A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs (2006)

In their charge to the committee, the Air Force and the Director, Defense Research & Engineering (DDR&E), requested a detailed examination of the links that connect the propulsion technical base to needed future capabilities as defined. Capabilities-based planning, now currently being widely used throughout the Department of Defense (DoD), is a form of all-threats planning. It addresses the growing uncertainty in the threat environment by using a wide range of possible scenarios to bound requirements and thereby reduce the tendency to fixate on a certain threat, location, or set of conditions. Capabilities-based planning, which involves the analysis of alternatives (AoA) for any given capability, does not specify system solutions until after analysis is completed and a decision made.¹

This methodology requires that the technical base programs funded within the science and technology (S&T) budget cover a broad spectrum of alternatives to meet capabilities that could be needed one day. Clearly, the technical base managers would seek maximum definition of the capabilities likely to be needed, while the capability definers, usually the warfighters, would like the technical base to possess the flexibility and general wherewithal to support any defined need. Unfortunately, at the present time, neither group can attain the clarity it would like—for a number of reasons.

DoD has shifted during the past 4 years from the threat-based model that dominated defense planning in the past to a model based on capabilities—a model that focuses more on how an adversary might fight than specifically on who the adversary might be or where the war might occur. This model is designed to plan for uncertainty, the defining characteristic of today’s strategic environment, which presents four kinds of challenges: traditional, irregular, catastrophic, and disruptive. Box 1-2 in Chapter 1 describes each kind and gives examples.

Neither the Joint Capabilities Integration and Development System (JCIDS) nor supporting activities such as science and technology comprehensive reviews of the Office of the Secretary of Defense (OSD) is mature, nor has either been fully implemented.² Technology area reviews and assessments (TARAs) are scheduled biennially resuming in 2006 (in 2005 they were cancelled). In addition, joint warfighting capability gaps based on future joint concepts have not yet been prioritized. A recent National Research Council (NRC) study called for the Navy to establish a formal science and technology mechanism that will identify and address naval aviation capability gaps (NRC, 2006).

In 1989, the Deputy Secretary of Defense challenged the services to create a new approach to increase efficiency in research, development, testing, and engineering (RDT&E) activities (DMR 922) (NRAC, 2002). In 1991, the Service Assistant Secretaries directed the implementation of the Defense Science and Technology Reliance Program (the Reliance Program, for short) under the Joint Directors of Laboratories, and from 1992 to 1994, the Defense Nuclear Agency (DNA), the Defense Threat Reduction

Agency (DTRA), the Ballistic Missile Defense Organization (BMDO), and the Defense Advanced Research Projects Agency (DARPA) were added to the Reliance Program. In the late 1990s, joint integration, planning documentation, and an emphasis on warfighter requirements were also added to the program (CRS, 1999; Etter, 2002; Ray, 2005).

While it is widely asserted that the Air Force has been designated as the Reliance Program executive agent for propulsion, to the best of the committee’s knowledge, no service has been so designated since propulsion has never been considered a single entity. In fact, historically, aerospace propulsion was treated as three separate areas: (1) aircraft propulsion (gas turbines), (2) rocket propulsion, and (3) other (generally high-speed, air-breathing ramjets, ducted rockets, etc). In the S&T arena, the Air Force has been by far the largest investor in both aircraft propulsion and rocket propulsion (Richman, 2005). Nonetheless, the other services make important investments in aircraft and rocket propulsion that are coordinated through various steering committees and formal agreements, which are described later (Richman, 2005).

In summary, DoD is in transition from threat-based defense planning to capabilities-based defense planning, and the capabilities that will be required during the study time frame (the late 2010s), as well as the associated activities, analyses, and documentation, are immature and there are numerous gaps in their assessment.

With this in mind, the committee sought to determine the extent to which future capabilities are clearly defined and how the propulsion technical base has been structured to realize them. One would expect to see a propulsion technical base consisting of numerous technology readiness level (TRL) 2/3 programs awaiting orders to be matured to TRL 6/7.³ To do this successfully, realistic development roadmaps and funding profiles for crossing the gulf between TRL 3 and 6 would have been drawn up and kept up to date to form the basis for program objectives memoranda (POMs).⁴ If this had been done, the committee’s data-gathering efforts would have been relatively straightforward. In general, however, the committee members assigned this task found, with a few exceptions, neither well-defined capabilities nor realistic technology transition planning.

Given that there were no comprehensive or detailed statements of needed capabilities, the committee invited the Office of the Secretary of Defense (OSD), the DDR&E, the Joint Staff, the Army, the Navy and the Air Force to present capabilities requirements for the 2018 time frame and beyond for the four warfighting challenges listed in Box 1-2. The committee also received presentations from the National Aeronautics and Space Administration (NASA), DARPA, and various representatives of academia and industry.

America’s Air Force Vision 2020 is illustrative of the DoD capabilities-based planning process. It lays out the Air Force concept of operations (CONOPS). Its capabilities reviews and risk analyses (CRRAs) review the task or missions: global strike, homeland security, global mobility, global persistent attack, nuclear response, space and command, control, communications, computers, intelligence, surveillance, and reconnaissance (space and C4ISR); and agile combat support (Mitchell, 2004). The capabilities required are command and control, intelligence, surveillance and reconnaissance, force application and force projection. A review of the Master Capabilities Library and the Air Force’s presentations to the committee turned up several required propulsion capabilities and technical engineering goals for the time frame 2018 and beyond, some of which are shown in Figure 2-1 and discussed below.

