Within the next few years, we will begin work on the sixth generation [fighter] capabilities necessary for future air dominance.” The Secretary of the Air Force, Michael B. Donley, and the USAF Chief of Staff, Gen. Norton A. Schwartz, issued that statement in an April 13 Washington Post article.
The Air Force may have to move a little faster to develop that next generation fighter. While anticipated F-22 and F-35 inventories seem settled, there won’t be enough to fix shortfalls in the fighter fleet over the next 20 years, as legacy fighters retire faster than fifth generation replacements appear.
The Air Force will have to answer a host of tough questions about the nature of the next fighter.
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From left to right, USAF fighter generations one through five, plus a placeholder for generation six. *Illustrations not to scale. (Illustrations by Zaur Eylanbekov)
Should it provide a true “quantum leap” in capability, from fifth to sixth generation, or will some interim level of technology suffice? When will it have to appear? What kinds of fighters will potential adversaries be fielding in the next 20 years? And, if the program is delayed, will a defense industry with nothing to work on in the meantime lose its know-how to deliver the needed system?
What seems certain is that more is riding on the Air Force’s answers than just replacing worn-out combat aircraft.
Initial concept studies for what would become the F-22 began in the early 1980s, when production of the F-15 was just hitting its stride. It took 20 years to go from those concepts to initial operational capability. Industry leaders believe that it will probably take another 20 years to field a next generation fighter.
That may be late to need. By 2030, according to internal USAF analyses, the service could be as many as 971 aircraft short of its minimum required inventory of 2,250 fighters. That assumes that all planned F-35s are built and delivered on time and at a rate of at least 48 per year. The shortfall is due to the mandatory retirement of F-15s and F-16s that will have exceeded their service lives and may no longer be safe to fly.
Defense Secretary Robert M. Gates has set the tone for the tactical aviation debate. He opposed the F-22 as being an expensive, “exquisite” solution to air combat requirements, and has put emphasis on the less costly F-35 Lightning II instead. He considers it exemplary of the kind of multirole platforms, applicable to a wide variety of uses, that he believes the US military should be buying in coming years. He and his technology managers have described this approach as the “75 percent” solution.
Gates has also forecast that a Russian fifth generation fighter will be operational in 2016—Russia says it will fly the fighter this year—and a Chinese version just four years later. Given that US legacy fighters are already matched or outclassed by “generation four-plus-plus” fighters, if Russia and China build their fifth generation fighters in large numbers, the US would be at a clear airpower disadvantage in the middle of the 2020s. That’s a distinct possibility, as both countries have openly stated their intentions to build world-class air fleets. If they do, the 75 percent solution fails.
What You See Is What You Get
The Air Force declined to offer official comment on the status of its sixth generation fighter efforts. Privately, senior leaders have said they have been waiting to see how the F-22 and F-35 issues sorted out before establishing a structured program for a next generation fighter.
The Air Force has a large classified budget, but it seems there is no “black” sixth generation fighter program waiting in the wings. A senior industry official, with long-term, intimate knowledge of classified efforts, said the F-22 wasn’t stopped at 187 aircraft because a secret, better fighter is nearly ready to be deployed. He said, “What you see is what you get.”
That opinion was borne out in interviews with the top aeronautic technologists of Boeing, Lockheed Martin, and Northrop Grumman, the three largest remaining US airframers. They said they were unaware of an official, dedicated Air Force sixth generation fighter program and are anxiously waiting to see what capabilities the service wants in such a fighter.
The possibilities for a sixth generation fighter seem almost the stuff of science fiction.
It would likely be far stealthier than even the fifth generation aircraft. It may be able to change its shape in flight, “morphing” to optimize for either speed or persistence, and its engines will likely be retunable in-flight for efficient supersonic cruise or subsonic loitering.
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A Northrop Grumman artist’s conception of a sixth generation fighter employing directed energy weapons and stealthy data networking. (Northrop Grumman illustration)
The sixth generation fighter will likely have directed energy weapons—high-powered microwaves and lasers for defense against incoming missiles or as offensive weapons themselves. Munitions would likely be of the “dial an effect” type, able to cause anything from impairment to destruction of an air or ground target.
