Why NASA Can't Get It Right

ANATOMY OF A FLAW NASA spent more than two years and $1 billion to make sure that the accident that doomed Columbia in 2003 couldn't happen again. Despite assurances that it was safe to launch Discovery, several pieces of foam broke free during takeoff last week, forcing an embarrassed NASA to put all future flights on hold

WHAT WENT WRONG . . . The largest piece of foam missed Discovery entirely. Another piece may have struck the wing but did no obvious damage. Protective tiles on the orbiter's underside, including one near its vulnerable nosewheel well, seem to have been gouged during launch, perhaps by more falling foam

•UNDER THE SHUTTLE The orbiter didn't escape unharmed. There are at least 25 dings on its underside, including one near the nose, where temperatures can climb dangerously high •FOAM DEBRIS The biggest chunk was 2 to 3 ft. wide (0.6 to 0.9 m), about 1 ft. long (0.3 m) and up to 8 in. (20 cm) thick; it probably weighed 0.9 lbs. (0.4 kg), about half the size of the piece that downed Columbia •THE TROUBLESOME RAMP Most of the falling bits came from the so-called PAL ramp, a ridge of hand-sprayed foam designed to protect fuel lines from buffeting on takeoff •EXTERNAL FUEL TANK The tank, 154 ft. (47 m) tall and 27.6 ft. (8.4 m) wide, carries 535,000 gal. (2 million liters) of frigid liquid oxygen and hydrogen fuel. It is covered by polyurethane-like foam that keeps the fuel cool, prevents ice from forming on the exterior and protects the tank from overheating during launch

•FOAM -- 1 in. (2.5 cm) •Fuel •Aluminum casing •Epoxy

•Jettisoned external booster

. . .WHAT MIGHT BE DONE ABOUT IT . . . The Discovery crew will be testing several new ways NASA has devised to diagnose and fix launch damage before a shuttle returns to Earth •THE SPACE STATION Astronauts aboard the space station are taking high-resolution photographs of each shuttle before it docks with the station. That's one way the small "divots," or scrapes--including the one near the nosewheel well--were found on Discovery's underbelly •THE ROBOTIC ARM Discovery is equipped with a new 50-ft. (15.2-m) robotic arm that will reach out from the cargo bay to take infrared pictures of the orbiter at very close range, looking for potential problem areas •THE PATCH KIT Discovery's astronauts will test a tile-repair technique using a sort of paste--but not, unless absolutely necessary, on damaged tiles

. . . AND WHAT DANGERS LIE AHEAD During re-entry, Discovery's nose and the leading edges of the shuttle's wings--and the atmosphere surrounding them--could heat to as much as 3000ºF (1650ºC). Any chink in the shuttle's heat-resistant armor could allow superheated air to penetrate unprotected areas, where it would act like a blowtorch--the same process that destroyed Columbia •TILE DAMAGE One gouge is close to the wheel well, where an influx of hot gases could cause an explosion