A Cold Soak, a Plume, a Fireball

Some of the faces seemed out of a distant past. William Rogers, the New York City lawyer and former Secretary of State who had lost Washington turf battles to Henry Kissinger in the Nixon Administration. Neil Armstrong, who had taken "one giant leap for mankind" on the moon in 1969. Richard Feynman, the Caltech physicist who won his Nobel Prize 20 years ago. Others were fresher, including Astronaut Sally Ride, who in 1983 became the first American woman in space. They and nine other experts were appointed last week to a presidential commission charged with finding out why the space shuttle Challenger had blown up 73 seconds after lift-off from Cape Canaveral, killing its seven-member crew. Without even waiting to assemble a staff, the panel promptly went to work, first grilling top NASA officials in public, then probing more deeply in closed sessions.

Much of the public quizzing focused on the Challenger's two solid-fuel rocket boosters, each 149 ft. tall and 12.2 ft. in diameter. Photographs released by NASA left no doubt that an abnormal plume of flame had appeared on the right-hand booster just before a huge fireball engulfed the entire space vehicle. Although NASA's acting administrator, William Graham, said the flame's location had not been pinpointed, it appeared to be about 36 ft. above the bottom of the rocket's nozzle, near an attachment ring where the lower part of the booster was connected to the external liquid-fuel tank. This ring, in turn, was just above one of the three special joints coupling the rocket's stacked solid-fuel segments. Externally, 177 high-strength steel pins held these joints together. Internally the joints were sealed with two large rubber O rings.

NASA's space-flight director, Jesse Moore, told the panel that the errant flame was first visible at 59.8 seconds into the flight. Graham explained on TV that the flame "appears to grow and grow . . . until it finally goes to the explosion point." Thus the controllers and astronauts had only 13 seconds to discover the problem and react. But NASA officials testified that escape would have been impossible in any case. Arnold Aldrich, shuttle manager at the Johnson Space Center, told the commissioners that Challenger could not have separated from the boosters and the tank until the solid-fuel rockets had completed their uncontrolled firing, about two minutes after lift-off. Any earlier separation, he said, would have thrown the shuttle into the wake of the powerful rocket motors, a situation that "is thought to be unsurvivable."

But how had that seemingly fatal plume developed on the booster's side? The panelists kept asking about the unusually cold weather at the launch site. The temperature had dropped to 24 degrees F early that morning and had risen to only 38 degrees at the 11:38 a.m. lift-off. Buffeted by overnight winds of up to 35 m.p.h., the shuttle had gone through what meteorologists call a "cold soak," conditions more severe than those at any of the previous 24 shuttle launches. NASA manuals say that the solid fuel in a booster should be ignited only when the rubber-like mixture is between 40 degrees and 90 degrees . Morton Thiokol, the rocket manufacturer, also specifies that the fuel's temperature should never be allowed to fall below freezing. The insulated boosters contain no internal heat sensors, but NASA technicians calculated the mean temperature to be 55 degrees .