Materials and microelectronics technologies would combine to make the aircraft a large integrated sensor, possibly eliminating the need for a nose radar as it is known today. It would be equipped for making cyber attacks as well as achieving kinetic effects, but would still have to be cost-effective to make, service, and modify.
Moreover, the rapid advancement of unmanned aircraft technologies could, in 20 years or so, make feasible production of an autonomous robotic fighter. However, that is considered less likely than the emergence of an uninhabited but remotely piloted aircraft with an off-board “crew,” possibly comprising many operators.
Not clear, yet, is whether the mission should be fulfilled by a single, multirole platform or a series of smaller, specialized aircraft, working in concert.
“I think this next round [of fighter development] is probably going to be dominated by ever-increasing amounts of command and control information,” said Paul K. Meyer, vice president and general manager of Northrop Grumman’s Advanced Programs and Technology Division.
Meyer forecast that vast amounts of data will be available to the pilot, who may or may not be on board the aircraft. The pilot will see wide-ranging, intuitive views of “the extended world” around the aircraft, he noted. The aircraft will collect its own data and seamlessly fuse it with off-board sensors, including those on other aircraft. The difference from fifth generation will be the level of detail and certainty—the long-sought automatic target recognition.
Directed Energy Weapons
Embedded sensors and microelectronics will also make possible sensor arrays in “locations that previously weren’t available because of either heat or the curvature of the surface,” providing more powerful and comprehensive views of the battlefield, Meyer noted. Although the aircraft probably won’t be autonomous, he said, it will be able to “learn” and advise the pilot as to what actions to take—specifically, whether a target should be incapacitated temporarily, damaged, or destroyed.
Traditional electronics will probably give way to photonics, said Darryl W. Davis, president of Boeing’s advanced systems division.
“You could have fewer wires,” said Davis. “You’re on a multiplexed, fiber-optic bus … that connects all the systems, and because you can do things at different wavelengths of light, you can move lots of data around airplanes much faster, with much less weight in terms of … wire bundles.”
Fiber optics would also be resistant to jamming or spoofing of data and less prone to cyber attack.
A “digital wingman” could accompany the main fighter as an extra sensor-shooter smart enough to take verbal instructions, Meyer forecasted.
Directed energy weapons could play a big role in deciding how agile a sixth generation fighter would have to be, Meyer noted. “Speed of light” weapons, he added, could “negate” the importance of “the maneuverability we see in today’s fashionable fighters.” There won’t be time to maneuver away from a directed energy attack.
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F-22 Raptors on a training mission soar over the mountains near Elmendorf AFB, Alaska. The fifth generation fighter features all-aspect stealth and full-sensor fusion. (USAF photo)
Pulse weapons could also fry an enemy aircraft’s systems—or those of a ground target. Based on what “we have seen and we make at Northrop Grumman,” Meyer said, “in the next 20 years … that type of technology is going to be available.”
With an appropriate engine—possibly an auxiliary engine—on board to provide power for directed energy weapons, there could be an “unlimited magazine” of shots, Meyer said.
Hypersonics—that is, the ability of an air vehicle to travel at five times the speed of sound, or faster—has routinely been suggested as an attribute of sixth generation fighters, but the industry leaders are skeptical the capability will be ready in time.
While there have been some successes with experimental hypersonic propulsion, the total amount of true hypersonic flying time is less than 15 minutes, and the leap to an operational fighter in 20 years might be a leap too far.
“It entails a whole new range of materials development, due to … sensors, fuzes, apertures, etc.,” Meyer noted, “all of which must operate in that intense heat environment at … Mach 5-plus.”
Still, “it is indeed an option that we would consider” because targets will be fleeting and require quick, surgical strikes at great distances. However, such an approach would probably be incompatible with a loitering capability.
Davis said he thinks hypersonics “will start to show up in sixth generation,” but not initially as the platform’s power plant, but rather in the aircraft’s kinetic munitions.
“I think it will start with applications to weapons,” Davis said. And they may not necessarily be just weapons but “high-speed reconnaissance platforms for short missions on the way to the target.”
