News | March 25, 2003

New ideas point toward a better aircraft

HAMPTON -- As the Columbia investigation holds the future of the space shuttle program in the balance, engineers at NASA Langley Research Center are developing new heat-protection systems for the next generation of orbiters. NASA wants to fly a new type of shuttlecraft within the next decade or two. In addition to making space travel cheaper and more efficient, the agency wants to improve the protective skin that helps spacecraft survive the fiery temperatures of re-entry. Investigators are looking at whether tile damage during Columbia's launch may have led to the Feb. 1 disaster. The shuttle's fragile ceramic tiles have come under scrutiny because they easily chip and break when under pressure. Since rain damages ceramic tiles, NASA makes sure the space shuttle doesn't takeoff or land in the rain, but it's costly when rain delays shuttle missions. The tiles are glued on with adhesives, which makes them difficult to temporarily remove for inspection. Each of the 27,000 shuttle tiles is cut to a different shape, so it's time-consuming and costly to replace them between flights. Before the shuttle's first flight in 1981, Langley ran aerodynamic and temperature tests on the tiles, which were developed at Ames Research Center in California. Terrific technology for its time, the ceramic thermal protection system has turned out to be a huge "time sink" and "money sink," said Mark Shuart, director of structures and materials at Langley. "What we found out over time is it is a bear to maintain," Shuart said. For more than 30 years, Langley Research Center has been studying how to make thermal protection systems out of metal instead of ceramic. In the 1960s, aircraft manufacturer McDonnell Douglas proposed using a metallic thermal protection system for the space shuttle and ran tests at Langley, said Paul Czysz, an aerospace engineer who worked for the company for decades before it merged with Boeing in 1997. NASA headquarters made the mistake of opting for ceramics instead of metal, said Czysz, professor emeritus at Parks College of Engineering and Aviation at St. Louis University. "I know they had a lot of money tied up in this simple solution," he said about ceramics. "I can hold it in my hand and it's one-inch thick. All I have to do is stick some silicon glue on it. What could be simpler? But it can't be repaired." Shuart said NASA made the best decision based on the available technologies of the time. One of the leading ideas today is a metallic shield called ARMOR, which stands for Adaptable, Robust, Metallic, Operable, Reusable - words that sum up the qualities of the protection system. The metallic panels would essentially snap on and off, making them much easier to repair or replace in between and perhaps during flights, Shuart said. The Columbia disaster also has drawn attention to the difficulty of replacing the ceramic tiles during flights. ARMOR consists of 3-inch thick panels made of titanium and a nickel alloy called Inconel. Although you won't find household items made of Inconel, it is used for turbine engine components and cryogenic storage tanks. While debris can make ceramic tiles break like fine china, ARMOR gets dings like a car door. "It may dent slightly, but it does not break or flake off," Shuart said. It also doesn't rust. The details of exactly how ARMOR will cover the orbiter will have to wait until NASA makes a final commitment to the next generation of spacecraft, which might happen in 2008. Other NASA centers are also studying different types of metallic protection systems. ARMOR isn't perfect. Production costs are probably higher than ceramic tiles, but Shuart hopes the new system would actually save money in the long run because repair expenses would be lower. ARMOR cannot withstand temperatures beyond 2,000 degrees Fahrenheit, which means it might not be used on the part of the spacecraft that can reach 3,000 degrees during re-entry. Researchers hope to increase ARMOR's temperature resistance in the future. There are several steps left before Americans will see a fully implemented, metallic thermal protection system on a spacecraft. The next will be a flight in 2006 aboard an experimental craft called the X-37, a robotic space plane that will test technologies in the harsh environments of space and re-entry. The X-37 will carry only a few panels of ARMOR to see how they hold up. The X-37 can't reach orbit without the space shuttle or an expendable launch vehicle. It is a precursor to the Orbital Space Plane, which itself will act as a bridge between the space shuttle and the next generation of spacecraft. It's too early to say exactly what these new vehicles will look like. NASA hopes to use the Orbital Space Plane to ferry astronauts to and from the International Space Station in 2012. It will be a relatively small vehicle without enough room to carry all the provisions the space station needs. The agency is studying whether to have a "next generation" vehicle, larger than the Orbital Space Plane, replace the space shuttle and service the space station beginning between 2015 and 2020. ARMOR's best chances of being used as a thermal protection system is on the next generation of spacecraft, not the orbital space plane. Marshall Space Flight Center in Alabama leads the Next Generation Launch Technology program, but gets plenty of help from NASA's research centers. Langley has multiple tasks including developing launch systems and technology like ARMOR. Mark Saunders directs Langley's space access and exploration program office. "The ultimate goal is to make more reliable, lower cost, safer vehicles," he said.