Before the sun had even risen over Wallops Island, Va., on 10 December 2005, a joint Office of Naval Research/Defense Advanced Research Projects Agency vehicle achieved a world first. At an altitude of 63,000 feet, the Freeflight Atmospheric Scramjet Test Technique (FASTT) vehicle became the first air-breathing, liquid hydrocarbon fuel-powered scramjet engine to fly.
After launching from the NASA Wallops Flight Facility on a two-stage, Terrier-Orion unguided solid-rocket system, the approximately 106-inch long, 11-inch diameter, missile-shaped vehicle raced at 5,300 feet per second (Mach 5.5) for 15 seconds before a controlled splashdown into the Atlantic Ocean. The FASTT vehicle project is part of the joint ONR/DARPA Hypersonic Flight Demonstration (HyFly) program and is designed to demonstrate low-cost flight test techniques and obtain in-flight engine performance data at hypersonic speeds. The overall goal of HyFly is to flight-test key technologies enabling a long range, high-speed cruise missile that can cruise at speeds up to Mach 6.
A scramjet is a supersonic combustion ramjet. Ramjets, which use low subsonic combustion are limited in speed capability. Scramjets have the ability to operate above Mach 5. The hybrid engines of HyFly have no moving parts and offer a lighter weight alternative to other types of propulsion systems. Instead of carrying an oxygen tank, air passing through the vehicle is mixed with fuel. The HyFly program is based on a hybrid scramjet technology called the dual combustor ramjet, developed at the Johns Hopkins University Applied Physics Laboratory. In this powerplant, supersonic air entering through one inlet is slowed to subsonic speeds, mixed with JP-10 fuel and ignited. The expanding combustion products are then mixed with supersonic air entering through a second inlet and are more completely burned in a supersonic combustor.
By using a conventional fuel and not relying on toxic additives as do other scramjet designs, this engine is safer for shipboard use. It can be powered all the way to the target, and that target or its coordinates can be changed as necessary. The test program will culminate in successful tests of sustained flight at Mach 6, thereby demonstrating the readiness of key technologies such as the liquid-hydrocarbon fueled hybrid scramjet engine and high temperature capable structures.
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