NASA Still Vexed by Foam Woes

The problem of foam debris -- believed to have brought down the Columbia -- may never be completely solved and could damage space shuttles on future missions, two members of the Columbia Accident Investigation Board said this week.

The orbiter’s delicate thermal protection system was gravely damaged by a large chunk of foam during January’s launch -- the latest instance of insulation falling off the space shuttle’s giant external tank during the program’s 22-year history.

“NASA has never been able to solve the problem of foam coming off the tank,” said Roger E. Tetrault, an accident board member. “And we still haven’t found anything that is a ‘Eureka!’ solution. To say we are going to remove all foam debris may be impossible.”

The accident board is scheduled to release its final report in less than two weeks, and the recommendation for fixing the foam is likely to require only that NASA minimize the amount of foam coming off the shuttle’s external tank, Tetrault said.

Another shuttle loss, Tetrault said, “is possible but highly unlikely.” Douglas D. Osheroff, another board member and a Nobel Prize-winning physicist at Stanford University, agreed that another foam-related accident is “certainly a possibility.”

NASA officials say they are continuing to study the foam problem at the Marshall Space Flight Center in Huntsville, Ala., but have not yet disclosed their plan and declined requests for interviews. NASA officials this week also would not comment on the probability of another Columbia-type accident.

After the Los Angeles Times submitted detailed questions about the foam, NASA spokesman Alan Feinberg responded only: “Our goal is to reduce or eliminate foam debris generation during ascent. Everything else NASA is doing is to mitigate the risks to the Orbiter and its crew.”

In the seven months since the Columbia tragedy, the accident board has made a series of preliminary recommendations that would warn astronauts if an obiter were damaged by foam during launch and allow them to seek refuge in the international space station.

While such a plan might assure the safety of the crew, it could still result in the destruction of an orbiter. With only three orbiters left, the U.S. space flight program could be crippled by another loss, experts say.

The agency’s critics say it is failing to make the kind of far-reaching safety improvements that came in the aftermath of the Challenger accident 17 years ago.

“The more they study the foam, the less they understand it,” said space expert John Pike, director of GlobalSecurity.Org, a research firm. “NASA’s difficulty in finding a robust fix is indicative of the fact that the agency still has problems.”

Getting every ounce of the foam to stick to the external tank has bedeviled NASA engineers for 22 years. The tank is covered by 4,800 pounds of sprayed-on foam, primarily polyurethane.

The shuttle accelerates from zero to more than 17,000 mph in eight minutes, buffeting the foam with strong vibrations and powerful aerodynamic forces. The outer skin of the foam is heated during the ascent to several hundred degrees Fahrenheit, while the inner surface is chilled to 423 degrees below zero by liquid hydrogen and 298 degrees below zero by liquid oxygen.

Osheroff said experiments he is conducting demonstrate the difficulty of understanding why foam falls off the external tank. Any number of theories have been proposed in past years, but many of them have been debunked since the Columbia.

If NASA does return to flying the shuttle without conclusively solving the foam problem, it would mark a departure from its handling of the Challenger accident.

When investigators determined that a joint in the solid rocket motors had leaked hot gases in the Challenger explosion, NASA addressed the defect with at least four major changes, any one of which would have sufficed, according to Challenger-era engineers. As a result, the solid rocket motors are considered one of the safest parts of the shuttle system.

But the Challenger fixes took almost three years and required significant investments. By contrast, NASA officials have attempted this time to avoid a lengthy grounding of the fleet.

In the weeks after the Columbia accident, NASA officials signaled that the shuttles could return to flight by this fall. That later slipped to early winter, then spring. Only last week, NASA space flight chief William F. Readdy told reporters that the spring window may be ambitious.

Thus, seven months after the accident, NASA still has not unveiled an engineering solution to the cause of the accident and has no schedule for resuming flights.

Pike, a frequent critic of NASA, said the agency lacks the political standing in the Bush administration to get safety upgrades adequately funded. Ironically, it was lack of funding that forced NASA to forgo upgrades and modernization of the shuttle fleet, according to Columbia investigators. Now NASA may not even have the money to fix the foam problem -- the direct cause of the accident, Pike said.

The 1.65-pound piece of foam that struck the Columbia’s left wing 82 seconds after launch came off an area known as the bipod attachment on the shuttle’s external tank. Large pieces of foam debris had fallen off that specific point on at least six prior flights.

NASA is eliminating or redesigning the foam insulation in that area so that it should never again be a threat to the shuttles. But comparably large pieces of foam -- up to 28 inches long in the case of the shuttle flight on Oct. 18, 1993 -- have fallen off other areas of the external tank, according to internal NASA documents released under the Freedom of Information Act.

Osheroff said a number of foam debris incidents have originated in an area known as the inter-tank region, just under the tapered nose of the tank, and the place where the solid rocket boosters attach to the tank.

Why foam falls off any area of the tank remains a scientific mystery.

A wide range of theories have attempted to explain the problem, including the formation of liquid nitrogen inside voids in the foam, water vapor penetrating the foam structure, and even a change in the blowing agent used to spray the foam. At one point, investigators thought that epoxy adhesives used to help bond the foam to the tank were failing.

But foam is an inherently weak substance, Osheroff said. Trapped bubbles in the foam carry air pressure normal at sea level. As the shuttle ascends, atmospheric pressure drops sharply and creates imbalances that want to blow the foam apart.

Osheroff said Columbia investigators and NASA have made important advances in their understanding of foam, and he vowed in an interview to continue his research even after the accident board dissolves in coming weeks.