Challenger disaster investigation

01 · The briefing

Begin with the question.

On the morning of 28 January 1986, Space Shuttle Challenger lifted off from Kennedy Space Center on mission 51-L. The flight ended 73 seconds later. The failure lay in a joint between two lower segments of the right solid rocket motor, where O-rings were meant to stop hot gases escaping. Those seals had shown erosion and gas leakage on earlier flights, and that morning was colder than any previous launch. Three explanations compete in public discussion. One holds that the seal failure was a sudden, random defect. A second holds that the risk was known and accepted as part of routine operations. A third holds that a single low temperature reading explains everything. The investigation has to separate what was observed on earlier flights, what the decision-makers knew before the launch, and what engineers recommended in writing. Each of these bears on a different question about the cause. The Commission later examined the design history, the test record and the decisions made in the days before launch. Its findings are a starting point here, but the case asks you to judge which evidence the decision-makers actually had, and which evidence bears on the cause, before accepting any single explanation.

Pipes and walkways of a launch pad thickly coated with icicles. — Where it happened28 Jan 1986 Ice on the launch pad structure on the day of Challenger's launch, 28 January 1986. Photo: NASA · Public domain · Wikimedia Commons.

The timeline

1981 (STS-2)
Erosion is recorded in a field joint on an early flight, the first entry in the Commission's distress table.
1985-01 (51-C)
A field joint on flight 51-C shows erosion at a recorded joint temperature of 53 degrees Fahrenheit, the coldest distressed joint before 51-L.
1985-10 (61-A)
Flight 61-A records blow-by in a field joint at about 75 degrees Fahrenheit, a different kind of gas-path damage.
1986-01-27
In the evening teleconference, contractor engineers oppose launch below 53 degrees Fahrenheit. After an off-net caucus of about 30 minutes, contractor management reverses its position and recommends launch.
1986-01-28
Challenger launches at 11:38 a.m. Eastern time with an ambient temperature of 36 degrees Fahrenheit; the flight ends 73 seconds later.

A researched reconstruction for learning. These reasoning steps simplify a complex record; no score can capture the full history.

02 · The evidence

What does the record show?

Read each exhibit before settling on an explanation. The source links below every exhibit lead to the record behind it.

Exhibit 01

A pattern of erosion, not one event

The Commission's field-joint table lists ten distressed joints in 150 flight exposures, including erosion on several flights and blow-by on 61-A. The table shows that the damage recurred before 51-L. It does not by itself give the probability of loss on a given launch.

Source record s2history.nasa.gov

Exhibit 02

The coldest joint on record

The Commission records an ambient launch temperature of 36 degrees Fahrenheit, 15 degrees below the next coldest previous launch, and estimates the coldest point on the right aft field joint at 28 degrees, plus or minus 5. These are measurements and estimates for one joint on one morning. They do not show how the seal would have behaved on a warmer day.

Source record s2history.nasa.gov

Exhibit 03

A written warning

The Commission's summary of Chapter V states that the contractor's initial written recommendation advised against launch below 53 degrees Fahrenheit. It also says the decision-makers were unaware of that recommendation and of the engineers' continuing opposition after management reversed its position.

Source record s3history.nasa.gov

Exhibit 04

The off-net caucus

The evening teleconference recessed for an off-net caucus of about 30 minutes at the contractor's offices. Testimony in the report describes engineers continuing to object, and a manager saying that a management decision was needed before a final rationale was read from notes. The accounts differ on some points, so the caucus is best read as a documented sequence rather than a full transcript.

Source record s3history.nasa.gov

Exhibit 05

Erosion as a warning sign

Feynman's appendix to the Commission report argues that the O-rings were not designed to erode. He treats erosion as a clue that something was wrong, not as evidence that the joint was safe.

Source record s4history.nasa.gov

03 · Your reasoning

Follow the strongest explanation.

Cut-out portrait of Richard P. Feynman. — In the roomRichard P. FeynmanPhysicist and member of the Rogers Commission; Appendix F of the report gives his own assessment of shuttle reliability.1986 Photo: Unknown author · Public domain · Wikimedia Commons.

Choose an interpretation, then compare it with the evidence. You can revise your choice. The goal is understanding, not a perfect score.

Reasoning step 01 of 03

Which reading of the flight history best fits the Commission's distress table?Several earlier joints showed erosion or blow-by, so the joint's behavior was already a documented concern before 51-L.This matches the table: erosion on STS-2, 41-B, 41-D, 51-C and 61-C, and blow-by on 61-A, all recorded before 51-L.The seals had eroded on many flights without losing a vehicle, so erosion was an ordinary and harmless condition.A long run without loss is not evidence that the joint was safe. The table records recurring distress, and the Commission treated it as a warning.Only the 51-L joint showed damage, so earlier flights tell us nothing about the risk.The table lists ten distressed joints including 51-L, so this reading ignores the recorded pattern.

