The final flight of NASA's X-43A hypersonic research aircraft is still on schedule for Monday afternoon, Nov. 15, weather permitting. The mission is intended to flight-validate the operation of the X-43A's supersonic-combustion ramjet - or scramjet - engine at a record airspeed of almost Mach 10, or 10 times the speed of sound. The X-43A and its modified Pegasus booster rocket was mated to NASA's B-52B launch aircraft on Thursday, Nov. 11. Pre-flight checks of the X-43A and the booster are occurring Friday and Saturday, with final closeouts and fueling slated for Sunday, Nov. 14th. Takeoff on Nov. 15 is tentatively scheduled for about 1 p.m. Pacific time, with launch about an hour later over the Pacific test range off the coast of Southern California.
As with the first two flights, the third X-43A will be carried aloft by NASA's B-52B launch aircraft from NASA's Dryden Flight Research Center on Edwards Air Force Base. The B-52B "mothership" will release the combined X-43A and Pegasus booster stack at 40,000 feet altitude off the coast of Southern California. The booster will then accelerate the experimental vehicle to nearly Mach 10, or almost 7,000 mph, at approximately 110,000 feet altitude. At booster burnout, the 2,800-pound, wedge-shaped X-43A will separate, and fly briefly on a preprogrammed path, performing a set of tasks and maneuvers before splashdown in the ocean.
The last X-43A vehicle has additional thermal protection for the Mach 10 flight, since it will experience heating roughly twice that of the Mach 7 vehicle. Reinforced carbon-carbon composite material has been added to the leading edges of the vehicle's vertical fins to handle the higher temperatures.
For the Mach 10 flight, which equates to approximately 7,000 mph, the booster rocket will launch the X-43A to 110,000 feet before it separates and the X-43A operates its scramjet. The research vehicle will travel about 850 miles before splashing into the ocean. As with the previous X-43A vehicles, it will not be recovered.
...A scramjet (supersonic-combustion ramjet) is a ramjet engine in which the airflow through the whole engine remains supersonic. It is thought that a scramjet can operate from Mach 5-6 up to at least Mach 15.
The scramjet concept is simple: Accelerate the vehicle to about Mach 4 by a conventional jet engine, then start the scramjet engine (which has few or no moving parts) by introducing fuel and mixing it with oxygen obtained from the air and compressed for combustion. The air is naturally compressed by the forward speed of the vehicle and the shape of the inlet, similar to what turbines or pistons do in slower-moving airplanes and cars.
While the concept is simple, proving the concept has not been simple. At operational speeds, flow through the scramjet engine is supersonic - or faster than the speed of sound. At that speed, ignition and combustion take place in a matter of milliseconds. This is one reason it has taken researchers decades to demonstrate scramjet technologies, first in wind tunnels and computer simulations, and only recently in experimental flight tests.
The previous X-43A flight set a record at Mach 7.
In the process of demonstrating a scramjet-powered airplane in flight for the first time, the March 2004 flight set a world speed record for an "air breathing" (jet-powered) vehicle. It flew at nearly Mach 7, or 5,000 mph. It easily surpassed the previous record set by the military's now-retired SR-71 Blackbird high-altitude reconnaissance aircraft, which flew at about Mach 3.2.
To prepare for the Mach 10 flight, the third scramjet was upgraded slightly. A thicker layer of thermal insulation was added to the engine, wing edges, tail and nose. The nose is expected to reach about 2000°C - roughly 600 degrees hotter than the previous Mach 7 flight.
Reasons not to get too excited: The aircraft is unmanned. It is a throw-away that will not be recovered when it crashes into the Pacific Ocean. NASA has no follow-on money allocated to build on this design with a better hypersonic scramjet aircraft design. The whole Hyper-X project that produced three X-43A vehicles (this is the third and final) cost $230 million. But orders of magnitude larger sums must be spent operating the obsolete Space Shuttle to go visit the white elephant International Space Station to accomplish very little real science or technological advance.
Still, useful lessons will be learned from the X-43A. Some day a new effort that pushes the envelope of scramjet operation even further may build upon what was learned in this effort.
|Share |||Randall Parker, 2004 November 12 02:50 PM Airplanes and Spacecraft|