February 18, 2003. Copyright 2002. Graphic News. All rights reserved.

Insulation foam still shuttle disaster suspect

LONDON, February 18, Graphic News: The Columbia space shuttle almost certainly suffered a devastating puncture to its thermal covering which allowed super-heated air, or plasma, to penetrate deep inside the left wing during re-entry, say investigators.

The U.S. space agency NASA is looking at several theories which may explain how Columbia broke up upon re-entry on February 1 with the loss of its crew of seven. 

One critical finding is that a breach in the left wing -- along its leading edge, landing gear door or seals -- would have had to occur for temperatures in the left wheel well to rise as they did in the final seconds before breakup began, according to data developed by a NASA thermal analysis team.

The breach could have been caused by a meteor or space debris, or the landing gear compartment door could have been blown open during atmospheric re-entry -- allowing 1,100 degree Centigrade (2,000 degree Farenheit) plasma to effectively melt Columbia's wing.

The analysis is important because it indicates that missing thermal tiles alone on the wheel well door would not cause a temperature rise like that detected before breakup, officials in Houston said. However, the investigation continues to implicate insulation from the external tank which slammed into the left wing during launch as part of the fatal chain of events.

NASA asked Boeing to assess possible damage after footage from two cameras showed the bottom of ColumbiaÕs wing being struck by the foam 81 seconds after lift-off on January 16. Engineers believe the impact of the 2.7lb (1.2kg) piece of foam occurred while Columbia was travelling at about Mach 2.4, (1,780 mph, 2,860 km/h).

Aviation Week & Space Technology magazine -- which has reviewed the Boeing computer model -- reports that the study predicted several large gouges, each penetrating roughly 10 thermal tiles. The Boeing analysis uses a computer program known as Crater that officials characterize as conservative.

The study, presented on January 23, compared a previous incident of foam damage to thermal tiles during the June 1992 launch of Columbia. A wheel well camera observed a similar-size piece of foam striking at a similar speed, but at a shallow impact angle. The foam caused a 0.5-inch-deep (12.7-mm-deep) gouge in one of the aft lower tiles that was 9 inches (228mm) long and 4 inches (100mm) wide. Using the same data, BoeingÕs Crater program almost exactly predicted the damage. 

In the case of ColumbiaÕs January 16 launch, the speed was about the same but the impact angles were estimated to be much steeper, increasing the energy tenfold or more. Crater predicted big gouges, such as one 32 by 7 inches (813mm by 180mm), and 2.8-inches-deep (70mm) -- completely penetrating a 2.4-inch-thick (61mm) tile.

Crater also predicted an area at least six tiles long and more than one tile wide would be affected, most to a depth well beyond half the tile thickness, suggesting that most of these tiles would be lost. The report seen by Aviation Week states that loss of greater than half the tile depth can cause tile loss and structural temperatures to exceed design limits. 

While program officials say that Columbia should have been safe after accounting for tile erosion and possible loss of further tiles on re-entry, one retired senior NASA official was worried about these effects in a gouge that channels the hot re-entry plasma: ÒItÕs looking like the debris is a better suspect than we had thought before,Ó engineering professor Paul Fischbeck said Monday.

In a 1990 study and follow-up research, Fischbeck concluded that a shuttle could fail catastrophically if, during liftoff, debris hit the vulnerable underside of its wings, near the wheel wells. Meanwhile, the analysis of 32 seconds of additional data collected beyond the loss of communication with Columbia goes on.
/ENDS

Source: Aviation Week & Space Technology