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 3 of 7)
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.
Five sprayers were trained to apply foam to the intertank, and Richard hopes to certify five more. One crew is trained for "closing out," or finishing, the bipod area, another for protuberance-air-load (PAL) ramps, and another for the longeron, a structural support for the tank's aft orbiter attachment struts. Before Columbia, a close-out sprayer could have done the applications on any of those areas; today the workforce is divided into specialties.
Ron McQueen, a production supervisor of foam applications who has been with Lockheed Martin for 23 years, watches a video screen while two sprayers apply foam. A third sprayer is on hand only to watch what the other two are doing. Immediately after the application is complete, the video is run again, and the sprayers, the quality control people, the production supervisor, and several engineers watch the replay, looking, says McQueen, to see if anything has contaminated the foam, or if a void has developed, FOD has been introduced, or more than 45 seconds has elapsed between the first spray and the second. If they spot a defect over a large enough area, the foam will have to be removed and replaced.
"These new [procedures] were developed over a long period of time," says McQueen. "On the bipod, we probably worked for a year and a half coming up with a new [process], which we were all involved in-the supervisors, the hourly employees. [NASA and Lockheed Martin managers] took our suggestions right along with theirs."
Application is now a six-part process, not counting the video review and other quality control steps. Before the foam is applied to a real tank, it is applied to a high-fidelity mockup of the tank area to be sprayed. The sprayer applies foam to a "lead-in" test panel, then to the mockup, then to a "lead-out" test panel. All three are later dissected to see if any voids or weak areas developed in the foam. The steps are repeated for the tank that will eventually be sent into space, but only the lead-in and lead-out panels are dissected, unless the technicians see something unusual.