Evidence-based explanation

The distress table records erosion or blow-by on several earlier flights, which is the best-supported reading. The absence of an earlier loss does not show the joint was safe, and a single-joint view ignores the pattern. The pattern made the joint a known concern, although it does not say when a failure would occur.

Weigh it against

Exhibit 01A pattern of erosion, not one event Exhibit 05Erosion as a warning sign

Reasoning step 02 of 03

Which evidence would best distinguish a temperature-driven sealing failure from other explanations?A count of how many flights had been flown without losing a vehicle.A record of successful flights says little about the mechanism. It does not link any failure to joint temperature.Launch-day wind and cloud observations from the pad.Weather may matter to other risks, but it does not test whether the seal responds differently at low temperature.Joint temperatures on earlier flights set against the damage recorded, together with tests of how the seal responds at low temperature.This ties the observed damage to a measured variable and tests the proposed mechanism directly, which is why the Commission relied on such data.

Evidence-based explanation

Matching damage to joint temperature, and testing how the seal regains its shape at low temperature, can support or weaken a temperature mechanism. Flight counts and weather do not test the mechanism. The Commission combined such data with testing and analysis, so no single data set settles the question alone.

Weigh it against

Exhibit 01A pattern of erosion, not one event Exhibit 02The coldest joint on record

Reasoning step 03 of 03

Which change in the decision process best addresses the failure the Commission identified?Keep launch authority with program managers and treat engineers' concerns as advisory once the schedule is set.This keeps the concerns out of the decision, which is the process the Commission criticized.Relax the recorded temperature limit if earlier launches passed without a loss.The record shows erosion at 53 degrees, so passing without a loss is not evidence that the limit is unnecessary.Ensure written engineering recommendations, including temperature limits, reach the people who sign the launch decision before the decision is made.The Commission found that the decision-makers did not know of the contractor's written recommendation, so routing that information is the direct fix.

Evidence-based explanation

The Commission found that the decision was flawed because the people who decided did not know of the contractor's written recommendation or of the continuing engineering opposition. Routing that information into the decision addresses the gap directly. This is a process lesson drawn from the record, and it does not claim that a single change would have made every decision safe.

Weigh it against

Exhibit 03A written warning Exhibit 04The off-net caucus

04 · The findings

The chain behind the outcome.

The Commission concluded that the loss of Challenger was caused by a failure in the joint between the two lower segments of the right solid rocket motor, specifically the destruction of the seals meant to stop hot gases leaking through the joint during the burn. The record supports that mechanism: erosion and blow-by had been recorded on earlier flights, and the seal's resiliency was shown to decline at lower temperatures. Launch-day conditions were the coldest recorded for a launch, with an ambient temperature of 36 degrees Fahrenheit and an estimated joint temperature near 28 degrees at the coldest point. Those facts establish what was measured and estimated. They do not, by themselves, settle how the seal would have performed on a warmer morning. The decision chain is a separate question. The contractor's engineers recommended against launch below 53 degrees Fahrenheit in writing, then objected during a teleconference. After an off-net caucus, contractor management reversed its position. The Commission found the decision flawed because the decision-makers were unaware of the written recommendation and of the continuing engineering opposition. The chain of information, rather than one hidden fact, is the main lesson for decision making.

Black-and-white photograph of several men in dark suits walking across a grassy area, carrying briefcases, with rocket displays and a parked vehicle behind them. — How it ended1986 Members of the Rogers Commission arrive at Kennedy Space Center to investigate the accident. Photo: NASA · Public domain · Wikimedia Commons.

Contributing causes and conditions

The right solid rocket motor's aft field joint seal failed, letting hot gases escape during the burn.
Erosion and blow-by had recurred on earlier flights, so the seal was already a known vulnerability.
Low joint temperature reduced O-ring resiliency, making the seal respond more slowly when the joint was pressurized.
The launch decision rested on incomplete information, because the written recommendation against cold launches did not reach the decision-makers.
Contractor management reversed its position during the teleconference after an off-net caucus of about 30 minutes, while engineers continued to object.

OutcomeChallenger disaster

Take the method with you

A pattern of recorded anomalies is evidence about a mechanism, not proof that the mechanism is safe because it has not yet failed.
A decision is only as well informed as the written information that reaches the person who signs it.
A stated temperature limit is a claim about a mechanism, so ask how the component responds below that limit.

You can read findings at any time. Exploring every reasoning step marks this case as complete in your notebook.

Open another investigation

Cold seals and the launch call