Shuttle probe starts new phase. Rogers panel to prepare recommendations; redesigning boosters likely to be a top one

The hard evidence finally came in this week on how the space shuttle Challenger came mysteriously to explode on the chilly Florida morning of Jan. 28. Later this week, researchers from the National Aeronautics and Space Administrations and teams from the presidential commission investigating the Challenger explosion will turn over their findings to the whole commission.

This marks the beginning of the second stage of the commission's work: shaping the volumes of information it has collected into recommendations for the future.

One recommendation is certain to be redesigning the joints in the solid-rocket boosters that caused the explosion.

The telltale chunk of the right-hand booster was brought up from under 560 feet of Atlantic on Monday. The one-foot by two-foot hole burned along the bottom joint of the piece confirmed what investigators had already concluded about the cause of the explosion.

The work of fixing the joints so they don't leak in the future has already begun. At the Marshall Space Flight Center in Huntsville, Ala., a team of about 70 engineers is already working on 10 different options for revising the controversial joint.

The key question behind this work is how long the shuttle program will be grounded before new joints are fully tested and ready to fly again. NASA still uses 12 months as a planning guideline. Congressional aides, however, see 18 months as a more realistic figure.

The problem is that 6,000-degree gas inside Challenger's rocket booster leaked past the two O-rings that seal the joint between sections of the rocket. This burn-through torched a hole in the rocket and then torched through bracket that holds the bottom end of the booster to the rest of the shuttle system.

The causes of this leak, engineers are saying, was probably some combination of unusually cold weather, sloppy assembly, the bulging and twisting of the whole rocket during firing, harsh winds during the ascent, and leaks in the sealing putty on the inside of the joint.

Some members of the presidential commission, chaired by former Secretary of State William Rogers, have harshly criticized the basic design of the joint.

The possibilities for new designs include joints without O-rings at all. None of the options under review, reportedly, use putty. All of them use some kind of catch-ring to keep the joint from twisting apart and unsealing when the rocket bulges.

A solid-rocket expert outside NASA, Gary Flandro of Georgia Tech, says that the most important problem for the joint is not with the joint itself. Rather it lies in the roughly six-inch air gap inside the rocket between the massive sections of rubbery fuel. The gap, he says, allows the gas shooting down the center hollow of the rocket to blast directly onto the outside joint. Instead, he suggests, the solid fuel sections inside the rocket should themselves be bonded together. ``Closing that [gap] up is, I think, the key to solving the problem,'' says Dr. Flandro.