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created: 1 March 04
Air & Space Power Journal - Spring 2004
Maj Michael F. Kelly, USAF, Retired
|Editorial Abstract: Gen Hap Arnold’s commitment to “preeminence in research,” the belief that technology superiority leads to air and space superiority, remains the hallmark of Air Force culture. Air Force success in providing the nation with a rapid air and space response capability requires researchers to continue to provide advancements in a number of technologies. Propulsion and power solutions for aircraft, weapons, and space systems are especially important technologies and are recognized as critical enablers, also making the test facilities that support the research and development of those revolutionary and transformational technologies critical to our progress.|
Gen Henry H. “Hap” Arnold, architect of American airpower, said it plainly and persuasively nearly six decades ago, “The first essential of air power is preeminence in research.” That simple, yet prescient statement in the early, heady days of flight revealed Arnold’s vision for aeronautical research and development that went on to profoundly shape the future Air Force.1 By combining his vision, political savvy, piloting skills, and engineering knowledge, Arnold was able to forge a mission and place for the US Air Force. As one of the country’s first to earn his military aviator wings from the Wright brothers, he was especially interested in the development of sophisticated air and space technology that could give the United States an edge in achieving air superiority. Arnold went on to foster the development of such transformational innovations as jet aircraft, rocketry, and supersonic flight.2
In many ways Arnold institutionalized a commitment to research that remains evident today as the Air Force upholds a position of technological leadership—leadership that delivers a steady infusion of new technology to war fighters through high-risk, high-payoff research in the Air Force Research Laboratory (AFRL). More importantly, his vision of building technological superiority laid the foundation for our capacity to achieve today’s Air Force distinctive capabilities—air and space superiority, information superiority, global attack, precision engagement, rapid global mobility, and agile combat support. Arnold’s commitment to technology superiority remains the hallmark of Air Force culture.
For over 85 years, Propulsion Directorate scientists, engineers, support personnel, and contractors have been answering Arnold’s call for world-class research that puts capabilities into the hands of Air Force war fighters to help them dominate air and space—now and in the future. Its 450 ongoing programs, over 1,000 people, and an annual budget of more than $300 million not only have provided a complete spectrum of advanced propulsion technologies for aircraft, rockets, and spacecraft but also have conducted leading-edge research and development in air and space fuels, propellants, and power systems.3 Their inventions have expanded the envelope of propulsion technologies and pushed air and space vehicles higher, faster, and farther—even into space—than Orville and Wilbur Wright ever could have imagined. Today, those technologies are flying in air and space on more than 130 military and commercial systems, including the F/A-22 Raptor, the newly christened F-35 Joint Strike Fighter (JSF), and the twin Mars rovers—Spirit and Opportunity, which successfully landed and began their explorations on the red planet in January 2004.4 This article discusses mainly the directorate’s efforts and their actual and potential impacts—efforts that have been accomplished, are in progress, and are planned for the future.
Technological advancements in the early days of flight brought a whole new set of challenges, and history books confirm the key role that propulsion technologies played in meeting those challenges and in the nation’s many air and space accomplishments. The late Melvin Kranzberg, professor of history at Case Western Reserve University in Cleveland, Ohio, said the technical innovation in the Wright brothers’ airplane quickly necessitated additional technical advances to make it more effective.5 Those advances in engines, cooling systems, propellers, power systems, and fuel were closely linked to the Power Plant Section at McCook Field in Dayton, Ohio—first home to the Army Air Corps’s aircraft-engineering functions and great-grandfather to today’s Propulsion Directorate. The innovations in propulsion and power that were inspired by the Wright brothers and accomplished through the years at McCook Field, Wright Field, and later, Wright-Patterson Air Force Base, Ohio, and Edwards Air Force Base, California, dramatically changed the course of aviation and its applications.
In the air and space age, propulsion research and development capabilities will continue to be of even greater and more urgent importance. F. Whitten Peters, former secretary of the Air Force and now vice-chairman of the Commission on the Future of the US Air and Space Industry, agreed with the judgment reached by that commission in 2002 that propulsion is the crucial enabler to the nation’s future air and space capabilities. The commission reached that conclusion after meeting with over 100 companies, government organizations, and interest groups, having heard from more than 60 witnesses and spoken with the government and industry representatives from seven foreign countries.6
With an eye on maintaining and strengthening future capabilities, the nation must build a rapid air and space response force enabling robust, distributed military operations across the service’s core competencies.7 As has been true in past endeavors, the long-term challenge in building a rapid air and space response capability will be developing the technologies that enable quick reaction to war-fighter operations or crises wherever needed, much like those Arnold envisioned in the early days of flight.
