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RedditThe Apollo 11 command module Columbia is clearly one of the National Air and Space Museum’s crown jewels. Displayed in the Milestones of Flight gallery, Columbia is surrounded by Charles Lindbergh’s Spirit of St. Louis, Chuck Yeager’s Bell X-1, and the North American Aviation X-15. While these aircraft hang high out of reach, Columbia is at ground level, and you can inspect every detail on the heat shield from just a nose away.
That’s precisely what NASA engineers need to do as they plan a similar carbon-based heat shield, but one about four feet wider, for the new Orion crew exploration vehicle, which will take astronauts back to the moon. The engineers would like to handle old, proven material, and even rough some up in the lab. The heat shield on Columbia and those of all the manned Apollo craft are off limits, as these vehicles, displayed in museums around the country, are national treasures.
But, as Betsy Pugel suspected, the Smithsonian doesn’t throw things away. Pugel, one of the scientists on the Orion heat shield project at NASA’s Goddard Space Flight Center in Maryland, and currently detailed to NASA Ames, doubles as a liaison between NASA and the Museum. Last spring she asked if there might be any Apollo heat shield material stored at the Paul E. Garber facility, the Museum’s warehouse in Suitland, Maryland. The answer: four crates’ worth. When she visited the warehouse in June, the collections staff pulled out an unused five- by two-foot manufacturing sample of Avcoat, the material used for Apollo. Made by contractor Avco, the sample was a glass- and quartz-reinforced epoxy injected into a hexagonal fiberglass honeycomb matrix several inches deep. “My jaw dropped,” Pugel says. “It was a piece that gave us direct insight into how they did it back in the ’60s. Seeing the real thing, in three dimensions, in color, goes beyond any documentation that we have.” The Garber staff also brought out pieces of charred heat shields from the earliest Apollo flights. Orion’s shield may end up similar to Avcoat, or a variation called Phenolic Impregnated Carbon Ablator.
Pugel contacted Ethiraj Venkatapathy, flight system manager for the Orion Thermal Protection System’s Advanced Development Project at NASA’s Ames Research Center in California. In August, Raj, as his colleagues call him, arrived at Garber with a dozen engineers from Ames, Langley Research Center in Virginia, Johnson Space Center in Houston, and Textron Inc., the Rhode Island company that now owns Avco. The engineers were led to a warehouse and presented with blackened chunks of heat shields from two unmanned, suborbital Apollo missions: AS-201, a 37-minute shot on February 26, 1966, that reached an altitude of about 300 miles and landed in the south Atlantic Ocean, and AS-202, launched on August 25 of that year, a 93-minute flight to a 700-mile altitude that traveled three-quarters of the way around the planet and landed near Wake Island in the Pacific.
Despite the fact that the engineers were wearing surgical gloves, the scene was reminiscent of kids on Christmas morning. The visitors examined the material with the curiosity of problem-solvers and the excitement of enthusiasts handling history.
“The shuttle tiles experience about 40 watts of thermal energy per square centimeter on the underbelly side,” said Raj. “The Orion thermal protection system will experience about 1,000 watts per square centimeter”—about 25 times the heat the shuttle encounters. A lunar mission will end with a reentry that is far faster than a shuttle reentry. The lunar craft’s speed will create temperatures around 10,000 degrees Kelvin—hotter than the surface of the sun—just inches in front of the shield. Raj pointed at the charred material. “We didn’t know if we could revive this technology.”
Collections staff shipped several pieces to Langley, where they’ll be tested for their ability to withstand friction with other hard surfaces, because Orion may touch down on land.
Steve Gayle, one of the Langley engineers, shook his head in amazement at the artifacts. “You can’t see some things until you pick up a piece,” he said. Gayle marveled at how engineers had fashioned the shield’s outer edge, or shoulder, and how the panels of metallic honeycomb substrate beneath the outer ablative material were joined to one another and to the stainless steel bottom of the vehicle. Though Gayle had studied engineering drawings of the old shield, he says he now better appreciates the design and manufacturing features.
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NASA should also look to an earlier project Orion for ablation data. Historian George Dyson wrote in "Project Orion: The true story of the Atomic Spaceship" (Henry Holt & Co.) that ablation could be reduced to zero by coating the ablation shield with a layer of oil. This particular Orion used external nuclear explosions which compressed propellant against a pusher plate to power the ship forward. If the new Orion capsule is to be reused without replacing the ablation material, NASA would do well to examine the data on the originally named craft to see if oil could be the answer.
Posted by David A. Czuba on February 7,2009 | 04:35PM