Mishaps Plagued Assembly of Rocket Joint, Panel Told

An extraordinary string of mishaps and irregularities bedeviled the assembly of the Challenger rocket joint that is suspected of rupturing before the spacecraft’s explosion, the presidential commission investigating the space shuttle disaster was told Friday.

Among the most serious of several problems listed during testimony was the failure of the right solid rocket’s aft section to fit properly into its adjoining section, forcing technicians here to take the uncommon but not unprecedented step of bending the delicately designed circular structure back into shape.

Commissioners were also shown pictures of what some experts believe were preflight flaws in one of the two rubbery O-rings designed to seal the joint, which testimony affirmed has become the most likely starting point in a chain reaction that resulted in the loss of the spacecraft and its crew of seven on Jan. 28.

National Aeronautics and Space Administration officials described a battery of tests now under way to determine what caused the rupture in the seam between the right-hand rocket’s lower and middle sections, which are constructed at a Morton Thiokol Inc. facility in Utah and assembled here.

William P. Rogers, chairman of the commission, questioned whether it was proper to allow NASA and Morton Thiokol to conduct the tests without oversight by outside experts.

Morton Thiokol engineers had warned the night before the launching that the bitter cold temperatures on the launching pad could undermine the ability of the O-rings to position themselves properly and to form a perfect seal when the rockets were ignited. NASA propulsion experts, however, challenged their data, and Morton Thiokol management overruled the engineers and consented to launch.

“Will the tests ever re-establish the confidence in that joint and these O-rings so that subsequent flights could continue with the same equipment that was on the Challenger?” Rogers asked Jerrol Littles, associate director for engineering at NASA’s Marshall Space Flight Center in Huntsville, Ala.

Littles’ answer was of a technical nature, and Rogers made it clear that his question was directed more toward credibility of the parties involved in the test.

“In other words,” Rogers persisted, “the Thiokol engineers thought that, in view of the weather conditions, the flight should not be launched, and wished the people at Marshall had felt the same way--and these are the very people who are conducting the tests. It would be wise to pick some other outside independent source to work with you on it.”

Littles said that NASA officials “certainly will look into” that suggestion.

Zeroing In on Booster

Another NASA witness, Thomas Lee, deputy director of the Marshall Center, said that while a leak in the spacecraft’s large external fuel tank has not been fully ruled out, it is becoming increasingly clear that the right-hand booster failed.

When asked by Rogers if the fuel tank had not been completely exonerated only because Marshall officials did not want to admit that the solid rocket booster was the source of the problem, Lee responded: “No sir, we know the SRB failed. We know the SRB is the failure.”

Much of the testimony Friday conducted before a large audience of tourists in a theater here, hinted at intramural blame-placing among NASA centers. While experts from the Kennedy Space Center maintained that there was no evidence indicating handling mishaps contributed to the disaster, witnesses from Marshall made suggestions to the contrary.

Four theories about what might have caused the joint to rupture were advanced by NASA witnesses, including the possibility that it was damaged during assembly or was equipped with a defective O-ring.

Mishaps Described

NASA officials from this space center described a number of mishaps that plagued the aft section during the assembly process.

The lower segment on the left-side rocket had to be replaced, making it necessary to add a new right-hand aft segment so that the thrust of the pair would be matched.

Normal stacking procedures were changed because of delays.

The procedural mistake eliminated a round of inspections for seven out of the 12 O-rings used in the six joints between sections of the twin rockets.

Rain leaked through a tarpaulin while the new right-hand aft section was stored outside for a day, making it necessary to carefully dry the precision-fitting section.

Tiny blemishes were detected in the groove at the top of the aft section, where a tongue from the section above slips in. Testing indicated that “pitting” was not so severe as to require more delicate sanding of the groove.

And a photograph showed that a tiny portion of the secondary, or backup, O-ring in the right-hand lower joint appeared not to have fit snugly against the outer surface of the piece, perhaps leaving an avenue for propellant to escape.

Significance Questioned

NASA and Morton Thiokol witnesses stress that most of these events were not unique to this particular launching, and none has yet been determined as significant.

The commission, however, seemed most interested in testimony about how a hydraulic lever had been applied to the right-hand middle section after workers found that the section did not fit perfectly into the U-shaped top of the lower section.

Richard P. Feynman, the Nobel Laureate physicist from Caltech in Pasadena, said workers he had interviewed privately here indicated that they had been concerned for some time about the problem of poor fit between rocket sections, “but had not done a good job of communicating their concerns up the line.”

Robert Lang, a NASA official, said that the hydraulic tool had been introduced two years ago, and used on six joints on various flights. He said that there did not appear to be any correlation between use of the so-called circumference alignment tool--also known as “a rounder”--and known previous cases of erosion of O-rings on other joints.

Pieces of the section are designed so that metal does not touch metal in the joint.

Lang said that in the case of the Challenger’s right-hand rocket, it was necessary to pull the tongue of the middle section inward by a quarter of an inch to ensure that metal did not touch metal.

Inside Rim Damage Possible

Feynman and other commissioners questioned whether it was possible that in perfecting the fit on the outside rim the technicians might have destroyed the fit on the inside rim of the U-shaped joint. This could prove crucial because it is on the inside part of the U-shaped joints that the O-rings fit, and with their questions the commissioners speculated whether the tight fit might have damaged the O-rings and made them unsuitable for sealing.

NASA officials conceded this possibility could not be ruled out and said it was the subject of investigation.