Space Shuttle Challenger disaster

51L/STS-33

Mission Insignia
Mission Statistics
Mission name:	51L/STS-33
Spacecraft name:	Challenger
Shuttle:	Challenger
Call sign:
Number of crew members:	7
Launch pad
Launch:	39-B (6), first shuttle launch from 39-B
Begin spacewalk:
End spacewalk:
Landing:	Scheduled for February 3, 1986 12:12 p.m. EST (17:12 GMT)
Duration:	0:00:01:13.213 6 d 34 min planned
Number of orbits:	96 planned
Apogee:
Perigee:
Period:
Orbit altitude:	150 nautical miles (280 km) planned
Orbit inclination:	28.5 degrees planned
Distance traveled:
Mass:
Crew photo
The crew Front row, left to right: Michael J. Smith, Francis "Dick" Scobee, and Ronald McNair Back row: Ellison Onizuka, Christa McAuliffe, Gregory Jarvis, and Judith Resnik
Navigation
Previous mission Next mission STS-61-C STS-26

The Space Shuttle Challenger disaster occurred on the morning of January 28, 1986, at 11:39 EST, when Space Shuttle Challenger was destroyed 73 seconds into its flight (mission 51L/STS-33, the 25th of the STS program and Challenger's 10th) because of the failure of an O-ring seal in the right solid rocket booster (SRB).

The seal failure caused a flame leak from the SRB that impinged upon the adjacent external propellant tank and aft SRB connecting strut. Within seconds the flame caused structural failure of the external tank, and the orbiter broke up from aerodynamic forces. All seven crew members were killed when the slowly tumbling detached crew compartment impacted the ocean. That compartment and many other vehicle fragments were recovered from the ocean floor.

The launch was televised live, although most viewers saw it tape-delayed later that day. Christa McAuliffe had been expected to be the first teacher in space, and students worldwide had expected to watch a television broadcast of her delivering a science lesson from space. Instead, thousands watched the disintegration of the shuttle either as it happened live or later that day.

In response to the tragedy, American President Ronald Reagan postponed his State of the Union address and gave a national address from the Oval Office of the White House where he said, "We will never forget them, nor the last time we saw them, this morning, as they prepared for their journey and waved goodbye and 'slipped the surly bonds of earth' to 'touch the face of God.'" U.S. manned space flights did not resume until over two years later, with the launch of the space shuttle Discovery on September 29th, 1988 with the Return to Flight mission STS-26.

Mission personnel and objectives

Crew

• Commander (CMD): Francis "Dick" Scobee (also flew on 41C/STS-13)
• Pilot (PLT): Michael J. Smith (first flight)
• Mission Specialist 1: Judith Resnik (also flew on 41D/STS-16)
• Mission Specialist 2: Ellison Onizuka (also flew on 51C/STS-20)
• Mission Specialist 3: Ronald McNair (also flew on 41B/STS-11)
• Payload Specialist 1: Gregory Jarvis (first flight)
• Payload Specialist 2: Christa McAuliffe (first flight)

Mission Control staff

• Flight Director (Flight): Jay Greene
• Flight Dynamics Officer (FDO): Brian Perry
• Capcom 1 ( CAPCOM): Richard Covey
• Capcom 2: Frederick Gregory
• Data Processing Systems Engineer (DPS): A.F. Algate
• Guidance, Navigation, and Controls Systems Engineer (GNC): Jeffrey Bantle
• Booster Systems Engineer (Booster): Jerry Borrer
• Propulsion Engineer (PROP): A.J. Ceccacci
• Electrical, Environmental, Consumables Manager (EECOM): John Rector
• Mechanical and Upper Stage Systems Officer (RMU): K.A. Reiley

Mission objectives

Planned objectives were deployment of Tracking Data Relay Satellite-2 (TDRS-2) and flying of Shuttle-Pointed Tool for Astronomy (SPARTAN-203)/Halley's Comet Experiment Deployable, a free-flying module designed to observe tail and coma of Halley's comet with two ultraviolet spectrometers and two cameras. Other payloads were Fluid Dynamics Experiment (FDE); Comet Halley Active Monitoring Program (CHAMP); Phase Partitioning Experiment (PPE); three Shuttle Student Involvement Program (SSIP) experiments; and two lessons for the Teacher in Space Project (TISP).

No mission objectives were accomplished.

