On January 28, 1986, the Challenger space shuttle broke apart 73 seconds after liftoff from Cape Canaveral, Florida, killing all seven astronauts aboard. The disaster was caused by a failure in a rubber O-ring seal on the right solid rocket booster, which was unable to close properly in the cold weather. The launch took place at 2.2 °C (36 °F), just above freezing, but the O-ring was estimated to be at −2 °C (28 °F), significantly colder than the recommended minimum of 11.7 °C (53 °F) set by engineers at Thiokol, the company that manufactured the O-rings. Despite these concerns, NASA approved the launch. The failure of the O-ring led to a leak of hot gases from the solid rocket booster, which caused the structure to disintegrate. The first visible sign of the problem was a puff of smoke from the seal 0.678 seconds after ignition. Engineers had warned that colder temperatures made the O-rings less flexible, slowing their ability to close the gap between segments of the rocket. Tests showed that at 25 °F (−3.9 °C), the O-rings could not form a proper seal, and the estimated temperature of the Challenger’s seal was within that range. Physicist Richard Feynman, who was part of the official investigation, demonstrated this issue by submerging a seal in ice water, showing that the material became too rigid to function effectively. Before the launch, Thiokol engineers had advised against flying below 53 °F (11.7 °C), a recommendation included in their report. However, NASA officials overruled this decision after a closed-door meeting, and the launch proceeded. The investigation later found that the Challenger’s seal had been the weakest of any previous launch, and the cold weather exacerbated the problem. The disaster was the result of a long history of known issues with the O-rings, which had been identified as early as 1977 but were not fully addressed. The Challenger was carrying a crew of seven, including teacher Christa McAuliffe, who was set to be the first classroom teacher in space. The shuttle launched from Launch Pad 39B at 11:38 a.m. and disintegrated 73.213 seconds later, with the last telemetry signal received at 73.618 seconds. President Ronald Reagan established a commission led by William P. Rogers to investigate the disaster. The findings led to a three-year halt in the space shuttle program, as NASA worked to redesign the O-rings and improve safety protocols.