dpw@bonnie.UUCP (David Williams) (02/11/86)
My copy of Aviation Week arrived today - the coverage in this issue
focuses primarily on the SRB and its components as the mechanisms for
destruction of Challenger. The last issue was printed at a time when
very little information was available, so it gives broad coverage to
shuttle systems, the crew, history of the shuttle, and its future
prospects. I recommend these issues as sources for answers to many of
the questions that have been appeared on the net.
I can summarize some of the points that have caught my eye:
- The hot exhaust jet from a seam in the right SRB (~5500 deg. F)
destroyed the struts that attach the booster to the base of the
external tank. The SRB was then free to pivot on its upper
strut crushing into both the liquid hydrogen and oxygen tanks
causing the explosion that destroyed the vehicle. In a photo
taken shortly after the explosion (both SRBs visible), a plume
of smoke and flame can be seen in the vicinity of the lower joint
between casings on the right SRB. Also, a closeup reveals the
nose cone to have been ripped away and parachutes trailing from
the top of the booster (meaning that the right SRB was going to
hit the water hard in any event).
- NASA is focusing attention on the combination of joints, o-rings,
filler, and connectors between SRB segments to find a means for
gases to escape the motor casing. There are 2 o-rings circling
the casing in a grooved joint to seal against leaks. A heat-
resistant putty fills space between the first o-ring and the
interior of the casing. Steel pins (177) in two rows hold adjacent
casing segments together. Previous flights of SRBs have resulted
in gases charring and leaking past the first o-ring.
- NASA officials believe it will be at least 6 months and more like
9 - 12 months before flights will resume. Ulysses and Galileo will
be delayed until the next Jovian launch window.
- National Transportation Safety Board members who are surveying the
debris from Challenger are "surprised" at the amount of damage done
to the aft parts of the shuttle by the gases from the SRB rupture
prior to the explosion. The lower tail section remains show severe
heat damage. [My feeling: Challenger was damaged beyond
airworthiness within a second or two of the booster buring through.]
- Flight cronology (from telemetry and photos):
liftoff - 104% thrust on main engines, 3.3 million pounds of
thrust on each SRB
20 sec. - main engines throttle down, SRB thrust to 2.4 M pounds
40 sec. - Challenger encountered a wind shear, engines all pivot
to compensate (SRBs _are_ gimbaled)
50 sec. - SRB thrust increases to 2.7 M lbs. (the propellant is
tailored through shape, retardants, etc. to change thrust)
on the left booster _only_, beginning of leak in right SRB
59 sec. - photos show a 4' x 8' plume emerging from lower casing
of the right SRB
70 sec. - plume lengthens, right SRB thrust is 4% low
71 sec. - right SRB thrust is 100,000 lbs low and begins to affect
the flight trajectory, flight controls command main engines and
SRB nozzles to swivel to compensate,
the plume severs the SRB/external tank struts, the 17 inch
liquid oxygen line on the outside of the tank breaks due to
heat or stress, rate gyros on the SRB show it pivoting on its
forward attachment to the external tank rupturing the liquid
hydrogen and oxygen tanks
- NASA managers and astronauts were _sharply_ critical of acting
director Graham's statements that a survivable abort mode existed
for the crew while the SRBs were still attached. They state that
there is no survivable abort mode for the kind of failure that
Challenger encountered: the shuttle would pivot around its aft
umbilical connections with the effect of ripping the wings off and
initiating an explosion.
- The two SRBs on Challenger's flight were "high performance" boosters
designed for extra thrust through lighter casings and improved
propellant burning pattern. Investigators will examine the
possiblilty that the new burning patterns caused turbulence and
extreme pressure fluctuations at the gaps in propellant between
casing segments.
- The propellant in the SRBs is considered to be well insulated against
fluctuations in outside (launch pad) temperatures - analysis
indicates a temperature of 55 deg. F inside the SRBs.
David Williams
AT&T Bell Laboratories
Morristown
whuxl!dpwems@amdahl.UUCP (ems) (02/19/86)
In article <708@bonnie.UUCP>, dpw@bonnie.UUCP (David Williams) writes: > > My copy of Aviation Week arrived today - the coverage in this issue > focuses primarily on the SRB and its components as the mechanisms for > destruction of Challenger. ... > > - The two SRBs on Challenger's flight were "high performance" boosters > designed for extra thrust through lighter casings and improved > propellant burning pattern. Investigators will examine the > possiblilty that the new burning patterns caused turbulence and > extreme pressure fluctuations at the gaps in propellant between > casing segments. > > - The propellant in the SRBs is considered to be well insulated against > fluctuations in outside (launch pad) temperatures - analysis > indicates a temperature of 55 deg. F inside the SRBs. Hmmm, and yet the outer layers MUST have been cooler (due to their being in close contact with ice, cold wind, etc ...) What would be the effect on the boosters of having such a thermal gradient? With a warm inside and a cold skin, one is tempted to think that the inside would be compressed somewhat and the outside streched a bit; but would it matter? Would it change the risk of gaps and poor sealing between segments and/or O rings? -- E. Michael Smith ...!{hplabs,ihnp4,amd,nsc}!amdahl!ems This is the obligatory disclaimer of everything.
lmc@cisden.UUCP (Lyle McElhaney) (02/21/86)
> What would be the effect on the boosters of having such a thermal > gradient? With a warm inside and a cold skin, one is tempted to > think that the inside would be compressed somewhat and the outside > streched a bit; but would it matter? Would it change the risk > of gaps and poor sealing between segments and/or O rings? > Speculating (since I've not actually ever had anything actually to do with the SRB's) I would presume that shuttle management presumed that the combination of the insulation that lines the inside of the SRB casing and the physical properties of the fuel itself would prevent any physical misalignment. The fuel is imbedded in an epoxy base which is, I believe, somewhat plastic and flexible. Obviously, though, something did go wrong. Lyle McElhaney ...hao!cisden!lmc