wader
Well-Known Angler
20 years after Columbia disaster, NASA remembers crew and lessons learned
Twenty years ago this Wednesday — on Feb. 1, 2003, at 8:48:39 a.m. EST — a sensor in the space shuttle Columbia's left wing first recorded unusual stress as the orbiter and its seven crew members headed back to Earth to close out a successful 16-day science mission.
Over the next 12 minutes, an on-board data recorder would track a cascade of alarming sensor readings and failures on the left side of the spacecraft that indicated a rapidly escalating catastrophe as the blazing heat of re-entry engulfed the ship.
But it initially played out behind the scenes in the ship's flight computers, which waged an increasingly desperate struggle to keep Columbia on track for a planned landing at the Kennedy Space Center in Florida where friends and family were waiting.
And so, at 8:53:26 a.m., Columbia crossed the coast of California, right on schedule, at an altitude of 44 miles while traveling 23 times the speed of sound.
Space enthusiasts across the western United States would capture dramatic video of Columbia's dawn descent, including unusual changes in the shuttle's white-hot plasma trail along with flare-like points of light separating and falling away. No one knew at the time what, if anything, the light show might mean.
But 16 days earlier, 81.7 seconds after liftoff, a briefcase-size chunk of lightweight foam insulation had broken away from Columbia's external tank as the spacecraft accelerated through 1,500 mph.
Tracking cameras showed the foam disappearing under the shuttle's left wing and emerging an instant later as a cloud of fine particles. Later analysis would show the foam impacted the underside of the left wing at a relative velocity of more than 500 mph, instantly disintegrating.
Engineers could not determine exactly where the foam had hit, and Columbia was not equipped with a robot arm to enable an inspection in space.
But an engineering analysis based on software modeling for much smaller impacts indicated the foam strike did not pose a "safety of flight" issue. Senior managers ruled out asking for spy satellite imagery that might, or might not, have allowed a more thorough analysis.
In any case, commander Rick Husband, pilot Willie McCool, mission specialists Kalpana Chawla, Laurel Clark, Michael Anderson, David Brown and Israeli guest astronaut Ilan Ramon were unaware of any problems as they returned to Earth, marveling at the pink glow out the cockpit windows as atmospheric friction built up in the moments before that first unusual sensor reading.
Then, around 8:54:24 a.m. — 5 minutes and 45 seconds after that initial reading was stored in the data recorder — the first indication of trouble showed up in telemetry reaching flight controllers at the Johnson Space Center in Houston: a loss of temperature readings from hydraulic lines in Columbia's left wing.
Four minutes later, Columbia's backup flight computer displayed a message in the cockpit indicating a loss of left main landing gear tire pressure readings. Husband called down to mission control, presumably to ask about the tire pressure, but his transmission was cut off.
"And Columbia, Houston, we see your tire pressure messages and we did not copy your last," astronaut Charles Hobaugh called up from Houston.
"Roger, uh," Husband began. But again, the transmission was interrupted. It was 8:59:32 a.m.
As engineers would later learn, Columbia veered out of control in the seconds that followed and broke apart 38 miles above central Texas while traveling at 18 times the speed of sound. All seven astronauts, unconscious moments after the crew cabin lost pressure, were killed by blunt force trauma when the cabin came apart in the hypersonic airflow.
It would take another two-and-a-half minutes or so for the harsh reality of Columbia's demise to reach the Kennedy Space Center where family members, NASA managers, the ground support team, reporters and photographers were standing by for the shuttle's homecoming.
Over the days, weeks and months that followed, the Columbia Accident Investigation Board uncovered a now-familiar history of external tank foam insulation problems, management miscues and poor internal communications that contributed to the mishap.
In a dramatic test, engineers used an air cannon to fire a piece of external tank foam at a wing leading edge mockup at the same angle and velocity as the one that damaged Columbia. The impact blasted a hole in the mockup's leading edge, conclusively proving the lightweight insulation could cause catastrophic damage in a worst-case scenario.
And that's exactly what happened to Columbia.
During re-entry, super-heated air rushed through a breach in the left wing leading edge, cutting through sensor wiring, melting internal spars and burning into the left landing gear wheel well. The wing eventually either folded over or broke away from the fuselage, throwing the ship out of control.
The Columbia disaster, like Challenger before it, triggered agency-wide soul-searching as the accident investigation proceeded.
NASA's mission management team was criticized for dismissing the foam strike based on what turned out to be a flawed engineering analysis. The shuttle was not equipped with a robot arm, tools or materials to repair major heat shield damage, and the MMT never considered a high-risk emergency spacewalk to inspect the damage site.
While a NASA study later showed a shuttle rescue mission was possible in theory, no one believed the agency would have launched another crew without first knowing what had happened to Columbia.
In short, Columbia's fate was sealed 81.7 seconds after liftoff. The real problem, the accident board concluded, was NASA's earlier failure to properly deal with an ongoing problem: heat shield debris hits from foam insulation coming off the external tank during ascent.
As was well known, every shuttle flight included foam hits to the orbiter's heat shield even though the agency had a clear-cut rule in place forbidding debris strikes. The rule was never strictly enforced and NASA eventually came to look at foam shedding as an "acceptable risk."
more HERE