Because of the extreme speed of hypersonic platforms and especially directed energy weapons, Davis thinks it will be critical to have “persistent eyes on target” because speed-of-light weapons can’t be recalled “once you’ve pulled the trigger,” and even at hypersonic speed, a target may move before the weapon arrives. That would suggest a flotilla of stealthy drones or sensors positioned around the battlefield.
Not only will hypersonics require years more work, Davis said it must be combined with other, variable-cycle engines that will allow an aircraft to take off from sea level, climb to high altitude, and then engage a hypersonic engine. Those enabling propulsion elements are not necessarily near at hand in a single package.
The sixth generation fighter, whatever it turns out to be, will still be a machine and will need to be serviced, repaired, and modified, according to Neil Kacena, deputy director of Lockheed Martin’s Skunk Works advanced projects division. He is less confident that major systems such as radar will be embedded in the aircraft skin.
“If the radar doesn’t work, and now you have to take the wing off, … then that may not be the technology that will find its way onto a sixth gen aircraft,” he said. In designing the next fighter, life cycle costs will be crucial, and so practical considerations will have to be accommodated.
Toward that end, he said, Lockheed Martin is working on new composite manufacturing techniques that use far fewer fasteners, less costly tooling, and therefore lower start-up and sustainment costs. It demonstrated those technologies recently on the Advanced Composite Cargo Aircraft program.
Given the anticipated capabilities of the Russian and Chinese fifth generation fighters, when will a sixth generation aircraft have to be available?
Davis said the Air Force and Navy, not industry, will have to decide how soon they need a new generation of fighters. However, “if the services are thinking they need something in 2020” when foreign fifth generation fighters could be proliferating in large numbers, “we’re going to have to do some things to our existing generation of platforms,” such as add the directed energy weapons or other enhancements.
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In Boeing’s conception, traditional electronics give way to photonics, reducing weight and increasing processing speed. (Boeing illustration)
Kacena agreed, saying that Lockheed Martin has “engaged with both services and supplied them data and our perspectives” about the next round of fighter development. If the need exists to make a true quantum leap, then sixth generation is the way to go, but, “if it’s driven by the reduction in force structure [and] … the equipment is just getting old and worn out in that time frame, then [we] may very well be on a path of continuous improvement of fifth generation capabilities.” Lockheed Martin makes both the F-22 and F-35.
He said the company’s goal is to find the knee in the curve where “you get them the most bang for the buck without an 80 to 90 percent solution. Something that doesn’t take them beyond the nonlinear increase in cost.”
Lt. Gen. David A. Deptula, the Air Force deputy chief of staff for intelligence-surveillance-reconnaissance and a fighter pilot, said the next fighter generation may well have characteristics fundamentally different from any seen today, but he urged defense decision-makers to keep an open mind and not ignore hard-learned lessons from history.
Although great strides have been made in unmanned aircraft, said Deptula, “we have a long way to go to achieve the degree of 360-degree spherical situation awareness, rapid assimilation of information, and translation of that information into action that the human brain, linked with its on-site sensors, can accomplish.”
Numbers Count, Too
Despite rapid increases in computer processing power, it will be difficult for a machine to cope with “an infinite number of potential situations that are occurring in split seconds,” Deptula added, noting that, until such a capability is proved, “we will still require manned aircraft.”
It’s important to note that America’s potential adversaries will have access to nearly all the technologies now only resident with US forces, Deptula said. Thinking 20 to 30 years out, it will be necessary to invest properly to retain things US forces depend on, such as air superiority.
However, he warned not to put too much emphasis on technology, per se. “Just as precision air weapons and, to a certain degree, cyberspace are redefining our definition of mass in today’s fight, we have to be very wary of how quickly ‘mass’ in its classic sense can return in an era of mass-precision and mass-cyber capabilities for all.”
In other words, numbers count, and too few fighters, even if they are extremely advanced, are still too few.
Hanging over the sixth generation fighter debate is this stark fact: The relevant program should now be well under way, but it has not even been defined. If the Pentagon wants a sixth generation capability, it will have to demonstrate that intent, and soon. Industry needs that clear signal if it is to invest its own money in developing the technologies needed to make the sixth generation fighter come about.
