---

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[19] Flight of the Space

Shuttle Challenger on Mission 51-L began at 11:38 a.m. Eastern

Standard Time on January 28, 1986. It ended 73 seconds later in an

explosive burn of hydrogen and oxygen propellants that destroyed the

External Tank and exposed the Orbiter to severe aerodynamic loads

that caused complete structural breakup. All seven crew members

perished. The two Solid Rocket Boosters flew out of the fireball and

were destroyed by the Air Force range safety officer 110 seconds

after launch.

The ambient air temperature at launch was 36

degrees Fahrenheit measured at ground level approximately 1,000 feet

from the 51-L mission launch pad 39B. This temperature was 15 degrees

colder than that of any previous launch.

The following description of the flight events

is based on visual examination and image enhancement of film from

NASA operated cameras and telemetry data transmitted from the Space

Shuttle to ground stations. The last telemetry data from the

Challenger was received 73.618 seconds after launch.

At 6.6 seconds before launch, the Challenger's

liquid fueled main engines were ignited in sequence and run up to

full thrust while the entire Shuttle structure was bolted to the

launch pad. Thrust of the main engines bends the Shuttle assembly

forward from the bolts anchoring it to the pad. When the Shuttle

assembly springs back to the vertical, the Solid Rocket Boosters'

restraining bolts are explosively released. During this prerelease

"twang" motion, structural loads are stored in the assembled

structure. These loads are released during the first few seconds of

flight in a structural vibration mode at a frequency of about 3

cycles per second. The maximum structural loads on the aft field

joints of the Solid Rocket Boosters occur during the "twang,"

exceeding even those of the maximum dynamic pressure period

experienced later in flight.

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. At 3.375 seconds the

last [20] smoke was visible below the Solid Rocket Boosters and

became indiscernible as it mixed with rocket plumes and surrounding

atmosphere.

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.

Launch sequence films from previous missions

were examined in detail to determine if there were any prior

indications of smoke of the color and composition that appeared

during the first few seconds of the 51-L mission. None were found.

Other vapors in this area were determined to be melting frost from

the bottom of the External Tank or steam from the rocket exhaust in

the pad's sound suppression water trays.

Shuttle main engines were throttled up to 104

percent of their rated thrust level, the Challenger executed a

programmed roll maneuver and the engines were throttled back to 94

percent.

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. Although flight 51-L loads exceeded prior experience

in both yaw and pitch planes at certain instants, the maxima had been

encountered on previous flights and were within design limits.

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.

At 45 seconds into the flight, three bright

flashes appeared downstream of the Challenger's right wing. Each

flash lasted less than one-thirtieth of' a second. Similar flashes

have been seen on other flights. Another appearance of a separate

bright spot was diagnosed by film analysis to be a reflection of main

engine exhaust on the Orbital Maneuvering System pods located at the

upper rear section of the Orbiter. The flashes were unrelated to the

later appearance of the flame plume from the right Solid Rocket

Booster.

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.

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.

At about 62 seconds into the flight, the

control system began to react to counter the forces caused by the

plume and its effects. The left Solid Rocket Booster thrust vector

control moved to counter the yaw caused by reduced thrust from the

leaking right Solid Rocket Booster. During the next nine seconds,

Space Shuttle control systems worked to correct anomalies in pitch

and yaw rates.

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 [21] 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

the 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.~3 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 the 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,O00 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.

Evidence in the recovered wreckage from the

51-L mission hardware supports this final sequence of events.







| | [22-23]

         Immediately after solid rocket motor ignition, dark smoke

         (arrows) swirled out between the right hand booster and the

         External Tank. The smoke's origin, behavior and duration was

         approximated by visual analysis and computer enhancement of

         film from five camera locations. Consensus: smoke was first

         discernible at .678 seconds Mission Elapsed Time in the

         vicinity of the right booster's aft field joint. | 
| | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 





| | [24-25] Multiple

         smoke puffs are visible in the photo above (arrows). They

         began at .836 seconds and continued through 2.500 seconds,

         occurring about 4 times a second. Upward motion of the

         vehicle caused the smoke to drift downward and blur into a

         single cloud. Smoke source is shown in the computer

         generated drawing (far right). | 
| | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | 





|[26-27]                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|At 58.788 seconds, the first

         flicker of flame appeared. Barely visible above, it grew

         into a large plume and began to impinge on the External Tank

         at about 60 seconds. Flame is pinpointed in the computer

         drawing between the right booster and the tank, as in the

         case of earlier smoke puffs. At far right (arrow), vapor is

         seen escaping from the apparently breached External

         Tank.