Mission parameters

• Mass:
  • Orbiter Liftoff: 121,778 kg
  • Orbiter Landing: 90,584 kg (planned)
  • Payload: 21,937 kg
• Perigee: ~285 km (planned)
• Apogee: ~295 km (planned)
• Inclination: 28.45° (planned)
• Period: ~90.4 min (planned)
• Duration: 6 days 0 hours 34 minutes (planned)

Pre-Launch conditions and delays

Launch delays

Challenger's launch was originally set for 15:43 EST on the 22nd of January. Delays with 61C/STS-32 caused the launch date to be pushed back to the 23rd and then to the 24th. Launch was re-scheduled for the 25th due to bad weather at the Transoceanic Abort Landing (TAL) site in Dakar, Senegal. NASA decided to use Casablanca as the TAL site, but because it was not equipped for night landings the launch had to be moved to the morning ( Florida time). Predictions of unacceptable weather at KSC ( Kennedy Space Center) caused the launch to be re-scheduled for 09:37 EST on the 27th. Launch was then delayed 24 hours when the closeout crew (in this case, the technicians at the pad) could not remove a 'closing fixture' from the orbiter's hatch. When the fixture was finally sawed off, cross winds at the SLF ( Shuttle Landing Facility) exceeded the limits for an Return to Launch Site (RTLS) abort. Launch on the 28th was delayed two hours when a fire detection system failed during liquid hydrogen tanking procedures.

The launch finally began at 11:38 EST on Tuesday, January 28, 1986.

Ice on launch pad

The night before launch, local temperatures dropped to the low 20s Fahrenheit (about -5º Celsius). This was unusually cold; nearby Floridians had the rare problem of removing ice from their car windshields the following morning.

Several launch pad water systems were opened slightly and allowed to flow into drains to keep the standing water from freezing and cracking the pipes. However the drains themselves froze and caused overflows. High wind gusts spread the water around the pad, and ice formed. The ice team, led by Charlie Stevenson, quickly went into action and began clearing away ice that posed a threat to Challenger's TPS ( Thermal Protection System). The ice team had experience with a similar (although, not as bad) incident on pad 39-A before the launch of 51C/STS-20. That launch had been postponed.

The temperature at liftoff was 36°F (2°C), 15°F (8°C) colder than any previous launch. The liquid oxygen and hydrogen stored in the large central foam-insulated External Tank were maintained at cryogenic temperatures, while the solid rocket boosters and their rubber O-rings remained at ambient temperature, only slightly above the freezing point of water.

Engineers at Morton Thiokol (manufacturer of the solid rocket boosters) knew that the temperatures were outside of the design range of the O-rings. They strongly objected to the launch, but were overruled by senior Thiokol management.

NASA and Thiokol management knew about serious O-ring erosion on earlier Shuttle flights. They planned steps to correct the problem, but decided to keep flying the shuttle in the interim, treating it as an acceptable flight risk.

January 28 launch and failure

Liftoff

6.6 seconds before liftoff, the SSMEs ( Space shuttle main engines) were started. (Until liftoff actually occurs, the SSMEs can be safely shut down and the launch aborted if necessary.) At liftoff time (T+0), the three SSMEs were at 100% of rated performance and began throttling up to 104% of rated performance under computer control. At this moment, the two SRBs were ignited and hold-down bolts were released with explosives, freeing the vehicle from the pad. With the first vertical motion of the vehicle, the gaseous hydrogen vent arm retracted from the ET but failed to latch back. Review of film shot by pad cameras showed that the arm did not re-contact the vehicle. The post-launch inspection of the pad also revealed that kick springs on four of the hold-down bolts were missing. They were also ruled out as a contributing factor in the accident.

The launch of STS-51L was the first STS launch from LC-39B (Launch Complex 39-B), north of LC-39A, the pad used for the first 24 STS missions. (The two launch pads can be easily distinguished in OTV (Operational Television) video. The OTV cameras throughout the launch complex have 3-digit identification numbers in the upper left-hand corner of the image. On 39-A, these numbers begin with a zero. On 39-B, these numbers begin with a one.)

Later review of launch film showed that at T+0.678, strong puffs of dark grey smoke emitted from the right-hand SRB near the aft strut that attaches the booster to the ET. The last smoke puff occurred at about T+2.733. The last view of smoke around the strut was at T+3.375.

