While the workers at Michoud were autopsying bipod ramps and other areas identified as tough sprays, engineers in the laboratory at Marshall were placing mockups of the tough-spray areas in thermal-vacuum chambers, which mimic the temperature and pressure extremes of launch. The engineers now have a failure curve: For a given void size at a given depth, they can predict the size and weight of a divot of foam that would be released during launch. Despite many attempts, they were unable to duplicate the failure at the bipod ramp.
If NASA had ever considered finding a new insulating material, it was only the briefest thought. "Could we develop a foam that could perform better structurally? Yeah, we probably could," said Otte. "But it typically takes us four to five years to develop a totally new foam system. And then of course we have to develop the processes to put it on and all the controls that we'd have to put in place."
Otte is an engineer in his 40s with a compact, athletic build and the air of a man proceeding methodically through a long list of action items. As he explained how the program he helps manage had gone wrong and what is being done to correct it, his tone was at times chastened, at other times confident in the investigation and NASA's ability to find and fix problems. Armed with an immense knowledge of his program-Otte has worked with the external tank since 1987-he seemed ever so slightly defensive of the agency "culture," a word the CAIB used to describe an organization-wide weakness, which the investigators partly blamed for the accident. "We've got 2,000 people, counting Lockheed Martin and NASA employees, who do this because they believe that this is what the country needs to do," Otte said. "Everybody has to have a paycheck, don't get me wrong, but these guys are involved in this because they believe in what they're doing. And they're proud of what they do. But they also understand that this is a risky business and they accept that. [Risk] is something that anybody that works shuttle understands. It's something the American people need to understand. If you're going to work shuttle and if the American people are going to fly shuttle, we have to be prepared to accept risks. If we're not, we shouldn't be in this business."
ET-120 has no bipod ramps. Unable to duplicate that fatal failure in the laboratory, the project office eliminated the foam covers altogether. Instead, ice formation will be prevented by four rod-shaped heaters at the feet of the bipod attachment post. The radical changes in the external tank program are not in structure, however. The real change is in the methods by which foam is applied to sections of the tank where foam had broken off...or could.
The Vehicle Assembly Building at Michoud is so vast it doesn't feel like a building; it feels like space, which happens to be enclosed. On the frequent steamy days in Louisiana, Michoud workers who walk for exercise do their miles in the air-conditioned comfort of the VAB.
Before entering the areas where workers were applying foam to ET-121, I was asked to remove my earrings and watch, seal them in a Ziploc bag, and carry them in a small waist pack with a Velcro closure. (A manager helped me wrap tape around my wedding and engagement rings.) Foreign object debris, or FOD, is something NASA, Lockheed Martin, and the United Space Alliance, the NASA contractor that prepares and helps launch the shuttles, have always taken seriously, though not seriously enough, according to the CAIB. Because FOD was the subject of one of the CAIB return-to-flight recommendations, new requirements and procedures have been established. At the beginning of every shift at Michoud, workers and supervisors spend at least 15 minutes discussing safety precautions, including how to search for and dispose of FOD.
Leon Richard (pronounced ri-SHARD, in the style of New Orleans, where he grew up) is in charge of "large acreage applications" for the external tank thermal protection system. He is a personable man who, even after 28 years with Lockheed Martin, clearly relishes the operations in the VAB. At one point in our tour, Richard, who worked his way up to senior manager from installation mechanic, swept his arm out over the great space and said, "This is my American dream."
Besides managing the machines that spray most of the tank with foam of a uniform thickness (after some machines spray it on, other machines shave away excesses), his crew applies foam to the intertank flanges, where big sections of the tank are joined. The greatest amount of foam loss, historically, has been from this area. One reason: The surface is covered by complex ridges and bumps.
In the bay where ET-121 was being outfitted, we rode an elevator 101 feet up to the intertank. There Richard showed me the crevices that had to be filled and the protrusions that had to be carefully covered. "We can't have any voids," he said, "which is what got us in this pickle in the first place."
The intertank has 108 hollow stringers and 52 solid ribs, stiffening structures that help the huge tank stand up to the stress imposed by seven million pounds of thrust. Around each flange, 178 bolts must be carefully covered, first with a sealant, then with foam. "It's 60 feet all the way around," said Richard. "Sixty tedious feet." Watching the painstaking work reminded me of scenes I'd witnessed at the Kennedy Space Center, where technicians removed individually numbered shuttle tiles, inspected and reapplied them, while others sewed insulation blankets beneath the orbiter's skin. For all its sophistication, the space shuttle has many parts that are essentially handmade.