NASA Reveals Options to O-Rings : Engineers Seek Redundant Design to Preclude Disasters

NASA engineers released plans Wednesday to redesign six key parts of the space shuttle’s ill-fated solid rocket boosters, including the flawed joint that caused January’s Challenger disaster and two seals that posed “serious” hazards on earlier shuttle flights.

The final blueprints, to be drawn up later this summer, also may replace the rubbery O-rings cited in the Challenger accident for rings made of metal or some other material, officials said.

“In all cases it will be a redundant system, a fully redundant system,” John Thomas, a NASA engineer in charge of the redesign project, said in a news conference televised from the agency’s Marshall Space Flight Center in Huntsville, Ala. “I think this design will preclude this disaster from happening again.”

The Challenger disaster occurred 73 seconds after its Jan. 28 launch, killing all seven of its crew, when a faulty joint in the right rocket booster allowed hot gases to escape and sear through an adjacent tank of explosive hydrogen.

Accident Traced to Joint

In a scathing report, the blue-ribbon presidential commission on the shuttle disaster concluded last month that NASA launched the Challenger despite warnings that the faulty joint was dangerous and had no redundant or “backup” safety device should it fail.

The redesign proposals were drafted by experts from NASA and Morton Thiokol Inc., manufacturer of the solid rocket booster. They stem from engineering reviews of the fatal joint and other points in the booster where similar gas leaks were believed possible.

The new boosters should be “extremely resistant to any failure” because of the engineers’ safety improvements, Thomas said, but he declined to say that they or any other rockets could be made completely foolproof.

Expects Little Added Weight

Thomas said the changes will add little if any weight to the boosters and, it is hoped, may be completed in time to allow the shuttle to return to space by NASA’s target date of July, 1987.542402661but some parts of existing booster segments can be used in the new rockets without changes.

The team of experts said it is considering two similar redesigns for the rocket seam blamed in the Challenger explosion, the “aft field joint” that linked two barrel-shaped segments near the bottom of each of the shuttle’s boosters. In that joint, the top segment, or “tang,” is lowered into a U-shaped “clevis” at the upper end of the lower segment.

Two O-rings between the tang and clevis are supposed to seal the booster’s hot gases inside the rocket case, but the stresses of launch cause the booster to flex slightly, opening a gap in the joint that the O-rings could not completely seal.

Stress Opened Gap

Both redesigns would lessen the effect of the flexing, essentially by adding a so-called “capture mechanism” to the upper portion of the tang that would create a closer fit between the tang and clevis and force hot gases to burn through several additional seals and rings before escaping.

One of the proposed designs also would place a new, wider band about the outside of the rocket joint, and the other would add a third O-ring to the current two. The third ring would be positioned so that any flexing in the rocket would cause it to seal, even if the other rings failed.

Thomas said either of the designs “resolves all the difficulties” in the joint outlined by the presidential commission on the shuttle.

In addition, the NASA engineers proposed to place cork and synthetic insulation--and even electric heaters--on the exterior of the boosters’ joints to keep them warm and free of rainwater during cold-weather launches. Low temperatures, which reduced the O-rings’ ability to expand and seal the rocket joint, are believed to have contributed to the shuttle accident.

The first full-scale tests of the redesigned boosters will not occur until November or December, Thomas said.