Challenger Tragedy: Presidential Report Continued
The Challenger Accident
Just after liftoff at .678 seconds into the flight, photographic data
show a strong puff of gray smoke was spurting from the vicinity of the aft
field joint on the right Solid
Rocket Booster. The two pad 39B cameras that would have recorded the
precise location of the puff were inoperative. Computer graphic analysis
of film from other cameras indicated the initial smoke came from the 270
to 310-degree sector of the circumference of the aft field joint of the
right Solid Rocket Booster. This area of the solid booster faces the
External Tank. The vaporized material streaming from the joint indicated
there was not complete sealing action within the joint.
Eight more distinctive puffs of increasingly blacker smoke were
recorded between .836 and 2.500 seconds. The smoke appeared to puff
upwards from the joint. While each smoke puff was being left behind by the
upward flight of the Shuttle, the next fresh
puff could be seen near the level of the joint. The multiple smoke puffs
in this sequence occurred at about four times per second, approximating
the frequency of the structural load dynamics and resultant joint flexing.
Computer graphics applied to NASA photos from a variety of cameras in this
sequence again placed the smoke puffs' origin in the 270- to 310-degree
sector of the original smoke spurt.
As the Shuttle increased its upward velocity, it flew past the emerging
and expanding smoke puffs. The last smoke was seen above the field joint
at 2.733 seconds.
The black color and dense composition of the smoke puffs suggest that
the grease, joint insulation and rubber O-rings in the joint seal were
being burned and eroded by the hot propellant gases.
At approximately 37 seconds, Challenger encountered the first of
several high-altitude wind shear conditions, which lasted until about 64
seconds. The wind shear created forces on the vehicle with relatively
large fluctuations. These were immediately sensed and countered by the
guidance, navigation and control system.
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Signs of black smoke immediately
after liftoff of the Shuttle Challenger. |
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NASA photo |
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The steering system (thrust vector control) of the Solid Rocket Booster
responded to all commands and wind shear effects. The wind shear caused
the steering system to be more active than on any previous flight.
Both the Shuttle main engines and the solid rockets operated at reduced
thrust approaching and passing through the area of maximum dynamic
pressure of 720 pounds per square foot. Main engines had been throttled up
to 104 percent thrust and the Solid Rocket Boosters were increasing their
thrust when the first flickering flame appeared on the right Solid Rocket
Booster in the area of the aft field joint. This first very small flame
was detected on image enhanced film at 58.788 seconds into the flight. It
appeared to originate at about 305 degrees around the booster
circumference at or near the aft field joint.
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Image taken 59.249 seconds into
flight shows a well-defined intense plume on side of right hand
solid rocket booster. |
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NASA photo |
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One film frame later from the same camera, the flame was visible
without image enhancement. It grew into a continuous, well-defined plume
at 59.262 seconds. At about the same time (60 seconds), telemetry showed a
pressure differential between the chamber pressures in the right and left
boosters. The right booster chamber pressure was lower, confirming the
growing leak in the area of the field joint.
As the flame plume increased in size, it was deflected rearward by the
aerodynamic slipstream and circumferentially by the protruding structure
of the upper ring attaching the booster to the External Tank. These
deflections directed the flame plume onto the surface of the External
Tank. This sequence of flame spreading is confirmed by analysis of the
recovered wreckage. The growing flame also impinged on the strut attaching
the Solid Rocket Booster to the External Tank.
The first visual indication that swirling flame from the right Solid
Rocket Booster breached the External Tank was at 64.660 seconds when there
was an abrupt change in the shape and color of the plume. This indicated
that it was mixing with leaking hydrogen from the External Tank.
Telemetered changes in the hydrogen tank pressurization confirmed the
leak. Within 45 milliseconds of the breach of the External Tank, a bright
sustained glow developed on the black-tiled underside of the Challenger
between it and the External Tank.
Beginning at about 72 seconds, a series of events occurred extremely
rapidly that terminated the flight. Telemetered data indicate a wide
variety of flight system actions that support the visual evidence of the
photos as the Shuttle struggled futilely against the forces that were
destroying it.
At about 72.20 seconds the lower strut linking the Solid Rocket Booster
and the External Tank was severed or pulled away from the weakened
hydrogen tank permitting the right Solid Rocket Booster to rotate around
the upper attachment strut. This rotation is indicated by divergent yaw
and pitch rates between the left and right Solid Rocket Boosters.
