NASA Considering Space Hit
NASA investigators remain unconvinced that the chunk of foam insulation that struck Columbia’s heat-resistant tiles on takeoff led to its destruction, and also are now considering the possibility the craft was struck by space debris while in orbit, the agency’s chief flight director said Tuesday.
“Did we take some hit?” Milt Heflin, the flight director, said in an interview Tuesday at Johnson Space Center. “That’s a possibility. Something was breached.”
NASA investigators have developed what has become known inside Johnson Space Center as a “fault tree” -- a list of potential mishaps and flaws that might have caused Columbia to break apart Saturday morning over East and central Texas.
The list, aimed at finding the cause of what NASA terms the “thermal event” that destroyed the shuttle, includes several theories. Although the current investigation focuses on several scenarios related to tile damage, some analysts also have questioned whether faulty wiring or corrosion could have played a role.
Nonetheless, the prime suspect remains the piece of foam insulation that fell off the external tank during the Jan. 16 liftoff, possibly damaging the protective tiles.
Tile vulnerability has been an object of warnings for years. One study prepared for NASA nearly a decade ago warned that insulation and ice debris could result in enough damage to doom the orbiter during reentry.
“We estimated that [the loss of a shuttle] was a possibility,” said Paul Fischbeck of Carnegie Mellon University in Pittsburgh, one of the authors.
Despite warnings that the shuttle could be endangered if debris struck its underbelly during liftoff, some engineers do not believe that any scenario would have been destructive enough to cause Columbia to crash.
NASA’s computers have calculated the potential damage caused by the foam insulation. Under two worst-case scenarios, NASA investigators say, the insulation either would have destroyed a single heat-resistant tile near the landing gear door or caused damage to a 32-by-7-inch patch of tiles along the shuttle fuselage.
That means the spacecraft’s tiles -- 24,000 ceramic pieces that have been problematic from the beginning of the shuttle program -- could have been damaged some other way, Heflin said, possibly by space junk or a tiny meteorite. NASA engineers say they are considering the possibility that a small piece of space debris could have grazed the shuttle, damaging or loosening tiles just enough to start a chain reaction once the craft started roaring through the atmosphere.
The ceramic tiles act as a protective armor around the body of the space shuttle, protecting it against the intense heat of reentry through the atmosphere. Although many tiles are damaged or knocked off during missions, missing tiles in a particularly vulnerable portion of the spacecraft, such as at the leading edge of its wings, could imperil its ability to fly.
The skepticism of some engineers and attempts to broaden the list of suspects failed to shift attention from insulation debris Tuesday as more reports documenting past warnings emerged.
“The foam insulation falling off the external tank could certainly damage tiles,” Fischbeck said in a telephone interview.
The 1994 report he co-authored with Elisabeth Pate-Cornell of Stanford University specifically cited concerns about Columbia, noting that tiles “were put in place under severe schedule constraints, which may have affected the quality of the work.”
Columbia was the first orbiter built, and the report found problems with tile adhesion and trapped water. Fischbeck and Pate-Cornell advised that the tiles be waterproofed. The report did not indicate whether those recommendations were followed, but Fischbeck said the agency took the recommendations seriously and made improvements.
NASA officials have said in news briefings that a 20-inch chunk of foam, weighing about 2.67 pounds, was videotaped falling off the external tank and striking the underside of Columbia’s left wing about 80 seconds after liftoff. That represented the largest piece of debris ever known to have fallen off the tank. At 80 seconds into flight, the orbiter was nearing a speed of 2,000 mph, meaning the foam carried substantial energy into the impact and could have caused serious tile damage, according to Fischbeck.
The 1994 report warned NASA of several scenarios that could cause catastrophic safety problems, including the potential for a “zipper effect” where the loss of a single tile would, in turn, cause adjacent tile losses until opening a large unprotected gap. Such exposure could make vital areas of the shuttle -- such as critical hydraulic lines, computers or fuel tanks -- vulnerable to destructive heat, the report said.
After the report was issued, Fischbeck said NASA took steps to sharply reduce foam debris. The experts also urged NASA to find ways to improve tile safety, despite budget cuts.
“NASA must find ways of being cost-effective, because it simply cannot afford financially or politically to lose another orbiter,” the report cautioned.
Heflin said his engineers have no hard evidence Columbia was struck by a piece of space junk or a space pebble, known as a micrometeor. What’s more, NASA takes great care during missions to avoid the man-made objects, from ejected payload shrouds to tools left behind by astronauts after spacewalks, that are in constant orbit. By some estimates, there are more than a million objects within 1,200 miles of the Earth’s surface.
Heflin also pointed out that the space debris theory has not supplanted the foam insulation theory, but has been placed alongside it on the “fault tree.”
Analysts inside and outside the space program are torn over the possibility that space debris is to blame. There are several problems with the theory.
First, the Air Force and NASA together perform a comprehensive analysis of a shuttle’s projected path before each mission to ensure that it is not struck by debris, said Howard Sands, a former NASA official who worked as a contracting officer for space shuttle logistics before he retired in 1986. The Air Force has the ability to pinpoint the location of space debris that is just centimeters in diameter, and would have warned NASA about the dangers of debris large enough to damage it.
Second, there are “clean” and “dirty” levels of orbit above Earth. The space shuttle typically coasts along at 15,000 mph in one of the relatively clean levels, close to the atmosphere. At that level, much of the debris left behind by earlier space flights or defunct satellites falls into the atmosphere and burns up before it can do damage.
