As NASA prepares a return-to-flight of its X-43A Hyper-X vehicle, the agency is holding its collective breath about the future of "air-breathing" engine technologies. A second vehicle is now being prepped to fly no later than mid-November.
It has been more than two years since the scramjet-powered vehicle suffered a setback in the skies above a Pacific Ocean test area. Deployed from a modified NASA B-52 aircraft on June 2, 2001, the sleek-looking craft mounted on a Pegasus booster -- called the stack -- veered out of control.
The stack was deliberately destroyed by an onboard explosive charge less than 50 seconds after release.
Results of a NASA mishap investigation board, charged to review the loss of the research vehicle, were formally issued last week.
The board reported that the flight failed because the X-43A's control system design was deficient in several analytical modeling areas. But in its deliberations, the expert panel of investigators also concluded that no single factor or potential contributing factor caused the mishap.
Three unpiloted vehicles
"Clearly, a lot is riding on this next flight," said Vince Rausch, Hyper-X program manager at the NASA Langley Research Center at Hampton, Virginia. Langley leads the X-43A program with flight operations conducted by the space agency’s Dryden Flight Research Center at Edwards, California.
"We’ve really worked hard to try and make certain that this next flight is successful. But this is still research. It’s still high risk…we can’t lose site of that," Rausch told SPACE.com. "We thought the booster would fly one way and it flew a different way."
The X-43A is designed to be the first scramjet-powered vehicle, capable of attaining speeds as high as Mach 10.
In the X-43A test program, three, 12-foot long, unmanned vehicles were fabricated to demonstrate scramjet, or supersonic-combustion ramjet, technologies.
An air-breathing propulsion system sustains combustion of fuel with atmospheric oxygen. The hope is to increase a vehicle’s payload capacity by not hauling along hefty amounts of oxygen and associated tanks. Hydrogen will fuel the Hype-X research vehicles, but it requires oxygen from the atmosphere to burn.
Benign trajectory
Rausch said that the second X-43A, its modified Pegasus booster, an adapter that joins the two, as well as the B-52 carrier aircraft are near ready to handle the vehicle’s return-to-flight.
A number of changes are being made to reduce risk for
the second flight. The next X-43A mission is slated to make a run at Mach 7, as the first flight was slated to do.
"But we have gone through and worked very hard to reduce the risk across the flight profile, from takeoff through the flight experiment," Rausch said.
For one, the X-43A and booster stack will be dispatched from the B-52 at some 40,000 feet – over double the height from where the first attempt was staged. That launch altitude change reduces dynamic pressures on the hardware as it slips through transonic flight.
"It’s a little bit more benign trajectory than we had the first time," Rausch said.
Beefing up control fins
On the Pegasus itself, Rausch said actuators that control fins on the aft end of the booster are being beefed up. A second motor to each actuator has been added, enabling the fins to take greater torque. Doing so also meant changes in gear material, to electronics, and using more batteries to power the extra motors. Also, less propellant will be carried onboard the Pegasus booster.
"We’ve done a lot of work on the booster. We’re also doing independent assessments all the way along the line," Rausch said.
The Hyper-X research vehicle will be separated from the Pegasus booster rocket by two small pistons. Shortly after separation, the Hyper-X scramjet engine will operate for ten-plus seconds to demonstrate forward thrust in flight.
When the scramjet engine test is complete, the vehicle will go into a high-speed maneuvering glide to collect up to six minutes of hypersonic aerodynamic data while flying to a mission completion point in the Naval Air Warfare Center Weapons Division Sea Range off the southern coast of California.
Reduce risk
Rausch said that the Hyper-X team is shooting for the X-43A re-flight no later than mid-November. "We’re doing our best to beat that."
Launch might take place earlier, in mid-October, but "given that the stars all align properly, Rausch said.
"The message here, Rausch said, "is that we’ve tried to look across the entire vehicle trajectory – from early takeoff, drop, all the way through the experiment – to reduce risk."
"But again, this is something that is a first. We won’t know for sure until we get it to flight," Rausch said. "This is research and that’s how you learn."
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