Clues Emerging From 15 Tons of Shuttle Debris

It rained for nearly an hour. Cargo doors, delicate thermal tiles, flaming chunks of rocket motor--broken bits of America’s space program--sailed down noiselessly over 554 square miles of the Atlantic Ocean.

The falling debris launched the largest ocean salvage effort ever attempted. After rocket tests, computer analyses and video replays have failed, investigators now are turning to the spacecraft itself for answers to a tragedy that occurred nine miles above their grasp.

Now, more than eight weeks after the Jan. 28 shuttle explosion, clues are emerging from the more than 15 tons of Challenger wreckage laid out on a warehouse floor at Cape Canaveral.

Investigators examining the debris have been able to determine precisely how the shuttle’s enormous fuel tank exploded, and they are nearing a final answer on where a failure occurred on the right solid rocket booster, the salvage director, Col. Edward A. O’Connor, said in an interview.

Investigators from the National Transportation Safety Board are analyzing the crushed crew compartment to determine how to offer astronauts on future shuttles a better chance of survival.

“A lot of the clues are very faint clues, but it’s amazing what we can recover with very little,” O’Connor said.

New Meeting Ground

It was the nation’s first in-flight space disaster, but the waters off Cape Canaveral have become a new meeting ground for salvage and reconstruction specialists versed in jetliner crash investigations.

Many of them hauled up wreckage from the Korean Air Lines jet shot down by the Soviets over the Sea of Japan in 1983 and the Air-India 747 that crashed off the Irish coast last year as a result of a bomb blast.

The techniques are the same. But there is really no comparison, and there may never be.

For one, the Air-India search covered 600 square miles, and the KAL salvage effort was concentrated in an area only about 10 miles in diameter. In the 11 days following the Challenger accident, Coast Guard ships and airplanes scoured 40,000 square miles of ocean for surface debris, picking up wreckage as far north as South Carolina.

‘An Awful, Sorrowful Task’

Since then, an armada of 11 ships, two manned submarines, two unmanned submersibles, four sonar systems and 401 Navy and contractor seamen has scoured 554 square miles of ocean bottom for additional wreckage, fighting swift currents and visibilities of less than a foot at times.

“It was an awful, sorrowful task. Every piece we pulled out of the water hurt a little,” Coast Guard Lt. John Philbin told reporters after the first few days of the search.

“It wasn’t unusual to see people just all of a sudden break down in tears,” said Petty Officer Brenda Toledo. “People who hadn’t smoked in 10 years, you’d see them just pick up a pack of cigarettes and start smoking.”

Yet the recovery effort has already yielded important evidence, some of which contradicts what investigators had earlier believed about the shuttle accident.

Analysis of Fuel Tank

For instance, analysis of pieces of the external fuel tank, which held 1.5 million pounds of volatile liquid hydrogen and oxygen at liftoff, shows that the tank did not explode when heated by fiery gases leaking from the right solid rocket booster, as earlier believed.

“In the external tank, we now know it was a catastrophic overload mechanism causing the failure. It was not an internal explosion. It was not anything hitting it as such,” said O’Connor, who is overseeing debris analysis for NASA’s investigating task force.

Microscopic examination of pieces of the aluminum tank and its connecting arms shows, rather, that the gyrations of the leaking rocket booster caused stresses on the tank it was never designed to withstand, even before the booster plunged into the tank.

Because of those twisting forces, the tank simply sprang a leak that allowed gases to escape, mingle and ignite, O’Connor said.

More Important Clues

The black thermal tiles that once protected Challenger’s outer skin provide even more important clues.

Because each one is individually numbered showing its location on the orbiter, investigators have been able to locate those tiles nearest the apparent leak in the solid rocket booster.

‘Flame Impingement’

Those tiles clearly show “flame impingement,” O’Connor said. They are pitted and scorched, providing a helpful road map to the point where flame emerged from the booster.

Moreover, they are pocked with tiny fragments of metal from the shuttle’s main engines--mounted on the rear of the orbiter--an indication that the engines themselves were flaming and beginning to melt before the explosion.

The flameout probably occurred after liquid hydrogen began to leak out of the fuel tank, forcing too rich a mixture of liquid oxygen into the main engines, O’Connor said.

Fragment of Rocket

On March 17, a massive oil rigging vessel, the Stena Workhorse, hauled up the most important piece of wreckage yet, a 560-pound rocket fragment that included part of the joint that is believed to have developed the fatal leak.

While investigators believe the 5-by-6-foot chunk came from a point on the booster directly opposite the failure point, it shows flame and soot patterns that would be consistent with a leak. Wind tunnel tests to duplicate the soot patterns will be able to definitively pinpoint the source of the flame, even if no additional booster segments are found, O’Connor said.

But NASA has directed salvagers nonetheless to concentrate their efforts on finding the fragment of the booster that includes the suspected failure point, as well as the segment directly above the leak.

“If we could recover that piece of case exactly (above) where the initial failure occurred, we would expect to see streaking going very high up the case. A failure would drive hot gases straight up, then, as burn-through progressed, the gases would go straight out,” O’Connor said.

Pattern of the Gases

Investigators are also looking for the section of fuel tank directly across from where the burn-through occurred to measure the pattern of the gases.