Initial ascent

As the vehicle cleared the tower, the SSMEs were operating at 104% of rated performance, and control had switched from the LCC ( Launch Control Center) at KSC to the MCC ( Mission Control Center) in Houston, Texas. Times are given in seconds after launch. Flight controller call signs or crew name identify the speaker. "Intercom" means crew-to-crew communication. Speakers:

• DPS: Data Processing Systems Engineer
• Flight: Flight director
• Smith: Michael J. Smith (pilot)
• Scobee: Dick Scobee (commander)
• Booster: Booster Systems Engineer
• CAPCOM: Capsule communicator
• FIDO: Flight Dynamics Officer
• GC: Ground Controller
• RSO: Range Safety Officer
• PAO: Public Affairs Officer (public announcer)

T+5.000 


seconds:
DPS: Liftoff 

confirmed.
Flight: 

Liftoff...

To prevent aerodynamic forces from tearing the shuttle apart, the SSMEs must throttle down to limit velocity in the dense lower atmosphere. At T+19.859, the flight software computed that the SRB were "hot", producing more thrust than planned. The flight software then modified the SSMEs throttle profile and throttled down early to 94%. Concurrently, the SRB thrust lessened according to a pre-defined schedule. At T+35.379, the SSMEs throttled back further to the pre-planned 65%.

Booster: Throttle down to 

94.
Flight: Ninety 
four...

T+40.000 

seconds:
Smith, 
intercom: There's Mach 

1.
Scobee: Going through 
19,000.

T+48.900 


seconds:
Booster: Three at 

65.
Flight: Sixty-five, 

FiDO...
FIDO: T-del confirms 

throttles.
Flight: 

Thank-you.

At T+51.860, the SSMEs began to throttle back up to 104% as the vehicle approached Max Q (the area of maximum aerodynamic pressure on the vehicle, approximately 720 pounds per square foot or 34 kilopascals).

T+57.000 

seconds:
Scobee, 
intercom: Throttling 

up.

Plume

At about T+58.788, a tracking film camera captured the beginnings of a plume near the aft attach strut on the right SRB. Unknown to those on Challenger or in Houston, ignited gas had begun to leak through a growing hole in one of the right-hand SRB's joints. Within a second, the plume was well defined and intense. Even had the crew or mission control known, nothing could have been done. Everything else was apparently normal and the crew called the expected "go" as the three SSMEs throttled up.

At an altitude of 35,000 feet, Challenger passes through Mach 1.5 (1.5 times the speed of sound).

 
T+62.000 

seconds:
 Smith, 
intercom: "Thirty-five thousand, going through one point 
five."

T+68.000 


seconds:
CAPCOM: Challenger, go at throttle 

up.
Scobee: Roger, go at throttle 

up.

Failure develops

At T+72.525, later analysis of telemetry data showed a sudden lateral acceleration to the right, which may have been felt by the crew. At T+72.564 - liquid hydrogen pressure in external tank begins decreasing due to rupture caused by SRB flame.

T+73.000 

seconds:
Smith, 
intercom: "Uh 

oh..."

This was the last intercom statement captured by the crew cabin recorder. Smith may have been responding to indications on main engine performance or falling pressures in the external fuel tank. At about T+73.162 the vehicle breakup began.

Post-breakup flight controller dialog

At T+79.000 a TV tracking camera showed a cloud of smoke and flame where Challenger had been, with large burning debris pieces falling toward the ocean.

T+89.000 


seconds:
Flight: "FIDO, 

trajectories"
FIDO: "Go 

ahead."
Flight: "Trajectory, 

FIDO"
FIDO: "Flight, FIDO, filters (radar) got discreting sources. We're 

go."
FIDO: "Flight, FIDO, till we get stuff back he's on his cue card for 
 abort 

modes"
Flight: "Procedures, any 

help?"
Unknown: "Negative, flight, no 

data."
GC: "Flight, GC, we've had negative contact, loss of downlink (of radio voice or data from 

Challenger)."
Flight: "OK, all operators, watch your data 

carefully."

At T+110.250 the Range safety officer sends radio signals that detonate the self-destruct packages on the solid rocket boosters (SRBs). He saw the breakup and judged the free-flying SRBs a possible threat to land or sea, so destroyed them, which is normal procedure for such a situation.

T+1 min. 56 


seconds
PAO: "Flight controllers here are looking very carefully at the situation. Obviously a major 
malfunction."

T+2 min. 1 


second
GC: "Flight, GC, negative 

downlink."
Flight: 
"Copy."

T+2 min. 8 


seconds
PAO: "We have no 

downlink."

