Frames from enhanced video just prior to (top) and after (below) show the piece of foam from the external fuel tank striking Columbia's wing. Photo: CAIB

During Columbia's launching Jan. 16, 2003, a suitcase-size piece of foam insulation broke away from an aerodynamically shaped ramp used to keep ice from forming on a strut connecting the shuttle's nose to its external fuel tank. The foam came off 81.7 seconds after liftoff and struck the underside of Columbia's left wing 0.2 seconds later, smashing into the lower side of a leading-edge RCC panel.

Ground cameras were unable to see the point of impact. One long-range tracker that might have shown the impact site was out of focus. And given the resolution of the cameras in place at the time, it's not clear obvious signs of damage would have been detected.

In any case, without the benefit of high-resolution video of the impact, mission managers were forced to rely on computer modeling and other indirect techniques for determining whether the foam strike could have caused any entry-critical damage. In the end, they wrongly concluded Columbia could safely re-enter as is.

Commander Rick Husband, pilot William McCool, Kalpana Chawla, Laurel Clark, Michael Anderson and Israeli astronaut Ilan Ramon were killed Feb. 1, 2003, when hot gas burned its way into the interior of the left wing through a presumed breach on or near the underside of RCC panel No. 9. The wing failed and the shuttle broke up 37 miles above Texas.

In the wake of the disaster, the Columbia Accident Investigation Board ordered sweeping changes, including "an aggressive program to eliminate all external tank thermal protection system debris shedding at the source with particular emphasis on the region where the bipod struts attack to the external tank."

The bipod ramp was intended to keep ice from forming around the struts due to the ultra-low temperatures of the shuttle's liquid oxygen and hydrogen propellants. NASA's solution was to simply eliminate the ramps and to install heaters on the strut attachment fittings to prevent ice buildups.

Tank engineers also implemented a variety of other changes to minimize foam shedding and while additional work remains to be done, NASA managers plan to ship the first upgraded tank to the Kennedy Space Center in the first week of January.

"Through all our testing, we believe the amount of foam that can come off the tank and not cause serious damage is .03 pounds," said Wayne Hale, deputy director of the shuttle program at the Johnson Space Center in Houston. "If you think about that, that is three one hundredths of a pound. That is something like six tenths of an ounce. So that's a pretty small piece of foam.

"All our investigations of the foam indicate we will not get a piece of foam coming off bigger than .008, eight one thousandths, or almost an order of magnitude smaller than the requirement."

It is not possible to eliminate all foam shedding, but "we're clearly moving toward an era where we expect to see much less damage in the tile and no critical damage that will require a repair," Hale said. "So that's our goal in this and it's beginning to look very positive that we'll be able to accomplish that level of control on the ET foam."

But to make absolutely sure, NASA must be able to inspect the tank and the space shuttle after launch with much greater precision than before. The CAIB recommended that NASA "upgrade the imaging system to be capable of providing a minimum of three useful views of the space shuttle from liftoff to at least solid rocket booster separation."

The panel also told NASA to look into putting cameras aboard ships and/or aircraft to provide additional coverage, to develop a capability to obtain high-resolution images of the tank after separation from the shuttle, to develop techniques for high-resolution imaging of the ship's underside and wing leading edges; and to make arrangements to obtain imagery from spy satellites if needed.

On its own, NASA managers decided to launch the first two post-Columbia shuttle flights in daylight to improve photo coverage and to time the launchings so the external tank, separating from the ship half a world away, also would be lighted by the sun.

To reach the space station, the shuttle must launch within a few minutes of when Earth's rotation carries the launch pad into the plane of the lab's orbit. And as a final complication, the shuttle can only visit the station when the "beta angle" - the angle between the plane of the station's orbit and the sun - ensures the shuttle-station stack will not get too hot.

Throwing all of those requirements together, NASA can only launch a shuttle to the station during relatively short windows. As of this writing, the next six allowable launch periods are:

• May 14 through June 3
• July 13 through Aug. 1
• Sept. 9 to Sept. 25
• October: None
• Nov. 7 through Nov. 10 (not thought to be viable)
• December: None
• Jan. 4, 2006, through Jan. 6 (bad beta angle)
• February: None
• March 4 through March 20

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