Shuttle Panel Cites Fuel Tank Blowout : Conclusion on Sequence of Disaster Reached by Presidential Commission

The presidential commission investigating the Jan. 28 Challenger disaster has concluded that the lowermost bulkhead in the vehicle’s 154-foot-tall external fuel tank blew out, adding a mighty surge to the space shuttle’s upward thrust a split second before it was enveloped in a fireball.

That conclusion is an important addition to the commission’s understanding of the sequence of events that led to Challenger’s destruction. The sequence began with the failure of an O-ring seal on the vehicle’s right solid fuel booster rocket. The seal’s failure caused the booster to emit a blowtorch-like flame near the external fuel tank’s lowest bulkhead.

The bulkhead’s subsequent blowout caused the surge, which was produced by the sudden massive venting of hydrogen from the ruptured tank. The surge and O-ring failure led the damaged rocket booster to pivot, breaking off Challenger’s wing. The rocket then crashed into the tank between the separate vessels containing liquid oxygen and liquid hydrogen, rupturing them both and creating the fireball that appeared from the ground to have been a violent explosion.

Effect of Flame Unclear

Commission sources, who declined to be identified, said it is not clear whether flame from the leaking rocket joint burned through the fuel tank or weakened the bulkhead so much that mounting pressure inside the tank blew it off.

But commission members have settled on the sequence of events leading to the fireball, the breakup of the spacecraft and the death of seven crew members 73 seconds after liftoff from the Kennedy Space Center in Florida.

Their report, due to reach President Reagan on June 6, sources said, will blame the disaster on the design of the solid rocket booster, the National Aeronautics and Space Administration’s failure to heed repeated warnings of disastrous consequences and a breakdown of the system designed to assure flight safety.

Wider Findings Seen

Although the commission’s primary charge was to find the probable cause of the accident that brought the U.S. space program to a standstill, it has already made it clear that it will go beyond that determination and the making of the kind of technical recommendations that come from investigations of airline crashes.

Former Secretary of State William P. Rogers, the commission’s chairman, has at times been sharply critical of NASA, most recently in a closed meeting in which he told the agency’s engineers that persistent problems with the solid rocket boosters’ joint seals had been “almost covered up, ever so slightly noted” as officials continued launching shuttle flights.

Such comments, beginning early in the investigation and often voiced in public, prompted criticism that he and the commission were engaged in a “witch hunt” and were searching for scapegoats before finding out what actually occurred.

The most pointed example of the commission’s activist posture came last week, however, when commission members privately persuaded acting NASA Administrator William R. Graham and shuttle chief Rear Adm. Richard H. Truly that they must bring in outside experts to oversee the redesign of the solid rocket booster’s flawed joint seals, which have been identified as the immediate cause of the tragedy.

A source familiar with the episode said several members of the commission thought they could not in good conscience submit their report to the President and disband, leaving the redesign in the hands of the Marshall Space Flight Center organization that still defended its decision to press ahead, despite warnings, with the Challenger launching.

Still ‘High-Risk’

The source said the commission will not only call for reform of what Rogers called NASA’s “flawed” decision-making process, but will emphasize that manned spaceflight must still be viewed as a “high-risk program.”

Most members of the commission, the source said, believe that the much-publicized teacher-in-space and journalist-in-space projects should be dropped, but there has been no decision to put such a recommendation in the report to the President.

New Hampshire schoolteacher Sharon Christa McAuliffe was one of the seven killed in the Challenger explosion. Riding in the spacecraft’s mid deck, she was to be what she called the first “ordinary person” in space.

In the wake of the accident, the Reagan Administration announced that the program would go on, and the selection process is under way to name a journalist to fly on a future shuttle mission.