Meeting and overcoming this challenge will require significant innovation. Already, scientists and engineers can imagine exciting possible solutions as current technology matures—from superconducting power generation that enables high-power, directed-energy weapons to supersonic and hypersonic engines that can power long-range strike aircraft and advanced rocket propulsion and air-breathing hypersonic engines to enable easy access to space. Work is also well under way developing electric-, solar-, laser-, and plasma-propulsion systems for mini- and microsatellites of the future.
While many of these technologies may seem like science fiction, so too were the jet engine, the airplane, and the rocket engine only 100 years ago. Fifty years from now, some of these new technologies may still seem like science fiction, but others will have moved into the realm of the possible. The task at hand for today’s scientists and engineers is to perform research that identifies those breakthrough technologies and moves them from science fiction to science fact.8
If the Air Force is to succeed in providing the nation with a rapid air and space response capability, researchers must provide a number of technologies including a focus on propulsion and power solutions for aircraft, weapons, and space systems.9 Although it is important to recognize propulsion as a critical enabler, so too are the test facilities that support the research and development of these revolutionary and transformational technologies.
Revolutionary Propulsion and Power for Aircraft
Propulsion researchers are already testing one of the most promising technologies supporting this capability: a supersonic combustion ramjet, or scramjet, engine that uses conventional jet fuels to reach hypersonic speeds—speeds over Mach 5. With technology of this type the Air Force could deliver a useful payload anywhere on Earth in a few hours, providing a force tailored to accomplish national objectives rapidly anywhere on the world’s surface and in the near-Earth air and space domain.
This new scramjet technology has the potential to power future hypersonic vehicles, such as cruise missiles and long-range strike and reconnaissance aircraft, at speeds up to eight times the speed of sound. While today’s aircraft and missiles only fly up to the Mach 3 range, new hypersonic aircraft and weapons would offer a faster response to war fighters, giving them the ability to take out time-critical targets within a few hours, if not minutes.
Dubbed “HyTech,” for hypersonic technology, the program got its start in 1995 in the wake of the cancelled National Aero-Space Plane program—an effort aimed at developing a hydrogen-fueled, scramjet-powered, single-stage-to-orbit vehicle capable of aircraftlike horizontal takeoffs and landings. In contrast, the Air Force’s version of the scramjet is designed to run on JP-7 fuel, a more logistically supportable fuel than hydrogen. While the National Aeronautics and Space Administration (NASA) continues to pursue the development of a hydrogen-fueled system with its “Hyper-X” program, the Air Force, by using hydrocarbon fuels like JP-7 instead of hydrogen, hopes to one day deploy these systems anywhere, anytime, and anyplace.
Wind-tunnel tests on the engine, completed in June 2003, successfully demonstrated the operability, performance, and structural durability of the scramjet system. Building on more than 2,000 tests from components through an integrated, flight-weight engine, the directorate’s scientists and engineers, as well as contractors from Pratt and Whitney and the United Technology Resource Center, have demonstrated that the engine works, and they are excited about extending this technology to systems that will give war fighters a distinct advantage over future enemies. With 25 runs at Mach 4.5 and Mach 6.5, the flight-weight engine reliably produced significant net positive thrust, which is important because it demonstrates the ability to efficiently burn fuel and accelerate a vehicle at these speeds. The thermal characteristics and structural durability of the engine were also validated at both speeds.
Another propulsion team is exploring the pulsed detonation engine, or PDE—a new type of engine which may well be the first of its type to power an aircraft in flight. For years, propulsion researchers around the world have searched for a better, more efficient way to increase speed and improve the performance of aircraft. They believe that the PDE may one day fill that critical gap in America’s ability to reach simple, low-cost, high-speed flight. Today, the PDE these researchers have developed creates thrust by using a series of controlled explosions of fuel and air in detonation tubes that look like long exhaust pipes. By designing a process in which the detonations of the fuel and air mixture are controlled, researchers were able to develop sufficient thrust to power future aircraft. The propulsion team is well on its way to proving the PDE concept as an inexpensive, simply constructed, and more efficient engine for tomorrow’s war fighters. In fact, the PDE could bring a new level of efficiency and thrust capability to propulsion systems in the Mach 2 to Mach 4 range by improving fuel economy, demonstrating high thrust-to-weight ratios, and simplifying the engine’s mechanical structure.
