henry@utzoo.UUCP (Henry Spencer) (03/14/86)
Since nobody has been posting this stuff, and I suspect a lot of people
don't have easy access to Aviation Week and Space Technology, herewith
some info from recent issues.
The Feb 17 issue contains a full-page photo which just about resolves the
problem at a glance. It's yet another photo of the mess just after the
explosion, but this one is taken from a revealing angle. You can clearly
see that the starboard SRB is trailing a *second* plume of exhaust from
its side. Furthermore, on looking closely, the nose of that SRB is
damaged and its recovery chutes are falling out. This considerably
strengthens the theory that the bottom attachment point broke loose
and the top of the SRB pivoted into the tank; one would expect the
SRB nose to be damaged then.
The Feb 24 issue (the latest I have -- long propagation delays) has a
photo clearly showing the puff of black smoke just after liftoff.
It also mentions that the primary seal is normally pushed out of its
seat by a seal integrity test during booster assembly; it is pushed
back into place by motor pressure after ignition! The secondary seal
has to hold things together until the primary seal seats itself. But
at 0.6 seconds after ignition, deflection of the motor structure is
expected to unseat the secondary seal! If the primary seal is slow in
seating (e.g. because it's cold and stiff), and the secondary seal
unseats, you might well get a puff of black smoke, implying serious
erosion of the seals and burning of the grease and putty in the joint.
Then the primary seal would finally seat, sealing the joint... for
the moment, until the damaged primary seal wears down and the stresses
from wind shear and dynamic pressure flex the joint.
There are also some other tracking photos supporting various aspects
of the following timeline, mostly derived from telemetry (times are
in seconds from nominal launch):
0.0587 SRBs lit. Liftoff.
0.445 Black smoke at or near aft joint on right SRB.
12 Last black smoke. Roll maneuver underway.
20.084 Throttle-back begins.
40 Guidance reacts to a wind shear.
58.774 Black smoke again.
59 Maximum dynamic pressure.
59.249 Flame plume from side of right booster.
60.164 Right booster's internal pressure starts to diverge from that of
left booster. Flame plume growing.
62.484 Right outboard elevon commanded to move. Some main-engine gimballing
in next three seconds. These events probably due to winds rather
than to the booster failure.
66.174 Bright spots of fire on top (side nearest orbiter) of right booster.
Joint rupture spreading?
66.484 Liquid hydrogen pressure in external tank anomalous.
67.684 Pressure-change rate in liquid oxygen inlet altering. Possibly
result of completion of throttle-up.
72.141 Shit hits fan. Vehicle tugged to right at 0.227 G. Lower attach
point of right booster has failed?
72.201 Rate gyros on right booster indicate lower attach point failure,
lower end moving outward, upper end moving inward toward tank.
72.281 Rate gyros indicate outward motion of aft end of booster complicated
by "upward" motion towards orbiter. This would explain the charring
of the aft right portions of the orbiter. Booster may even have
struck, perhaps severed, the right wing.
72.661 Vehicle yawing to left, acceleration 0.254 G.
72.884 Inlet pressures to main engines dropping. Tank rupture by nose
of booster underway? Feed lines severed?
73.044 Right booster pressure down 24 psi below left booster. Data is
still coming because the data lines run through the upper attach
point, which is still intact.
73.175 Massive cloud of oxygen or hydrogen gas streaming aft along tank
from rupture caused by booster nose. [This is visible in one of
the photos AW&ST has printed.] Some gas at bottom of tank too;
tank starting to break up?
73.200 Flash of fire under nose of orbiter.
73.226 Powerful explosion near right forward booster attach point,
presumably due to propellants from ruptured tank mixing.
73.399 Massive disturbances in main-engine propellant flow. Hydrogen
turbopumps approach red-line limits. External tank exploding.
73.534 No. 1 main engine shuts down due to propellant-flow disturbances.
73.605 Telemetry stops.
--
Henry Spencer @ U of Toronto Zoology
{allegra,ihnp4,linus,decvax}!utzoo!henryjer@peora.UUCP (J. Eric Roskos) (03/19/86)
> 73.175 Massive cloud of oxygen or hydrogen gas streaming aft along tank > from rupture caused by booster nose. [This is visible in one of > the photos AW&ST has printed.] Some gas at bottom of tank too; > tank starting to break up? This raises a question which I had not mentioned in here previously, because of the requests not to have people "speculating"; but I still haven't seen any comment on it, and I am curious. In the original "NASA Select" photos made with the remote tracking camera (the one which shows the closeup of the shuttle), at the time that the visible vapors begin moving down parallel to the "bottom" surface of the external tank, it appears that a substantial structural failure also occurs at the aft end of the tank, near where the left SRB is attached. Specifically, it *appears* that a curved rectangular strip of the tank breaks away, allowing a very dense layer of vapors to come out the left side of the tank wall slightly ahead of the aft end of the tank. These vapors come out over the *external* surface of the rectangular strip I mentioned, suggesting that there is a gap in the wall of the tank at that point. (If some vapors had just appeared trailing from the aft end, you would have to try to see whether they were visible along the left side of the spherical bottom of the tank to be able to decide their general point of origin; but these clearly seem to come from the left side wall of the tank on the cylindrical part of the tank instead.) However, in all the published descriptions, all I've seen are statements that the *right* supporting strut breaks away. Are the supporting struts (or the sides of the tank) tied together structurally in such a way that the loads from the SRBs are balanced, such that when the right one came loose, it would cause the left one to pull the aft left side of the external tank off? -- E. Roskos
john@gcc-milo.ARPA (John Allred) (03/20/86)
In article <2036@peora.UUCP> jer@peora.UUCP (J. Eric Roskos) writes: >In the original "NASA Select" photos made with the remote tracking camera >(the one which shows the closeup of the shuttle), at the time that the >visible vapors begin moving down parallel to the "bottom" surface of the >external tank, it appears that a substantial structural failure also >occurs at the aft end of the tank, near where the left SRB is attached. >However, in all the published descriptions, all I've seen are statements >that the *right* supporting strut breaks away. Are the supporting struts >(or the sides of the tank) tied together structurally in such a way >that the loads from the SRBs are balanced, such that when the right one >came loose, it would cause the left one to pull the aft left side of the >external tank off? The terms 'left' and 'right' are relative. They assume that you are facing the top of the orbiter. The right SRB is the prime candidate for causing the destruction of the orbiter. Since the shuttle rolls over during ascent, the right SRB appears on the left side of the vehicle.-- John Allred General Computer Company uucp: seismo!harvard!gcc-milo!john
dbb@aicchi.UUCP (Burch) (03/26/86)
Hmmm... The time sequence sure gives lie to the "They didn't know what hit them." hypothesis, doesn't it? There is an interesting article on the cover of this week's EE Times... Their "expert" thinks it likely that the destruct charges of the flight safety system exacerbated the 51L problem. He points out the the flash point of the explosive used is only 350 F. -- -David B. (Ben) Burch Analyst's International Corp. Chicago Branch (ihnp4!aicchi!dbb) "Argue for your limitations, and they are yours"