January 28 launch and failure Space Shuttle Challenger disaster

1 january 28 launch , failure

1.1 liftoff , initial ascent
1.2 plume
1.3 vehicle breakup
1.4 post-breakup flight controller dialogue
1.5 cause , time of death
1.6 prospect of crew escape

january 28 launch , failure

liftoff , initial ascent


gray smoke escaping right side srb

the following account of accident derived real time telemetry data , photographic analysis, transcripts of air-to-ground , mission control voice communications. times given in seconds after launch , correspond telemetry time-codes closest instrumented event each described event.

the space shuttle main engines (ssmes) ignited @ t-6.6 seconds. ssmes liquid-fueled , safely shut down (and launch aborted if necessary) until solid rocket boosters ignited @ t=0 (which @ 11:38:00.010 est) , hold-down bolts released explosives, freeing vehicle pad. @ lift off, 3 ssmes @ 100% of original rated performance, , began throttling 104% under computer control. first vertical motion of vehicle, gaseous hydrogen vent arm retracted external tank (et) failed latch back. review of film shot pad cameras showed arm did not re-contact vehicle, , ruled out contributing factor in accident. post-launch inspection of pad revealed kick springs on 4 of hold-down bolts missing, ruled out possible cause.

challenger launch , breakup

later review of launch film showed @ t+0.678, strong puffs of dark gray smoke emitted right-hand srb near aft strut attaches booster et. last smoke puff occurred @ t+2.733. last view of smoke around strut @ t+3.375. later determined these smoke puffs caused opening , closing of aft field joint of right-hand srb. booster s casing had ballooned under stress of ignition. result of ballooning, metal parts of casing bent away each other, opening gap through hot gases—above 2,760 °c (5,000 °f)—leaked. had occurred in previous launches, each time primary o-ring had shifted out of groove , formed seal. although srb not designed function way, appeared work enough, , morton-thiokol changed design specs accommodate process, known extrusion.

while extrusion taking place, hot gases leaked past (a process called blow-by ), damaging o-rings until seal made. investigations morton-thiokol engineers determined amount of damage o-rings directly related time took extrusion occur, , cold weather, causing o-rings harden, lengthened time of extrusion. (the redesigned srb field joint used subsequent challenger accident used additional interlocking mortise , tang third o-ring, mitigating blow-by.)

on morning of disaster, primary o-ring had become hard due cold not seal in time. temperature had dropped below glass transition temperature of o-rings. above glass transition temperature, o-rings display properties of elasticity , flexibility, while below glass transition temperature, become rigid , brittle. secondary o-ring not in seated position due metal bending. there no barrier gases, , both o-rings vaporized across 70 degrees of arc. aluminum oxides burned solid propellant sealed damaged joint, temporarily replacing o-ring seal before flame passed through joint.

as vehicle cleared tower, ssmes operating @ 104% of rated maximum thrust, , control switched launch control center (lcc) @ kennedy mission control center (mcc) @ johnson space center in houston, texas. prevent aerodynamic forces structurally overloading orbiter, @ t+28 ssmes began throttling down limit velocity of shuttle in dense lower atmosphere, per normal operating procedure. @ t+35.379, ssmes throttled further planned 65%. 5 seconds later, @ 5,800 metres (19,000 ft), challenger passed through mach 1. @ t+51.860, ssmes began throttling 104% vehicle passed beyond max q, period of maximum aerodynamic pressure on vehicle.

plume

plume on right srb @ t+ 58.788 seconds

beginning @ t+37 , 27 seconds, shuttle experienced series of wind shear events stronger on previous flight.

at t+58.788, tracking film camera captured beginnings of plume near aft attach strut on right srb. unknown on challenger or in houston, hot gas had begun leak through growing hole in 1 of right-hand srbs joints. force of wind shear shattered temporary oxide seal had taken place of damaged o-rings, removing last barrier flame passing through joint. had not been wind shear, fortuitous oxide seal might have held through booster burnout.

within second, plume became defined , intense. internal pressure in right srb began drop because of rapidly enlarging hole in failed joint, , @ t+60.238 there visual evidence of flame burning through joint , impinging on external tank.