At T+2 min 20 seconds a TV tracking camera shows falling bits of debris create and white contrails against the blue sky. Larger objects plummet toward the ocean, streaming thin vapor trails.

T+2 min. 25 


seconds
FIDO: "Flight, 

FIDO."
Flight: "Go 

ahead."
FIDO: "RSO (range safety officer) reports vehicle 
exploded."
Flight: (after a long 
pause): "Copy. FIDO, can we get any reports from recovery 

forces?"
FIDO: "Stand 
by."

T+2 min. 45 


seconds
Flight: "GC, all operators, contingency procedures in 

effect."

Failure sequence

This sequence is from real time telemetry data and photographic analysis. Times are seconds after liftoff.

T+60.004: Internal pressure in the right-side SRB begins to drop because of the rapidly enlarging hole in the failed joint

T+60.238: Initial evidence of flame through the rupture impinging on the external tank

T+64.660: The plume suddenly changes shape, indicating a leak has begun in the liquid hydrogen tank, the aft portion of the external tank

T+64.937: Main engine nozzles pivot under computer control to compensate for the unbalanced thrust produced by the booster burn through

T+66.764: Pressure in the shuttle's external liquid hydrogen tank begins to drop, indicating a massive leak

T+72.284: The right SRB apparently pulls away from the aft strut attaching it to the external tank

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

With the external tank disintegrating, Challenger veered from its correct attitude with respect to the local air flow and was immediately torn apart by aerodynamic forces. The two SRBs, which can withstand greater aerodynamic loads, separated from the ET and began to fly independently

No "explosion"

The Shuttle and External Tank did not actually " explode"; there was no detonation. Instead they rapidly disintegrated under tremendous aerodynamic forces, since the shuttle was near "Max Q", or maximum aerodynamic pressure. The more robustly constructed crew cabin and SRBs survived the breakup. As the detached cabin continued along its ballistic trajectory, the fuel and oxidizer stored in the ET and orbiter reaction control system burned in a few seconds, producing a massive fireball. Had there been a true explosion, the entire Shuttle would have been instantly destroyed, killing the crew at that moment.

The two separated SRBs continued to burn as they flew out of the fireball.

NASA's photo and TV support team, led by Charlie Stevenson, assisted in the analysis of this aspect of the disaster.

Cause and time of death

At least some of the astronauts were likely alive and briefly conscious after the breakup, because three of the four personal egress air packs (PEAPs) on the flight deck were found activated. Investigators found their remaining unused air supply roughly consistent with the expected consumption during the 2 minute 45 second post-breakup trajectory. PEAP switch design makes activation from the vehicle breakup or water impact very unlikely.

At vehicle breakup, the robustly constructed crew cabin detached in one piece and slowly tumbled. NASA estimated separation forces at about 12 to 20 times the force of gravity (g) very briefly; within two seconds forces were below four g, within ten seconds the cabin was in free fall. These forces were likely insufficient to cause major injury.

Whether the astronauts remained conscious long after the breakup is unknown, and largely depends on whether the detached crew cabin maintained pressure integrity. If it did not, time of useful consciousness at that altitude is just a few seconds. The PEAPs supplied only unpressurized air, not oxygen, hence would not have helped much.

The crew cabin impacted the ocean surface at roughly 207 miles per hour, causing deceleration of over 200 g, far beyond the structural limits of the crew compartment or crew survivability levels.

Solid rocket boosters destroyed

After the orbiter and external tank disintegrated at about T+73.213 seconds, the two SRBs ( Solid Rocket Booster) continued in uncontrolled powered flight for another 37 seconds. The SRB casings are one-half-inch thick steel and much stronger than the orbiter and ET. The RSO ( Range Safety Officer) then detonated the self-destruct packages on board both boosters to prevent damage to objects on earth.

The same destruct signal would have destroyed the External Tank had it not already disintegrated. The orbiter carries relatively little propellant, so it does not have its own destruct package.

Crew escape was not possible

Crew escape was not possible during powered flight.

Modified SR-71 ejection seats and full pressure suits were used on the first four shuttle orbital missions, considered test flights. They were removed for the operational missions that followed, during which the astronauts wore only cloth flight suits.