Evolutionary Propulsion and Power for Aircraft
The directorate is also pursuing improvements in more traditional turbine engine technologies to improve performance and reliability while reducing sustainment costs. Turbine engine research, development, acquisition, and sustainment are major Department of Defense (DOD) businesses with a collective annual investment of more than $5.7 billion, excluding fuel cost. Sustainment consumes 62 percent of that budget—more than $3.5 billion—which is why the Air Force’s science and technology leaders place such great emphasis on reducing those costs.10 Keeping sustainment expenses in check is one of the goals of the air-breathing propulsion technology efforts in progress today, as well as those currently in the planning phases.
The Army, Navy, Air Force, Defense Advanced Research Projects Agency (DARPA), NASA, and major US engine manufacturers have been jointly developing and demonstrating cutting-edge propulsion technologies for over a decade under the Integrated High Performance Turbine Engine Technology (IHPTET) program. That program has the goal of doubling propulsion-system capability and reducing acquisition and maintenance costs 35 percent by 2005. IHPTET technologies not only have successfully transitioned into many of the Air Force’s legacy propulsion systems powering today’s frontline military aircraft, but also are providing the enabling technologies for a wide range of new systems such as the JSF.11
Nearly every technology developed under the IHPTET program can, in some way, transition to the commercial sector to improve the performance, reliability, life, and operational cost characteristics of commercial turbine engines—in aircraft, marine, and industrial applications. These contributions help sustain the positive balance of air and space trade and maintain US market share in today’s highly competitive, global economy. Without IHPTET program success, aggressive propulsion-technology development programs sponsored by world competitors would quickly challenge the US military and economic advantage in turbine propulsion.12
Recent IHPTET successes are providing technologies that allow critical modernization of the F100, F110, and F404 families of engines—the backbone of Air Force frontline aircraft. Also, the knowledge necessary to fix problems currently encountered in the engines of the Air Force, Navy, and Army operational fleets is available because of IHPTET achievements. For example, IHPTET provided the key fan technology for the F118 engine powering the B-2 and demonstrated viability of the majority of technologies chosen for the F119 engine in the F/A-22. IHPTET is also the critical base for all JSF propulsion concepts and other new engines, such as the F414 powering the F/A-18E/F Super Hornet.13 As a result of these recent accomplishments, turbofan and turbojet designs now being developed can achieve a 40 percent increase in thrust-to-weight and a 20 percent reduction in fuel burn over baseline engines; turboprop and turboshaft engines can attain similar results with a 40 percent gain in horsepower-to-weight and a 20 percent improvement in specific fuel consumption; and air-breathing missile engines can have a 35 percent increase in thrust-to-airflow, burn 20 percent less fuel, and cost 30 percent less.
The performance improvements demonstrated in IHPTET efforts are also being traded to provide increased component lives or cost reductions in fielded systems. The third-phase goal of gaining a 100 percent increase in thrust-to-weight capability will enable specific system payoffs such as sustained Mach 3+ in an F-15–sized aircraft; greater range and payload in an F-18–sized, short takeoff and vertical landing (STOVL) aircraft; a 100 percent range and payload increase in a CH-47–sized helicopter; and intercontinental range in an air launched cruise missile (ALCM) sized missile.14
Building on the IHPTET’s successes, the Versatile Affordable Advanced Turbine Engine (VAATE) program is focused on achieving a tenfold improvement in turbine engine affordability by the year 2017 through a joint DOD, NASA, Department of Energy, and air and space industry effort. In parallel with increases in turbine-engine capability, the VAATE program places major emphasis on research and development, production, and maintenance costs. Its engines will contain numerous technology innovations, providing the war fighter the most versatile and affordable propulsion for legacy (F-16, F-15, and B-1), pipeline (F/A-22, F-35, unmanned combat aerial vehicle [UCAV]), and future military systems (long-range strike aircraft, global-reach transport, and supersonic UCAVs).15
For the future, VAATE technologies will assure further dramatic improvements in turbine-engine affordability, not only for military applications such as aircraft, rotorcraft, missiles, and unmanned air vehicles (UAV), but also for America’s domestic applications. VAATE attributes include an integrated inlet system; a low-emission combustion system; long-life, high-temperature turbines; high-temperature bearings and lubricants; and an automatic, adaptive-engine health-management system.