Moreover, the sixth generation program is necessary to keep the US aerospace industry on the cutting edge. Unless it is challenged, if the “90 percent” solution is needed in the future, industry may not be able to answer the call.
Under Gates, Pentagon technology leaders have said they want to avoid cost and schedule problems by deferring development until technologies are more mature. Unfortunately, this safe and steady approach does not stimulate leap-ahead technologies.
Meyer said, “We need to have challenges to our innovative thoughts, our engineering talents, our technology integration and development that would … push us … to the point where industry has to perform beyond expectations.”
He noted that today’s F-35 is predicated on largely proven technologies and “affordability,” but it was the B-2 and F-22 programs that really paved the way for the systems that underpin modern air combat.
The B-2 bomber, he noted, “was a program of significant discovery,” because it involved a great deal of invention to meet required performance. The B-2 demanded “taking … basic research and developing it in the early … phases” of the program, which yielded nonfaceted stealth, enhanced range and payload, nuclear hardening, new antennas, radars, and flight controls.
Today, Meyer said, most programs are entering full-scale development only when they’ve reached a technology readiness level of six or higher (see chart).
“We probably had elements on the B-2 … that were at four, and a lot at five,” Meyer said.
Programs such as the sixth generation fighter “are the ones we relish because they make us think, they make us take risks that we wouldn’t normally take, and in taking on those risks we’ve discovered the new technologies that have made our industry great,” he asserted.
Davis said that other countries are going to school on the US fighter industry and taking its lessons to heart.
“We still think you have to build things—fly them and test them—in order to know what works and what doesn’t,” said Davis. “And, at some point, if you don’t do that, just do it theoretically, it doesn’t get you where you need to be.”
He added, “If we don’t continue to move forward, they will catch us.”
The definition of fighter generations has long been subject to debate. However, most agree that the generations break down along these broad lines:
Generation 1: Jet propulsion (F-80, German Me 262).
Generation 2: Swept wings; range-only radar; infrared missiles (F-86, MiG-15).
Generation 3: Supersonic speed; pulse radar; able to shoot at targets beyond visual range (“Century Series” fighters such as F-105; F-4; MiG-17; MiG-21).
Generation 4: Pulse-doppler radar; high maneuverability; look-down, shoot-down missiles (F-15, F-16, Mirage 2000, MiG-29).
Generation 4+: High agility; sensor fusion; reduced signatures (Eurofighter Typhoon, Su-30, advanced versions of F-16 and F/A-18, Rafale).
Generation 4++: Active electronically scanned arrays; continued reduced signatures or some “active” (waveform canceling) stealth; some supercruise (Su-35, F-15SE).
Generation 5: All-aspect stealth with internal weapons, extreme agility, full-sensor fusion, integrated avionics, some or full supercruise (F-22, F-35).
Potential Generation 6: extreme stealth; efficient in all flight regimes (subsonic to multi-Mach); possible “morphing” capability; smart skins; highly networked; extremely sensitive sensors; optionally manned; directed energy weapons.
Technology Readiness Levels
Pentagon leaders now seek to reduce weapon risks and costs by deferring production until technologies are mature. Pentagon technology readiness levels—TRLs—are defined as follows:
TRL 1: Basic principles observed and reported. Earliest transition from basic scientific research to applied research and development. Paper studies of a technology’s basic properties.
TRL 2: Invention begins; practical applications developed. No proof or detailed analysis yet.
TRL 3: Active R&D begins. Analytical and lab studies to validate predictions. Components not yet integrated.
TRL 4: Basic elements are shown to work together in a “breadboard,” or lab setting.
TRL 5: Fidelity of demonstrations rises. Basic pieces are integrated in a somewhat realistic way. Can be tested in a simulated environment.
TRL 6: Representative model or prototype. A major step up in readiness for use. Possible field tests.
TRL 7: Prototype of system in operational environment is demonstrated—test bed aircraft, for example.
TRL 8: Final form of the technology is proved to work. Usually the end of system development. Weapon is tested in its final form.
TRL 9: Field use of the technology in its final form, under realistic conditions.
A team led by NASA and The Boeing Company has completed the first phase of flight tests on the subscale X-48B blended wing body aircraft at the agency’s Dryden Flight Research Center in Edwards, Calif.
