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Mach 10 Meteor: X-43A Scramjet Flight is Risky Business
11.12.04
 
Infrared of Mach 6.8 X-43A flight. It looked so easy last March when NASA's X-43A team succeeded in sending the second X-43A scramjet to a world record speed of Mach 6.83, but looks are deceiving.

Blazing through the sky at Mach 10 is next on the project's agenda as the third X-43A flight date fast approaches. This attempt is high risk, so no detail is too small to leave to chance.

Image right: Infrared image of the world-record Mach 6.8 flight of the second X-43A scramjet on March 27, 2004. U.S. Army.

When the second X-43A research vehicle flew Mach 6.83, or nearly seven times the speed of sound (the speed of sound is about 760 mph at sea level), the friction-generated 2600-degree Fahrenheit temperature on the leading edges of the vehicle's horizontal tails was more than enough to melt unprotected metal. Carbon-carbon thermal protection material kept them cool enough to withstand the searing heat. This is a challenge for even the most advanced thermal protection materials.

When the third and final X-43A flies in November, blistering temperatures created by the Mach 10 (7000 mph) speed will be in the neighborhood of 3600 degrees, the hotspot this time being the nose of the vehicle. The heat distribution is different this time around due to material differences. For further protection, Vehicle 3 will have additional thermal coatings on the horizontal tails' carbon-carbon leading edges.

Another change in preparation for Mach 10 is that Vehicle 3's vertical tails are solid, as opposed to the ribbed structure construction used on Vehicles 1 and 2. Carbon-carbon leading edges have been added to the vertical tails as well.

The separation of the research vehicle from the booster is going to be performed at a higher speed than the Mach 7 flight, but dynamic pressure will be lower due to the planned higher separation altitude this time.

An important product of flight research is data collection, and one of the prime data objectives for the Hyper-X program is validation of scramjet ground predictions. Prior to the Mach 7 flight, engineers were able to use hypersonic wind tunnel data for risk reduction tests. However, they couldn't do this in preparation for the upcoming Mach 10 flight, as fewer ground test facilities were available.

"One of the more significant challenges we faced in preparing for the Mach 10 flight is the reduced amount of ground test data," said Laurie Marshall, NASA Dryden Flight Research Center's X-43A Vehicle 3 chief engineer. "For Flight 2 we were able to do more wind tunnel work than we could for Flight 3. In some cases the same tests couldn't be repeated; the facilities and capabilities just aren't there. So having to design a vehicle and engine that can survive the environment and complete the mission successfully without some of that data was a challenge," Marshall said.

Another of the exciting things about the Mach 10 flight of the X-43A is that NASA will be able to gather data that has never before been obtained.

"That's why we're doing this, that's why we have to fly," Marshall said. "The research data that we will obtain with this flight at Mach 10 can't be obtained on the ground."

Gray Creech
NASA Dryden Flight Research Center