doubt the SRB nozzles are on gimbals >like those of the main engines. At burnout explosive bolts separate the >SRBs from the rest of the orbiter which continues to accelerate away >on its main engines. I'll admit I don't know the cause for the smooth >peeling away of the SRBs following burnout. Maybe the top bolts blow >first, and the aerodynamics do the rest. > I don't know if the SRBs recovery aids (chutes, etc) are autonomous, but I do know a few other relavent things. First, they CAN NOT steer themselves after the separate. You are right there are no control surfaces. However, they do have steerable nozzles, complete with hydraulic power systems to run them. Of course that does not help much after they are burned out. In addition, that steering is commanded by the orbiter computers. No orbiter, no steering. When the SRBs separate, there are some "small" (only by comparison) engines that burn to push them away from the shuttle. If you happen to have one of the large photos of Columbia on the pad by Impact photography, you will notice some yellow covers on the SRBs near the top. I believe those are where the separation engines are. (The yellow covers are removed for flight.) >During an abort I suspect the orbiter must be flown away from the >tank/SRB assembly. Does anyone know if there is a small fuel >reserve within the orbiter for such an occasion? The main situations that aborts are supposed to cover are cases where the main engines shut down (one or more). If this happens early in the flight and a return-to-launch-site abort is commanded, the solids burn completely before they separate, although the do change the orientation so as to slow the shuttle back down. After the SRBs separate, the remaining main engines (fueled by the ET) are used to get the vehicle into an energy state from which it can glide back to the runway. Then the engines shut down and the tank separates. The orbiter has NO, 0, rien fuel reserve to burn the main engines with after the ET is gone. They do have the regular on-orbit engines, of course. Of marginal use when not in orbit. Finally, there is (or was at the time of the first flight, at least) a "contingency" abort mode in which the shuttle is separated from the ET/SRB assembly before the SRBs finish firing. The chances of surviving such an abort were thought to be only marginally better than riding out whatever emergency it was designed for. I guess at this point, marginally would have been a whole heck of a lot better than what happened. Burns ...decwrl!rhea!star!fisher