The remotely piloted, 500-pound airplane with the silhouette resembling a manta ray – also called a hybrid wing body — is a tool of NASA’s new Environmentally Responsible Aviation, or ERA, Project, which aims to develop the technology needed to create a quieter, cleaner, and more fuel-efficient airplane for the future.
A flying test bed such as the X-48B enables NASA to assess and validate the key technologies. The recently concluded flight tests ascertained the handling and flying qualities of such an aircraft at speeds typical of landings and takeoffs.
“This project is a huge success,” said Fay Collier, manager of the ERA Project in NASA’s Aeronautics Research Mission Directorate. “Bottom line: the team has proven the ability to fly tailless aircraft to the edge of the low-speed envelope safely.”
Until recently, Collier was principal investigator for NASA’s Subsonic Fixed Wing Project, which established the partnership with Boeing to conduct initial, fundamental technology development efforts with the X-48B. The ERA Project he now leads is part of a new research program NASA initiated to help further mature promising technology before transfer to industry.
The team completed the 80th and last flight of the project’s first phase on March 19, 2010, almost three years after the X-48B’s first flight on July 20, 2007.
Cranfield Aerospace Limited technician Ian Brooks prepares the X-48B for flight. (NASA Photo / Tony Landis)
In addition to NASA and Boeing, the team includes Cranfield Aerospace Limited of the United Kingdom, and the U.S. Air Force Research Laboratory of Dayton, Ohio.
In the mid-2000s, NASA identified low-speed flight controls as a development challenge for aircraft such as the hybrid wing body. This challenge, and the challenge of building a non-circular, pressurized fuselage structure, have been the initial focuses of research since then. The ultimate goal is to develop technology for an environmentally friendly aircraft that makes less noise, burns less fuel, and emits less noxious exhaust.
“These 80 research flights provided engineers with invaluable test data and allowed the team to completely meet the initial project test objectives,” said Tim Risch, Dryden’s X-48B project manager.
The milestones accomplished by the team focused on three main technical objectives: flight envelope expansion, aircraft performance characterization, and validation of flight control software limiters.
The first objective, envelope expansion, consisted of 20 flights over a year-long period. For these flights, the aircraft was flown through a variety of maneuvers intended to define the overall flight capabilities and discern the general stability and handling characteristics of the aircraft. Completion of these tests resulted in a preliminary flight envelope adequate for transition to higher risk testing.
The second objective, aircraft performance characterization, focused on stall testing to define the boundaries of controlled flight, engine-out maneuvering to understand how to control the aircraft if one or more engines malfunctioned, and parameter identification flights to evaluate how movements of flight control surfaces affected the airplane’s performance.
In 52 flights from July 2008 through December 2009, engineers quantified the dynamic response of the aircraft by sending computer commands to the X-48B’s flight control surfaces and measuring how quickly the plane responded to the inputs.
NASA Dryden engineer Gary Cosentino prepares the X-48B for flight. (NASA Photo / Tony Landis)
The third and most important objective were limiter assaults, in which the remote pilot deliberately exceeded the defined boundaries of controllability – such as angle of attack, sideslip angle and acceleration — to see whether the airplane’s computer could keep it flying steady. Eight flight tests validated the programmed limiters and gave the team confidence that a robust, versatile, and safe control system could be developed for such an aircraft.
Tests with the X-48B will continue later this year, after a new flight computer is installed and checked out. The next series of flight tests will focus on additional parameter identification investigations.
NASA has a second hybrid wing body aircraft, the X-48C, which it has modified for a noise profile even lower than the X-48B’s, and is preparing for test flights to investigate other controllability factors.
Before unpiloted or remotely piloted aircraft can safely operate in the same airspace as other, piloted aircraft, robotic aircraft and their operators will need to demonstrate a high level of operational robustness and the ability to “sense and avoid” other air traffic. The Unmanned Aircraft Systems Airspace Operations Challenge (UAS AOC) is focused on developing some of the key technologies that will make UAS integration into the National Airspace System possible.
