In a bid to keep hypersonics alive at NASA, the team working on the agency's X-43A "Hyper-X" program is developing a plan for a modest follow-on effort that would begin in 2006.

The future of hypersonics at NASA has been in doubt following the announcement of President Bush's new vision for space exploration, given its apparent focus on expendable rockets. A follow-on to the X-43A, the larger X-43C, already has been canceled by the agency's new Office of Exploration Systems to free funding for other uses (DAILY, March 19).

Responsibility for hypersonics research has been transferred to NASA's Office of Aeronautics (Code R), which asked the X-43A team to develop a proposal for a new program, according to David Reubush, deputy manager of the Flight Vehicles and Systems Program Office at NASA's Langley Research Center in Hampton, Va.

The proposed effort is a "much lower-level hypersonics program that would be a follow-on to X-43A, doing basically technology development, as opposed to trying to fly vehicles," Reubush told The DAILY. "If there would be any flight vehicles, they would be very much smaller-scale even than the X-43A. This is a low-budget, keep-hypersonics-going kind of activity."

If approved by Code R, the program would be submitted to NASA leadership this summer as part of the office's fiscal year 2006 budget proposal, according to Reubush. The first five years would focus on Mach 5-6 vehicles, the next five years on Mach 8-9 vehicles and the third five years on Mach 13-15 vehicles.

Supersonic combustion ramjets, or scramjets, have fewer moving parts than traditional turbojet engines and draw their oxygen for combustion from the atmosphere rather than carrying it, which allows more weight for payload. NASA has been pursuing scramjet technology with an eye toward future reusable launch vehicles that would take off from runways using turbojets, then use scramjets at higher speeds to achieve Earth orbit.

Whereas the Hyper-X vehicles were "point designs" built according to the specific Mach numbers at which they were intended to fly, the proposed follow-on program will develop new engines with variable geometry that will work over a range of Mach numbers. The team also will focus on developing new engine materials that will be lighter and more resistant to heat, according to Reubush.

"The goal is to have technology ready at the end of a five-year period to do a real vehicle if somebody so desired," he said.

X-43A final flight

The 12-foot X-43A is a scramjet-powered demonstrator designed to advance hypersonic, or faster than Mach 5, engine technology. The Hyper-X Launch Vehicle (HXLV), based on Orbital Sciences' Pegasus XL, boosts the X-43A to its release altitude after being dropped from the wing of a B-52. The cost of the X-43A program, which began in 1996, is estimated at $230-250 million.

The Hyper-X program achieved the fastest flight of an air-breathing aircraft March 27 during a successful Mach 7 (5,000 mph) flight off the coast of California (DAILY, March 30). The program plans one final flight at Mach 10 (7,500 mph), which is expected to take place in September or October.

The last X-43A demonstrator is being outfitted with additional thermal protection for the Mach 10 flight, during which it will experience heating roughly twice that experienced at Mach 7. Reinforced carbon-carbon is being added to the leading edges of the vehicle's vertical fins to handle the higher temperatures.

For the Mach 10 flight, the HXLV will boost the X-43A to 110,000 feet before it separates and fires its scramjet until it runs out of fuel. The vehicle will travel about 850 miles before crashing into the ocean at a pre-determined point. As with the previous Hyper-X demonstrators, it will not be recovered.

NASA's Langley Research Center and Dryden Flight Research Center conduct the Hyper-X program. ATK GASL in Tullahoma, Tenn., built the X-43A vehicle and engine, with Boeing Phantom Works providing the thermal protection and onboard systems.