Scramjet programs

When the second X-15 aircraft (piloted by John B. McKay) crashed on flight 74, it was damaged but survived well enough to be rebuilt. North American Aviation rebuilt it as the X-15-A2. Among other things, one of the changes was provisions for a dummy scramjet to test if wind tunnel testing was correct. Unfortunately, on the final flight of the X-15-A2 (flight 188), the shock waves sent out by the scramjet at Mach 6.7 caused extremely intense heating of over 2,700 °F (1,480 °C). This then drilled into the ventral fin and melted large holes. The plane survived but never flew again. Test data were limited due to the limited flights of the scramjet before the X-15-A2 and the X-15 project on the whole were cancelled.¹

From 1962–1978, the Johns Hopkins Applied Physics Laboratory (APL) undertook a classified program (declassified in 1993) to develop a family of missiles called SCRAM⁸ (Supersonic Combustion RAmjet Missile). They were intended to fit on to the Talos MK12 launcher system or the Terrier MK10 launcher. Testing of engine modules in a direct-connect, and a free-jet, facility took place at a variety of Mach numbers and pressures (altitudes). These included Mach 4 (24,000 ft), Mach 5.3 (46,000 ft), Mach 7.8 (67,000 ft) and Mach 10 (88,000 ft). Tests showed that acceptable combustion efficiency was only achieved with over 20% pentaborane (B₅H₉) in MCPD (C₁₂H₁₆). Tests with pure pentaborane (HiCal) showed that a net thrust could be achieved at Mach 7. An accelerative capability equivalent to 11g was observed for Mach 5 flight at sea level.

In 1986 United States president Ronald Reagan announced the National Aerospace Plane (NASP) program, intended to develop two X-30 aircraft capable of single stage to orbit (SSTO), as well as horizontal takeoff and landing from conventional runways. The aircraft was to be a hydrogen fuelled air-breathing space plane, with a low speed accelerator system to bring the aircraft up to Mach 3, where the main dual-mode scramjet engines (ramjet/scramjet) would take over. At the edge of the atmosphere, a rocket was to take over and provide the final energy for orbital insertion. It was based on a classified DARPA research program called Copper Canyon. This research program suggested that Mach 25 might be possible. As the program proceeded it became clear that Mach 17 was probably the limit, whilst the weight penalty and complexity of the skin heat exchanger and other propulsion systems was going to be substantial. The program was established by the secretary of defence in 1985, and was funded to the end of FY1994, when the decision was made that the 15 billion dollars required to build the two X-30 test craft were excessive.

Although the more visible parts of the program were cancelled, NASP provided a large amount of basic research, which flowed into following projects. For example, The NASP reaction model⁷ for hydrogen combustion in air (31 reactions, 16 species), is still extensively used where computational power is sufficient not to have to use reduced reaction models.

At a test facility at Arnold Air Force Base in the U.S. state of Tennessee, the General Applied Science Laboratory (GASL) fired a projectile equipped with a hydrocarbon-powered scramjet engine from a large gun. On July 26, 2001, the four inch (100 mm) wide projectile covered a distance of 260 feet (79 m) in 30 milliseconds (roughly 5,900 mph or 9,500 km/h).[1] The projectile is supposedly a model for a missile design. Many do not consider this to be a scramjet "flight," as the test took place near ground level. However, the test environment was described as being very realistic.

The $250 million NASA Langley Hyper-X X-43A effort was an outgrowth of the canceled National Aerospace Plane (NASP) program on which NASA was a collaborator. Rather than developing and flying a large, expensive spaceplane with orbital capability, Hyper-X flew small test vehicles to demonstrate hydrogen-fueled scramjet engines. NASA worked with contractors Boeing, Microcraft, and the General Applied Science Laboratory (GASL) on the project.

NASA's Hyper-X program is the successor to the National Aerospace Plane (NASP) program which was cancelled in November 1994. This program involves flight testing through the construction of the X-43 vehicles. NASA first successfully flew its X-43A scramjet test vehicle on March 27, 2004 (an earlier test, on June 2, 2001, went out of control and had to be destroyed). Unlike the University of Queensland's vehicle, it took a horizontal trajectory. After it separated from its mother craft and booster, it briefly achieved a speed of 5,000 miles per hour (8,000 km/h), the equivalent of Mach 7, easily breaking the previous speed record for level flight of an air-breathing vehicle. Its engines ran for eleven seconds, and in that time it covered a distance of 15 miles (24 km). The Guinness Book of Records certified the X-43A's flight as the current Aircraft Speed Record holder on 30 August 2004. The third X-43 flight set a new speed record of 6,600 mph (10,620 km/h), nearly Mach 10 on 16 November 2004. It was boosted by a modified Pegasus rocket which was launched from a Boeing B-52 at 13,157 meters (43,166 ft). After a free flight where the scramjet operated for about ten seconds the craft made a planned crash into the Pacific Ocean off the coast of southern California. The X-43A craft were designed to crash into the ocean without recovery. Duct geometry and performance of the X-43 are classified.