|[28-29]                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|Camera views indicate the

         beginning of rupture of the liquid hydrogen and liquid

         oxygen tanks within the External Tank. A small flash (arrows

         above) intensified rapidly, then diminished. A second flash,

         attributed to rupture of the liquid oxygen tank, occurred

         above the booster/tank forward attachment (below left) and

         grew in milliseconds to the maximum size indicated in the

         computer drawing.
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 





| | [30-31]

         Structural breakup of the vehicle began at approximately 73

         seconds. Fire spread very rapidly. Above [left], a bright

         flash (arrow) is evident near the nose the Orbiter,

         suggesting spillage and ignition of the spacecraft's

         reaction control system propellants. At left, the two Solid

         Rocket Boosters thrust away from the fire, crisscrossing to

         from a "V". The right booster- identifiable by its failure

         plume- now to the left of its counterpart. At right, the

         boosters diverge farther; the External Tank wreckage is

         obscured by smoke and vapor. The Orbiter engines still

         firing, is visible at bottom center. | 
| | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 





| | [32-33] At about

         76 seconds, unidentifiable fragments of the Shuttle vehicle

         can be seen tumbling against a background of fire, smoke and

         vaporized propellants from the External Tank (left). In the

         photo at right, the left booster (far right) soars away,

         still thrusting. The reddish-brown cloud envelops the

         disintegrating Orbiter. The color is characteristic of the

         nitrogen tetroxide oxidizer in the Orbiter Reaction Control

         System propellant. | 
| | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | 





|[34-35]                                                                                                                                                                                                                                                                                                                   
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|Hurtling out of the fireball

         at 78 seconds (left) are the Orbiter's left wing (top

         arrow), the main engines (center arrow) and the forward

         fuselage (bottom arrow). In the photo below [bottom right],

         it plummets Earthward, trailed by smoking fragments of

         Challenger





|[36]                                                                                                                                                                                                                                                                                                            
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|At 11:44 a.m. Eastern

         Standard Time, a GOES environment-monitoring satellite

         operated by the National Oceanic and Atmospheric

         Administration acquired this image of the smoke and vapor

         cloud from the 51-L accident. The coast of Florida is

         outlined in red.

---

[37-39]STS 51-L Sequence of Major Events

Mission Time

            

            (GMT, in

            hr:min:sec)EventElapsed Time

            (secs.)Source.16:37:53.444ME - 3 Ignition

         Command- 6.566GPC37:53.564ME - 2 Ignition

         Command- 6.446GPC37:53.684ME - 1 Ignition

         Command- 6.326GPC38:00.010SRM Ignition Command

         (T=O)0.000GPC38:00.018Holddown Post 2 PIC

         firing0.008E8 Camera38:00.260First Continuous Vertical

         Motion0.250E9 Camera38:00.688Confirmed smoke above field

         joint on RH SRM0.678E60 Camera38:00.846Eight puffs of smoke (from

         0.836 thru 2.500 sec MET)0.836E63 Camera38:02.743Last positive evidence of

         smoke above right aft SRB/ET attach ring2.733CZR-1 Camera38:03.385Last positive visual

         indication of smoke3.375E60 Camera38:04.349SSME 104% Command4.339E41M2076D38:05.684RH SRM pressure 11.8 psi

         above nominal5.674B47P2302C38:07.734Roll maneuver

         initiated7.724V9OR5301C38:19.869SSME 94% Command19.859E41M2076D38:21.134Roll maneuver

         completed21.124V9OR5301C38:35.389SSME 65% Command35.379E41M2076D38:37.000Roll and Yaw Attitude