The VAATE program is now an approved DOD technology objective and recently awarded its first major procurement activity to multiple defense contractors for approximately $350 million. Contracts are focused on material systems, advanced-fuel technology, and other system technologies required to enable a supersonic, long-range strike capability.16
Electrical Power for Aircraft
A revolutionary transformation in aircraft electrical-power technologies that promises greater aircraft reliability and a significantly smaller logistical tail to support tomorrow’s air and space force is under way. The More Electric Aircraft (MEA) program is a reality that has been demonstrated in the newly christened F-35 JSF. By teaming with sister services, universities, and air and space industry partners, the directorate’s power-technology researchers have translated three decades of technological progress into stunning advances that promise greater war-fighter capability and a 20 percent reduction of Air and Space ground equipment (AGE).
The fundamental transformation uses electrical power to drive aircraft subsystems currently powered by hydraulic, pneumatic, or mechanical means. It provides aircraft designers with more options to power gearboxes, hydraulic pumps, electrical generators, flight-control actuators, and a host of other aircraft subsystems.17 New concepts like electric environmental control and electric fuel pumps, along with magnetic bearings for generators and eventually “more electric” turbine engines, are in the works. They promise dramatic simplifications in aircraft system design, while improving reliability and maintainability in the years to come.
The MEA effort also promises to reduce the bulky and heavy AGE required at home and downrange during deployments and contingencies. Currently, the AGE that supports 24 F-16 Falcons includes electric generators, hydrazine servicing carts, air conditioners, high-pressure air carts, and hydraulic-fluid “mules”; 16 C-141 Starlifters are required for its transport. There could be a reduction of up to 20 percent in the size and weight of equipment required to support MEA units; the freed airlift could be used to transport other war-fighting assets.
To succeed in providing the full spectrum of rapid air and space response, Air Force researchers must provide a number of technologies that include a focus on propulsion and power solutions for weapons and space systems. As with other efforts, the directorate is collaborating with other government agencies, industry, and academia to develop, demonstrate, and transition propulsion and power technologies for use in these applications. Those efforts have the potential for evolutionary and revolutionary developments in a variety of air-breathing weapons, hypersonic and supersonic cruise missiles, airborne directed-energy weapons, rocket-powered missile systems, intercontinental ballistic missiles (ICBM), space launch, tactical missiles, and spacecraft propulsion.
Propulsion and Power for Weapons
The most strenuous near-term weapons application is for a scramjet-powered, fast-reaction, long-range, air-to-ground missile cruising at greater than Mach 6—more than 4,500 mph. That missile could be launched from a bomber or fighter, and its rocket booster would accelerate it to speeds of about Mach 4 where its scramjet would start and continue its acceleration to a cruising speed above Mach 6. Although its maximum flight duration is about 10 minutes, it flies seven times faster than a conventional cruise weapon to quickly cover hundreds of miles to reach time-critical targets. A single shooter employing this hypersonic weapon can cover 49 times the area reachable with a conventional cruise weapon.
In the supersonic realm of weaponry, the VAATE program discussed earlier will enable a supersonic, long-range, modular cruise missile with a Mach 3.5+ cruise capability. This advanced weapon will also provide a rapid response time to target, coupled with a flexible mission profile, by using affordable, reliable, and high-performance turbine engines.
The directorate’s work in advanced electrical power and thermal management technologies is also enabling concepts like high-power laser weapons on fighter aircraft, high-power microwave weapons for attacking electronics, and nonlethal millimeter wave technologies that use electromagnetic energy to repel advancing adversaries. Recent advancements have been made in several areas addressing the challenges of supporting these futuristic weapons.18
One of the most critical problems facing the future implementation of these directed-energy weapon (DEW) systems is adequate electrical power. Adding DEWs to the war-fighter’s arsenal would provide the Air Force with a significant transformational capability. Scientists and engineers are aggressively working to mature the technologies needed to package and deliver multimegawatts of power in the confined space of a fighter aircraft or space platform. They are developing a new class of electrical components that operate at higher temperatures, such as switches and capacitors, along with superconductivity and thermal-management technologies. All have shown tremendous progress in recent years. For example, those involved in the developmental testing of diamond-like carbon capacitors say their progress is the most significant in decades. In fact, directorate researchers have enabled the production of capacitors with improved energy density and temperature capabilities that are more than two times better than today’s state-of-the-art capacitors. These improvements are crucial for airborne applications of DEW because they offer considerable savings in system weight, improved electrical performance, and the ability to withstand high-temperature operating environments.