The NASA Langley, Marshall, and Glenn Centers are now all heavily engaged in hypersonic propulsion studies. The Glenn Center is taking leadership on a Mach 4 turbine engine of interest to the USAF. As for the X-43A Hyper-X, three follow-on projects are now under consideration:

X-43B: A scaled-up version of the X-43A, to be powered by the Integrated Systems Test of an Air-Breathing Rocket (ISTAR) engine. ISTAR will use a hydrocarbon-based liquid-rocket mode for initial boost, a ramjet mode for speeds above Mach 2.5, and a scramjet mode for speeds above Mach 5 to take it to maximum speeds of at least Mach 7. A version intended for space launch could then return to rocket mode for final boost into space. ISTAR is based on a proprietary Aerojet design called a "strutjet", which is currently undergoing wind-tunnel testing. NASA's Marshall Space Propulsion Center has introduced an Integrated Systems Test of the Air-Breathing Rocket (ISTAR) program, prompting Pratt & Whitney, Aerojet, and Rocketdyne to join forces for development.

X-43C: NASA is in discussions with the Air Force on development of a variant of the X-43A that would use the HyTECH hydrocarbon-fueled scramjet engine. The US Air Force and Pratt and Whitney have cooperated on the Hypersonic Technology (HyTECH) scramjet engine, which has now been demonstrated in a wind-tunnel environment.

While most scramjet designs to date have used hydrogen fuel, HyTech runs on conventional kerosene-type hydrocarbon fuels, which are much more practical for support of operational vehicles. A full-scale engine is now being built, which will use its own fuel for cooling. Using fuel for engine cooling is nothing new, but the cooling system will also act as a chemical reactor, breaking long-chain hydrocarbons down into short-chain hydrocarbons that burn more rapidly.

X-43D: A version of the X-43A with a hydrogen-powered scramjet engine with a maximum speed of Mach 15.

On December 10, 2005, Alliant Techsystems (ATK) successfully flight-tested an air-breathing, liquid JP-10 (hydrocarbon) fuelled scramjet-powered free-flight vehicle from NASA's Wallops Flight Facility, Wallops Island, Virginia. The flight test was conducted under the Defense Advanced Research Projects Agency (DARPA)/ Office of Naval Research (ONR) Freeflight Atmospheric Scramjet Test Technique (FASTT) project. This latest flight was a culmination of a three-year, three-flight program to successfully demonstrate the feasibility of using ground-launched sounding rockets as a low-cost approach to hypersonic flight testing, and represents the world's first flight test of an air-breathing, scramjet-powered vehicle using hydrocarbon fuel.

Begun in late 2002, the FASTT project entailed the design and fabrication of three flight vehicles and a ground test engine rig to undergo wind tunnel testing. The first and second payloads were dubbed surrogate payload vehicles and matched closely the scramjet flight article, but lacked the internal flowpath and fuel system. They were designed as test rounds to validate vehicle subsystems, such as booster stack combination performance, fin sets, payload deployment mechanism, telemetry and trackability, and inlet shroud, before flight testing the more complicated scramjet flowpath, which was to undergo proof-of-concept testing in a wind tunnel prior to flight testing.

The first surrogate vehicle, SPV1, was launched aboard an unguided Terrier/Improved Orion two-stage solid rocket motor stack from Wallops Island on October 18, 2003, approximately 12 months after program initiation. This had the exact outer mold line of the eventual shrouded scramjet payload and contained full onboard instrumentation and telemetry suites. The vehicle was boosted to approximately 4,600 ft/s (1,400 m/s) and 52,000 ft (16,000 m) altitude, where it was deployed to free-flight, deployed its shroud at high dynamic pressure, and flew an un-powered trajectory to splashdown. All on-board subsystems worked flawlessly. The boost stage however inserted the payload at lower than desired flight speed, altitude, and flight path angle. The second surrogate vehicle, SPV2 was launched aboard the identical booster stack from Wallops Island on April 16, 2004, approximately six months after the first launch. After making slight trajectory corrections to account for launch rail effects, higher than anticipated drag, and actual booster performance, the payload was inserted nominally above 5,200 ft/s (1,600 m/s) and 61,000 ft (19,000 m) altitude. The full complement of subsystems were again proven out in flight on this successful flight test. The results of these two flight tests are summarized in a technical paper AIAA-2005-3297, presented at the 13th International Space Planes and Hypersonics Systems and Technologies Conference (see )in Capua, Italy.

