U.S. Navy engineers at the Naval Air Warfare Center Weapons Division recently designed and flew a prototype ramjet missile in just six months. The engineers not only met their deadline, they flew the missile using off-the-shelf equipment, items so inexpensive they were paid for with a credit card. The result is a missile that could join the fleet in 3-4 years.The United States military is currently in the midst of a major strategic shift. The post 9/11 era has seen the armed services concentrate on fighting insurgencies and anti-terrorism operations. While American involvement in such conflicts will persist for the foreseeable future like it or not, the U.S. must also contend with an increasingly aggressive Russia and China. Deterring conflict with such "near peer" competitors will require smart, fast, highly responsive weapons capable of striking targets at great distances.
One important technology for this goal is ramjet propulsion. First conceived 90 years ago, ramjet propulsion involves using a missile's forward motion to push air into its engine. This pushes oxygen into the combustion chamber where, mixed with fuel, it provides thrust. In theory, this is a simpler technology than the traditional use of a compressor to shovel air into the engine, and can propel objects at speeds of up to Mach 6. In addition to being faster, ramjets can travel three times as far on the same amount of fuel as a standard rocket motor. The result is a missile that gives enemy air defenses less time to react and flies farther than conventional missiles.
The downside to ramjet propulsion is that needs to be fed air in order to work so aircraft or missiles can't use it to take off from a complete stop. Instead, the object being propelled needs a booster, like a rocket motor, to quickly accelerate it to speeds where the ramjet is receiving enough air to take over.
Engineers at the Naval Air Warfare Center Weapons Division in China Lake, California were recently challenged to design and fly a ramjet missile engine in six months. This is a lightning-fast timetable in a world where it takes 20 years to develop a fighter plane. Still, the team was able to get the job done by staying small, buying cheap, and testing often.
Matt Walker, head of the Airbreathing Propulsion Section at NAWCWD, told Naval Aviation News, "If you have a small team, you can just get together and draw on a whiteboard on the fly and not have to worry about getting the large team involved and buy-in from everyone." This also meant keeping defense contractors, which tend to move slowly and conservatively and with an eye for profit, out of the design process.
The team needed to find a rocket capable of boosting the ramjet. Instead of developing one on their own, they used a model rocket engine that cost $900. They were even able to buy the parts with a credit card, avoiding the time-consuming defense acquisition process. The ability to simply order an and have it delivered instead of starting up a rocket motor factory made the process even faster, and the low, low cost meant they could afford to test often.
The team also assumed from the outset that their designs would fail, a lot. But it also knew it would learn from each failure and could quickly incorporate lessons learned. By the third launch, they had a working scramjet missile propulsion unit.
The team is continuing to work on their missile project, refining the design to make it more practical. Instead of having the rocket as a booster stage that falls off after acceleration is complete, the team is making the rocket and ramjet share a single body that shares the combustion chamber. The team also believes they could have a working missile for the fleet in 3-4 years.