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Hypersonic Flight Technologies: Vehicles only decades away

Hypersonics Research

NASA continues to research hypersonics flight technology. NASA will be flight testing by decade's end Hyper-X aircraft that are expected to yield a new generation of vehicles that routinely fly about 100,000 feet above Earth's surface and reach sustained travel speeds in excess of Mach 5, or about 3,750 mph -- the point at which "supersonic" flight becomes "hypersonic" flight. It also may be the point at which traditional air transportation becomes as outmoded as the covered wagon. Revolutionizing the way we gain access to space is NASA's primary goal for its hypersonics research program. This hypersonics research will support future-generation reusable launch vehicles and improve access to space. Over the next 20 years, the U.S. will develop and test a series of ground and flight demonstrators. The flight demonstrators -- the Hyper-X series -- will be powered by air-breathing rocket- or turbine-based engines and ram/scramjets.

Air-breathing engines for hypersonic applications are known as "combined cycle" systems because they use a graduating series of propulsion systems in flight to reach an optimum travel speed, or to leave the atmosphere altogether. Air-breathing engines achieve their efficiency gains over rocket systems by getting their oxygen for combustion from the atmosphere, as opposed to a rocket which must carry its oxygen. These systems capture air from the atmosphere during flight -- an arrangement that improves efficiency up to 5-10 times greater than that of conventional chemical rockets.

Once a hypersonic vehicle has accelerated to more than twice the speed of sound, the turbine or rockets are turned off, and the engine relies solely on oxygen in the atmosphere to burn fuel. When the vehicle has accelerated to more than 10 to 15 times the speed of sound, the engine converts to a conventional rocket-powered system to propel the craft into orbit or sustain its top suborbital flight speed.

Despite the astounding paradigm shift it promises for suborbital and orbital flight, the concept of hypersonic flight is not a new one. NASA's hypersonics program is built on research dating back to the 1950s.

But the new effort -- leveraging technology resources and manufacturing capabilities unavailable 30 years ago -- is intended to yield practical results before mid-century: a future fleet of government and commercial hypersonic vehicles, traveling between dozens or even hundreds of "skyports" around the world and far beyond.

The Hyper-X series
NASA's series of hypersonic flight demonstrators includes three air-breathing vehicles: the X-43A, X-43B and X-43C

The X-43A, an unpiloted research craft mounted atop a modified Pegasus booster rocket, was first flown in June 2001. During the flight, an in-flight incident forced the mission to be aborted. NASA has planned three X-43A flights; two more X-43A flight demonstrators built in early 2002, are being prepared for flight testing at NASA's Dryden Flight Research Center in Edwards, Calif. Fueled by hydrogen, the X-43A is intended to achieve Mach 7 and possibly Mach 10, or speeds of approximately 5,000 and 7,500 mph, respectively.

The X-43C demonstrator, powered by a scramjet engine developed by the U.S. Air Force, is now in development. The X-43C is expected to accelerate from Mach 5 to Mach 7, reaching a maximum potential speed of about 5,000 mph. NASA will begin flight-testing the X-43C in 2008.

The largest of the Hyper-X test vehicles, the X-43B, could be developed -- and would fly -- later this decade. Successful ground- and flight-testing of various engine configurations aboard the X-43A and X-43C will determine whether a rocket- or turbine-based combined-cycle engine powers the X-43B.

All three X-43 flight demonstrator projects are managed by NASA's Langley Research Center in Hampton, Va.

Next-generation flight solutions
NASA expects to spend about $700 million on hypersonics research and development over the next five years. NASA anticipates the investment will yield unprecedented results, opening up new commercial markets for industry, furthering human and robotic exploration of the solar system and significantly improving national security.

Testing conducted over the last four years has proved that air-breathing propulsion is the most promising technology seen to date for accomplishing NASA's third-generation space transportation goals. Those goals -- focusing on radically safer, more reliable and less expensive access to space -- permeate not just the Hypersonics Technology Program, but all NASA's space transportation and propulsion systems programs.

NASA is working to develop the technology for a second-generation vehicle that could lead to a replacement for the first-generation Space Shuttle by 2012 -- providing a vastly safer, more cost efficient and more reliable fleet of vehicles. The third-generation program seeks, by the year 2025, to develop advanced reusable launch vehicles and associated flight and transportation technologies that will allow for even more significant reductions in payload costs, and even greater improvements in safety and reliability.

More about NASA's Hypersonics Team
NASA is leading national research into hypersonics systems development, analysis and integration. Spearheaded by the Marshall Center, the program includes researchers at Ames Research Center in Moffett Field, Calif.; Dryden Flight Research Center in Edwards, Calif.; Glenn Research Center in Cleveland,Ohio; Kennedy Space Center, Fla.; Langley Research Center in Hampton, Va.; and the Air Force Research Laboratory, which encompasses research and development facilities at nine U.S. Air Force bases. NASA is also partnering with leading academic institutions and industry partners around the nation.

Narrowing Down The Future
The Space Shuttle is an efficient, safe, powerful vehicle to begin with, so it's hard to improve on that. But since the Shuttle is expected to end its lifespan in approximately 2012, now is the time to plan its replacement.

When it comes to launching a space vehicle, the first few hundred kilometers are the toughest part of the trip. A large part of the energy requirements for space flight are used in escaping the Earth's gravitational forces and achieving orbit (or traveling to even further destinations). Then, there's the design. Some of the designs lift off vertically (the way the Shuttle does now) while others launch horizontally (more like an airplane). Ejection seats and flyaway crew modules are part of the designs under consideration. NASA expects to narrow down the options even further in 2003 by selecting two finalists in the competition.

Other improvements to the current program are in the works. A new thermal-protection system called Adaptable, Robust, Metallic, Operable, and Reusable (ARMOR) will function like the Space Shuttle's lightweight protective skin, but will be able to withstand temperatures of up to 1,648 degrees Celsius (3,000 degrees Fahrenheit). The Shuttle's temperature limit is about 1,093 °C (2,000 °F).

NASA's Space Launch Initiative doesn't focus exclusively on the vehicle that will take astronauts into space. Its purpose is to design an entire system: an Earth-to-orbit reusable launch vehicle, on-orbit transfer vehicles, upper stages to put satellites into orbits, mission planning, ground and flight operations, and support infrastructure for orbit and on the ground. The plan is to accomplish this, while at the same time trimming costs, improving reliability and safety, and reducing risks-by the year 2012.

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