The ground test engine hardware was fabricated over 18 months and underwent a four-month engine validation testing program in the ATK GASL freejet wind tunnel complex Leg 6, located in Ronkonkoma, New York. Ignition, fuel throttling, and engine operation were wrung out over a range of expected flight conditions. After a delay of two months to modify flight hardware based on ground test findings, the first powered vehicle, FFV1, was launched without incident, propelled to speeds of 5,300 ft/s (1,600 m/s) at 63,000 ft (19,000 m) altitude, roughly Mach 5.5. Over 140 inlet, combustor, and vehicle outer mold line pressure, temperatures, and vehicle accelerations as well as fuel pressure, timing feedback, and power systems monitoring were recorded. The vehicle executed the prescribed test sequences flawlessly for 15 seconds, before continuing on to splashdown into the Atlantic Ocean. Further details can be found in the technical paper AIAA-2006-8119,[2] presented at the 14th International Space Planes and Hypersonics Systems and Technologies Conference, in Canberra, Australia.

Alliant Techsystems Inc. (ATK) GASL Division led the contractor team for the FASTT project, developed and integrated the scramjet vehicle, and acted as mission managers for the three flights. Launch vehicle integration and processing was performed by Rocket Support Services (formerly DTI Associates), Glen Burnie, MD; the flight shroud was developed by Systima Technologies, Inc., Bothell, Washington; electrical systems, telemetry and instrumentation was handled by the NASA Sounding Rocket Office Contract (NSROC); flight test support was provided by the NASA Wallops Flight Facility; and technical support was provided by the Johns Hopkins Applied Physics Laboratory, Baltimore, MD. GASL previously built and integrated the engine flowpaths and fuel systems for the three X-43A flight vehicles, working closely with air framer and systems integrator Boeing, NASA Langley, and NASA Dryden on the successful Hyper-X Program.

To be completed

Hy-V is a scramjet experiment to obtain and compare ground test and flight test supersonic combustion data. The general goal of the project is to validate wind tunnel test results that will eventually be used to develop computational codes. The primary investigators are the University of Virginia, Virginia Tech, and Alliant Techsystems, and the test will be launched on a Terrier-Orion sounding rocket from NASA's Wallops Island site.[3]

The Boeing X-51 is a scramjet demonstration aircraft for hypersonic (Mach 7, around 8,050 km/h) flight testing. The X-51 WaveRider program is a consortium of the US Air Force, DARPA, NASA, Boeing and Pratt & Whitney Rocketdyne. The program is managed by the Propulsion Directorate within the United States Air Force Research Laboratory (AFRL).[4]

The X-51 is a descendant of earlier efforts including the Advanced Rapid Response Missile Demonstrator and the liquid hydrocarbon-fuelled scramjet engine developed under the USAF's HyTech program. The first free-flight of the X-51 took place in May 2010. On 1 May 2013, the X-51 performed its first fully successful flight test, flying for 240 seconds until running out of fuel; this test was the longest air-breathing hypersonic flight. This test signified the completion of the program.[5][6]

The Hypersonic Air-breathing Weapon Concept (HAWC, pronounced Hawk) is a scramjet powered air-launched hypersonic cruise missile without a warhead that is being developed by DARPA and uses its own kinetic energy upon impact to destroy the target. It was first successfully tested in September 2021.[7] Another successful test was carried out in mid-March 2022 amid the Russian invasion of Ukraine but further details were kept secret to avoid escalating tensions with Russia only to be leaked by an unnamed Pentagon official in early April. The missile was successfully launched from a B-52 strategic bomber off the west coast and flew above 65,000 feet for more than 300 miles (483 km).[8]

Follow-on tactical range Hypersonic Attack Cruise Missile (HACM) will be built by Raytheon Technologies and will use a Northrop Grumman scramjet.[9][10]

Leidos was awarded a contract to develop the unmanned scramjet-powered Mayhem (Expendable Hypersonic Multi-mission ISR (intelligence, surveillance, and reconnaissance) and Strike program) hypersonic technology demonstrator, in December 2022.[11][12]

On July 30, 2002, the University of Queensland's HyShot team (and international partners) conducted the first-ever successful test flight of a scramjet.

