Trying to prevent a repeat of the Challenger disaster, NASA used heaters Wednesday to warm the space shuttle Endeavour for a scheduled liftoff today in the early morning cold.
NASA expected it to be 44 degrees for the 1:18 a.m. PST launch on a satellite-retrieval mission. That would probably be warm enough under the rules established after the 1986 catastrophe.
The temperature was 36 degrees, the coldest ever for a shuttle launch, when Challenger exploded 10 years ago this month, killing all seven crew members. Investigators found that the cold had stiffened O-rings in the shuttle's booster rockets, allowing hot gas to seep out.
After the accident, NASA adopted a formula involving low temperature, wind and humidity in determining whether it is safe to launch. Heaters also were added to protect the joints and O-ring seals in the boosters and other components.
Shuttle operations director Bob Sieck said the main concern is ice buildup on Endeavour's external fuel tank; NASA began filling it late Wednesday with super-cold liquid hydrogen and oxygen. Chunks of ice could break off at liftoff and damage the shuttle.
Six astronauts, one of them Japanese, plan to retrieve a Japanese science satellite that has been in orbit for nearly a year.