karn@petrus.UUCP (Phil R. Karn) (02/19/86)
Recently there has been much discussion about the inherent complexity of
the Shuttle SRBs. I did a little reading on their nearest cousins, the
solid rocket boosters used on the Air Force Titan-IIIs, and found a couple
of interesting facts:
1. The Titan SRBs are segmented much like the Shuttle SRBs. The Titan III-C
uses five 10' segments, while the newer Titan 34D SRB uses "5 1/2 segments"
(5 10' segments plus one 5.8' segment). This is contrary to a comment
seen in the media where somebody said "you'd never see the military
use a solid rocket built like that" (referring to the segmented design).
2. I cannot find any indication in my references of a Titan SRB failure,
although they would not cover events in the past few years.
Titan III mission failures seem to have been dominated mostly by upper stage
failures, particularly the apparently notorious "transtage", which often
failed to re-ignite in a sequence of multiple burns.
3. The Titan SRB uses a very unusual Thrust Vector Control system. From
David Baker's book The Rocket:
"Flight control was maintained via a thrust-vector system that obviated
the need for flexible nozzle extensions to simulate the gimbal operation
used by liquid propellant engines. Nitrogen tetroxide was fed to the
base of the solid propellant motor and injected into the exhaust stream.
This had the effect of creating a shock wave which deflected the exhaust
plume by the desired amount. Commands from the guidance equipment would
dictate the precise amount of fluid injection necessary to change the
direction of flights; it was a principle that substituted the exhaust
vanes of early rockets with a working fluid."
This accounts for the little ("only" 4 tons worth of N2O4) tanks you see
strapped to the side of each SRB in a Titan-III.
I am puzzled by how this system operates. Also, if it works well, I'm curious
why it was not used in the Shuttle SRB. An Air Force publication I have
says the Titan SRB is capable of a vector angle of 5 degrees, very close
to the gimbaling capability of the Shuttle SRB. The movable nozzles on
the latter are very complex, and require elaborate provisions to protect
them from burn-through (which nearly occurred on STS-8).
Can anyone comment on this?
Phil Karnrjnoe@riccb.UUCP (Roger J. Noe) (02/22/86)
> 1. The Titan SRBs are segmented much like the Shuttle SRBs. The Titan III-C > uses five 10' segments, while the newer Titan 34D SRB uses "5 1/2 segments" > (5 10' segments plus one 5.8' segment). This is contrary to a comment > seen in the media where somebody said "you'd never see the military > use a solid rocket built like that" (referring to the segmented design). > > 2. I cannot find any indication in my references of a Titan SRB failure, > although they would not cover events in the past few years. > Titan III mission failures seem to have been dominated mostly by upper stage > failures, particularly the apparently notorious "transtage", which often > failed to re-ignite in a sequence of multiple burns. Yes, there was a 34D accident last summer or fall, I think it was. It was totally destroyed. That made it the first bad Titan accident in quite a long time. I think it remains as THE costliest space vehicle incident as far as impact on insurance goes. -- Roger Noe ihnp4!riccb!rjnoe