The next-generation high-temperature superconducting wire, dubbed YBCO for its molecular configuration of yttrium, barium, and copper oxide, is another key DEW-enabling technology. By using YBCO conductor technology, high-speed and high-temperature superconducting generators can produce megawatts of electrical power while weighing up to 80 percent less than traditional iron-core generators.
Conceptually, one- to five-megawatt power generators would allow the electrical DEW to operate as long as jet fuel is available to turn the turbine engines, thereby providing a “deep ammunition magazine.” Aerial refueling would eliminate the requirement to land and rearm the aircraft in a conventional sense. In contrast, the Airborne Laser (ABL) program’s platform uses a chemically fueled laser to shoot down ballistic missiles while they are still over an enemy’s own territory. When all chemical reactants are expended, the aircraft must return to base for reloading.19
Propulsion and Power for Missiles
The ICBM is a more traditional weapon with propulsion and power requirements. Although many thought the end of the Cold War would mean the end of the ICBM with its nuclear warheads, this has not been the case. The proliferation of both nuclear and nonnuclear weapons of mass destruction (WMD) into nations and nonstate groups, including terrorists, presents serious challenges to the United States that necessitate the need for a continued nuclear force. However, this nuclear force must have global reach and the capability to be tailored to fit the target’s unique requirements. Directorate scientists and engineers, having been involved in every ICBM development since the Atlas and Thor, foresaw this need and continued to pursue improvements in solid-rocket propulsion for next-generation ballistic and tactical missiles. Their $68 million missile research investments gave the Peacekeeper the ability to carry more than twice the payload of the Minuteman III, while fitting within the same silo, and saved the Peacekeeper program over $22 billion, a 32,000:1 return on research investment. Researchers continue to make important improvements in ICBM technologies, allowing the next ICBM to greatly exceed the range of the current Minuteman III.20
Propulsion and Power for Space
Scientists and engineers are also focused on the heavens with such collaborative efforts as the Integrated High Payoff Rocket Propulsion Technology (IHPRPT) program, a national initiative to improve and double capabilities across the broad spectrum of our nation’s rocket propulsion technology by 2010.21 This program addresses propulsion needs across space launch, ICBMs, tactical missiles, and spacecraft propulsion. It is also one of the few times since the development of the space shuttle main engine more than 30 years ago when the Air Force and NASA are jointly developing reusable rocket-engine boost technology for future DOD and NASA launch vehicles.