NASA reasoned that retaining ejection seats was possible for the commander and pilot, but they were impractical for the rest of the crew, especially the three below deck. Unlike a fighter pilot under a thin canopy, the crew below deck were in the center of the forward fuselage, surrounded by vehicle structure on all sides. Additionally, ejection seats might have problems at Max Q (period of maximum aerodynamic pressure), or because of the SRB exhaust plume. The seats were primarily intended for an escape during landing, since the shuttle is unpowered when landing and has only one chance to make the runway. It would be possible to design the crew cabin as a self-contained escape vessel, but this would have been prohibitively expensive, complex, and have added excessive weight to the vehicle. For more details see shuttle ejection escape systems.

While launch escape systems were often considered during shuttle development, NASA eventually decided the shuttle was sufficiently reliable to not need one. Also launch escape systems entail significant weight and space penalties, and the associated pyrotechnics incur safety issues. Several fighter pilots have been killed due to uncommanded ejections. After the Challenger loss, a bail-out system was designed to give the crew the option to leave the shuttle under certain conditions, not including the Challenger scenario. For more details see Post-Challenger abort enhancements.

Aftermath

Investigation

The Presidential Commission on the Space Shuttle Challenger Accident, also known as the Rogers Commission, was formed to investigate the disaster. The Commission members were Chairman William P. Rogers, Vice Chairman Neil Armstrong, David Acheson, Eugene Covert, Richard Feynman, Robert Hotz, Donald Kutyna, Sally Ride, Robert Rummel, Joseph Sutter, Arthur Walker, Albert Wheelon, and Chuck Yeager.

Feynman famously demonstrated during a televised hearing how the O-rings became less resilient and subject to seal failures at ice-cold temperatures by immersing a sample of the material in a glass of ice water. He was so critical of flaws in NASA's "safety culture" that he threatened to not sign off on the report unless it included his assessment, which appeared as Appendix F. He pointed to the discrepancy between management claiming a 1 in 100,000 chance of serious failure and the engineers claiming 1 in only 100, a risk one thousand times greater. The commission was known as the Rogers commission after its chairman. The commission worked for several months and published a report of their findings.

Cause of failure

For various reasons the SRBs are fabricated in four separate segments, not as a single unit. The four SRB segments are then shipped from the manufacturer to Cape Kennedy where they are assembled "in the field". A joint exists between each SRB segment called a "field joint". The joint exists in both the SRB solid propellant and the 1/2 inch thick outer steel casing. Each field joint is sealed with two O-rings between the steel casing segments.

The entire length of the SRB is internally hollow, like a lead pencil without the lead. During operation, the entire internal length of the SRB is internally burning and under pressure. The Challenger accident happened because the aft field joint of the right SRB failed, allowing the pressurized hot gasses and eventually flame to "blow by" the O-ring and impact the adjacent external tank, causing structural failure.

In hindsight the field joint was inadequately designed, but likely would not have caused a fatal problem if launched under normal Florida temperatures (over 50 degrees F). The abnormally low temperatures of the last Challenger mission, combined with the inadequate joint design produced a seal failure. Engineers at SRB manufacturer Morton Thiokol were aware of the problem and warned against launching, but organizational and management problems prevented their warning from reaching NASA.

Seventeen years later, similar management problems would contribute to the loss of Columbia.

Tributes

On the night of the disaster, President Ronald Reagan had been scheduled to give his annual State of the Union address. He initially announced that the address would go on as scheduled, but under mounting pressure he postponed the State of the Union address for a week and gave a national address on the Challenger disaster from the Oval Office of the White House. [4] At its end, he made the following statement, quoting from the poem "High Flight" by John Gillespie Magee, Jr.: "We will never forget them, nor the last time we saw them, this morning, as they prepared for their journey and waved goodbye and 'slipped the surly bonds of earth' to 'touch the face of God.'" Three days later, he and his wife Nancy traveled to the Johnson Space Center for a memorial service to honor the astronauts.

Funeral ceremonies

The remains of the crew that were identifiable were returned to their families on April 29, 1986. Two of the crewmembers, Dick Scobee and Michael Smith, were buried by their families at Arlington National Cemetery at individual grave sites. The rest were buried together at the Space Shuttle Challenger Memorial in Arlington on May 20, 1986.

Recovery of debris

Debris from Challenger washed up on Florida beaches for years after the incident. On December 17, 1996, more than ten years after the incident, two large pieces of the shuttle washed up on Cocoa Beach. [5]

On board the Challenger was an American flag that was sponsored by Boy Scout Troop 514 of Monument, Colorado. It was recovered intact, still sealed in its cargo bag.