Copyright 1986 The New York Times Company
The New York Times
February 15, 1986, Saturday, Late City Final Edition
SECTION: Section 1; Page 8, Column 3; National Desk
LENGTH: 1104 words


BYLINE: By WILLIAM J. BROAD, Special to the New York Times


Engineers at Morton Thiokol, Inc., are working on new designs to correct a technical flaw in the seams that connected segments of booster rocket of the space shuttle Challenger.

Although company officials conceded that the booster joint has had a long history of problems on shuttle flights, they emphasize that it has not been proved to have been the cause of the Challenger explosion, which killed all seven crew members.

The National Aeronautics and Space Administration decided several months ago that there were problems with the seams but that they would not threaten the safety of the shuttles. The problems involve O rings, seals that are meant to stop flames and hot gasses from escaping the side of the booster rocket.

The new designs are undergoing ''lots of testing,'' Gilbert Moore, a spokesman for the company's facility at Brigham City, Utah, where the booster's motors are designed and manufactured, said yesterday in an interview.

Redesign Could Cause Delays

The redesign effort could be crucial to the future of the shuttle program. If the booster joint indeed turns out to be a problem, experts estimate that its redesign, remanufacture, testing and safety certification could be a slow process, possibly precluding shuttle flights for years.

Nowhere is concern about the technical flaw in the booster rocket more striking that in papers released this week by the Presidential commission investigating the disaster. There, in a document dated Aug. 26, 1985, Morton Thiokol engineers outlined 43 possible solutions to problems in a system of O rings. This system was meant to create a leak-proof seal between the booster rocket's four main segments, keeping hot flames and gasses flowing toward the rear of the rocket and away from seams between the segments.

''It's a staggering list,'' Mr. Moore conceeded yesterday.

O rings are implicated mainly because photographs of Challenger's ascent show a rupture in their general location on the side of the solid-fuel booster rocket, which is 149 feet long and 12 feet in diameter. Some aerospace experts believe their failure allowed flames to escape, igniting Challenger's main fuel tank and creating a huge fireball in the Florida sky.

Problems With Rotation

Many of the O ring solutions considered by Morton Thiokol attempt to get around the problem by addressing the ''rotation'' of the booster's tongue-and-groove joints, a motion that can create a slight gap in the booster's side just seconds after liftoff.

The ''rotation'' occurs because explosive energies inside the booster force the relatively thin steel skins of booster segments outward, puffing them out like a fat stomach. The joints between the segments resist this outward motion because they are made of thicker metal. The result is a ''rotation,'' albeit a very minor one, between elements of the joints. It is called ''rotation'' because there is a slight pivoting motion about the metal pins that hold the segments together.

The trouble with the rotation is that it can unseat and expose the O rings, allowing gasses and flames to escape, according to Morton Thiokol engineers in their report of Aug. 16, 1985, which outlined the 43 solutions.

One of the first options for redesign was to create a staggered firebreak inside the circumference of the booster seam so that flames and gasses would be unable to reach the O rings even if they were unseated by joint rotation. A barrier of fire-proof rubber, the engineers wrote, ''will not allow a direct path for hot gas jet impingement on the O-ring.''

Another option was to have a solid firebreak of fireproof materials between the segments.

Another option was to install a mesh of copper wire that would absorb heat of passing gasses. ''Copper is 10,000 times more heat absorbent than putty,'' the engineers noted.

Still another was to create a firebreak of special rope, which, the engineers said, ''has a 3200 F capability'' to withstand heat.

Reinforcement of System

A different approach centered on reinforcing the O ring system itself, making the rings larger or more numerous. Normally there are two O rings, a primary and a secondary. Several of the new designs center on different ways to using three O rings.

Another generic approach was to try to prevent ''rotation'' of the tongue-and-groove joint. Here one solution was to add two bands of metal about the outer casing of the rocket booster, above its upper and lower extremities, to minimize the expansion of the casing and thus the ''rotation.''

A final group of solutions focused on minimizing the effects of rotation by building on the interior of the booster a ''capture feature'' that would hold down the outer portion of the groove joint that supports the O rings.

At a news conference in Washington on Wednesday, Lawrence B. Mulloy, project manager for solid-fuel booster rockets at the Marshall Space Flight Center in Huntsville, Ala., said the space agency had long been aware of the O-ring problem and that the contemplated solutions were ''in the handout,'' referring to the packet of documents released this week by the Presidential Commission. Before the Challenger explosion, he added, the space agency had narrowed its candidates for a solution, focusing on a capture feature and a larger O ring.

Thomas S. Russell, vice president in charge of corporate development and strategic planning at Morton Thiokol, said the space agency last week asked the firm to stop preparing booster motor cases, installing liners in cases and putting fuel in motor segments for its current generation of boosters.

''We've basically stopped any work that would have to be undone if they decided they need to change the design of the booster segments,'' he said in an interview.

He added that it was ''premature'' to try to pin down the cause of the Challenger accident and that the various options for redesign were meant ''to try to address some of the concerns'' that had recently come to light about the troublesome joints.

----Morton Thiokol Plans Layoffs BRIGHAM CITY, Utah, Feb. 12 (AP) - Morton Thiokol, the sole producer of the space shuttle's solid-fuel booster rockets that are under scrutiny in the explosion of the Challenger, announced today that it will lay off 200 full-time employees and place another 1,400 on a four-day work week. Gil Moore, a company spokesman, confirmed the layoffs at the Wasatch Division west of here and said they would affect employees who have been working directly on the space shuttle program.

The layoffs will take effect Feb. 21, andthe shorter work weeks will begin Feb. 24, Mr. Moore said.

GRAPHIC: Diagrams of booster rocket