May 19, 2006 4:00 AM PDT
NASA searches for a better heat shield
The research could lead to the improvement of the so-called heat shields that are critical to space flight. The space shuttle Columbia, for example, exploded during re-entry into the atmosphere in February 2003 when a hole in its outer surface caused the craft to break apart under extreme temperatures.
Right now, NASA is designing a heat shield for the Crew Exploration Vehicle, a planned spacecraft the Bush administration hopes will transport six astronauts to the moon and back by 2012. On Thursday, NASA Ames opened the lab, called the arc jet facility, to the press and demonstrated a test that was akin to seeing a lightning bolt up close.
Designing a heat shield for the CEV will be a challenge because it will travel beyond what scientists call low-Earth orbit. A craft traveling to the moon can reach speeds of 25,000 miles per hour upon re-entry--8,000 miles per hour faster than a spaceship returning from low-Earth orbit. The difference in speed can make temperatures the ship has to withstand increase more than tenfold, said James Reuther, product manager of heat-shield testing for the CEV.
"It's a real challenge," Reuther said.
The arc jet where NASA tests materials is a 20-foot-long hollow tube with air running through it. When it's turned on, two charges are emitted, which create a bolt of lightning. That lighting, or plasma torch, gets directed on shield materials the size of hockey pucks, which are at the end of the tube. The lightning inside the tunnel travels at supersonic speed, or 17,000 miles per hour, and heats up to two or three times the temperature of the sun.
With the conditions of atmospheric re-entry simulated, NASA scientists can measure the effect on various materials and whether they can take the heat. They also use computer simulations to predict the materials' sturdiness. When the heat shield is eventually built, it will be 16.5 feet in diameter and shaped like an upside-down frisbee attached to the base of the CEV's crew capsule.
Nothing's too hot for NASA
Designing heat shields for the Crew Exploration Vehicle.
Better heat resistance won't be the only difference in the planned spacecraft's heat shield. Researchers are also looking at ways to build the heat shield out of a series of "blades" that would melt away as the ship re-enters the atmosphere. Current heat shield designs, like those on the bottom of the space shuttle fleet, rely on tiles that can be reused.
So far, NASA is studying five test materials for these blades. They include a honeycomb structure with blades made of resin and quartz and another made of something called Pica, which is a thermo-protection material designed at Ames that combines various ceramics and composites. The others are handmade, and their details haven't been revealed yet.
NASA Ames has been involved in testing heat-resistant materials for 45 years. Its facility is the largest in the United States; the arc jet can generate up to 60 million watts of energy.
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