The Space Shuttle Returns
How NASA recovered from the Columbia tragedy and tackled the job of getting the shuttle flying again.
- By Linda Shiner
- Air & Space magazine, May 2005
(Page 2 of 7)
"You spray it down and it goes on about like water," said Otte. "Then you build it up in layers as you spray it on. When you spray it around [protuberances], the foam can lap over itself and create voids. It can cause pressure as it's expanding. If the geometry is right, it can pull on the foam that you just sprayed underneath it. Those are the types of features that we saw inside the foam structure at the bipod ramp."
Until 2003, each tank had two such ramps-wedges of foam covering the feet of a V-shape (hence bipod) fitting that connects the orbiter to the tank. Oddly, the right one had never been known to shed foam; only the left was troublesome, and it was the instrument of Columbia's destruction. The irony is that the foam ramps were applied to prevent ice from forming on the bipod attachment post; NASA feared that during launch, ice on the post could break away and damage the orbiter.
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.