Today marks the 35th anniversary of the Space Shuttle Challenger disaster which occurred on January 28, 1986, when the NASA Space Shuttle orbiter Challenger (mission STS-51-L) broke apart 73 seconds into its flight leading to the deaths of its seven crew members. STS-51-L was the 25th American Space Shuttle Program flight since the program began in 1981. It was also the first mission to have a civilian on board, American teacher Christa McAuliffe. The spacecraft disintegrated over the Atlantic Ocean, off the coast of Cape Canaveral, Florida at 11:39 EST (16:39 UTC). According to the Report of the Presidential Commission on the Space Shuttle Challenger Accident, weather conditions were likely one of the factors that contributed to the incident. Tests conducted during the subsequent investigation showed that O-rings were much less resilient at lower temperatures, but the extreme cold at the Kennedy Space Center was not the only weather factor involved with this tragedy.
Weather’s role in scheduling changes prior to the actual launch day
Challenger’s launch had originally been scheduled for the afternoon of January 22nd. After a two-day slip related to the previous shuttle mission, bad weather at an emergency landing site in Senegal and problems with an alternate site in Morocco delayed the launch to Sunday, January 26th. Air Force weather forecasters provided a pessimistic Sunday forecast to NASA managers the night before, causing managers to postpone Sunday’s launch in advance. However, as it turned out, the weather was fine on that Sunday morning leading launch director Gene Thomas to say “Sunday morning, the weather was perfect. We got a bad report. It happens.”
The countdown then proceeded towards a launch on Monday, January 27th at 9:37 a.m. After the crew boarded Challenger, a tool used to close the hatch became stuck. The ground crew eventually removed the tool, but by that time crosswinds at the Shuttle Landing Facility rose above the acceptable limit for a Return-To-Launch-Site (RTLS) emergency landing. At 12:35 p.m., the launch was scrubbed for January 27th and rescheduled for Tuesday, January 28th at 9:38 a.m. After Monday’s scrub, weather forecasters briefed managers on the outlook for Tuesday morning, January 28th. Clear skies were forecast, but unseasonably cold weather was expected to sweep through central Florida. The minimum predicted air temperature at the launch pad bottomed out at 22°F for the hours just before dawn on Tuesday, January 28th.
With sub-freezing temperatures predicted, ground crews drained most of the water pipes at the launch pad to minimize ice formation. Those that could not be drained were left running overnight, and strong wind gusts blew water onto pad structures where it subsequently froze. The ice inspection team was sent to the launch pad several times overnight to evaluate conditions at the launch pad. Before each shuttle launch, the ice team would do a review of any potential ice buildup on the external tank caused by the supercooled liquid oxygen and hydrogen in the tank. Ice on the tank and launch pad structure was considered a debris hazard because it could break off and damage the shuttle’s fragile thermal protection tiles (i.e., heat shield). Upon seeing the amount of ice on the pad, the launch team decided to delay the launch to 11:38 a.m. in order to give the sun time to melt some of the ice and minimize the debris risk.