Even before investigators determine the precise cause of the space shuttle Columbia disaster, NASA officials have begun a far-ranging internal review that could lead to an overhaul of the key aspects of the shuttle's design and operations.
The review, ordered late last month by Ronald D. Dittemore, the space shuttle program manager, addresses several recurrent problems that have been exposed since the Feb. 1 accident. They include the loss of chunks of foam insulation from the huge external fuel tank near a "bipod" metal frame that connects the tank to the orbiter.
Investigators believe that large pieces of the foam or ice that broke away from the external tank on liftoff may have damaged the shuttle's heat shielding in the area of the left wing, allowing superheated gases to penetrate the shuttle's aluminum skin as it plunged back into Earth's atmosphere. Also today, a new analysis of Columbia's telemetry was released. It indicated that the space shuttle was skidding and spinning out of control during the last two seconds of data transmission just before the main body of the orbiter broke up, killing the crew of seven.
On Feb. 25, investigators said that their first review of the last two-second burst of data, sent about 9 a.m. Eastern time, showed the shuttle still on course and in the proper orientation, although it had lost hydraulic pressure on the left side, indicating severe damage to the left wing.
The new timeline released by NASA and the investigative board describes a very different scenario. In it, the shuttle began to spin out of control, then break up seconds after three large pieces of debris were photographed peeling off the shuttle.
For weeks, experts inside and outside NASA have been working to reconstruct the incomplete data transmitted in the final 32 seconds of the flight. The last two seconds of data -- which followed 25 seconds of silence when the shuttle's antenna was blocked by its vertical tail -- were fragmentary and "dirty," and required extraordinary technical enhancement to discern the latest, still tentative, findings.
The latest analysis showed that sensors in the left wing and in the left maneuvering rockets had stopped reporting data as the orbiter continued to spin out of control.
The data also raise the possibility that shuttle commander Rick Husband or co-pilot William McCool may have tried to override the shuttle's autopilot during those final seconds and take control. However, NASA officials stressed today that the data are suspect and that it was possible that Husband accidentally tripped the control stick.
The letter from Dittemore, released over the weekend, said the improvements under consideration would be essential to returning the three remaining shuttles to flight, regardless of the findings of the investigation headed by retired Adm. Harold W. Gehman Jr.
Sensitive to criticism that the astronauts were sent into space without any way of inspecting the spacecraft for damage to the heat-shielding tiles, or of making repairs, NASA officials are also studying ways to identify and repair damage to the tiles or the leading edge of the shuttle's wings, which bear the brunt of the intense heat during reentry. Dittemore's letter said the reassessment should concentrate on the possibility of utilizing the international space station as a repair platform.
NASA is looking at ways to improve existing ground-based and flight-based photographic and radar equipment to detect damage. Another possibility would be to install television cameras on the external tanks of future shuttle flights, as NASA did for the first time on a mission last October, to provide images of the thermal protection system during launch.
Officials also plan to reexamine the possibility of modifying the trajectory of the shuttle to minimize entry heating.
"With an eye towards returning to flight, there are some actions the program feels we should look at immediately, in parallel with the activities that are underway with the Columbia accident investigation board, while supporting their work," James A. Hartsfield, a NASA spokesman, said today. "These are actions we feel are prudent to take right now."
Dittemore's letter indicated that NASA is taking more aggressive steps to correct problems and prepare for the resumption of shuttle operations than senior officials in Washington had indicated. NASA Administrator Sean O'Keefe has said that most of what NASA does to address safety problems with the aging shuttle fleet will be dictated by the findings of the investigating board, which for over a month has tried to piece together clues to explain the chain of events that led to the disintegration of the Columbia over east Texas.