Why did the space shuttle burn up? (Columbia Disaster).

The space shuttle Columbia, which tore apart killing all seven of its crew on Feb. 1 just minutes before it was scheduled to land, may have been doomed since its liftoff. That's when an estimated 2.7-pound chunk of insulating foam, perhaps combined with ice, came loose from the main external fuel tank and struck the underside of the shuttle's left wing near the wheel well. The chunk was the largest piece of debris known to have struck a shuttle during launch.

Engineers first became aware of the mishap while watching a video of the liftoff on Jan. 17, the day after launch. After a weeklong analysis, while Columbia was still in orbit, they concluded that the shuttle had not suffered significant damage. That analysis focused mainly on the heat-resistant ceramic tiles that protect the shuttle during its fiery reentry through Earth's atmosphere.

But in light of a 40[degrees]F temperature spike in a left-side brake line and other equipment, as well as increased drag on the left side of the craft just minutes before the breakup, that assessment is now under scrutiny.

"We are completely redoing the analysis from scratch," said shuttle program manager Ron Dittemore of NASA's Johnson Space Center in Houston at a Feb. 4 press briefing. "We want to know if we made any erroneous assumptions"

Tiles have frequently come loose on the space shuttle fleet but have never caused a crash. On Columbia's maiden journey in April 1981, some 15 tiles were thought to have loosened when foam from a fuel tank struck just after liftoff. In that case, and on at least one similar occurrence on another shuttle, engineers correctly predicted that dislodged tiles would not lead to a catastrophe.

Dittemore cautions that the loss of tiles, despite coming under early suspicion as the cause for the crash, may have nothing to do with the disaster. He notes that the relatively modest warming recorded over a 6-minute period beginning at 8:52 a.m. EST was small compared with the 2,500[degrees]F temperature that some parts of the shuttle's exterior endured, as expected, as the craft plunged through Earth's atmosphere at more than 18 times the speed of sound.

The data suggest "there's some other missing link that we don't have yet," Dittemore said Feb. 4. The problem may have originated elsewhere on the shuttle.

Mark Drela, an aerodynamics researcher at the Massachusetts Institute of Technology (MIT), still suspects that tile damage was the culprit. The small temperature increases that were recorded may simply reflect that "the temperature sensors may not have been in the most vulnerable place," he suggests. Reports that fragments were already falling from Columbia as it flew over California, several minutes before it broke apart over Texas, are consistent with the gradual intensifying of a problem that might have begun with a few tiles loosened or dislodged at liftoff. Drela suggests, "There wasn't one giant blowup but gradual [deterioration] over several minutes.

"It's like a domino effect," Drela says. "If one piece of tile falls off in a vulnerable spot during reentry, heat melts the underlying aluminum skin like a blowtorch and then adjacent pieces of tile fall off as heat penetrates from inside the structure."

Age also may have played a role in the demise of the 22-year-old Columbia, the oldest of the fleet of four shuttles. "It's like an aging car," Drela says. Even with constant upgrades and maintenance, he adds, "things are more likely to break down.... You can't overhaul every square millimeter of the shuttle"

In congressional testimony last year, Richard D. Blomberg, former chairman of the Aerospace Safety and Advisory Panel, which NASA created after the 1986 Challenger accident, put it this way: "As [shuttle] components and subsystems age beyond their design lives, they may fail more often and with new and unanticipated failure modes."

Age need not be factor, contends Jeffrey A. Hamilton, an MIT astronomer and former NASA astronaut who has flown on five shuttle missions, including two on Columbia. With proper maintenance, many airplanes built in the 1960s are still flying safely, he notes.

NASA has been walking a fiscal tightrope for a decade, although President Bush's budget proposal released this week includes a boost for the agency's research and development (see story on page 86). Hamilton says that NASA hasn't cut corners on shuttle safety.

However, in 2001, NASA rejected a plan for a detachable shuttle cockpit that would be an emergency-escape vehicle, in part because it would be too costly.

The Aerospace Safety and Advisory Panel has become increasingly worried about NASA's ability to manage the space shuttle program safely. The panel's 2001 annual report to NASA contained "the strongest safety concerns that the panel has voiced in the 15 years I was involved with it" says Blomberg, who is no longer a panel member. Driving that concern, he noted during congressional testimony in 2002, are "unrealistically short planning horizons being used to make decisions about space shuttle flight-system improvements, the restoration of aging infrastructure, personnel-succession planning, and logistics."

Just as it did after the Challenger shuttle blew up, NASA has put a moratorium on all shuttle flights. The crew on the Earth-orbiting International Space Station now has enough supplies to last to the end of June, the agency says.

Columbia's final mission was one of the few shuttle missions devoted entirely to science. Experiments on board included observations of atmospheric ozone levels, the wind-driven redistribution of dust from deserts, the behavior of fireballs in microgravity, bacteria adjusting their respiration to conditions in space, and magnetic fields' influence on plant-root cells. The astronauts monitored their own physiological functions during rest and exercise to explore aspects of the cardiovascular system normally masked by gravity. The findings may help patients on Earth (SN: 6/15/02, p.376).

Some of the data from these and other experiments were transmitted to Earth during Columbia's mission. They will serve as part of the legacy of the seven astronaut-scientists who were lost.