The crew cabin, found in several broken pieces about 17 miles off the coast, is not expected to yield much information about what caused the explosion.

Yet the fact that its components were found clustered so closely together on the sea floor suggests that much of it may have been intact when it hit the ocean surface--providing valuable information for safety board investigators.

“We’re very much interested in cabin safety, cockpit safety, and I can see a parallel in trying to determine as much as can be determined about the dynamics of the astronauts, to see if there would be a similar accident, whether there would be any possibility of saving the crew,” said safety board spokesman Ira Furman.

Tapes May Yield Clues

Tapes from Challenger’s operating computers, retrieved from the crew cabin, are being carefully cleaned and dried now in the hope that they may tell what happened in the last few milliseconds of the flight after all communications with the ground were cut off.

Investigators may find out from the tapes, for example, whether commander Francis R. (Dick) Scobee made any last-minute attempts to retrieve data from the computers about unusual rumblings crew members may have felt in the spacecraft.

Meanwhile, surface ships equipped with sonar have scanned nearly the entire sea bottom looking for the critical pieces of rocket booster debris that are likely to provide the only final answer to what happened to Challenger.

A little more than 590 sonar contacts have been made. Submarines have gone down to probe 101 of those contacts. Thirty of them proved to be shuttle debris.

More Pieces Found

The Navy salvage ship Preserver reported Saturday that it had retrieved several more small, unidentified pieces of the shuttle.

“The divers have identified several pieces on the bottom, but they’re heavily silted and have to be dug out,” the Preserver radioed.

The rest of the sonar contacts were beer cans, old outboard motors, oil drums, shipwrecks, even a nearly intact DC-3.

Radar tracking the careening right booster during the moments after the explosion shows it broke into at least four pieces, scattering into even smaller debris along a 42-mile path.

One of the most promising booster debris sites lies nearly 2,000 feet below the surface--far below the range of human divers.

Work Often Tedious

Accordingly, the work is slow, very often tedious. Small submarines scoot slowly across the ocean floor, probing the murky waters with underwater cameras. Hauling a single piece of wreckage to the surface can take as long as 18 hours.

The frustration bubbles easily to the surface, said the first officer of one salvage ship, who asked not to be identified.

“We (are) sitting out there, we got NASA guys, we got Morton Thiokol (manufacturer of the rocket boosters), we got astronauts--everybody trying to save their ass.”

It often seems that observers on ship seem primarily interested in proving they were not responsible for the accident rather than searching for the ultimate answer, he said.

Cost of Search

So far the search has cost $6.8 million. Navy salvage officials say they hope to round up the most important pieces of debris by April 17, when NASA is due to present its findings on the explosion to a presidential investigative commission.

In all likelihood only a fraction of the shuttle will have been retrieved by then. But that may be all that is needed to answer investigators’ questions, Navy officials said.

The difficulty of the task was underlined last week when for seven straight days the largest and most complicated salvage effort in history ground to a halt to wait out the stiff breezes and high seas that made underwater operations impossible.

‘Passionately Involved’

Still, said Daniel Schwartz, captain of the Seward Johnson, a private scientific research ship, “This is something that we’re all passionately involved in.”

The Seward Johnson, with its sophisticated four-man submarine, the Johnson Sea Link II, has located some of the most critical rocket segments uncovered during the search.

Many members of the Fort Pierce, Fla.-based crew were watching that Jan. 28 morning when the shuttle blew up.

“We knew almost immediately that our unique ocean-searching capabilities would be needed,” Schwartz said.

“We’ve always felt very close to the space program. They’re explorers of outer space, we’re explorers of inner space--an environment equally harsh.”

RECOVERING THE CHALLENGER

Orbiter 20% recovered, including 75% of the main engines and 75% of the crew module. Specific components:

Majority of rudder speed brake Portion of aft thrust structure Majority of main propulsion system Body flap Portion of base heat shield Right elevon Lower skin panels Liquid oxygen umbilical Main landing gear doors Lower forward and aft fuselage panels Portion of crew module Right aft side wall Portion of payload bay doors Portion of radiators SOLID ROCKET BOOSTERS 10% recovered, including:

External tank attach segment 2 aft center segments Forward cylinder fragments

Rate gyro Systems tunnel from forward skirt Nose cones Parachute RIGHT SOLID ROCKET BOOSTER Located but not recovered

1. Portion of nose cap

2. Portion of forward skirt

3. Aft skirt assembly

4. Lower portion of aft segment

EXTERNAL FUEL TANK 10% recovered, including:

10-12% of liquid hydrogen tank Majority of range safety destruct system

Portion of liquid oxygen feed line 40-50% of inner tank skin Less than 1% of liquid oxygen tank Nose cone skin PAYLOAD Tracking data relay satellite: less than 1% recovered

Inertial upper stage propulsion system for launching satellite into orbit from Challenger payload bay: 65% recovered

KEY PARTS STILL MISSING 1. The fragment of the right solid rocket booster that includes the portion of the joint suspected of failure. 2. The segment of the rocket directly above the leak, which could indicate how failure progressed. 3. The section of external fuel tank directly across from where the burnthrough occurred, which could reveal the pattern of escaping gases.

4. The remainder of military tracking data relay satellite. Recovery is important to measure

the kinds of loads it encountered during the accident, and also for security reasons.