Laser Might Have Found Shuttle Flaw

After years of concern about foam insulation breaking off and damaging space shuttle thermal tiles, NASA (news - web sites) started evaluating — but not widely using — a technology that could detect subtle defects in the foam.

The process, laser shearography, was not used to check the insulation of the space shuttle Columbia's external tank before its final flight. But it has been used on other rockets as well as other parts of the shuttle, according to Laser Technology Inc., which makes the technology.

"It was under evaluation and still is," said John Newman, Laser Technology's chief executive. "I'm not prepared to say why it was or wasn't used."

On Friday, spokesmen for NASA's Marshall Space Flight Center in Alabama and Lockheed Martin Co., which builds the tanks at a plant in New Orleans, declined to comment on the new technology. The space agency has noted that any new process used on the shuttle requires lengthy testing before being implemented.

Records show NASA ordered one of the laser systems as recently as three years ago.

A 2 1/2-pound chunk of insulation that appeared to fly off and hit Columbia's heat-protecting tiles is one area of investigation into why the shuttle broke apart on its descent Feb. 1, killing all seven astronauts.

Laser shearography promised to address a concern since the earliest days of the shuttle program — insulation peeling off and striking the tiles. Recent changes in the composition of the spray-on foam and adhesives have made it more susceptible to flaking off, experts said.

Most of the foam is applied at the Michoud Assembly Facility in New Orleans, and more is applied just before launch at Kennedy Space Center (news - web sites) in Florida.

The spray-on foam "has a history of debonding, sometimes striking the orbiter and causing damage," according to one report written in 2001 by Christopher Davis, an engineer at Kennedy Space Center. "For this reason, shearography provides an opportunity to evaluate known areas of concern."

Laser shearography involves vibrating the material very slightly. A laser is beamed on the surface and a digital camera records differences in the surface of the material.

In the case of foam insulation, the technology is useful in finding areas where it has "disbonded" from the aluminum-lithium skin of the massive external fuel tanks, Newman said.

The system can scan an area of about 32-by-36-inches every half-second, meaning the entire tank could have been tested in about 24 hours, Newman said. It can detect deformation as small as 20 nanometers. (A nanometer is about 10,000 times narrower than a human hair.)

But even this technology can't detect all possible problems, Newman said. "We can only see debonds. We can't see where the foam is weak."

The devices, which were first introduced in 1987, start at $100,000. Besides rockets, it has been used in the testing of tires, orthopedic implants, aircraft engine parts, concrete and even golf balls, he said.

Records show NASA awarded several contracts to Norristown, Pa.-based Laser Technology since 1995, including $265,485 in 1995 and $175,600 in 2000 for laser shearograph systems and $42,933 in 1999 for repairs to the equipment.

In recent years, the flaking problem has become more common as NASA. Contractors changed the composition of the spray-on foam and adhesives to comply with health and environmental regulations, said Alfred F. Daech, a former consultant with Martin Marietta, now part of Lockheed Martin. Chromium and freon were removed.

The problem dates back to the first shuttle launch, when Daech and others were called to the launch pad because a large bubble appeared in the external tank insulation. They were able to fix that problem without delaying the launch.

"Someone had wiped it with a rag. You could see the swirls," he said. "Improper cleaning was the culprit, usually."

Then there was always Mother Nature to contend with. Birds would leave their droppings on the tanks at Michoud. And in 1995, at Kennedy's launch pad, a pair of woodpeckers drilled nearly 200 holes in the insulation of Discovery's tank. The spaceship had to be sent back to the hangar and each hole patched.

Newman said he hopes his company will play a role in ensuring the safety of future shuttles if in fact wayward foam turns out to be the cause of the latest disaster.

Why do you worry about environmental aspects on a container of very non-environmental caustic liquid?

Stupidity in regulations!

I'm getting tired of the media's attempts to spin NASA as a group of incompetent boobs sitting around wasting money. Not that NASA is perfect by any stretch of the imagination, it's honestly getting rediculous.

I have a statistic for them. Per mile, the American space program has the greatest safety record of any mode of transportation in history. :)

"very non-environmental caustic liquid?"

The External Tank is filled with liquid hydrogen and liquid oxygen; the small amount of hydrazine and nitrogen tetroxide used for the RCS system is carried inside the shuttle. Just as a note, the first External Tanks were painted white. To save money and weight, painting was discontinued and the tanks are left with the natural reddish orange color of the insulation.

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.