STS-51-L Mission timeline

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STS-51-L Mission patch.

STS-51-L Mission timeline is a detailed timeline of events from the ignition of Challenger's main engines to the remote destruction of the two solid rocket boosters, and includes a transcript of crew conversations from the cockpit voice recorder on board the Orbiter.

STS-51-L was the twenty-fifth flight in the American Space Shuttle program, and marked the first time a civilian had flown aboard the Space Shuttle. The mission used Space Shuttle Challenger, which lifted off from launch pad 39B on January 28, 1986, from Kennedy Space Center, Florida. The mission ended in disaster following the destruction of Challenger 73 seconds after lift-off, because of the failure of an O-ring seal on Challenger's right solid rocket booster, which led to the rapid disintegration of the shuttle stack from overwhelming aerodynamic pressures. The seven-member crew was killed sometime after the breakup of the vehicle.

Summary timeline[edit]

Space Shuttle Challenger lifts off on her final mission

Following several days of lengthy delays, Challenger finally lifted off at 16:38:00 UTC on 28 January 1986. Her three main engines were ignited at T-6.6 seconds, and at T-0 the solid rocket boosters were ignited, lifting the shuttle stack off launchpad 39-B at Kennedy Space Center. Almost immediately, cameras recording the launch registered the presence of smoke at the field joint next to the attachment strut on the right-hand SRB, indicating the failure of the O-rings that were supposed to seal the joint against the "blow-by" of hot gases from the boosters. However, sometime at around T+2 seconds, a piece of solid fuel from inside the booster moved inside the joint and provided a temporary seal against the blow-by, allowing the launch to proceed normally for around forty seconds.

However, at around T+36 seconds and an altitude of just over 10,000 feet (3,000 m), Challenger experienced the strongest wind shear ever felt during a Space Shuttle launch. The pitch and yaw commanded by the shuttle's computers in order to counter this wind caused the solid fuel plug to become dislodged from the field joint on the right SRB.

Cameras capture the plume of flame on Challenger's right-hand SRB.

At around T+58, cameras noted the creation of a plume on the aft attachment strut on the right-hand SRB, as ignited gas began to force itself through a rapidly growing hole in the field joint. Within a second, the plume became well defined and intense. Internal pressure in the right SRB began to drop because of the rapidly enlarging hole in the failed joint, and at T+60 there was visual evidence of flame coming through the joint and impinging on the external tank. As the mission clock passed up through T+64 seconds, the plume suddenly changed shape, showing that it had burned a hole in the liquid hydrogen tank in Challenger's ET, causing the tank to leak. The pressure in the tank began to drop, and Challenger's onboard computers began to pivot the nozzles of the SSMEs to counter the now-unbalanced thrust between the two SRBs.

At this stage, the situation still seemed normal both to the astronauts and to flight controllers. At T+68, the CAPCOM informed the crew that they were "GO at throttle up," and Commander Dick Scobee confirmed the call. His response, "Roger, GO at throttle up," was the last communication from Challenger on the air-to-ground loop.

Challenger begins to disintegrate.

At around T+72, the right SRB apparently pulled away from the aft strut attaching it to the external tank. Later analysis of telemetry data showed a sudden lateral acceleration to the right at T+72.525, which may have been felt by the crew. The last statement captured by the crew cabin recorder came just half a second after this acceleration, when Pilot Michael J. Smith said, "Uh oh." Smith may also have been responding to onboard indications of main engine performance or to falling pressures in the external fuel tank.

At T+73.124, the aft dome of the liquid hydrogen tank failed, producing a propulsive force that pushed the hydrogen tank into the liquid oxygen tank in the forward part of the external tank. At the same time, the right SRB rotated about the forward attach strut, and struck the intertank structure.

The breakup of the vehicle began at T+73.162 seconds, at an altitude of 48,000 feet (14.6 kilometres (9.1 mi)).[1] With the external tank disintegrating, Challenger veered from its correct attitude with respect to the local air flow and was immediately torn apart by abnormal aerodynamic forces, resulting in a load factor of up to 20g – well over its design limit. The two SRBs, which could withstand greater aerodynamic loads, separated from the ET and continued in uncontrolled powered flight for another 37 seconds. The SRB casings were made of 12.7 millimetres (0.50 in) thick steel and were much stronger than the orbiter and ET; thus, both SRBs survived the breakup of the space shuttle stack, even though the right SRB was still suffering the effects of the joint burn-through that had set the destruction of Challenger in motion.[2] The boosters were destroyed by the range safety system at around 110 seconds after launch.

