Other hardware problems found in shuttle program

When a space shuttle begins its thunderous ascent, the heavy-duty bolts and nuts that secure it firmly to the launch pad are designed to explode and release the vehicle as it surges into the skies with almost 8 million pounds of thrust.

But if one or more of those sturdy fixtures fails to give, experts say, the result could be a horrific conflagration that could kill the crew and send torn shuttle components cartwheeling off the launch pad.

During the launch of the shuttle Atlantis in October, one of two duplicate signals that trigger the release system failed. The second signal worked, and the shuttle flew. But members of the Columbia Accident Investigation Board have put this component among a list of potential safety threats that NASA should correct or otherwise address -- even though these problems had no bearing on the Feb. 1 destruction of the shuttle Columbia and its seven astronauts. The board may require some of the changes before the shuttles return to flight.

The list also includes:

A weak design in a device that catches heavy metal debris from the explosive separation of the shuttle's spent rocket boosters during ascent.

Hazardous fuel in the orbiter's auxiliary power units that, among other things, power the shuttle's flight controls.

Possible cracks in "Stoody balls" deep in the orbiter's main propulsion system that allow flexibility in the system during the violent vibrations of launch.

By highlighting areas unrelated to the foam problem, the board is putting pressure on the space agency to deal with problems that in some cases have festered for years.

"We've got a responsibility to help NASA listen for the next event that could be catastrophic," said Air Force Maj. Gen. John Barry, a board member.

The board doesn't plan to release a final report before late July, but it has issued some preliminary recommendations, with more expected soon, and its members have discussed at least some of these issues.

One is the set of four huge bolts that secure each of the 14-story rocket boosters -- and through them the entire shuttle -- to massive "hold-down posts" on the mobile launch pad. The bolts are supposed to blow at liftoff. Unlike the shuttle's main engines, the solid-fuel boosters, once ignited, cannot be shut down, so a failure to blow off the bolts could be catastrophic.

In addition to the October incident, shuttle records reviewed by The Washington Post show that during a Columbia liftoff in 1992, one of the hold-down devices did fail to release. The hardware stayed attached to a booster as it lifted off and tore a piece of material from the booster's base.

The system may need more redundancy, Barry said. But beyond that, the board's inquiry revealed an engineering "integration" problem among the NASA facilities responsible for the various pieces of it.

The other pyrotechnic system under scrutiny involves the set of nuts and bolts that attach the two boosters to the external propellant tank and that are supposed to explosively separate the spent boosters during ascent.

In a review of radar images, investigators discovered that a piece of debris -- possibly either a 40-pound chunk of a broken bolt or the 11-pound container designed to capture it -- flew off Columbia as the boosters separated just over two minutes after its Jan. 16 liftoff.

Investigators then learned that NASA had certified the system as safe for flight without testing the actual flight hardware, and that subsequent tests had been inadequate. Experiments done for the board showed that the bolt catchers were weaker than engineers had thought.

Barry suggested the device could pose "serious risk to the orbiters" and may need to be strengthened. The heavy metal debris could inflict much worse damage if it struck a critical surface than the foam believed to have brought down Columbia.

Board members and others have also expressed concern about the auxiliary power units (APUs), turbine-driven systems that power the orbiter's hydraulic system, which performs crucial steering and other functions during liftoff and landing. The three units, located in the orbiter's back end, use highly toxic, flammable, corrosive and expensive hydrazine fuel.

In a recent interview, Bryan O'Connor, NASA's chief of shuttle safety and a former astronaut, listed the APUs as chief among his concerns during landings. In 1983, he noted, a crew aboard Columbia landed with two of the three APUs on fire. "Hydrazine is kind of bad stuff," he said.

The board says there is also uncertainty about the soundness of the crucial "ball strut tie rod assembly" in the liquid oxygen lines that feed the shuttle main engines.

Engineers discovered cracks in one of the metal alloy balls that rest inside the intersection of several propellant lines in a veritable rat's nest of plumbing in the orbiter's aft section. The balls operate "something like the universal joint in your car," said NASA spokesman Kyle Herring. In December, engineers discovered a crack in one of the balls -- sometimes called "Stoody balls" after the manufacturer -- while inspecting a 17-inch-diameter liquid oxygen feed-line in the shuttle Discovery. The troubleshooting forced a delay of Columbia's final mission.

Cracks in the balls, which are no more than 2 1/4 inches in diameter, could lead to a rupture and possible catastrophic leak, according to NASA documents.