IHPRPT teams with industry and focuses their research and development efforts in such areas as new propellants that break through the performance barrier of traditional chemical propellants. Their research and development (R&D) also includes new and more affordable propulsion subsystems for solid rocket motors and liquid-rocket engines; and electric propulsion for satellites; laser propulsion; and solar propulsion for orbit transfer.22
A joint Air Force and NASA rocket-engine program called the Integrated Powerhead Demonstrator (IPD) will demonstrate new designs and techniques for application in future liquid-rocket engines to enhance performance and save weight and costs. The program is a combination of research efforts and validation testing to provide new, more efficient portions of the rocket engine that precondition and pump liquid fuels and oxidizers into the main engine. The technology developed under the IPD program will provide the world’s first hydrogen-fueled rocket engine with oxygen-rich staged combustion. The IPD test program expects to place a fully integrated engine on the NASA Stennis test-stand facilities for testing in 2004.23
While rocket engines have been around for decades, continued research like that being conducted through the IPD test program will lead to a very high return on this investment since propulsion remains a significant percentage of any vehicle’s weight and cost. For instance, in space launch vehicles, propulsion accounts for 70 to 90 percent of the vehicle weight and 40 to 60 percent of the system costs. Satellite propulsion represents 50 to 70 percent of the weight and 25 to 40 percent of the costs. Also, a satellite’s life span is limited to the lesser of either power or propulsion life, which is why researchers strive to develop smaller, lighter, more powerful, and more affordable propulsion and power systems to improve the capabilities in tomorrow’s space vehicles.24
These new launch vehicles could eventually meet an on-demand space-surge capability. It stands that if the Air Force could quickly provide joint force commanders with whatever space assets are required, then the Air Force could strategically respond to situations and minimize the need for ultrahigh-resolution worldwide intelligence, surveillance, and reconnaissance assets in predictable orbits. Propulsion researchers are leading the way in arming the country’s joint force commanders with the ability to respond rapidly in any given situation by supplying space assets in near real time. This can be accomplished by either launching and maneuvering new assets into place or by moving existing space platforms or weapons to wherever they are required within several hours.25
Part of the HyTech program discussed earlier includes an effort to build a durable engine that provides affordable, reusable, on-demand space-access systems. The joint Air Force– NASA X43C program will demonstrate key technologies supporting this application. Conceivably, a two-stage-to-orbit vehicle could take off like a conventional aircraft powered by an advanced turbine engine like those being developed under VAATE and then reach Earth’s upper atmosphere by combined scramjet-rocket power to put a payload into space. This concept would provide both ground basing and orbit flexibility at only half the cost of today’s approaches, thereby giving the Air Force more affordable access to space.
The nation currently has no truly reusable rocket engines for space launch. The space shuttle engines, based on research from the 1960s, are routinely pulled for maintenance and service after nearly every flight. If we are to achieve operationally responsive space lift by using truly reusable launch vehicles, the nation needs engines that can last a minimum of 50 flights between overhauls. So, while pursuing long-term, high-risk, high-payoff efforts like hypersonic engines for space access, researchers are also pursuing significant advances in liquid-rocket engines. Current and planned programs are developing the materials, components, fuels, and other technologies to enable truly reusable launch vehicles. In the future, hypersonics and rockets will come together in combined cycle engines providing further improvements in performance, cost, and responsiveness. Within 20 years, the nation will see the Wright brothers’ vision being taken into space by operationally responsive launch vehicles, which will change the face of battle for many years to come.26
In the nearer term, the Air Force has an increased requirement for propulsive microsatellites to support a range of future specialized missions. In conjunction with an operationally responsive space-lift capability, microsatellites could be used to rapidly reconstitute space assets that have failed, ensuring the war fighter uninterrupted service. Individual microsatellites can approach and inspect damaged satellites so the operator can then deploy specialized microsatellites to enact repairs, upgrade electronics, or refill propellant tanks.
Scientists have invented the micropulsed plasma thruster, or microPPT. This miniaturized propulsion system weighs about 100 grams and provides precise impulse bits in the 10-micronewton range. These impulse bits provide attitude control on present 100-kilogram (kg) small satellites and station keeping, as well as primary propulsion on next-generation 25 kg microsatellites. The primary attractive features are the use of a solid, inert propellant (Teflon); expected high, specific impulse when combined with electromagnetic acceleration; and a simple, lightweight design based largely on commercial, flight-qualified electronic components. A comparatively simple version of the microPPT is undergoing flight engineering and qualification for demonstration aboard the US Air Force Academy FalconSat III satellite scheduled to launch in 2006. Five microPPTs are manifested on the flight to increase attitude control for the vehicle.27
The intent in facing these technology challenges head-on is to seek out both linear and nonlinear solutions that provide significantly increased capabilities to America’s war fighters. The linear challenges will be met with science and technology efforts maturing before 2020, which are continuations of today’s current technology. These efforts offer lower risk and modest payoff, and they include reusable boost and orbit-transfer vehicles, solid and hybrid expendable launch vehicles, and satellite propulsion. The service’s nonlinear challenges are efforts maturing after 2020 that are new technology breakthroughs involving higher risk but very high payoff. These include space ramjets, magnetohydrodynamics-enhanced propulsion, and directed-energy launches.28
While these technology developments could lead to many strategic and force-structure implications, the Propulsion Directorate’s goal remains focused on developing new propulsion and power technologies that support the Air Force vision of rapid air and space response. That focus is documented in a mutually supportive and coherent plan for air, space, and energy technologies that covers the next 20 to 50 years.
