NASA X43A jet

The U.S. space agency NASA plans to launch an experimental aircraft Monday that it hopes will set a new world record for air speed.

If weather permits, an unpiloted wedge-shaped X-43 aircraft will drop from the wing of a B-52 bomber over the Pacific Ocean off the California Coast at an altitude of 12 kilometers. At this point, a Pegasus rocket to which the research craft is mated, will boost the X-43 to 33 kilometers, an altitude nearly three times higher. There, the X-43 is to separate and its revolutionary jet engine is to fire and propel it for about 10 seconds at the unprecedented speed of Mach 10 before splashing down into the ocean. That is ten times the speed of sound, or 12,000 kilometers per hour.

The mission is a near duplicate of one last March that set the current world air speed record of Mach 7. Project Manager Joel Sitz says it is the last of three flights since 2001 to test the so-called scramjet, which NASA believes could play a role in future space launches. "It was nice to see the successful separation on the second flight, so we're looking forward to another one of those. It's a high risk event for us, hard to predict what is going to happen sometimes," he said.

That risk was apparent during the first attempt to fly the X-43 in 2001, which failed. The Pegasus booster rocket veered out of control shortly after its release from the bomber, so ground controllers blew it up and the X-43 with it.

The scramjet at the heart of the program is unlike rocket engines that must haul heavy loads of liquid oxygen to burn with liquid hydrogen as fuel. Instead, it sucks atmospheric oxygen into its combustion chamber. Therefore a scramjet-powered spacecraft could reduce launch costs by being much lighter.

Because of the faster speed during the third test, engineers have added extra carbon thermal coating to the nose and leading edges of the wings and tail like that used on space shuttles. This is to protect the aircraft against temperatures expected to reach 2,000 degrees Celsius from friction with the atmosphere. This is about 600 degrees hotter than the temperatures reached during the March test.

Joel Sitz says that even if the third X-43 flight fails, the overall program will still be a success. "Having had a success on the second flight builds our confidence in the analysis and the ground tools, prediction tools that are used for future aircraft, he said. "That's the reason I call this program a success regardless of what happens next. We have that confidence, we've opened the door, we've been there, and we can give industry and other government programs the confidence to carry on."

The future of the scramjet is uncertain at NASA, but the U.S. Air Force is moving to develop such technology for hypersonic aircraft that would take mere hours to reach any spot on the planet.