NASA, along with a number of international partners, is currently working on the HIFiRE (Hypersonic International Flight Research Experimentation Program) program to advance hypersonic flight.
Hypersonic flight is typically defined as beginning at Mach 5 – five times the speed of sound.
The above-mentioned research program is aimed at exploring the fundamental technologies required to achieve practical hypersonic flight. Indeed, being able to fly at hypersonic speeds could revolutionize high speed, long distance flight and provide more cost-effective access to space.
During a recent experiment the scramjet – aboard its sounding rocket – managed to climb to about 100,000 feet (30,480 meters) in altitude, accelerating from Mach 6 to Mach 8 (4,567 to 6,090 miles per hour; 7,350 to 9,800 kilometers per hour) and operating for about 12 seconds.
The HIFiRE 2 scramjet research payload included a hypersonic inward turning inlet, followed by a scramjet combustor and dual-exhaust nozzle. More than 700 instruments on board recorded and transmitted data to researchers on the ground.
“This is the first time we have flight tested a hydrocarbon-fueled scramjet accelerating from Mach 6 to Mach 8. At Mach 6 the inlet compression and combustion process was designed to reduce the flow to below Mach 1 – subsonic combustion,” explained NASA Hypersonics Project Scientist Ken Rock, based at NASA’S Langley Research Center in Hampton, Va.
“But at Mach 8 flight the flow remained greater than Mach 1 or supersonic throughout the engine. So this test will give us unique scientific data about scramjets transitioning from subsonic to supersonic combustion – something we can’t simulate in wind tunnels.”
The data collected during the execution of the HIFiRE experiments is expected to contribute to the development of future high-speed air-breathing engine concepts, while helping improve design, modeling, and simulation tools.
The success of the three-stage launch system, consisting of two Terrier boost motors and an Oriole sustainer motor, is another important achievement of the HIFiRE 2 mission. According to NASA, HIFiRE 2, the first flight of this sounding rocket configuration, opens the door for a new high-performance flight tests to support future Air Force and Navy flight research.
To be sure, demonstrating supersonic combustion in flight with a hydrocarbon fueled scramjet – compared to a hydrogen-fueled scramjet – is significant. While hydrogen fuel is more reactive, hydrocarbon fuel offers numerous benefits, including operational simplicity and higher fuel density, ultimately allowing a hypersonic vehicle to carry more fuel.