1. C. V. Glines, “Book review of Hap Arnold and the Evolution of American Air Power by Dik Alan Daso,” Aviation History Magazine, http://www.historybookworld.com/ reviews/hbwevolutionofamericanairpower.html.
2. Pamela Feltus, “Henry ‘Hap’ Arnold,” History of Flight Essays, US Centennial of Flight Web site, http:// www.centennialofflight.gov/essay/Air_Power/Hap_ Arnold/AP16.htm.
3. Kristen Schario, “Powering the Future,” Technology Horizons Magazine (PR-01-08), December 2001, http:// www.afrlhorizons.com/Briefs/Dec01/PR0108.html.
5. Melvin Kranzberg and Carroll W. Pursell Jr., eds., Technology in Western Civilization: Technology in the Twentieth Century (New York: Oxford University Press, 1993).
6. F. Whitten Peters (keynote address, 2002 Turbine Engine Technology Symposium, Dayton, OH, September 9, 2002).
7. Dr. Alan Garscadden and Michael Kelly, “Rapid Air and Space Response: Technological Capabilities Can Provide a Roadmap for War-Fighter Operations,” Technical Horizons Magazine, December 2003, http://www.afrl horizons.com/Briefs/Dec03/PR0305.html.
10. IHPTET brochure, http://www.pr.afrl.af.mil/ divisions/prt/ihptet/ihptet_brochure.pdf.
12. S. Michael Gahn and Robert W. Morris Jr., eds., “Integrated High Performance Turbine Engine Technology (IHPTET) Program Brochure,” 2002, http://www. pr.afrl.af.mil/divisions/prt/ihptet/ihptet_brochure.pdf.
15. IHPTET brochure.
17. Michael Kelly, “Power Technologies Create Revolution,” Leading Edge Magazine, January 2003, 12, https:// www/afmc-mil.wpafb.af.mil/organizations/HQ-AFMPC/ PA/leading_edge/archives/2003/Jan/JanWeb.pdf.
18. Michael Kelly, “Powering Transformation: Path to Tactical Directed-Energy Weapons Now Reality Thanks to New Power Technologies,” Leading Edge Magazine, August 2003, 10, https://www.afmc-mil.wpafb.af.mil/organizations /HQ-AFMC/PA/leading_edge/archives/2003/Aug/ Augweb03.pdf.
20. John Remen, Air Force Research Laboratory Propulsion Directorate, Space & Missile Propulsion Division’s strategic development manager, interview by the author, September 2003.
21. Schario, “Powering the Future.”
22. “Integrated High Payoff Rocket Propulsion Technology (IHPRPT) Program Background,” http://www.pr. afrl.af.mil/technology/IHPRPT/ihprpt.html.
23. Ranney Adams, “Air Force Research Laboratory Leading U.S. Rocket Engine Innovations,” Aerotech News and Review, July 14, 2003, http://www.aerotechnews.com/ StoryArchive/2003/071403/afrl.html.
24. Schario, “Powering the Future.”
25. Garscadden and Kelly, “Rapid Air and Space Response.”
26. Remen, interview.
27. Dr. Greg Spanjers, “New Satellite Propulsion System Has Mass Below 100 Grams,” Technology Horizons Magazine, December 2001.
28. Garscadden and Kelly, “Rapid Air and Space Response.”
Maj Michael F. Kelly, USAF, retired (APA, Community College of the Air Force; BA, Southwest Texas State University; MA, University of Oklahoma), is the executive director of military communications at the United Services Automobile Association. Major Kelly served in wing through major command public affairs positions and received the 1999 Secretary of the Air Force Public Affairs Company Grade Officer Excellence Award. He was the chief of internal communication at Air Force Materiel Command prior to his retirement in 2002 and then worked for Universal Technology Corporation, a contractor supporting the Air Force Research Laboratory’s Propulsion Directorate. He has authored numerous articles in Leading Edge Magazine and AFRL Technology Horizons magazine. Major Kelly is a distinguished graduate of Officer Training School, Defense Information School’s Basic Journalist Course, and the Public Affairs Officer Course. He is also a graduate of Squadron Officer School, Air Command and Staff College, and several professional courses.
The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, academic environment of Air University. They do not reflect the official position of the U.S. Government, Department of Defense, the United States Air Force or the Air University.
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