         Response to Wind (36.990 to 62.990 sec)36.990V95H352nC38:51.870SSME 104% Command51.860E41M2076D38:58.798First evidence of flame on

         RH SRM58.788E207 Camera38:59.010Reconstructed Max Q (720

         psf)59.000BET38:59.272Continuous well defined

         plume on RH SRM59.262E207 Camera38: 59.763Flame from RH SRM in + Z

         direction (seen from south side of vehicle)59.753E204 Camera39:00.014SRM pressure divergence (RH

         vs. LH)60.004B47P230239:00.248First evidence of plume

         deflection, intermittent60.238E207 Camera39:00.258First evidence of SRB plume

         attaching to ET ring frame60.248E203 Camera39:00.998First evidence of plume

         deflection, continuous60.988E207 Camera39:01.734Peak roll rate response to

         wind61.724V9OR5301C39:02.094Peak TVC response to

         wind62.084B58H1150C39:02.414Peak yaw rate response to

         wind62.404V9OR5341C39:02.494RH outboard elevon actuator

         hinge moment spike62.484V58P0966C39:03.934RH outboard elevon actuator

         delta pressure change63.924V58P0966C39:03.974Start of planned pitch rate

         maneuver63.964V9OR5321C39:04.670Change in anomalous plume

         shape (LH2 tank leak near 2058 ring frame)64.660E204 Camera39:04.715Bright sustained glow on

         sides of ET64.705E204 Camera39:04.947Start SSME gimbal angle

         large pitch variations64.937V58HllOOA39:05.174Beginning of transient

         motion due to changes in aero forces due to plume65.164V9OR5321C39:05.534LH outboard elevon actuator

         delta pressure change65.524V58P0866C39:06.774Start ET

         LH2ullage pressure deviations66.764T41P1700C39:12.214Start divergent yaw rates

         (RH vs. LH SRB)72.204V9OR2528C39:12.294Start divergent pitch rates

         (RH vs. LH SRB)72.284V9OR2525C39:12.488SRB major high-rate

         actuator command72.478V79H2111A39:12.507SSME roll gimbal rates 5

         deg/sec72.497V58HllOOA39:12.535Vehicle max + Y lateral

         acceleration ( + .227 g)72.525V98A1581C39:12.574SRB major high-rate

         actuator motion72.564B58H1151C39:12.574Start of H2 tank pressure

         decrease with 2 flow control valves open72.564T41P1700C39:12.634Last state vector

         downlinked72.624Data reduction39:12.974Start of sharp MPS LOX

         inlet pressure drop72.964V41P1330C39:13.020Last full computer frame of

         TDRS data73.010Data reduction39:13.054Start of sharp MPS

         LH2inlet pressure drop73.044V41Pl lOOC39:13.055Vehicle max -Y lateral

         acceleration (-.254 g)73.045V98A1581C39:13.134Circumferential white

         pattern on ET aft dome (LH2 tank failure)73.124E204 Camera39:13.134RH SRM pressure 19 psi

         lower than LH SRM73.124B47P2302C39:13.147First hint of vapor at

         intertank73.137E207 Camera39:13.153All engine systems start

         responding to loss of fuel and LOX inlet pressure73.143SSME team39:13.172Sudden cloud along ET

         between intertank and aft dome73.162E207 Camera39:13.201Flash between Orbiter and

         LH2tank73.191E204 Camera39:13.221SSME telemetry data

         interference from 73.211 to 73.30373.211.39:13.223Flash near SRB fwd attach

         and brightening of flash between Orbiter and ET73.213E204 Camera39:13.292First indication intense

         white flash at SRB fwd attach point73.282E204 Camera39:13.337Greatly increased intensity

         of white flash73.327E204 Camera39:13.387Start RCS jet chamber

         pressure fluctuations73.377V42P1552A39:13.393All engines approaching

         HPFT discharge temp redline limits73.383E41TnO1OD39:13.492ME-2 HPFT disch. temp Chan.

