Columbia and other space shuttles have a history of computer glitches that have been linked to control systems, including left-wing steering controls, but NASA officials say it is too early to determine whether those glitches could have played any role in Saturday's shuttle disaster.
While suspicions about the cause of the crash of Columbia center on the spacecraft's left wing and the possibility that it could have been damaged during launch, a NASA spokesperson said it is too early in the investigation to determine if a malfunction in any of the space shuttle's five redundant control computers contributed to the craft's breakup.
However, Columbia and other space shuttles have experienced a series of control computer failures during the past two decades, including one that had a direct link to the spacecraft's left-wing control systems.
During a March 1996 return flight, NASA officials discovered a computer circuit problem that controlled steering hardware on Columbia's left wing. The computer circuit was responsible for controlling the spacecraft's left rudder, flaps and other critical landing functions.
Speaking at a news conference prior to Columbia's landing in 1996, NASA spokesman Rob Navius downplayed the seriousness of the computer problem. "There are three additional paths of data that are up and running in perfect shape, and there's multiple redundancy that would permit a safe landing," he said. Although Columbia landed without incident, NASA officials said in news accounts at the time that the failure was significant enough that, had it happened earlier in the flight, the agency would likely have ordered the shuttle home early.
NASA was also forced in 1983 to delay a landing by Columbia for several hours because of the failure of two onboard control computers. According to an Air Force study of early space shuttle flights, the problem was significant. After the two general-purpose computers failed, "only one of the two computers could be reinitiated," according to the Air Force study, "The Cape: Military Space Operations 1971 - 1992."
In fact, the failure of Columbia's computers was serious enough to force the flight director to wave off the planned de-orbit and reschedule the landing to give officials time to study the computer problem. Columbia landed seven hours and 48 minutes later than scheduled.
Commercial off-the-shelf computer technologies, both hardware and software, form the centerpiece of the space shuttle's command, control, communications and navigation system. And while multiple redundancies have been designed into each system, former shuttle astronauts interviewed on television after the Saturday crash said that any failure in the autopilot that caused a sudden change in the orientation of Columbia during re-entry could be a factor in the disaster.
NASA designed the shuttle to be controlled almost totally by onboard computer hardware and software systems. It found that direct manual intervention was impractical for handling the shuttle during ascent, orbit or re-entry because of the required precision of reaction times, systems complexity and size of the vehicle. According to a 1991 report by the General Accounting Office, the investigative arm of Congress, "sequencing of certain shuttle events must occur within milliseconds of the desired times, as operations 10 to 400 milliseconds early or late could cause loss of crew, loss of vehicle, or mission failure."
That same report criticized NASA for canceling independent verification of the shuttle software.
A computer problem plagued the very first Columbia mission, STS-1, on April 12, 1981. In an obscure article for the magazine ACM Software Engineering Notes titled "The Bug Heard Round the World," John R. Garman, the deputy chief of the Spacecraft Software Division at the Johnson Space Center, detailed problems with onboard computer system that caused each computer to believe it was a different time of day.
Columbia isn't the only shuttle to have experienced problems with onboard computer systems. A 1985 launch of the space shuttle Discovery was delayed when the spacecraft's four main computers sent test commands to a fifth backup system and failed twice.