"Stephen Horgan" wrote in message
ups.com...
Ares 1 or the 'Stick' is based on the shuttle SRB. The grandfather of
manned space flight, Von Braun, was of the opinion that solid rockets
should not be used for personnel because they cannot be turned off when
ignited and they have a higher failure rate than liquid fuelled
equivalents. Of course the SRB has only failed once in STS operation,
but that was enough to cause the Challenger catastrophe.

Actually, you can install thurst termination systems on the SRB. The ones
installed on the shuttle unzipper the casing along the length.
Unfortunately this event would be extremely violent. So some here do say
that you can "turn off" the thrust of a large SRB, but I have no idea if the
CEV designers will design the CEV such that it could survive thrust
termination. The obvious way to do this would be to first fire the escape
tower, and then the thurst termination system.

Unfortunately, the Titan program showed us that there are failure modes of
large, segmented boosters that give little to no warning before the things
violently destroy themselves, so the above wouldn't necessarily help in all
cases.

So, does the use of the SRB for Ares make sense or not? Or are we
waiting on an accident in the future?

Possibly. Of greater significance is the fact that it will be a 5-segment
SRB instead of the 4-segment shuttle SRB that we have a lot of experience
with. Adding that fifth segment (with it's new fuel cross section and
thrust versus time curve) essentially makes it a new SRB.

Also, Aries I requires a roll control package for the SRB, and an all new
upper stage which uses an engine that while based on the venerable J-2 used
on the Saturns, was never fully developed. In other words, we have zero
flight experience with the upper stage and its engine.

Put all this together and the "safe, simple, soon" claims of ATK are clearly
marketing intended to hide the fact that this design has serious "image
problems" when it comes to safety, complexity (with its 5th segment and
upper stage this thing is a bit too long and slender which could cause
design challenges), and schedules.

Then there is the whole philosophy of keeping as much shuttle infrastructure
around as possible for Aries V. This added overhead won't make Aries I
inexpensive at the low flight rates expected.

EELV's are looking better to me every day.

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)