STS-51-L Mission timeline

STS-51-L Mission Patch

STS-51-L Mission timeline is a detailed timeline of events from the ignition of Challengers 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 of the American Space Shuttle program, which 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 in 1986 from Kennedy Space Centre, 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 due to overwhelming aerodynamic pressures. The seven-member crew was killed some time after the breakup of the vehicle.

Summary timeline

Space Shuttle Challenger lifts off on her final, doomed 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 Centre. 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, and, as such, the launch proceeded normally for around forty seconds after launch.

However, at around T+36 seconds and an altitude of just over 10,000 feet, Challenger experienced the strongest wind shear ever felt by 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, and from that moment on the fate of both Challenger and her crew was sealed.

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 - ignited gas had begun 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, whilst meanwhile Challenger's onboard computers began to pivot the nozzles of the SSMEs in order 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 and at an altitude of 48,000 feet (14.6 km). 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 can withstand greater aerodynamic loads, separated from the ET and continued in uncontrolled powered flight for another 37 seconds. The SRB casings were made of half an inch (12.7 mm) 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.

The Challenger fireball, following total disintegration of the shuttle stack.

Detailed timeline and transcript

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 - Auxilixary Power Unit
  • ET - External Tank
  • GPC - General Purpose Computer
  • HPFT - High Pressure Fuel Turbopump
  • LH2 - Liquid Hydrogen
  • LO2 - Liquid Oxygen (same as LOX)
  • MEC - Main Engine Controller
  • PIC - Pyrotechnics Initiator Controller
  • psf - Pounds per square foot
  • psi - Pounds per square inch
  • RCS - Reaction Control System
  • CDR - Commander
  • PLT - Pilot
  • MS1/MS2 - Mission specialist
Space Shuttle Challenger Disaster Timeline
Time (UTC) (hr:min:sec)Mission Elapsed Time (MET) (sec)EventSource
16:37:53.444-6.566SSME-3 ignition command.GPC
16:37:53.564-6.446SSME-2 ignition command.GPC
16:37:53.684-6.326SSME-1 ignition command.GPC
16:37:54-6CDR: "There they go guys!"

MS2: "All right!"

CDR: "Three at a hundred."

16:38:000MS2 "Aall riight!"CVR
16:38:00.0100.000SRB ignition command.GPC
16:38:00.0180.008Holddown Post 2 PIC firing.E8 Camera
16:38:00.2600.250First continuous vertical motion.E9 Camera
The O-rings in the right-hand SRB field joint fail.
16:38:00.6880.678First confirmed puff of smoke appears above SRB/ET attachment ring field joint on right-hand SRB.E60 Camera
16:38:00.8460.836Eight puffs of smoke appear above field joint, lasting from T+0.836 to T+2.5 seconds MET.E63 Camera
16:38:011PLT "Here we go."CVR
16:38:02.7432.733Last evidence of smoke from field joint.CZR-1 Camera
A solid-fuel 'plug' seals the gap formed by the O-ring 'blow-by'.
16:38:03.3853.375Last evidence of smoke.E60 camera
16:38:04.3494.339SSMEs throttled up to 104%E41M2076D
16:38:05.6845.674Right-hand SRB pressure 11.8 psi above normal.B47P2302C
16:38:077CDR: "Houston, Challenger - Roll program."CVR
16:38:07.7347.724Roll program initiated.V90R5301C
16:38:1111PLT: "Go you Mother!"CVR
16:38:1414MS1: "LVLH"CVR
16:38:1515MS2: "(Expletive) hot!"CVR
16:38:1616CDR: "Ooohh-kaaay."CVR
16:38:1919PLT: "Looks like we've got a lotta wind here today."CVR
16:38:19.86919.859SSMEs throttled back to 94%E41M2076D
16:38:2020CDR: "Yeah."CVR
16:38:21.13421.124Roll program completed.VP0R5301C
16:38:2222CDR: "It's a little hard to see out my window here."CVR
16:38:2828PLT: "There's ten thousand feet and Mach point five."CVR
16:38:3535CDR: "Point nine."CVR
16:38:35.38935.379SSMEs throttled back to 65%E41M2076D
16:38:37.00036.990Roll and Yaw Attitude Response to wind shear (36.990 to 62.990 sec).V95H352nC
The solid fuel 'plug' is dislodged.
16:38:4040PLT: "There's Mach one."CVR
16:38:4141CDR: "Going through nineteen thousand."CVR
16:38:4343CDR: "OK, we're throttling down."CVR
16:38:51.87051.860SSMEs throttled up to 104%E41M2076D
16:38:5757CDR: "Throttling up."CVR
16:38:5858PLT: "Throttle up."CVR
16:38:58.79858.788First evidence of flame on right-hand SRB.E207 Camera
16:38:5959CDR: "Roger."CVR
16:38:59.01059.000Reconstructed Max Q (720 psf)Best estimated trajectory
16:38:59.27259.262Continuous well-defined plume of flame on right-hand SRB.E207 Camera
16:38:59.76359.753Flame from right-hand SRB in downwards direction (seen from south side of vehicle).E204 Camera
16:38:6060PLT: "Feel that mother go!"