This competition is being formulated as part of NASA’s Centennial Challenge Program, which is designed to foster individual, academic, and private sector innovation to solve difficult problems that are important to NASA and the nation. This Centennial Challenge will be conducted in two parts: Phase 1 of the Challenge is scheduled to be held in Spring, 2014 and Phase 2 of the Challenge will be held approximately one year after Phase 1 has been successfully completed.
Phase 1 of the Challenge focuses on important aspects of safe airspace operations, robustness to system failures, and seeks to encourage competitors to get an early start on developing some of the skills critical to Phase 2. Specific skills that Phase 1 competitors will need to demonstrate include:
- Safe Airspace Operations:
- Separation Assurance using ADS-B
- 4 Dimensional Trajectories
- Ground Control Operations
- Robustness to System Failures:
- Lost Link
- GPS Unavailable
- GPS Unreliable
- Preparation for Phase 2 Competition:
- Uncooperative Air Traffic Detection
There are other technical challenges that must be solved to enable the integration of UAS in the NAS, but a competitor that successfully demonstrates the skills required in Phase 1 will be able to field a robust UAS that is significantly closer to the goals of UAS-NAS integration embodied in theNextGen Airspace Concept. The total prize money available for Phase 1 of the competition is $500,000.
The experimental X-51A Waverider is an unmanned, autonomous supersonic combustion ramjet-powered hypersonic flight test demonstrator for the U.S. Air Force.
The X-51A is designed to be launched from an airborne B-52 Stratofortress bomber. The flight test vehicle stack is approximately 25 feet long and includes a modified solid rocket booster from an Army Tactical Missile, a connecting interstage, and the X-51A cruiser. The nearly wingless cruiser is designed to ride its own shockwave, thus the nickname, Waverider. The distinctive, shark-nosed cruiser has small controllable fins and houses the heart of the system, an SJY61 supersonic combustion ramjet or scramjet engine built by Pratt & Whitney Rocketdyne designed to burn JP-7 jet fuel. Boeing’s Phantom Works performed overall air vehicle design, assembly and testing for the X-51′s various component systems.
The X-51 was made primarily using standard aerospace materials such as aluminum, steel, inconel, and titanium. Some carbon/carbon composites of the leading edges of fins and cowls are used. For thermal protection, the vehicle utilizes a Boeing designed silica-based thermal protection system as well as Boeing Reusable Insulation tiles, similar to those on board the NASA Space Shuttle Orbiters.
Four X-51As were built for the Air Force. The X-51A program is a technology demonstrator and was not designed to be a prototype for weapon system. It was designed to pave the way to future hypersonic weapons, hypersonic intelligence, surveillance and reconnaissance, and future access to space. Since scramjets are able to burn atmospheric oxygen, they don’t need to carry large fuel tanks containing oxidizer like conventional rockets, and are being explored as a way to more efficiently launch payloads into orbit.
In addition to scalable scramjet propulsion, other key technologies that will be demonstrated by the X-51A include thermal protection systems materials, airframe and engine integration, and high-speed stability and control.
The X-51A represents one of the service’s most significant reinvestments in hypersonic flight since the rocket-powered X-15 program which flew 50 years earlier.
Air Force officials anticipate the X-51A program will provide a foundation of knowledge required to develop the game changing technologies needed for future access to space and hypersonic weapon applications. For example, hypersonic speeds on the order of flying 600 nautical miles in 10 minutes may provide the ability to accurately engage a long-distance target very rapidly.
The X-51A program is a collaborative effort of the Air Force Research Laboratory and the Defense Advanced Research Projects Agency, with industry partners The Boeing Company and Pratt & Whitney Rocketdyne. Program management is accomplished by the Air Force Research Laboratory Propulsion Directorate at Wright-Patterson Air Force Base, Ohio.
Hypersonic flight, normally defined as beginning at Mach 5, five times the speed of sound, presents unique technical challenges with heat and pressure, which make conventional turbine engines impractical. Program officials said producing thrust with a scramjet has been compared to lighting a match in a hurricane and keeping it burning.