         A vote for shutdown; 2 strikes on Chan. B73.482MEC data39:13.492ME-2 controller last time

         word update73.482MEC data39: 13.513ME-3 in shutdown due to

         HPFT discharge temperature redline exceedance73.503MEC data39:13.513ME-3 controller last time

         word update73.503MEC data39:13.533ME-1 in shutdown due to

         HPFT discharge temperature redline exceedance73.523Calculation39:13.553ME-1 last telemetered data

         point73.543Calculation39:13.628Last validated Orbiter

         telemetry measurement73.618V46P0120A39:13.641End of last reconstructed

         data frame with valid synchronization and frame count73.631Data reduction39:14.140Last radio frequency signal

         from Orbiter74.130Data reduction39:14.597Bright flash in vicinity of

         Orbiter nose74.587E204 Camera39:16.447RH SRB nose cap sep/chute

         deployment76.437E207 Camera39:50.260RH SRB RSS destruct110.250E202 Camera39:50.262LH SRB RSS destruct110.252E230 Camera

ACT POS- Actuator PositionMEC- Main Engine

         ControllerAPU- Auxiliary Power

         UnitMET- Mission Elapsed

         TimeBET- Best Estimated

         TrajectoryMPS- Main Propulsion

         SystemCH- ChannelPC- Chamber PressureDISC- DischargePIC- Pyrotechnics Initiator

         ControllerET- External Tankpsf- Pounds per square

         footGG- Gas GeneratorRCS- Reaction Control

         SystemGPC- General Purpose

         ComputerRGA- Rate Gyro AssemblyGMT- Greenwich Mean

         TimeRH- RighthandHPFT- High Pressure Fuel

         TurbopumpRSS- Range Safety

         SystemLH- LefthandSRB- Solid Rocket

         BoosterLH2- Liquid HydrogenSRM- Solid Rocket MotorLO2- Liquid OxygenSSME- Space Shuttle Main

         EngineMAX Q- Maximum Dynamic

         PressureTEMP- TemperatureME- Main Engine (same as

         SSME)TVC- Thrust Vector

         Control

Note: The shuttle coordinate system used in

Chapter 2 is, relative to the Orbiter, as follows:

Shuttle to Ground Telemetry

Channels



Channel

            IdentifierSample Rate

            

            (Samples/sec)Sample Period

            

            (sec)Description.B47P1302C12.5.080LH SRM CHAMBER

         PRESSUREB47P2302C12.5.080RH SRM CHAMBER

         PRESSUREB58H1150C25.040LH SRB TVC TILT ACT

         POSB58H1151C25.040LH SRB TVC ROCK ACT

         POSE41M2076D25.040ME-3 VEHICLE COMMANDE41T1O1OD25.040ME-1 HPFT DISC TEMP-CH

         AE41T2010D25.040ME-2 HPFT DISC TEMP-CH

         AE41T3010D25.040ME-3 HPFT DISC TEMP-CH

         AT41P1700C5.200ET LH2 ULLAGE

         PRESSUREV41P11OOC12.5.080MPS LH2 INLET PRESS

         (ME-1)V41P1330C12.5.080MPS LO2 INLET PRESS

         (ME-3)V42P1552A25.040RCS THRUSTER PCV46P0120A100.010APU-1 GG CHAMBER

         PRESSV58H11OOA25.040ME-PITCH ACTUATOR

         POSV58P0866C12.5.080LH OB ELEVON PRI DELTA

         PV58P0966C12.5.080RH OB ELEVON PRI DELTA

         PV79H2111A25.040LH SRB TILT ACT

         DRIVERV90R2525C5.200SEL LH SRB PITCH

         RATEV90R2528C5.200SEL RH SRB YAW RATEV90R5301C5.200SELECTED RGA ROLL

         RATEV90R5321C5.200SELECTED RGA PITCH

         RATEV90R5341C5.200SELECTED RGA YAW

         RATEV95H3522C12.5.080BODY YAW ATTITUDE

         ERRORV95H3523C12.5.080BODY ROLL ATTITUDE

         ERRORV98A1581C25.040LATERAL ACCELERATION