Re: Thoughts on VSE Launch Vehicles

George William Herbert wrote:
>
> There has been far more than just one single spectacular failure
> of a solid booster in recent history. Just off the top of my head....
>
> Jan 17, 1997: GEM on a Delta 7925 suffers catastrophic case
> failure and the vehicle explodes shortly after liftoff
> at the Cape.
>
> Aug 2, 1993: Titan IV SRM suffers propellent grain failure
> and explosion 101 sec after liftoff from Vandenberg.
>
> Apr 18, 1986: Titan 34D SRM suffers case burnthrough and
> catastrophic failure and explosion 8.5 sec after liftoff
> from Vandenberg.
>
> And then there was the Titan IV SRMU pad explosion we're
> talking about on April 1, 1991, where the booster blew
> up its test pad and the mountain side in a qualification
> (non-flight) test.
>
> And, of course, Challenger, and 11 other non-fatal
> joint/seal/O-ring failures in prior Shuttle flights...

The April 1 ATK-SAIC reliability study
"http://www.boom.net/~jake/atk_ docs/ATK_Thiokol_SRB.J_2S_PRA. pdf"
implies that most of these incidents could have been
survivable because they did not involve propellant
detonation, but case burst with propellant dispersal.
A CEV might be able to survive the pressure waves
produced by these incidents, at least according to
some smart guys at SAIC who will never have to ride
atop an SRB. They predicted that only 1 out of
3,145 crews launched by an SRB/J2S equipped with an
effective escape system would be lost.

Personally, I don't trust this probabilistic risk
assessment stuff, because it always seems to
underestimate the real risks. SAIC says that SRB
failures of all types will happen only about one
time in every 3,000 launches. I think that most
engineers who have been around these machines for
any length of time would say that this one in
3,000 stuff is bonafide hogwash.

I think that the only safe assumption to make is
that SRBs will fail in the future roughly as often
as they have failed in the past - something like
one failure in every 200 to 250 SRB burns. But
some of these failures are going to be survivable.
The big question is how many. If three out of
four are survivable, then the SRB loss of crew
probability could approach 1 in 1,000.

But then there is the upper stage to worry about,
and staging events, etc. Not all upper stage
failures, even benign early shutdowns, are
survivable. Crews could survive the initial event,
only to be lost during or after their descent. My
guess is that upper stage failure survival rates
are going to be only somewhat better than SRB rates.
The net result would be a total launch vehicle loss
of crew probability of something better than
1 in 500.

This doesn't sound superior, but I think that an
EELV, when you consider that it has more complex
components and more components altogether so that
the base failure rate is higher than SRB, would
provide roughly the same crew survival results.

- Ed Kyle

.

Relevant Pages

  • Re: GRIFFINS DRIVE FOR SHUTTLE-DERIVED
    ... redesigned SRB. ... > like the Shuttle is, not only is the "twang" eliminated, but the CEV can ... > to fail, and do this in a totally automated fast-response way if the SRB ... Depends on the failure mode of the SRB. ...
    (sci.space.policy)
  • Re: Second Guessing NASA VSE
    ... Compared to the in flight SSME failure rate? ... If a SRB burn through results in a roll torque, ... force the use of the CEV escape system before the roll becomes excessive. ...
    (sci.space.policy)
  • Re: GRIFFINS DRIVE FOR SHUTTLE-DERIVED
    ... it' has a very low potential failure rate. ... > 176 separate SRB operational firings with no SRB failures. ... The recent SAIC report says the PLOC (probable loss of crew) is 100% ... "SRB-Control" failure (i.e. the steerable nozzle fails). ...
    (sci.space.policy)
  • Re: Second Guessing NASA VSE
    ... Compared to the in flight SSME failure rate? ... burn through resulting in failure of the core stage causing loss of a ... NASA originally was worried about foam after a debris hit on an SRB ...
    (sci.space.policy)
  • Re: GRIFFINS DRIVE FOR SHUTTLE-DERIVED
    ... you could introduce the Titan III SRB Dyna-Soar/MOL fuel ... Take a look at Figure 1.4 Conditional Probability of Loss of Crew Risk, ... Even ATK acknowledges that there *are* failure modes for an SRB with upper ... rare occasions that it will fail, it will fail less gracefully than one ...
    (sci.space.policy)