“Up higher, things can stay around for hundreds, maybe thousands of years,” said a Boeing engineer who works on the international space station, which orbits in a higher and much “dirtier” path. The engineer spoke on the condition of anonymity. “Down where the shuttle is, things are kind of getting sucked into the Earth’s orbit like there’s a big vacuum cleaner,” he said.
Finally, if something struck the shuttle with enough force to ultimately bring it down, many analysts say NASA, its crew and the craft’s computers would have known instantly. NASA’s test facility in White Sands, N.M., recently conducted a study of the potential impact of space debris. The conclusion: A piece of plastic the size of a walnut could tear a 5-inch-wide hole through aluminum as thick as the Los Angeles telephone book. In other words, one analyst said Tuesday, if the shuttle struck something, “everybody would know. It would be loud.”
“That stuff moves so fast relative to the shuttle,” said the analyst, speaking on condition of anonymity.
On the other hand, “there is a lot of debris up there,” said William Ailor, president of Aerospace Corp., a nonprofit group in El Segundo that provides technical support to the Air Force and studies orbital matter. After all, Ailor said, “we’ve been in space for 40 years.”
There are enough pieces of debris in space that some scientists have proposed a variety of remedies. Some hope to install robotic arms on spacecraft that can grab old satellites and pull them into orbits where they can’t do any damage.
NASA has had to adjust the flight path of space shuttles at least eight times to avoid large pieces of debris, Ailor said. Most of the debris is found at extremely high levels of orbit, where satellites are kept -- more than 250 miles higher than the space shuttle typically flies. Studies show that all but 9,000 of the pieces are smaller than a tennis ball, including thousands of tiny particles left behind by solid rocket motors.
In addition, there are countless micrometeorites, some of them smaller than the diameter of a strand of hair, Ailor said. Most of them are so tiny that they can do no damage to a spacecraft as large as a commercial airplane. One study showed that a craft that had been in space for more than five years was struck by these particles more than 30,000 times, with no ill effect.
Still, NASA has discovered pockmarks on at least two shuttle windshields after the crafts returned safely, Sands said, possibly because of collisions with that matter in space. A speck of paint once chipped the windshield of the space shuttle Challenger during a mission completed before it exploded in 1986. Some have estimated that the speck was traveling 20 times faster than a bullet travels on Earth.
That sort of matter could weigh just enough to damage a thermal tile, Ailor said. And, Sands added, it’s possible that a piece of space debris could have broken off a satellite or a larger piece of space trash during Columbia’s 16-day mission, and didn’t show up on engineers’ maps until it was too late. “It could happen,” Sands said. “It is a possibility.”
Meanwhile, NASA expanded its search Tuesday for Columbia’s wreckage by several states.
After scouring the ground for clues in Texas and Louisiana -- and discounting reports that the shuttle may have begun breaking up farther west -- NASA sent investigators to California and Arizona when credible reports surfaced that pieces of Columbia may have landed there. If the debris proves to be from the shuttle, it may offer an early glimpse of what was happening before Columbia broke up over Texas.
Michael Kostelnik, the high-ranking NASA official responsible for the shuttle and space station programs, said what may prove to be the wreckage of the shuttle’s main engines has been located in Louisiana. Heavy pieces, like the engines, would travel farther after the spaceship broke up.
Kostelnik said he did not know the location of the reported debris in California and Arizona.
“It’s not clear what the material is,” Kostelnik added. “We have had some e-mail correspondence that potentially looks like it could be either [tiles] or potentially wing material. If it is wing material, obviously that would be very important to the investigation.
“Certainly something that early in the event is most important,” Kostelnik said.
NASA’s main priority for now is to recover the remains of the astronauts’ bodies, and thereafter to hunt for the most important pieces of wreckage. The crew compartment has not been recovered in any identifiable form, Kostelnik said, though pieces of it may be in official custody.
Times staff writers Ricardo Alonso-Zaldivar in Washington and Eric Malnic in Houston and Nona Yates in Los Angeles contributed to this report.
Foam insulation’s role:
Some questions and answers about foam insulation, suspected of being a factor in the space shuttle Columbia tragedy:
Question: What does this insulation on the external fuel tank normally do, and how large was the chunk that broke off?
Answer: The polyurethane material’s job is to keep liquid hydrogen and the liquid oxygen, stored separately in the shuttle’s huge fuel tank, very cold. It is lightweight, somewhat like Styrofoam, but is applied in liquid form and dries to a firm surface. During Columbia’s liftoff Jan. 16, NASA says, a fragment measuring about 20 inches by 16 inches by 6 inches, and weighing 2.67 pounds, broke off. It may have damaged heat tiles that keep the shuttle from burning up during reentry into the atmosphere.
Q: How could tile damage doom the shuttle?
A: After initial damage, the fast flow of air in the damaged area could have peeled more tiles off. Without protection against the intense heat of reentry, which can reach 3,000 degrees, vulnerable areas of the shuttle’s structure and electronics could have been damaged, eventually leading to the breakup.
Q: Has foam insulation come off in previous shuttle flights?
A: Yes. But the damage from those incidents wasn’t serious enough to trigger catastrophe.
Q: Why wasn’t damage to the Columbia tiles on Jan. 16 fixed before reentry?
A: NASA says there was no way for the crew to repair tiles in orbit. The space agency also had concluded that the incident posed no danger.
Source: Associated Press