At 73.124 seconds,. a circumferential white vapor pattern was observed
blooming from the side of the External Tank bottom dome. This was the
beginning of the structural failure of hydrogen tank that culminated in
the entire aft dome dropping away. This released massive amounts of liquid
hydrogen from the tank and created a sudden forward thrust of about 2.8
million pounds, pushing the hydrogen tank upward into the intertank
structure. At about the same time, the rotating right Solid Rocket Booster
impacted the intertank structure and the lower part of the liquid oxygen
tank. These structures failed at 73.137 seconds as evidenced by the white
vapors appearing in the intertank region.
Within milliseconds there was massive, almost explosive, burning of the
hydrogen streaming from the failed tank bottom and liquid oxygen breach in
the area of the intertank.
At this point in its trajectory, while traveling at a Mach number of
1.92 at an altitude of 46,000 feet, the Challenger was totally enveloped
in the explosive burn. The Challenger's reaction control system ruptured
and a hypergolic burn of its propellants occurred as it exited the
oxygen-hydrogen flames. The reddish brown colors of the hypergolic fuel
burn are visible on the edge of the main fireball. The Orbiter, under
severe aerodynamic loads, broke into several large sections which emerged
from the fireball. Separate sections that can be identified on film
include the main engine/tail section with the engines still burning, one
wing of the Orbiter, and the forward fuselage trailing a mass of umbilical
lines pulled loose from the payload bay.
Sequence of Major Events of the Challenger Accident
Mission Time Elapsed
(GMT, in hr:min:sec) Event Time (secs.) Source
16:37:53.444 ME-3 Ignition Command -6.566 GPC
37:53.564 ME-2 Ignition Command -6.446 GPC
37:53.684 ME-1 Ignition Command -6.326 GPC
38:00.010 SRM Ignition Command (T=0) 0.000 GPC
38:00.018 Holddown Post 2 PIC firing 0.008 E8 Camera
38:00.260 First Continuous Vertical Motion 0.250 E9 Camera
38:00.688 Confirmed smoke above field joint
on RH SRM 0.678 E60 Camera
38:00.846 Eight puffs of smoke (from 0.836
thru 2.500 sec MET) 0.836 E63 Camera
38:02.743 Last positive evidence of smoke
above right aft SRB/ET attach ring 2.733 CZR-1 Camera
38:03.385 Last positive visual indication
of smoke 3.375 E60 Camera
38:04.349 SSME 104% Command 4.339 E41M2076D
38:05.684 RH SRM pressure 11.8 psi above
nominal 5.674 B47P2302C
38:07.734 Roll maneuver initiated 7.724 V90R5301C
38:19.869 SSME 94% Command 19.859 E41M2076D
38:21.134 Roll maneuver completed 21.124 VP0R5301C
38:35.389 SSME 65% Command 35.379 E41M2076D
38:37.000 Roll and Yaw Attitude Response to
Wind (36.990 to 62.990 sec) 36.990 V95H352nC
38:51.870 SSME 104% Command 51.860 E41M2076D
38:58.798 First evidence of flame on RH SRM 58.788 E207 Camera
38:59.010 Reconstructed Max Q (720 psf) 59.000 BET
38:59.272 Continuous well defined plume
on RH SRM 59.262 E207 Camera
38:59.763 Flame from RH SRM in +Z direction
(seen from south side of vehicle) 59.753 E204 Camera
39:00.014 SRM pressure divergence (RH vs. LH) 60.004 B47P2302
39:00.248 First evidence of plume deflection,
intermittent 60.238 E207 Camera
39:00.258 First evidence of SRB plume
attaching to ET ring frame 60.248 E203 Camera
39:00.998 First evidence of plume deflection,
continuous 60.988 E207 Camera
39:01.734 Peak roll rate response to wind 61.724 V90R5301C
39:02.094 Peak TVC response to wind 62.084 B58H1150C
39:02.414 Peak yaw response to wind 62.404 V90R5341C
39:02.494 RH outboard elevon actuator hinge
moment spike 62.484 V58P0966C
39:03.934 RH outboard elevon actuator delta
pressure change 63.924 V58P0966C
39:03.974 Start of planned pitch rate
maneuver 63.964 V90R5321C
39:04.670 Change in anomalous plume shape
(LH2 tank leak near 2058 ring
frame) 64.660 E204 Camera
39:04.715 Bright sustained glow on sides
of ET 64.705 E204 Camera
39:04.947 Start SSME gimbal angle large
pitch variations 64.937 V58H1100A
39:05.174 Beginning of transient motion due
to changes in aero forces due to
