(4 of 7)
Of all the changes, none was more carefully scrutinized than the redesign of what proved to be Challenger's fatal flaw: the joint between segments of the solid-fuel rocket booster. Zeroing in on the booster joints, which are sealed by rubber O rings that are supposed to prevent leaks of superhot gas from the burning fuel, a team composed of outside experts as well as specialists from NASA and Morton Thiokol, manufacturer of the rocket, evolved a design that eventually withstood five full-scale, two-minute stationary firing tests at Thiokol's Utah proving grounds.
- Still, gnawing doubts remained. Despite exhaustive ground testing of the new and modified shuttle parts, none had been tried in the harsh environment of a launch, or in orbit or re-entry. Moreover, some of them are among the more than 1,500 "criticality 1" parts -- that is, items without backup whose failure could end the mission, perhaps catastrophically.
NASA took steps to improve the astronauts' chances of survival should such a mishap occur. For the first time since the summer of 1982, the crew left the launch pad ensconced in bulky space suits, each partly pressurized and equipped with an oxygen tank, a parachute and an inflatable raft. In addition, a new emergency escape system was designed to give the astronauts a chance to leave the orbiter quickly in the event of a "benign disaster" after the boosters had fallen away. In such a crisis, the crew would jettison the huge external fuel tank and stabilize the winged orbiter into a downward glide. Then, when the craft descended to an altitude of about 30,000 ft., the astronauts would set off explosive bolts, blowing a newly installed hatch off the ship, and extend the 12-ft. telescoping escape pole, which is positioned to guide them away from the orbiter's wing and tail. One by one, each would slip a ring attached to his suit around the pole and would slide off into the thin air, deploy his parachute and drop into the ocean, where his radio transmitter would lead rescuers to him. The escape procedure would work, of course, only under circumstances that leave the vehicle intact and under control.
Right up to the moment of Discovery's launch, the space agency displayed caution -- and in the view of some critics, excessive caution -- in preparing to resume shuttle flights. Time and again during the past year, as problems cropped up during tests of new and redesigned shuttle equipment, officials pushed back Discovery's launch date, from February to August, finally settling on Sept. 29. Even during the final stages of the countdown, mission manager Crippen polled top weather advisers individually before waiving the restriction about the winds aloft.
NASA's new manner was in marked contrast to its bold, often arrogant and occasionally careless approach in pre-Challenger days. NASA initially promoted the shuttle as a routine "space truck," an efficient, economical transport vehicle capable of lofting any payload -- commercial, scientific or military -- into orbit. Washington succumbed to that pitch, allowing NASA to decree ! that expendable rockets such as the Delta, Atlas and Titan be phased out in favor of the shuttle.