at t+64.660, plume changed shape, indicating leak had begun in liquid hydrogen tank, located in aft portion of external tank. nozzles of main engines pivoted under computer control compensate unbalanced thrust produced booster burn-through. pressure in shuttle s external liquid hydrogen tank began drop @ t+66.764, indicating effect of leak.

at stage situation still seemed normal both crew , flight controllers. @ t+68, capcom richard o. covey informed crew go @ throttle , , commander dick scobee confirmed, roger, go @ throttle ; last communication challenger on air-to-ground loop.

vehicle breakup


a tracking camera located north of pad captured srb plume burned through external tank. damaged srb seen exiting vapor cloud clear signs of o-ring failure on 1 of segments.



challenger begins disintegrate.

at t+72.284, right srb pulled away aft strut attaching external tank. later analysis of telemetry data showed sudden lateral acceleration right @ t+72.525, may have been felt crew. last statement captured crew cabin recorder came half second after acceleration, when pilot michael j. smith said uh-oh. smith may have been responding onboard indications of main engine performance, or falling pressures in external fuel tank.

at t+73.124, aft dome of liquid hydrogen tank failed, producing propulsive force rammed hydrogen tank liquid oxygen tank in forward part of et. @ same time, right srb rotated forward attach strut, , struck intertank structure. external tank @ point suffered complete structural failure, lh2 , lox tanks rupturing, mixing, , igniting, creating fireball enveloped whole stack.

the breakup of vehicle began @ t+73.162 seconds , @ altitude of 48,000 feet (15 km). external tank disintegrating (and semi-detached right srb contributing thrust on anomalous vector), challenger veered correct attitude respect local airflow, resulting in load factor of 20 (or 20 g), on design limit of 5 g , ripped apart abnormal aerodynamic forces (contrary popular belief, orbiter did not explode force of external tank breakup within structural limits). 2 srbs, withstand greater aerodynamic loads, separated et , continued in uncontrolled powered flight. srb casings made of half-inch (12.7 mm) thick steel , stronger orbiter , et; thus, both srbs survived breakup of space shuttle stack, though right srb still suffering effects of joint burn-through had set destruction of challenger in motion.

the more robustly constructed crew cabin survived breakup of launch vehicle, designed survive 20 psi while estimated pressure had been subjected during orbiter breakup 4–5 psi.; while srbs subsequently destroyed remotely range safety officer, detached cabin continued along ballistic trajectory , observed exiting cloud of gases @ t+75.237. twenty-five seconds after breakup of vehicle, altitude of crew compartment peaked @ height of 65,000 feet (20 km). cabin stabilized during descent large mass of electrical wires trailing behind it.

the thiokol engineers had opposed decision launch watching events on television. had believed o-ring failure have occurred @ liftoff, , happy see shuttle leave launch pad. @ 1 minute after liftoff, friend of boisjoly said him oh god. made it. made it! boisjoly recalled when shuttle destroyed few seconds later, knew happened.

post-breakup flight controller dialogue

jay greene @ console after breakup of challenger




mission control during liftoff of challenger (sts-51-l)

in mission control, there burst of static on air-to-ground loop challenger disintegrated. television screens showed cloud of smoke , water vapor (the product of hydrogen+oxygen combustion) challenger had been, pieces of debris falling toward ocean. @ t+89, flight director jay greene prompted flight dynamics officer (fido) information. fido responded [radar] filter has discreting sources , further indication challenger had broken multiple pieces. moments later, ground controller reported negative contact (and) loss of downlink of radio , telemetry data challenger. greene ordered team watch data , sign orbiter had escaped.

at t+110.250, range safety officer (rso) @ cape canaveral air force station sent radio signals activated range safety system s destruct packages on board both solid rocket boosters. normal contingency procedure, undertaken because rso judged free-flying srbs possible threat land or sea. same destruct signal have destroyed external tank had not disintegrated. srbs close end of scheduled burn (t+110 seconds after launch) , had exhausted propellants when destruct command sent, little, if explosive force generated event.

public affairs officer steve nesbitt reported: flight controllers here looking @ situation. major malfunction. have no downlink.