The Air Force currently plans to fly each X-51A on identical flight profiles. Like the X-15, the X-51A is designed to be carried aloft by a B-52 mother ship launched from the Air Force Flight Test Center at Edwards Air Force Base, Calif. It is released at approximately 50,000 feet over the Pacific Ocean Point Mugu Naval Air Warfare Center Sea Range. The solid rocket booster accelerates the X-51A for 30 seconds to approximately Mach 4.5, before being jettisoned. Then the cruiser’s scramjet engine, remarkable because it has virtually no moving parts, ignites. The ignition sequence begins burning ethylene, transitioning over approximately 10 seconds to the same JP-7 jet fuel once used by the SR-71 Blackbird.
Powered by its scramjet engine, the X-51A will accelerate to approximately Mach 6 as it climbs to nearly 70,000 feet. Hypersonic combustion generates intense heat so routing of the engine’s own JP-7 fuel will serve to both cool the engine and heat the fuel to optimum operating temperature for combustion. The fuel load and flight profile provides for a 240-second engine burn, transmitting vast amounts of telemetry data on its systems to orbiting aircraft and ground stations, before the vehicle exhausts its fuel supply, splashes down into the Pacific and is destroyed, as planned. Flight test vehicles are not recovered.
The X-51A development team elected from the outset not to build recovery systems in the flight test vehicles, in an effort to control costs and focus funding on the vehicle’s fuel-cooled scramjet engine. A U.S. Navy P-3 Orion aids in transmitting telemetry data to engineers at both Naval Air Station Point Mugu and Vandenberg AFB, Calif., before it arrives at its final destination, the Ridley Mission Control Center at Edwards AFB.
Conceived in 2004, the X-51A made its first “captive carry” flight Dec. 9, 2009. The flight test verified the B-52′s high-altitude performance and handling qualities with the X-51 attached and tested communications and telemetry systems, but the vehicle remained attached to the B-52s wing.
The X-51A made history during its first supersonic combustion ramjet-powered hypersonic flight May 26, 2010, off the southern California Pacific coast. Officials said the flight test vehicle flew as anticipated for nearly 200 seconds, with the scramjet accelerating the vehicle to approximately Mach 5, nearly 3,400 miles per hour. The fuel-cooled scramjet performed as planned transmitting normal telemetry for more than 140 seconds, then observing a decrease in thrust and acceleration for another 30 seconds. An anomaly then resulted in a loss of telemetry, and the test was terminated and vehicle was destroyed by flight controllers on command.
Despite the anomaly, the May 26 flight is considered the first use of a practical hydrocarbon fueled scramjet in flight. The longest previous hypersonic scramjet flight test performed by a NASA X-43 in 2004 was faster, but lasted only about 12 seconds and used less logistically supportable hydrogen fuel.
Following an extensive analysis of flight data from the X-51A’s first hypersonic flight test, slight modifications are planned to strengthen the rear seal area near the engine exhaust nozzles for the three remaining X-51As.
The next two X-51A flights ended prematurely. The second vehicle was boosted by the rocket to just over Mach 5, separated and lit the scramjet on ethylene. When the vehicle attempted to transition to JP7 fuel operation, it experienced an inlet un-start. The hypersonic vehicle attempted to restart and oriented itself to optimize engine start conditions, but was unsuccessful. The vehicle continued in a controlled flight orientation until it flew into the ocean within the test range.
The third X-51A safely separated from the B-52, however after 16 seconds under the rocket booster, a fault was identified with one of the cruiser control fins. Once the X-51 separated from the rocket booster, approximately 15 seconds later, the cruiser was not able to maintain control due to the faulty control fin and was lost.
The final flight of the X-51A occurred May 1, 2013 and was the most successful in terms of meeting all the experiment objectives. The cruiser traveled more than 230 nautical miles in just over six minutes reaching a peak speed of Mach 5.1.
Overall the more than 9 minutes of data collected from the X-51A program was an unprecedented achievement proving the viability of air-breathing, high-speed scramjet propulsion using hydrocarbon fuel.
