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Why Challenger broke apart 73 seconds after launch

On this day · 28 January 1986
100 sec read
Why Challenger broke apart 73 seconds after launch

A cold-stiffened O-ring doomed Challenger in 1986 — but the orbiter didn't simply explode, and its crew cabin survived the breakup.

Verified · NASA

Space Shuttle Challenger broke apart 73 seconds after lifting off from Kennedy Space Center at 11:38 a.m. on January 28, 1986, killing all seven astronauts of mission STS-51L. A failed O-ring seal in a joint of the right solid rocket booster let hot gas escape and burn into the external tank.

The Rogers Commission recorded an air temperature of 36 °F (2 °C) near the pad, 15 degrees colder than any previous launch, and put the coldest point on the failed joint at about 28 °F. Engineers at booster maker Morton Thiokol had recommended in writing against launching below 53 °F. Thiokol’s managers reversed that position, and the commission found that the officials who made the launch decision were never told of it.

It didn’t simply explode

Challenger is usually said to have exploded, but the commission was more precise: an explosive burn of the tank’s hydrogen and oxygen exposed the orbiter to aerodynamic loads that tore it apart. NASA’s crew investigation, led by biomedical specialist Joseph Kerwin, judged the breakup forces of roughly 12 to 20 g brief and probably not enough to kill or seriously injure the crew.

The crew cabin separated, kept climbing to about 65,000 feet, then fell for 2 minutes 45 seconds before striking the ocean at about 207 mph. Of four emergency air packs recovered, three had been switched on. Whether the crew stayed conscious could not be determined.

The last words on the cockpit recorder were pilot Michael Smith’s: “Uh oh.” With him died commander Dick Scobee, Judith Resnik, Ronald McNair, Ellison Onizuka, Gregory Jarvis and teacher Christa McAuliffe.

In his appendix to the commission’s report, physicist Richard Feynman noted that estimates of the odds of losing a shuttle ranged from 1 in 100, from working engineers, to 1 in 100,000, from management. His conclusion:

“For a successful technology, reality must take precedence over public relations, for nature cannot be fooled.” — Richard Feynman, 1986

A second orbiter, Columbia, was lost on reentry in 2003.

73 sec
into flight
36°F
at launch
65,000 ft
cabin's peak altitude

Sources & references

7 references

Well-established. Corroborated by 2 independent sources.

1 NASA Space agency It ended 73 seconds later in an explosive burn of hydrogen and oxygen propellants that destroyed the External Tank and exposed the Orbiter to severe aerodynamic loads that caused complete structural breakup. … The ambient air temperature at launch was 36 degrees Fahrenheit measured at ground level approximately 1,000 feet from the 51-L mission launch pad 39B. This temperature was 15 degrees colder than that of any previous launch. nasa.gov ↗
2 NASA Space agency Those who made that decision were unaware of the recent history of problems concerning the O-rings and the joint and were unaware of the initial written recommendation of the contractor advising against the launch at temperatures below 53 degrees Fahrenheit and the continuing opposition of the engineers at Thiokol after the management reversed its position. nasa.gov ↗
3 NASA Space agency The temperature at the 300 degree position on the right aft field joint circumference was estimated to be 28degrees +/- 5 degrees Fahrenheit. This was the coldest point on the joint. nasa.gov ↗
4 NASA Space agency the forces to which the crew were exposed during Orbiter breakup were probably not sufficient to cause death or serious injury; and … After vehicle breakup, the crew compartment continued its upward trajectory, peaking at an altitude of 65,000 feet approximately 25 seconds after breakup. It then descended striking the ocean surface about two minutes and forty-five seconds after breakup at a velocity of about 207 miles per hour. … The range of most probable maximum accelerations is from 12 to 20 G’s in the vertical axis. These accelerations were quite brief … Four PEAP’s were recovered, and there is evidence that three had been activated. nasa.gov ↗
5 NASA Space agency T+1:13 PLT Uhoh. T+1:13 LOSS OF ALL DATA. nasa.gov ↗
6 NASA Space agency It appears that there are enormous differences of opinion as to the probability of a failure with loss of vehicle and of human life. The estimates range from roughly 1 in 100 to 1 in 100,000. nasa.gov ↗
7 Space Center Houston science institution The cause of explosion was determined to be an o-ring failure in the right solid rocket booster. Cold weather was determined to be a contributing factor. spacecenter.org ↗
✓ Last reviewed

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