The team took a unique approach to the problem of accelerating the engine to the necessary speed by using a Terrier-Orion sounding rocket to take the aircraft up on a parabolic trajectory to an altitude of 314 km. As the craft re-entered the atmosphere, it dropped to a speed of Mach 7.6. The scramjet engine then started, and it flew at about Mach 7.6 for 6 seconds. . This was achieved on a lean budget of just A$1.5 million (US$1.1 million), a tiny fraction of NASA's US$250 million to develop the X-43A. This involved many of the same researchers involved in the University of Queensland report in 1995 of the first development of a scramjet that achieved more thrust than drag².

On Saturday, March 25, 2006, researchers at the University of Queensland conducted another successful test flight of a HyShot Scramjet at the Woomera Test Range in South Australia. The Hyshot III with its £1,200,000 engine made an apparently successful flight (and planned crash landing) reaching in the order of 7.6 Mach.

NASA has partially explained the tremendous difference in cost between the two projects by pointing out that the American vehicle has an engine fully incorporated into an airframe with a full complement of flight control surfaces available.

In the second HyShot mission, no net thrust was achieved. (The thrust was less than the drag.)[13]

The HyShot program currently consists of the following tests:

• HyShot 1 - UQ 2-D scramjet. Failed launch due to rocket fin puncture by a rock on the landing pad.
• HyShot 2 - UQ 2-D scramjet. Successful, July 30, 2002
• HyShot 3-7 - NASA tests. Cancelled after announcement of manned Mars mission.
• HyShot 8 (Now known as HyShot III) - QinetiQ 4-chamber scramjet. Successful, March 25, 2006.
• HyShot 9 (Now known as HyShot IV) - UQ 2D scramjet with JAXA hypermixer. Successful, March 30, 2006.
• HyShot 10 - HyCAUSE - DSTO scramjet. Successful June 15, 2007.

Sponsorship for the HyShot Flight Program was obtained from the University of Queensland, Astrotech Space Operations, Defence Evaluation and Research Agency (DERA (now Qinetiq), UK), National Aeronautics and Space Agency (NASA, USA), Defence, Science and Technology Organisation (DSTO, Australia), Dept. of Defence (Australia), Dept. of Industry Science and Resources (Australia), the German Aerospace Centre (DLR, Germany), Seoul National University (Korea), the Australian Research Council, Australian Space Research Institute (ASRI), Alesi Technologies (Australia), National Aerospace Laboratories (NAL, Japan), NQEA (Australia), Australian Research and Development Unit (ARDU, Australia), the Air Force Office of Scientific Research (AFOSR, USA) and Luxfer, Australia.

Terrier Terrier Oriole - HiFire-2

Hypersonic International Flight Research and Experimentation (HIFiRE) is a joint program of the US Department of Defense and Australian DST Group. The "purpose of this program is to investigate fundamental hypersonic phenomena and accelerate the development of aerospace vehicle technologies deemed critical to long range precision strike"[14] by using an "affordable, accessible, prototype experimentation strategy".[15]

• HIFiRE 0 May 7, 2009 - First HIFiRE hypersonic test flight [16]
• HIFiRE 1 March 22, 2010 - Axisymmetric conical boundary layer transition [17][18][19]
• HIFiRE 2 May 1, 2012 - Accelerating velocity profile of an hydrocarbon-fueled axisymmetric scramjet [20][21][22]
• HIFiRE 3 Sept 13, 2012 - Radical farming [23] of an hydrogen-fueled axisymmetric scramjet [24]
• HIFiRE 4 June 30, 2017 - Aerodynamic performance of a hypersonic waverider
• HIFiRE 5 April 23, 2012 - Elliptical forebody boundary layer transition (failed because reaching only Mach 3)
• HIFiRE 5b May 18, 2016 - Elliptical forebody boundary layer transition
• HiFIRE 6 Cancelled ? - Adaptive flight control of an hypersonic vehicle
• HIFiRE 7 March 30, 2015 - Free flight of an hydrocarbon fueled scramjet with REST inlet
• HIFiRE 8 Cancelled ? - Sustained flight of an hypersonic vehicle integrating an hydrocarbon fueled scramjet with REST inlet

In 2012 the HIFiRE program was recognized with the prestigious von Karman Award by the International Congress of the Aeronautical Sciences.[25]