The Challenger fireball, following total disintegration of the shuttle stack.
The right SRB exits the fireball. The anomalous plume that caused the disaster is clearly visible.

Detailed timeline and transcript[edit]

The following timeline provides a detailed list of the major events of the launch of STS-51-L, culminating in the destruction of Challenger. The list also contains a transcript from the shuttle's Cockpit Voice Recorder (CVR), from ignition of the main engines to T+73 seconds. Acronyms used in the timeline are as follows:

  • APU - Auxiliary Power Unit
  • CDR - Commander
  • CVR - Cockpit Voice Recorder
  • ET - External Tank
  • GLS - Ground Launch Sequencer
  • GPC - General Purpose Computer
  • HPFT - High Pressure Fuel Turbopump
  • LH2 - Liquid Hydrogen
  • LO2 - Liquid Oxygen (same as LOX)
  • LVLH - Local Vertical/Local Horizontal
  • MCC - Mission Control Center
  • MEC - Main Engine Controller
  • MS1/MS2 - Mission Specialist
  • PAO - Public Affairs Officer
  • PIC - Pyrotechnics Initiator Controller
  • PLT - Pilot
  • psf - Pounds per square foot
  • psi - Pounds per square inch
  • RCS - Reaction Control System
  • SRB - Solid Rocket Booster

Time (UTC) (hr:min:sec) Mission Elapsed Time (MET) (sec) Event Source
16:37:53.444 -6.566 SSME-3 ignition command. GPC
16:37:53.564 -6.446 SSME-2 ignition command. GPC
16:37:53.684 -6.326 SSME-1 ignition command. GPC
16:37:54 -6 CDR: "There they go guys!"

MS2: "All right!"

CDR: "Three at a hundred."

16:38:00.010 0.000 SRB ignition command. GPC
16:38:00.018 0.008 Holddown Post 2 PIC firing. E8 Camera
16:38:00 0 MS2: "Aall riight!" CVR
16:38:00.260 0.250 First continuous vertical motion. E9 Camera
The O-rings in the right-hand SRB field joint fail.
16:38:00.688 0.678 First confirmed puff of smoke appears above SRB/ET attachment ring field joint on right-hand SRB. E60 Camera
16:38:00.846 0.836 Eight puffs of smoke appear above field joint, lasting from T+0.836 to T+2.5 seconds MET. E63 Camera
16:38:00.900 0.890 Ground launch sequence computers begin post-liftoff "safing" of launch pad structures and equipment. GLS
16:38:01 1 PLT: "Here we go." CVR
16:38:02.743 2.733 Last evidence of smoke from field joint. CZR-1 Camera
16:38:03 3 PAO: "Liftoff of the 25th space shuttle mission, and it has cleared the tower." NASA TV
A solid-fuel 'plug' seals the gap formed by the O-ring 'blow-by'.
16:38:03.385 3.375 Last evidence of smoke. E60 camera
16:38:04.349 4.339 SSMEs throttled up to 104% E41M2076D
16:38:05 5 DPS: "Liftoff confirmed."

Flight Director: "Liftoff..."

16:38:05.684 5.674 Right-hand SRB pressure 11.8 psi above normal. B47P2302C
16:38:07 7 CDR: "Houston, Challenger - Roll program." CVR
16:38:07.734 7.724 Roll program initiated. V90R5301C
16:38:10 10 CAPCOM: "Roger roll, Challenger."

FIDO: "Good roll, flight." Flight Director: "Rog, good roll."

16:38:11 11 PLT: "Go you Mother!" CVR
16:38:14 14 MS1: "LVLH" CVR
16:38:15 15 MS2: "(Expletive) hot!"

CDR: "OK."

16:38:16 16 PAO: "Good roll program confirmed. Challenger now heading downrange." NASA TV
16:38:19 19 PLT: "Looks like we've got a lotta wind here today." CVR
16:38:19.869 19.859 SSMEs throttled back to 94% E41M2076D
16:38:20 20 CDR: "Yeah." CVR
16:38:21.134 21.124 Roll program completed. VP0R5301C
16:38:22 22 CDR: "It's a little hard to see out my window here." CVR
16:38:27 27 BOOSTER: "Throttle down to 94."

Flight Director: "Ninety four..."