plume 65.164 V90R5321C
39:06.774 Start ET LH2 ullage pressure
deviations 66.764 T41P1700C
39:12.214 Start divergent yaw rates
(RH vs. LH SRB) 72.204 V90R2528C
39:12.294 Start divergent pitch rates
(RH vs. LH SRB) 72.284 V90R2525C
39:12.488 SRB major high-rate actuator
command 72.478 V79H2111A
39:12.507 SSME roll gimball rates 5 deg/sec 72.497 V58H1100A
39:12.535 Vehicle max +Y lateral
acceleration (+.227 g) 72.525 V98A1581C
39:12.574 SRB major high-rate actuator
motion 72.564 B58H1151C
39:12.574 Start of H2 tank pressure decrease
with 2 flow control valves open 72.564 T41P1700C
39:12.634 Last state vector downlinked 72.624 Data reduction
39:12.974 Start of sharp MPS LOX inlet
pressure drop 72.964 V41P1330C
39:13.020 Last full computer frame of TDRS
data 73.010 Data reduction
39:13.054 Start of sharp MPS LH2 inlet
pressure drop 73.044 V41P1100C
39:13.055 Vehicle max -Y lateral
accelerarion (-.254 g) 73.045 V98A1581C
39:13.134 Circumferential white pattern on
ET aft dome (LH2 tank failure) 73.124 E204 Camera
39:13.134 RH SRM pressure 19 psi lower
than LH SRM 73.124 B47P2302C
39:13.147 First hint of vapor at intertank E207 Camera
39:13.153 All engine systems start responding
to loss of fuel and LOX inlet
pressure 73.143 SSME team
39:13.172 Sudden cloud a long ET between
intertank and aft dome 73.162 E207 Camera
39:13.201 Flash between Orbiter & LH2 tank 73.191 E204 Camera
39:13.221 SSME telemetry data interference
from 73.211 to 73.303 73.211
39:13.223 Flash near SRB fwd attach and
brightening of flash between
Orbiter and ET 73.213 E204 Camera
39:13.292 First indication intense white
flash at SRB fwd attach point 73.282 E204 Camera
39:13.337 Greatly increased intensity of
white flash 73.327 E204 Camera
39:13.387 Start RCS jet chamber pressure
fluctuations 73.377 V42P1552A
39:13.393 All engines approaching HPFT
discharge temp redline limits 73.383 E41Tn010D
39:13.492 ME-2 HPFT disch. temp Chan. A vote
for shutdown; 2 strikes on Chan. B 73.482 MEC data
39:13.492 ME-2 controller last time word
update 73.482 MEC data
39:13.513 ME-3 in shutdown due to HPFT discharge
temperature redline exceedance 73.503 MEC data
39:13.513 ME-3 controller last time word
update 73.503 MEC data
39:13.533 ME-1 in shutdown due to HPFT discharge
temperature redline exceedance 73.523 Calculation
39:13.553 ME-1 last telemetered data point 73.543 Calculation
39:13.628 Last validated Orbiter telemetry
measurement 73.618 V46P0120A
39:13.641 End of last reconstructured data
frame with valid synchronization
and frame count 73.631 Data reduction
39:14.140 Last radio frequency signal from
Orbiter 74.130 Data reduction
39:14.597 Bright flash in vicinity of Orbiter
nose 74.587 E204 Camera
39:16.447 RH SRB nose cap sep/chute
deployment 76.437 E207 Camera
39:50.260 RH SRB RSS destruct 110.250 E202 Camera
39:50.262 LH SRB RSS destruct 110.252 E230 Camera
ACT POS -- Actuator Position
APU -- Auxilixary Power Unit
BET -- Best Estimated Trajectory
CH -- Channel
DISC -- Discharge
ET -- External Tank
GG -- Gas Generator
GPC -- General Purpose Computer
GMT -- Greenwich Mean Time
HPFT -- High Pressure Fuel Turbopump
LH -- Lefthand
LH2 -- Liquid Hydrogen
LO2 -- Liquid Oxygen (same as LOX)
MAX Q -- Maximum Dynamic Pressure
ME -- Main Engine (same as SSME)
MEC -- Main Engine Controller
MET -- Mission Elapsed Time
MPS -- Main Propulsion System
PC -- Chamber Pressure
PIC -- Pyrotechnics Initiator Controller
psf -- Pounds per square foot
RCS -- Reaction Control System
RGA -- Rate Gyro Assembly
RH -- Righthand
RSS -- Range Safety System
SRM -- Solid Rocket Motor
SSME -- Space Shuttle Main Engine
TEMP -- Temperature
TVC -- Thrust Vector Control
NOTE: The Shuttle coordinate system used is relative to the Orbiter,
as follows:
+X direction = forward (tail to nose)
-X direction = rearward (nose to tail)
+Y direction = right (toward the right wing tip)
-Y direction = left (toward the left wing tip)
+Z direction = down
-Z direction = up
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Source: NASA. |
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