Posted on: Tuesday, February 4, 2003

COLUMBIA LOST
Actions of shuttle's 'brains' examined

By Ariana Eunjung Cha
Washington Post

HOUSTON — As they hurtled to Earth, the seven astronauts aboard the space shuttle Columbia ceded control of their spacecraft to a sophisticated flight-control system made up of four onboard computers and a backup.

The machines were supposed to analyze information from the orbiter's sensors and satellite systems, and make the hundreds of decisions each millisecond needed to keep the shuttle safe and on course.

Although early attention in the investigation into the loss of the shuttle has focused on possible problems with the heat-resistant tiles, NASA investigators say a major part of their inquiry is determining whether something might have gone wrong with the shuttle's "brains," the computerized flight controls.

The onboard computers recorded a surge in temperature on the left side of the shuttle and detected increased drag on the left wing. They directed the craft to compensate for the changes by firing two of four right-side jets designed to keep the shuttle on a straight course — the biggest shift of direction ever ordered on re-entry.

Ron Dittemore, the NASA shuttle program manager at the Johnson Space Center here, said all indications so far are that the main computers were functioning properly, but that it was hard to tell what happened after communications with the shuttle were cut off at 8:59 a.m.

Investigators are running simulations to determine whether the computers might have under- or overcompensated.

"The flight-control system was commanding surfaces to get the vehicle back to where it believed it should be, more to the roll to the right," Dittemore said.

Still, he acknowledged that what seemed to happen to the Columbia was not an ordinary event: "What's a little bit unusual about this one is that, even though it was within the capability of the flight-control system to respond to this increased drag, the degree of which the elevons were trying to correct is outside our family of experience."

Software programs that control aircraft and other critical systems are among the most robust pieces of code ever developed, commonplace not just on spacecraft but on most commercial airliners and other aircraft.

Four of the five computers on the Columbia ran identical software and compared results with each other before giving the go-ahead to take a specific action. The fifth computer ran a different version of the software and was to be used only if the others failed.