After some tweaking, Air Force set to blast second hypersonic jet

Air Force to fly X-51 Waverider scramjet to Mach 6

Air Force researchers said they a prepped for a second test run of its X-51A Waverider hypersonic jet which they ultimately expect to hit speeds upwards of Mach 6.

The X-51 test will be the second of flight of the four scramjets built for the Air Force tests by Boeing and Pratt & Whitney Rocketdyne. The X-51A made history on its inaugural hypersonic flight test on May 26, 2010 when it was launched from under the wing of a B-52, released, and accelerated to Mach 5 under scramjet power. It was about 10 times longer than any previous hypersonic scramjet flight and "80 to 90% " of flight test objectives were achieved, program officials said.

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While it was historic, everything didn't operate perfectly on the first flight test.  For example, the 4,000lb X-51 didn't accelerate as quickly as anticipated and the flight test had to be terminated after 143 seconds under scramjet power. A perfect flight would have lasted another 100 seconds and accelerated the X-51A cruiser to Mach 6, according to the Air Force. 

After months of pouring over the details of the flight, the X-51 team "focused on the interface between the rear of the fuel-cooled engine and its vehicle mounted nozzle," said Air Force Research Laboratory X-51A program manager Charlie Brink. An "apparent thermal seal breach" at the interface which was not as tight as it needed to be. This caused some of the hot gases that should have provided thrust to leak into the rear of the cruiser. All of the remaining X-51As have been modified with the new beefed up design, he stated.

Hypersonic combustion generates intense heat and routing of the engine's own JP-7 fuel will help keep the engine operating properly, the Air Force stated. As the scramjet engine ignites it will initially burn a mix of ethylene and JP-7 jet fuel before switching exclusively to JP-7. 

The Air Force describes the X-51 as virtually wingless, designed to ride its own shockwave. The heart of the system is its Pratt & Whitney Rocketdyne SJY61 scramjet engine, but other key technologies will be demonstrated including thermal protection systems materials, airframe and engine integration, and high-speed stability and control. Since scramjets are able to burn atmospheric oxygen, they don't need to carry large fuel tanks containing oxidizer like conventional rockets, and are being explored as a way to more efficiently launch payloads into orbit.

The second X-51A Waverider hypersonic flight test could happen as early as March 22,

Others are interested in hypersonic research as well.  Last Fall, NASA said it was looking for more research and development of hypersonic spacecraft that could travel at incredible speeds - in the neighborhood of Mach 20. NASA issued a call for research on what it called "air-breathing access to space and entry, descent and landing of high-mass vehicles in planetary atmospheres."

 "It is envisioned that air breathing propulsion will dramatically increase the reliability and safety of future launch vehicles and ultimately lower the cost of delivering payloads to orbit. The design of these reusable air breathing hypersonic vehicles is challenging in several critical technology areas. The development of hypersonic-unique air breathing propulsion systems that operate efficiently and effectively from Mach 0 to 20, and the efficient integration of the air breathing propulsion system with the airframe are critical to both integrated vehicle performance and controllability. Since these vehicles fly from the Earth's surface at low speeds and enter space and re-enter the atmosphere at hypersonic speeds, the vehicle performance, controllability, and energy management across the entire Mach range is another significant challenge requiring rapid and accurate computational tools for vehicle design...Further research is required to integrate these discipline tools in a multi-disciplinary design environment."

NASA stated that the Hypersonics Project also has a goal of developing and maturing fundamental technologies required to build future planetary atmospheric entry, descent and landing systems that will enable large science missions and human exploration of Mars. In addition, the Project is interested in those technologies that are crosscutting and may be applicable to a range of other decent and landing systems as well.

Follow Michael Cooney on Twitter: nwwlayer8  

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