The presidential commission investigating the Challenger explosion has concluded that the crucial decision to launch the shuttle on Jan. 28 "may have been flawed," commission chairman William P. Rogers announced yesterday.
As a result, Rogers said in a statement, the commission has requested that NASA bar any of the officials who participated in the launch decision from taking part in the internal space agency investigation now under way into the Jan. 28 explosion that killed seven astronauts, including schoolteacher Christa McAuliffe.
Rogers said President Reagan has been advised of the commission's finding and the request, made to the acting administrator of the National Aeronautics and Space Administration, William P. Graham.
NASA officials also said yesterday that it is possible that the ship's commander, Francis R. (Dick) Scobee, noticed a sharp movement of the Challenger in its last second of flight and may have been attempting to call Mission Control at the moment of the explosion.
A detailed chronology of the flight released yesterday by NASA also indicated that with about 11 seconds remaining in the flight, the ship's computers began an attempt to compensate for uneven thrust from the boosters, and it is possible that the movement of the shuttle's control mechanisms may have registered on a video display terminal in front of pilot Michael J. Smith. But it is uncertain whether the crew could have discerned any movement at that time.
Rogers, a former secretary of state, was not available for comment on his statement, released through a spokesman. But a source familiar with the commission probe said its members "have concerns about whether reservations on the part of those determining Challenger's flight-readiness were given appropriate attention" at the highest levels of NASA.
The source said that the commissioners' concerns are focused on whether possible apprehensions by underlings about the impact of the unusual cold weather on the Challenger, and longer-term NASA worries over seals in the solid rocket boosters had been adequately considered by the team of senior NASA officials who decided to give the go-ahead. The Challenger flight had been delayed because of mechanical problems, and then because of a cold snap that set in two days before the eventual liftoff. The night before the launch, temperatures dipped into the mid-20s.
Engineers at Morton Thiokol, manufacturers of the solid rocket boosters (SRBs), asked via a conference call whether the temperatures were too low to allow launch the next day. After a series of conversations between NASA officials at various centers and Thiokol officials, it was decided that the launch could proceed. At the moment of ignition, at 11:38 a.m. Jan. 28, it was 38 degrees Fahrenheit near the pad. None of the previous 24 successful shuttle flights had been launched at less than 51 degrees F.
The commission has been told in recent days of evidence-gathering that the rubberlike seals at the joints of the segmented solid rocket boosters can become stiff at low temperatures, impairing their ability to keep exhaust gases from escaping through the solid rocket booster joints.
The source said the commission's decision to separate these launch decision-makers from the inquiry "is consistent with customary practice with investigations of accidents, that those involved not participate in the investigation. . . you are not investigating yourself."
The decision marks an important moment in the effort to determine why the shuttle blew up, moving it from an inquiry in which both NASA and the commission participated equally, into a framework resembling a quasijudicial proceeding.
The source emphasized that the commission does not believe that information is being withheld. "The commission is fully satisfied with the cooperation of NASA to this point," said the source, who cannot be identified. "It's not a coverup at all."
It is understood that the commission's decision came after the panel spent two days at the Kennedy Space Center at Cape Canaveral, gathering information and talking with officials there. The Kennedy facility is responsible for preparing and launching shuttles.
In recent days, there have been reports that a special team that visited the pad just before the Challenger launch had detected extremely low temperatures along the lower casing of the right solid rocket booster, the one suspected of malfunctioning and causing the disaster.
The authoritative aerospace magazine, Aviation Week & Space Technology, reported in this week's editions that the low temperature readings were never passed on to senior officials. The source declined to comment on this.
But he said, "It all comes down to who raises the red flags, at what level. . . who and why. . . and what do they do about it when they see them? That's really what this issue boils down to."
NASA officials said yesterday that a careful analysis of the precise time line chronology of the Challenger's last moments shows that barely a second before an explosion occurred near the right solid rocket booster, the ship's computers -- trying to compensate as the booster lost pressure -- yanked the vessel to the right and then to the left.
"That would have been felt," said Charles Redmond, an agency spokesman. "It's like wringing your head back and forth. You feel it."
Former and current officials of the space agency said that an explosion apparently is audible on a tape of the flight. The sound occurs just as data transmission from Challenger stops, and officials said the fatal explosion may have been heard through the commander's cockpit microphone as he clicked it on, possibly to ask controllers why the vessel was rocking.
A former Kennedy Space Center official said that there has been speculation -- much of it in Houston, where Mission Control is located and where telemetry data from the flight is monitored -- that the reason an apparent explosion is audible is because Scobee had turned his radio on in an attempt to speak.
There is some question of whether the crew might have felt earlier movements of the spacecraft's control surfaces as it attempted to compensate for its problems.
According to the chronology released by NASA, at about 60 seconds after blastoff, data radioed back from the suspect booster showed its internal pressure had dropped slightly and two seconds later, Challenger's computers began a battle to correct the problem.
Challenger's outermost right wing "elevon," or control flap, was ordered to move at about 62.4 seconds into the flight, apparently to correct for the thrust imbalance between the shuttle's solid rocket boosters. Normally, a NASA official said, the elevon would not move at this point in the climb toward orbit.
The elevon movement did not appear to work. At 63.9 seconds after launch the nozzle of the shuttle's right-hand liquid-fueled main engine moved and the spaceship began to pitch slightly as the computers adjusted the shuttle's flight path. The first heavy jolts to the spacecraft, which the crew might have felt, came just before the moment of explosion, which occurred at 73.226 seconds.