The HyFly (Hypersonic Flight Demonstration) program is a joint
project of the Office of Naval Research and Defense Advanced
Research Projects Agency (DARPA) to flight-test key
technologies enabling a long range, high-speed missile that can
cruise at speeds up to Mach 6.
HyFly will demonstrate engine and sustained missile
performance over a range of Mach numbers, including sustained
flight at Mach 6. It also will demonstrate the missile structures’
capability to withstand the high temperatures associated with
sustained flight at hypersonic speeds.
The HyFly program is based on a hybrid scramjet technology called the dual combustor ramjet, developed at the
Johns Hopkins University Applied Physics Laboratory. A scramjet is a supersonic combustion ramjet. Ramjets
(which use low subsonic combustion) are limited in speed capability, but scramjets can operate above Mach 5.
The dual combustor ramjet combines scramjet and ramjet flowpaths into an integrated engine to achieve
performance over a wide speed range. Fuel is mixed with air from the ram ducts in a subsonic gas generator,
where ignition and flameholding occur. Supersonic air from the scramducts is then added, and combustion is
completed in the combustor. The hybrid engine has no moving parts and offers a lighter weight alternative to
other types of propulsion systems. It is the first scramjet engine—hybrid or otherwise—to demonstrate operability
with liquid hydrocarbon fuel.
Both the 50-percent and the 100-percent scale models built under the HyFly program have successfully operated
using JP-10 fuel, which is qualified for use on Navy weapons. By using a conventional fuel and not relying on
toxic additives as do other scramjet designs, this engine is safer for shipboard use.
The HyFly program includes flight tests of the 50-percent scale engine boosted on a sounding rocket and air
launched shots of the 100-percent scale missile from an F-15. (Because they do not have turbines, all
ramjets/scramjets must be either carried or boosted to a certain speed before they can be activated.) The objective
of the 50-percent scale effort, known as the Freeflight Atmospheric Scramjet Test Technique (FASTT), is to
demonstrate low-cost flight test techniques and obtain in-flight engine performance data at hypersonic speeds
using a subscale derivative of the dual combustor ramjet. In booster-powered flights, both vehicles have
successfully achieved cruise vehicle trajectory insertion.
The program’s most recent milestone was achieved on December 10, 2005, with the world’s first flight of an air-
breathing, scramjet-powered vehicle using liquid hydrocarbon fuel. The FASTT vehicle was launched from the
NASA Wallops Flight Facility at Wallops Island, Va. It was boosted by a two-stage, Terrier-Orion unguided
solid-rocket system. Following separation from the booster, the scramjet engine ignited, propelling the vehicle to
speeds of 5,300 feet per second (Mach 5.5), at an altitude of 63,000 feet. The vehicle flew for more than 15
seconds under scramjet power, before a controlled splashdown into the Atlantic Ocean.
The HyFly program participants include: the Boeing-Aerojet team, which built the 100-percent scale missile and
will demonstrate the high temperature engine; ATK-GASL, which built and flew the 50-percent scale missile; the
Johns Hopkins University Applied Physics Laboratory, and the Naval Air Warfare Center Weapons Division at
China Lake and Pt. Mugu, Calif.