The Office of Naval Research and the Defense Applied Research Projects Agency (DARPA) in October will complete static ground testing of a technology demonstrator hypersonic missile, designated HyFly. that will travel at six limes the speed of sound (Mach 6). Flight tests are set for early 2007. If successful. HyFly may provide a range of critical new propulsion technologies and heat-resistant materials for future Navy shipboard, airborne, and submarine-launched missiles.
The missile initiative-referred to as a dual-combustor ramjet-builds on an innovative hybrid ramjet/scramjet engine design developed by the Johns Hopkins University Applied Physics Laboratory. Boeing is the program's prime contractor and Aerojet is the principal subcontractor for the engine. Navy program officials say that the unique HyFly design combines the attributes of a conventional ramjet and a pure scramjet (supersonic combustion ramjet), enabling the engine to achieve extremely high speeds while requiring a smaller booster than needed for a pure scramjet.
Officials say that the program remains high risk, involving new high-heat resistant materials as well as flight in a speed domain thus far flown only by NASA, for just a few seconds, in its X-43 program. The Mach 6 speed envisioned generates tremendous heat-up to 2,000° Fahrenheit on the external surface of the vehicle. Internally, the combustion of conventional liquid hydrocarbon-based fuels generates an extremely corrosive gas mix in the range of 4,000° F, a temperature range experienced only with the space shuttle.
The joint effort started in 2002 with the goal of building on earlier DARPA work in hypersonic flight. Last summer, the program completed an extensive series of performance and operability tests to evaluate the effects of high-speed air on the engine. In initial "direct-connect" tests at Johns Hopkins, air was pumped into the engine. Following those tests, the engine housed in a missile body went through "free-jet" testing in large wind tunnels at the Air Force's Arnold Engineering Development Center in Tullahoma, Tennessee, and at the NASA Langley facility in Hampton, Virginia. The testing at Arnold evaluated the engine at Mach 3.5; the Langley trials were at Mach 6.
The HyFly leading edges and control surfaces are built from a ceramic composite. The engine main body is fabricated from a carbon-carbon material that must be more heat resistant than the carbon-carbon tiles used for the space shuttle.
The February flight test for the missile, which was built at Boeing's St. Louis facility, is intended to prove the low-Mach performance in the dynamic conditions of flight that cannot be demonstrated in wind tunnels. For the test, to be conducted at the Pacific Missile Test Range, a U.S. Air Force F-15 will launch the missile and the engine started by a booster rocket integrated with the missile body, that accelerates it to about Mach 3.5. Following separation of the booster, the missile will be flown as near to full throttle as possible in order to collect data on pressures exerted on the engine.
The second and third test flights will be conducted in spring 2007. The second flight will demonstrate vehicle and engine efficiency and verify the vehicle's flight envelope. The third test, in May. will be a sustained Much 6 flight to evaluate engine performance and engine and vehicle structures. The Naval Air Warfare Center China Lake qualified the booster engine, which is derived from the Navy's supersonic low-altitude target (SLAT) program of the 1980s, which used a hybrid rocket/ramjet propulsion system.
Program officials say that, while no further testing for HyFly is currently planned, the Navy may, if funding becomes available, conduct an analysis of alternatives to look at potential future shipboard, airborne, and undersea strike weapons. Currently, the Navy's strike arsenal consists of the Tomahawk cruise missile, launched from Aegis cruisers and destroyers, the Harpoon and standoff land-attack extended-range (SLAM ER) strike variant of the Harpoon, and the aircraft-launched joint standoff weapon (JSOW).
The HyFly configuration was developed to be compatible with a broad set of platforms. The missile could be launched from ships and submarines, and from the Navy's F/A-18E/F fighter/attack aircraft, and the Air Force's B-52, B-1, and B-2 bombers. It will not, however, fit into the bomb wells of the new Navy-Air Force Joint Strike Fighter or the Air Force's F-22 Raptor.