Hypersonics: WaveRider X-51

Hypersonic , as the word suggests means “freakishly fast”. An unachievable and uneconomical phenomenon to some people. But human endeavors have always disregarded the word impossible. This is how you sow the seeds of the future. Otherwise, everything will be stationary. So, even in the field of hypersonic science we have men who have taken the responsibility to take further the development and experiment the unknown. The future of the hypersonic technology lies in the hands of Joseph Vogel and his team of accomplished men. As Director of Hypersonics for Advance Networks and Space Systems (AN&SS), Joseph Vogel is responsible for the execution of the AFRLs X-51A Hypersonic Engine Test Program. In addition, Joe is responsible for extending the X-51 program and for creating and executing Boeings air-breathing hypersonic capabilities strategy. Finally, Joe is responsible for collaborating across the Boeing Enterprise in the development and execution of an integrated roadmap for the maturation of Hypersonics technology for all potential commercial, DOD, and civil applications. Joseph Vogel received his Bachelor of Science in Mechanical Engineering from California State University Fullerton and MBA from California University of La Verne. His past experience  includes 12 years working for the National Aeronautics and Space Administration in various capacities supporting the Space Shuttle and Space Station Programs development and operations.

What’s of more interest here is the project his team is working on. The project is called The Waverider, a.k.a. the X-51. It is designed to fly more than six times faster than the speed of sound on ordinary jet fuel i.e. mach 6. The $240-million program, a joint effort by U.S. Air Force, Defense Advanced Research Projects Agency (DARPA), Pratt & Whitney Rocketdyne, and Boeing, the hypersonic vehicle is designed to be the first air-breathing craft to demonstrate sustained speeds in excess of Mach 4 using a “logistically friendly” hydrocarbon fuel. The only purpose of the air vehicle is to demonstrate the scramjet in several minutes of flight and relay the flight data before the vehicle plunges into the ocean. Says Vogel, “It is a vehicle designed around an engine.”

Rendering of waverider a.k.a. X-51

The WaveRider stays airborne, in part, with lift generated by the shock waves of its own flight. The design stems from the goal of the program — to demonstrate an air-breathing, hypersonic, combustion ramjet engine, known as a scramjet.The geometry of the X-51A’s engine is relatively simple, and it is constructed of Inconel, a readily available nickel-based alloy, not some “unobtanium.” What’s more, unlike the X-43, which used hydrogen as a fuel when it briefly demonstrated positive thrust and accelerated to Mach 9.6 after being launched by a Pegasus winged booster earlier in this decade, the X-51A runs on a hydrocarbon fuel–JP-7. The propellant is safe to handle due to its high flash point. Skunk Works legend Ben Rich famously told of dropping a match into a bucket of JP-7 only to see it extinguished.

Eventually, four X-51A vehicles are to be flown in tests at the Navy’s Pt. Mugu, Calif., range. Each time, the scramjet should run for about 300 sec., propelling the WaveRider in a regime from 62,000 ft. to as high as 100,000 ft.  On the first flight, the B-52 will drop the 3,942-pound “stack” consisting of the 25-foot long X-51 cruiser and its modified ATACMS missile rocket booster, at around 50,000 feet and Mach 0.8. The booster will accelerate the stack to Mach 4.6-4.8. During the boost, air will flow through the cruiser’s engine, exiting via a ducted interstage, warming the scramjet and its circulating fuel.

At the top of the boost phase, around 60,000 feet, the vehicle’s own guidance control unit and scramjet digital controller will command the X-51A to roll inverted, placing the inlet uppermost and giving the vehicle a positive angle-of-attack. At booster burnout and separation, the vehicle will briefly coast before ethylene is injected at 4,500 psi to light off the engine. Heated by the burning ethylene, fuel will be introduced and the two flows combusted simultaneously until thermal equilibrium is achieved and the vehicle can accelerate on JP-7 alone. Rolling upright, the X-51A is expected to cover almost 400 miles in five minutes and reach an altitude of around 100,000 feet before the fuel is exhausted and the vehicle ditches in the Pacific test range off southern California.

So what is a scramjet engine good for? Hypersonic bombers and cruise missiles that can strike anywhere in the world in a few hours, rapid and really cheap space launch (get going fast enough and you zoom into space without having to blast off in a rocket ship), getting from New York to Dubai in two hours…all will be possible with an engine that is very fuel-efficient for its application (versus a rocket, for example). The X-51 program is not a technology development effort for a specific application, whether it will be a tactical missile family or a passenger-carrying hypersonic transport. Rather, X-51 aims to demonstrate that hypersonic propulsion is practical for a variety of applications–ranging from high-speed missiles for rapid strikes from stand-off distances to global reach for reconnaissance to air-breathing propulsion for space access, probably as the reusable first stage of a two-stage-to-orbit launch vehicle.

Assuming the engine works and they’re able to manage the heat buildup during tests that begin in 2009, there is really no reason why we couldn’t scale this up for either a bomber or transport craft relatively soon thereafter (say 2020 or so for prototyping). And once the technology is pioneered by the initial military applications, commercial applications like space launch and transportation will soon follow. I wouldn’t be surprised if some smaller company like SpaceX would license this technology to build 2 stage-to-orbit reusable vehicles in the near to mid future.

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