NASA Unveils Proposed $300-Million Redesign of Shuttle Rocket Joint

The National Aeronautics and Space Administration on Tuesday unveiled a $300-million redesign of the faulty solid rocket joint that caused the Challenger space shuttle disaster last January.

Although the new design is still subject to change, space agency officials expressed confidence that they have removed flaws that permitted 5,900-degree gas to leak from Challenger’s right booster rocket, causing the conflagration that killed the shuttle’s seven crew members.

The pace of the redesign and testing program, which has been under way since early spring, will determine when the United States’ grounded space shuttle will fly again.

‘Made Good Progress’

“We have made good progress, and we’re well on the way to accomplishing a good, safe redesign,” John Thomas, manager of the redesign work at NASA’s Marshall Space Flight Center at Huntsville, Ala., said at a news conference. “We have taken every step to understand what failed on the Challenger and to incorporate a design that won’t allow that to happen again in the future.”

A new “capture” feature will strengthen the joint to eliminate bulging or rotation in the split second after ignition. It consists of a metal brace on the inside of the joint. An additional O-ring will be added to create a triple seal against a gas leak. Zinc chromate putty, which was supposed to have prevented the searing gases from reaching the O-ring seal in the Challenger booster, will now be replaced by a new flameproof compound.

Hope to Assure Seal

Engineers hope to prevent the creation of a tiny opening for flame to reach the O-ring assembly during the first half-second after ignition, when pressure inside the solid booster builds from zero to 900 pounds per square inch. And, with the third O-ring, they hope to assure that at least one ring will always seal, eliminating the possibility of the kind of fatal leak that occurred on Challenger last Jan. 28.

If approved by an oversight panel of the National Academy of Sciences’ National Research Council, the design shown Tuesday is expected to be formally adopted by the space agency next month. This would lead to a series of tests, culminating with a full-scale horizontal test-firing of the redesigned booster in September, 1987. The current plan is to launch the next shuttle mission in early 1988.

But, although Thomas expressed confidence in the new joint design, he said no decision has been made on the larger issue of whether to test-fire a full-scale version of the redesigned booster in a vertical position.

May Cause Delay

The Rogers Commission, which investigated the Challenger tragedy, stopped short of recommending a vertical test but urged NASA to consider it. However, NASA estimates that it would require a year to two years to prepare for such a test--making it impossible to return the shuttle to active status on the schedule now envisioned.

Thomas acknowledged that the new “capture” feature will make the assembly process at the Kennedy Space Center more difficult, and he said this remains a subject of concern to NASA engineers working on the redesign.

Uses New Material

The “capture” feature is designed to significantly reduce the gap between interlocking components of the joint created at the moment of ignition. In the old design, the joint rotation at ignition could for a split second open a gap as large as .03 of an inch but, with the “capture” feature, the gap will never exceed .006.

The new design calls also for fabricating O-rings from a new material that is more flame-resistant, and for mounting small heaters on the outside of the booster to prevent cold weather from stiffening the rings.

Although the cost of the program was estimated at $300 million, NASA officials said all joints and rocket casings manufactured for the current booster will be usable in the redesign.

In addition to the redesigning of the field joint that failed on Challenger, improvements are being made in the booster’s nozzle and in the joint where the nozzle connects to the lowermost rocket casing. Both had shown evidence of damage and had been a source of concern before the Challenger accident.

With the booster redesign apparently on schedule, President Reagan is expected within the next few days to announce his long-term plans for the shuttle fleet, laying out his proposal for financing a replacement for the Challenger and increasing the use of expendable launching vehicles for both military and commercial launchings.