On Wednesday, May 28, 2003, at 12:41 AM, David Weinshenker wrote:
IMHO, arguing about abort modes is way premature until you understand the credible failure modes. It's hard to make intelligent engineering decisions about _how_ to abort if you're just guessing as to why you may want to do so.
Good point.
A "single dead engine" failure, with everything else still working perfectly, seems to be taken as the "expected emergency" in many of these discussions: is that really the most likely problem motivating an abort? In other words, do we genuinely believe that combustion is temperamental, but control systems are reliable?
I don't think it's an issue of combustion being temperamental so much as the fact that the valves and throttling hardware are moving parts, hence more likely to fail than non moving parts. The times when they are most likely to fail are right at startup and at shutdown, so the total failure at 100m on liftoff scenario is unlikely. More likely is failure on the pad, or more worrisome for VTVL advocates, failure to relight for landing.
It's worth noting that XCOR's only engine failure during vehicle operation was during an attempt to shut down.
The control system issue is vital, but hard. Much easier to talk about engines :-) The obvious way to deal with possible failures is redundancy, but it's not clear to me how to do redundancy properly in control systems. I'd be very interested if anyone has pointers to good information on the subject.
......Andrew
-- Dr. Andrew Case, PhD. Institute for Research in Electronics and Applied Physics, University of Maryland, College Park "It is seldom that liberty of any kind is lost all at once." - David Hume
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