on mission control loop, greene ordered contingency procedures put effect; these procedures included locking doors of control center, shutting down telephone communications outside world, , following checklists ensured relevant data correctly recorded , preserved.

nesbitt relayed information public: have report flight dynamics officer vehicle has exploded. flight director confirms that. looking @ checking recovery forces see can done @ point.

cause , time of death

the crew cabin, made of reinforced aluminum, particularly robust section of orbiter. during vehicle breakup, detached in 1 piece , tumbled ballistic arc. nasa estimated load factor @ separation between 12 , 20 g; within 2 seconds had dropped below 4 g , within 10 seconds cabin in free fall. forces involved @ stage insufficient cause major injury.

at least of crew alive , @ least briefly conscious after breakup, 3 of 4 recovered personal egress air packs (peaps) on flight deck found have been activated. investigators found remaining unused air supply consistent expected consumption during 2 minute 45 second post-breakup trajectory.

while analyzing wreckage, investigators discovered several electrical system switches on pilot mike smith s right-hand panel had been moved usual launch positions. fellow astronaut richard mullane wrote, these switches protected lever locks required them pulled outward against spring force before moved new position. later tests established neither force of explosion nor impact ocean have moved them, indicating smith made switch changes, presumably in futile attempt restore electrical power cockpit after crew cabin detached rest of orbiter.

whether crew members remained conscious long after breakup unknown, , largely depends on whether detached crew cabin maintained pressure integrity. if did not, time of useful consciousness @ altitude few seconds; peaps supplied unpressurized air, , hence not have helped crew retain consciousness. if, on other hand, cabin not depressurized or depressurizing, may have been conscious entire fall until impact. recovery of cabin found middeck floor had not suffered buckling or tearing, result rapid decompression, providing evidence depressurization may have not happened @ once.

nasa routinely trained shuttle crews splashdown events, cabin hit ocean surface @ 207 mph (333 km/h), estimated deceleration @ impact of on 200 g, far beyond structural limits of crew compartment or crew survivability levels, , far greater automobile, aircraft, or train accident. crew have been torn seats , killed instantly extreme impact force.

on july 28, 1986, nasa s associate administrator space flight, former astronaut richard h. truly, released report on deaths of crew director of space , life sciences @ johnson space center, joseph p. kerwin. medical doctor , former astronaut, kerwin veteran of 1973 skylab 2 mission. according kerwin report:

the findings inconclusive. impact of crew compartment ocean surface violent evidence of damage occurring in seconds followed disintegration masked. our final conclusions are:

the cause of death of challenger astronauts cannot positively determined;
the forces crew exposed during orbiter breakup not sufficient cause death or serious injury; and
the crew possibly, not certainly, lost consciousness in seconds following orbiter breakup due in-flight loss of crew module pressure.

some experts believe if not of crew alive , possibly conscious during entire descent until impact ocean. astronaut , nasa lead accident investigator robert overmyer said, not flew dick scobee, owned plane together, , know scob did save crew. scob fought , every edge survive. flew ship without wings way down... alive.

prospect of crew escape

during powered flight of space shuttle, crew escape not possible. launch escape systems considered several times during shuttle development, nasa s conclusion shuttle s expected high reliability preclude need one. modified sr-71 blackbird ejection seats , full pressure suits used two-man crews on first 4 shuttle orbital missions, considered test flights, removed operational missions followed. (the columbia accident investigation board later declared, after 2003 columbia re-entry disaster, space shuttle system should never have been declared operational because experimental nature due limited number of flights compared certified commercial aircraft.) multi-deck design of crew cabin precluded use of such ejection seats larger crews. providing sort of launch escape system had been considered, deemed impractical due limited utility, technical complexity , excessive cost in dollars, weight or schedule delays.

after loss of challenger, question re-opened, , nasa considered several different options, including ejector seats, tractor rockets , emergency egress through bottom of orbiter. nasa once again concluded of launch escape systems considered impractical due sweeping vehicle modifications have been necessary , resultant limitations on crew size. system designed give crew option leave shuttle during gliding flight, system not have been usable in challenger situation.