Primary Function: Hypersonic scramjet-powered flight test demonstrator
Contractors: Boeing, Pratt & Whitney Rocketdyne
Power Plant: JP-7 fueled/cooled SJY61 supersonic combustion ramjet
Thrust: 500 – 1,000 pound class
Length: Full stack 25 feet; Cruiser 14 feet; Interstage 5 feet; Solid rocket booster 6 feet
Weight: Approx. 4,000 pounds
Fuel Capacity: Approx. 270 pounds JP-7
Speed: 3,600+ miles per hour (at Mach 6)
Range: 400+ nautical miles
Ceiling: 70,000 + feet
Crew: ground station monitored
Unit Cost: Unavailable
Initial Flight Test: May 26, 2010
Inventory: Four purpose-built for flight test, not designed for recovery (one vehicle expended as of Feb. 1, 2011)
A Defense Department report released today describes China’s military modernization and the Chinese army’s interaction with other forces, including those of the United States, a senior Pentagon official said today.
The annual report — titled “2013 Military and Security Developments Involving the People’s Republic of China” — went to Congress today and covers China’s security and military strategies; developments in China’s military doctrine, force structure and advanced technologies; the security situation in the Taiwan strait; U.S.–China military-to-military contacts and the U.S. strategy for such engagement; and the nature of China’s cyber activities directed against the Defense Department.
David F. Helvey, deputy assistant secretary of defense for East Asia, briefed Pentagon reporters on the report. He noted that the report, which DOD coordinates with other agencies, “reflects broadly the views held across the United States government.” The report is factual and not speculative, he noted.
Helvey said the trends in this year’s report show the rising power increasing its rapid military modernization program. “We see a good deal of continuity in terms of the modernization priorities,” Helvey noted, despite the 2012 and 2013 turnover to new leadership, which happens roughly every decade in China.
The report notes China launched its first aircraft carrier in 2012 and is sustaining investments in advanced short- and medium-range conventional ballistic missiles, land-attack and anti-ship cruise missiles, counter-space weapons and military cyberspace systems.
Helvey noted these technologies all bolster China’s anti-access and area-denial capabilities.
“The issue here is not one particular weapons system,” he said. “It’s the integration and overlapping nature of these weapons systems into a regime that can potentially impede or restrict free military operations in the Western Pacific. So that’s something that we monitor and are concerned about.”
Helvey said the report provides a lot of information, but also raises some questions. “What concerns me is the extent to which China’s military modernization occurs in the absence of the kind of openness and transparency that others are certainly asking of China,” he added.
That lack of transparency, he noted, has effects on the security calculations of others in the region. “And so it’s that uncertainty, I think, that’s of greater concern,” he said.
Helvey added the report noted China has “increased assertiveness with respect to its maritime territorial claims” over the past year. China disputes sovereignty with Japan over islands in the East China Sea, and has other territorial disputes with regional neighbors in the South China Sea.
“With respect to these claims, we encourage all parties to the different disputes or interactions to address their issues peacefully, through diplomatic channels in a manner consistent with international law,” he said.
Helvey noted China’s relations with Taiwan have been consistent. “Over the past year, cross-strait relations have improved,” he said. “However, China’s military buildup shows no signs of slowing.”
China also is building its space and cyberspace capabilities, Helvey said. He noted that in 2012, China conducted 18 space launches and expanded its space-based intelligence, surveillance, reconnaissance, navigation, meteorological and communication satellite constellations.
“At the same time, China continues to invest in a multidimensional program to deny others access to and use of space,” Helvey said.
Addressing China’s cyber capabilities, Helvey said the Chinese army continues to develop doctrine, training and exercises that emphasize information technology and operations.
“In addition, in 2012, numerous computer systems around the world, including those owned by the United States government, continued to be targeted for intrusions, some of which appear to be attributable directly to [Chinese] government and military organizations,” he added.
Helvey noted a positive trend in U.S.-China engagements over the year, including several senior-leader visits culminating in then-Defense Secretary Leon E. Panetta’s visit to Beijing in September.
The two sides also explored practical areas of cooperation, he said, including the first counterpiracy exercise conducted in September by Chinese and U.S. forces, followed by the U.S. invitation to China to participate in the Rim of the Pacific exercise in 2014.
“We’ll continue to use military engagement with China as one of several means to expand areas where we can cooperate, discuss, frankly, our differences, and demonstrate the United States’ commitment to the security of the Asia-Pacific region,” Helvey said.