16:38:28 28 PLT: "There's ten thousand feet and Mach point five." CVR
16:38:28 28 PAO: "Engines beginning throttling down, now at 94 percent. Normal throttle for most of the flight is 104 percent. We'll throttle down to 65 percent shortly." NASA TV
16:38:30 30 [Garble] CVR
16:38:35 35 CDR: "Point nine." CVR
16:38:35.389 35.379 SSMEs throttled back to 65% E41M2076D
16:38:37.000 36.990 Roll and Yaw Attitude Response to wind shear (36.990 to 62.990 sec). V95H352nC
The solid fuel 'plug' is dislodged.
16:38:40 40 PLT: "There's Mach one." CVR
16:38:41 41 CDR: "Going through nineteen thousand." CVR
16:38:43 43 CDR: "OK, we're throttling down." CVR
16:38:45.227 45.217 A flash is observed downstream of the shuttle's right wing.
16:38:48.128 48.118 A second flash is seen trailing the right wing.
16:38:48.428 48.418 A third unexplained flash is seen downstream of the shuttle's right-hand wing - a brilliant orange ball of flame appears to emerge from under the right wing and quickly merges with the plume of the solid rocket boosters, a phenomenon noted on previous flights. 70mm Camera
16:38:49 49 BOOSTER: "Three at 65."

PAO: "...Three good fuel cells. Three good APUs..." Flight Director: "Sixty-five, FIDO..." FIDO: "T-del confirms throttles." Flight Director: "...Thank you."

16:38:51.870 51.860 SSMEs throttled up to 104% E41M2076D
16:38:52 52 PAO: "Velocity 2,257 feet per second (1,539 mph), altitude 4.3 nautical miles, downrange distance 3 nautical miles..." NASA TV
16:38:57 57 CDR: "Throttling up." CVR
16:38:58 58 PLT: "Throttle up." CVR
16:38:58.798 58.788 First evidence of flame on right-hand SRB. E207 Camera
16:38:59 59 CDR: "Roger." CVR
16:38:59.010 59.000 Reconstructed Max Q (720 psf) Best estimated trajectory
16:38:59.272 59.262 Continuous well-defined plume of flame on right-hand SRB. E207 Camera
16:38:59.763 59.753 Flame from right-hand SRB in downwards direction (seen from south side of vehicle). E204 Camera
16:38:60 60 PLT: "Feel that mother go!"


16:39:00.014 60.238 Pressures in right- and left-hand SRBs begin to diverge. B47P2302
16:39:00.248 60.238 First evidence of intermittent plume deflection. E207 Camera
16:39:00.258 60.248 First evidence of SRB plume attaching to ET ring frame. E203 Camera
16:39:00.998 60.988 First evidence of continuous plume deflection. E207 Camera
16:39:01.734 61.724 Peak roll rate in response to wind shear. V90R5301C
16:39:02 62 PLT: "Thirty-five thousand going through one point five." CVR
16:39:02.094 62.084 Peak TVC response to wind shear. B58H1150C
16:39:02.414 62.404 Peak yaw response to wind shear. V90R5341C
16:39:02.494 62.484 Right-hand outboard elevon actuator hinge moment spike. V58P0966C
16:39:03.934 63.924 RH outboard elevon actuator delta pressure change. V58P0966C
16:39:03.974 63.964 Start of planned pitch rate manoeuvre. V90R5321C
The plume of flame burns through the LH2 tank in the ET.
16:39:04.670 64.660 Change in anomalous plume shape (LH2 tank leak near 2058 ring frame). E204 Camera
16:39:04.715 64.705 Bright sustained glow on sides of ET E204 Camera
16:39:04.947 64.937 Start SSME gimbal angle large pitch variations V58H1100A
16:39:05 65 CDR: "Reading four eighty six on mine." CVR
16:39:05.174 65.164 Beginning of transient motion due to changes in aero forces due to plume. V90R5321C
16:39:06 66 BOOSTER: "Throttle up, three at 104."

Flight Director: "CAPCOM, go at throttle up."

16:39:06.774 66.764 Start ET LH2 ullage pressure deviations. T41P1700C
16:39:07 67 PLT: "Yep, that's what I've got, too." CVR
16:39:08 68 PAO: "Engines are throttling up. Three engines now at 104 percent."

CAPCOM: "Challenger, go at throttle up."

