[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.

[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)	Event	Elapsed 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=O)	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	V9OR5301C
38:19.869	SSME 94% Command	19.859	E41M2076D
38:21.134	Roll maneuver completed	21.124	V9OR5301C
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	V9OR5301C
39:02.094	Peak TVC response to wind	62.084	B58H1150C
39:02.414	Peak yaw rate response to wind	62.404	V9OR5341C
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	V9OR5321C
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	V58HllOOA
39:05.174	Beginning of transient motion due to changes in aero forces due to plume	65.164	V9OR5321C
39:05.534	LH outboard elevon actuator delta pressure change	65.524	V58P0866C
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	V9OR2528C
39:12.294	Start divergent pitch rates (RH vs. LH SRB)	72.284	V9OR2525C
39:12.488	SRB major high-rate actuator command	72.478	V79H2111A
39:12.507	SSME roll gimbal rates 5 deg/sec	72.497	V58HllOOA
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	V41Pl lOOC
39:13.055	Vehicle max -Y lateral acceleration (-.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	73.137	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 along ET between intertank and aft dome	73.162	E207 Camera
39:13.201	Flash between Orbiter and 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	E41TnO1OD
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 reconstructed 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		MEC	- Main Engine Controller
APU	- Auxiliary Power Unit		MET	- Mission Elapsed Time
BET	- Best Estimated Trajectory		MPS	- Main Propulsion System
CH	- Channel		PC	- Chamber Pressure
DISC	- Discharge		PIC	- Pyrotechnics Initiator Controller
ET	- External Tank		psf	- Pounds per square foot
GG	- Gas Generator		RCS	- Reaction Control System
GPC	- General Purpose Computer		RGA	- Rate Gyro Assembly
GMT	- Greenwich Mean Time		RH	- Righthand
HPFT	- High Pressure Fuel Turbopump		RSS	- Range Safety System
LH	- Lefthand		SRB	- Solid Rocket Booster
LH2	- Liquid Hydrogen		SRM	- Solid Rocket Motor
LO2	- Liquid Oxygen		SSME	- Space Shuttle Main Engine
MAX Q	- Maximum Dynamic Pressure		TEMP	- Temperature
ME	- 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:

+ 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 leftwing tip)

+ Z direction = down

- Z direction = up

 

 

 

Shuttle to Ground Telemetry Channels

Channel Identifier	Sample Rate (Samples/sec)	Sample Period (sec)	Description
.
B47P1302C	12.5	.080	LH SRM CHAMBER PRESSURE
B47P2302C	12.5	.080	RH SRM CHAMBER PRESSURE
B58H1150C	25	.040	LH SRB TVC TILT ACT POS
B58H1151C	25	.040	LH SRB TVC ROCK ACT POS
E41M2076D	25	.040	ME-3 VEHICLE COMMAND
E41T1O1OD	25	.040	ME-1 HPFT DISC TEMP-CH A
E41T2010D	25	.040	ME-2 HPFT DISC TEMP-CH A
E41T3010D	25	.040	ME-3 HPFT DISC TEMP-CH A
T41P1700C	5	.200	ET LH2 ULLAGE PRESSURE
V41P11OOC	12.5	.080	MPS LH2 INLET PRESS (ME-1)
V41P1330C	12.5	.080	MPS LO2 INLET PRESS (ME-3)
V42P1552A	25	.040	RCS THRUSTER PC
V46P0120A	100	.010	APU-1 GG CHAMBER PRESS
V58H11OOA	25	.040	ME-PITCH ACTUATOR POS
V58P0866C	12.5	.080	LH OB ELEVON PRI DELTA P
V58P0966C	12.5	.080	RH OB ELEVON PRI DELTA P
V79H2111A	25	.040	LH SRB TILT ACT DRIVER
V90R2525C	5	.200	SEL LH SRB PITCH RATE
V90R2528C	5	.200	SEL RH SRB YAW RATE
V90R5301C	5	.200	SELECTED RGA ROLL RATE
V90R5321C	5	.200	SELECTED RGA PITCH RATE
V90R5341C	5	.200	SELECTED RGA YAW RATE
V95H3522C	12.5	.080	BODY YAW ATTITUDE ERROR
V95H3523C	12.5	.080	BODY ROLL ATTITUDE ERROR
V98A1581C	25	.040	LATERAL ACCELERATION