16:39:00.01460.238Pressures in right- and left-hand SRBs begin to diverge.B47P2302
16:39:00.24860.238First evidence of intermittent plume deflection.E207 Camera
16:39:00.25860.248First evidence of SRB plume attaching to ET ring frame.E203 Camera
16:39:00.99860.988First evidence of continuous plume deflection.E207 Camera
16:39:01.73461.724Peak roll rate in response to wind shear.V90R5301C
16:39:0262PLT: "Thirty-five thousand going through one point five."CVR
16:39:02.09462.084Peak TVC response to wind shear.B58H1150C
16:39:02.41462.404Peak yaw response to wind shear.V90R5341C
16:39:02.49462.484Right-hand outboard elevon actuator hinge moment spike.V58P0966C
16:39:03.93463.924RH outboard elevon actuator delta pressure change.V58P0966C
16:39:03.97463.964Start of planned pitch rate manoeuvre.V90R5321C
The plume of flame burns through the LH2 tank in the ET.
16:39:04.67064.660Change in anomalous plume shape (LH2 tank leak near 2058 ring frame).E204 Camera
16:39:04.71564.705Bright sustained glow on sides of ETE204 Camera
16:39:04.94764.937Start SSME gimbal angle large pitch variationsV58H1100A
16:39:0565CDR: "Reading four eighty six on mine."CVR
16:39:05.17465.164Beginning of transient motion due to changes in aero forces due to plume.V90R5321C
16:39:06.77466.764Start ET LH2 ullage pressure deviations.T41P1700C
16:39:0767PLT: "Yep, that's what I've got, too."CVR
16:39:1070CDR: "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.
16:39:12.21472.204Left- and right-hand SRB yaw rates begin to diverge.V90R2528C
16:39:12.29472.284Left- and right-hand SRB pitch rates begin to diverge.V90R2525C
16:39:12.48872.478SRB major high-rate actuator command.V79H2111A
16:39:12.50772.497SSME roll gimball rates 5 deg/sec.V58H1100A
16:39:12.53572.525Vehicle max +Y lateral acceleration (+.227 g).V98A1581C
16:39:12.57472.564SRB major high-rate actuator motion.B58H1151C
16:39:12.57472.564Start of H2 tank pressure decrease with 2 flow control valves open.T41P1700C
16:39:12.63472.624Last state vector downlinked.Data reduction
16:39:12.97472.964Start of sharp MPS LOX inlet pressure drop.V41P1330C
16:39:1373PLT: "Uh-oh..."CVR
16:39:13.02073.010Last full computer frame of TDRS data.Data reduction
16:39:13.05473.044Start of sharp MPS LH2 inlet pressure drop.V41P1100C
16:39:13.05573.045Vehicle max -Y lateral acceleration (-.254 g).V98A1581C
Challenger begins to disintegrate.
16:39:13.13473.124Circumferential white pattern on ET aft dome (LH2 tank failure). The bottom of the ET is open and liquid hydrogen spills.E204 Camera
16:39:13.13473.124Right-hand SRB pressure 19 psi lower than left-hand SRBB47P2302C
16:39:13.14773.137First hint of vapour at intertank.E207 Camera
16:39:13.15373.143All engine systems start responding to loss of fuel and LOX inlet pressure.SSME team
16:39:13.17273.162Sudden 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
16:39:13.20173.191Flash between Orbiter & LH2 tank.E204 Camera
16:39:13.22173.211SSME telemetry data interference from 73.211 to 73.303.Data reduction
16:39:13.22373.213Flash near SRB forward attachment strut and brightening of flash between Orbiter and ETE204 Camera
16:39:13.29273.282First indication intense white flash at SRB fwd attach point.E204 Camera
16:39:13.33773.327Greatly increased intensity of white flash.E204 Camera
16:39:13.38773.377Start of RCS jet chamber pressure fluctuations.V42P1552A
16:39:13.39373.383All engines approaching HPFT discharge temp redline limits.E41Tn010D
16:39:13.49273.482ME-2 HPFT discharge temperature. Channel A votes for shutdown; 2 strikes on Channel B.MEC data
16:39:13.49273.482SSME-2 controller last time word update.MEC data
16:39:13.51373.503SSME-3 in shutdown due to HPFT discharge temperature redline exceedance.MEC data
16:39:13.51373.503SSME-3 controller last time word update.MEC data
16:39:13.53373.523SSME-1 in shutdown due to HPFT discharge temperature redline exceedance.Calculation
16:39:13.55373.543SSME-1 last telemetered data point.Calculation
16:39:13.62873.618Last validated Orbiter telemetry measurement.V46P0120A
16:39:13.64173.631End of last reconstructured data frame with valid synchronization and frame count.Data reduction
16:39:14.14074.130Last radio frequency signal from OrbiterData reduction
Loss of downlink - Challenger is lost.
16:39:14.59774.587Bright flash in vicinity of Orbiter nose.E204 Camera
16:39:16.44776.437Right-hand SRB nose cap separation & parachute deployment.E207 Camera
16:39:50.260110.250Destruction of right-hand SRB via Range Safety System.E202 Camera.
16:39:50.262110.252Destruction of left-hand SRB via Range Safety System.E230 Camera