16:39:10 70 CDR: "Roger, go at throttle up." (Last transmission on air-to-ground voice loop). CVR
The flame burns through the lower attachment strut on the right-hand SRB, causing the SRB to move away from the ET.
16:39:12.214 72.204 Left- and right-hand SRB yaw rates begin to diverge. V90R2528C
16:39:12.294 72.284 Left- and right-hand SRB pitch rates begin to diverge. V90R2525C
16:39:12.488 72.478 SRB major high-rate actuator command. V79H2111A
16:39:12.507 72.497 SSME roll gimbal rates 5 deg/sec. V58H1100A
16:39:12.535 72.525 Vehicle max +Y lateral acceleration (+.227 g). V98A1581C
16:39:12.574 72.564 SRB major high-rate actuator motion. B58H1151C
16:39:12.574 72.564 Start of H2 tank pressure decrease with 2 flow control valves open. T41P1700C
16:39:12.634 72.624 Last state vector downlinked. Data reduction
16:39:12.974 72.964 Start of sharp MPS LOX inlet pressure drop. V41P1330C
16:39:13 73 PLT: "Uh-oh..." CVR
16:39:13.020 73.010 Last full computer frame of TDRS data. Data reduction
16:39:13.054 73.044 Start of sharp MPS LH2 inlet pressure drop. V41P1100C
16:39:13.055 73.045 Vehicle max -Y lateral acceleration (-.254 g). V98A1581C
Challenger begins to disintegrate.
16:39:13.134 73.124 Circumferential white pattern on ET aft dome (LH2 tank failure). The bottom of the ET is open and liquid hydrogen spills. E204 Camera
16:39:13.134 73.124 Right-hand SRB pressure 19 psi lower than left-hand SRB B47P2302C
16:39:13.147 73.137 First hint of vapour at intertank. E207 Camera
16:39:13.153 73.143 All engine systems start responding to loss of fuel and LOX inlet pressure. SSME team
16:39:13.172 73.162 Sudden cloud along ET between intertank and aft dome. The right booster slams into the ET just as the LH2 tank is thrust into the oxygen tank. E207 Camera
16:39:13.201 73.191 Flash between Orbiter & LH2 tank. E204 Camera
16:39:13.221 73.211 SSME telemetry data interference from 73.211 to 73.303. Data reduction
16:39:13.223 73.213 Flash near SRB forward attachment strut and brightening of flash between Orbiter and ET E204 Camera
16:39:13.292 73.282 First indication intense white flash at SRB fwd attach point. E204 Camera
16:39:13.337 73.327 Greatly increased intensity of white flash. E204 Camera
16:39:13.387 73.377 Start of RCS jet chamber pressure fluctuations. V42P1552A
16:39:13.393 73.383 All engines approaching HPFT discharge temp redline limits. E41Tn010D
16:39:13.492 73.482 ME-2 HPFT discharge temperature. Channel A votes for shutdown; 2 strikes on Channel B. MEC data
16:39:13.492 73.482 SSME-2 controller last time word update. MEC data
16:39:13.513 73.503 SSME-3 in shutdown due to HPFT discharge temperature redline exceedance. MEC data
16:39:13.513 73.503 SSME-3 controller last time word update. MEC data
16:39:13.533 73.523 SSME-1 in shutdown due to HPFT discharge temperature redline exceedance. Calculation
16:39:13.553 73.543 SSME-1 last telemetered data point. Calculation
16:39:13.628 73.618 Last validated Orbiter telemetry measurement. V46P0120A
16:39:13.641 73.631 End of last reconstructured data frame with valid synchronization and frame count. Data reduction
16:39:14.140 74.130 Last radio frequency signal from Orbiter. Data reduction
Loss of downlink - Challenger is lost.
16:39:14.597 74.587 Bright flash in vicinity of Orbiter nose. E204 Camera
16:39:16.447 76.437 Right-hand SRB nose cap separation & parachute deployment. E207 Camera
16:39:17 77 PAO: "One minute fifteen seconds. Velocity: 2,900 feet per second (1977 mph). Altitude: 9 nautical miles. Downrange distance: 7 nautical miles." NASA TV & MCC
16:39:29 89 Flight Director: "FIDO, trajectories..."

FIDO: "Go ahead."
Flight Director: "Trajectory, FIDO."
FIDO: "Flight, FIDO, filters got discreting sources. We're go."
GC: "Flight, GC, we've had negative contact, loss of downlink."
Flight Director: "OK, all operators, watch your data carefully."
FIDO: "Flight, FIDO, till we get stuff back he's on his cue card for abort modes."
Flight Director: "Procedures, any help?"
Unknown: "Negative, flight, no data."

16:39:50.260 110.250 Destruction of right-hand SRB via Range Safety System. E202 Camera.
16:39:50.262 110.252 Destruction of left-hand SRB via Range Safety System. E230 Camera


 This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.

  1. ^ Kerwin, Joseph P. (1986). "Challenger crew cause and time of death". Retrieved July 4, 2006. 
  2. ^ Photo and TV Analysis Team Report (1986). Space Shuttle Challenger Accident Investigation. STS-51L Data and Analysis Task Force. 

External links[edit]