FIGURE 2-1 Propulsion research and engineering goals. SOURCE: Sega (2005).

Perhaps the most documented air-breathing capability is the long-range strike, which was the subject of multiple studies from FY01 to FY03. Rutledge (2005) defines it as the capability to achieve a desired effect(s) rapidly and/or persistently, on any target, in any environment, anywhere, at any time (Rutledge, 2005). To achieve long-range strike capabilities, DoD may leverage propulsion capabilities other than the traditional air-breathing approach. Moreover, a Long-Range Global Persistent Engagement Study, directed by the 2003 Defense Planning Guidance, highlights characteristics of future environments: little or no warning/build-up time; extensive denial of contiguous areas from which to operate, and possible chemical/biological contamination of the environments, which could influence possible capabilities solutions.

According to a 2004 study, the Air Force recognizes its need to upgrade long-range strike capabilities and has created two offices to focus its R&D efforts (Burdeshaw, 2004). Tasking and guidance for these offices were sent to the Air Force from the Office of the Under Secretary of Defense/Acquisition, Technology and Logistics (OUSD/AT&L) in November 2003. The Air Force was instructed to carry out the following tasks (Burdeshaw, 2004).

• Perform modeling, simulation, and analysis to identify important attributes and critical technologies.

• Develop a long-term S&T investment strategy that could allow transition to a development program in 2012-2015.

• Ensure that the investment strategy accounts for investments in related areas, such as C4ISR, and by other agencies (DARPA, NASA).

• Use a joint advanced strike technology approach.

• Augment its efforts with system-of-systems concepts following Air Force guidance.

Global mobility operations require robust, sustained airlift and air refueling for deployment, employment, and redeployment. There must be an ability to operate in adverse weather with flexible, adaptable (payload/configuration) airframes capable of surviving in radio frequency, infrared, and directed-energy environments. Airborne C4ISR capabilities would shorten the kill chain by achieving

better situational awareness, faster decision times, and greater precision. Platforms are globally connected and able to persist (every platform is a node in a network of sensors, datalinks, and fused intelligence). Munitions are smarter, and the difference between reconnaissance/surveillance and strike is blurred in the case of armed unmanned aerial systems (UASs), which can persist for hours or even days.

Survivability implies, among other things, low-signature stealth, which in turn demands the integration of inlet and exhaust systems into the airframe and proper flow control. Increased range, payload and operational flight envelope are also cross-cutting capabilities, the need for which affects designs and technologies for missile propulsion capabilities across platforms. For example, the Navy is addressing requirements for additional power density for advanced sensor suites, radars, cooling systems and directed-energy weapons; it has also identified environmental factors (noise, emissions) as posing a growing challenge to the deployment and basing of Navy aviation platforms (Gorton, 2005).

Not every new capability is the result of revolutionary technology. The Navy and the Air Force say that in 2018, 60 percent of the aircraft inventories will be made up of aircraft already in their inventories today. These factors underscore the importance of existing component improvement programs (CIP) which replace components having low mean time between failure with more advanced technology components and develop next-generation propulsion systems in an evolutionary manner.

For example, the joint government integrated high performance turbine engine technology (IHPTET) program initiated in the 1980s focused on doubling aircraft and missile propulsion performance while decreasing manufacturing and maintenance costs 35percent by 2003. The F119 engine for the F/A-22, for example, benefits from a substantial number of advanced technologies from the IHPTET program: According to the Director of the Joint Systems Program, a robust and healthy IHPTET program is vital to the Joint Strike Fighter (Haven, 2004). An ongoing transformational technology program for turbine engines is the Versatile Affordable Advanced Turbine Engines (VAATE) program, which is focused on advanced technologies for total propulsion systems. This government–industry collaboration program develops, demonstrates, and transitions advanced, multiuse turbine engine technologies.

A number of the presentations and the information made available to the committee reported that most of the helicopter and UAS turboshaft engines in DoD service today use 1960s and 1970s technology. Significant advances in technology over the past 20-30 years would therefore enable dramatic improvements in range, payload, durability, and cost of operation. Yet DoD has apparently elected to depend on spinoffs from commercial developments to meet its rotary-wing mission requirements when in fact commercial turboshaft engines cannot stand up to the DoD operating environment and mission scenarios. The Navy, in particular, specified an operating environment that was not typical of a commercial environment, an environment that required rapid throttle changes and high power for takeoffs and landings as well as the ability to withstand corrosive sea spray, sand, and foreign object damage (FOD).

The capabilities the Air Force needs for rotary propulsion are listed in Box 2-1.

The Army transformation plan calls for a force that is responsive, deployable, agile, versatile, lethal, survivable, sustainable and dominant at every point along the spectrum of operations, anywhere in the world. It calls for Army air platforms (manned and unmanned) that have greater range and payload capability and for aircraft that have a smaller logistics footprint to minimize operational and support costs. Figure 2-2 summarizes the Army rotary wing systems demands.

FIGURE 2-2 Rotary wing systems demands. SOURCE: Butler (2005).

The Air Force has stated its capability needs in the 2012-2017 time frame and the 2018 and beyond time frame for hovering/perching unmanned aerial systems (UASs), micro UASs, and advanced versions of each as well as hypersonic munitions with hard target kill capability.⁵ These needs may be summarized as follows:

• Micro class: 1-3 nautical miles (nm) range, daytime, fair weather, 0.5 lb payload, field-supportable, unique fuel requirements.

• Man-portable class: 1-2 hr endurance, 1-2 lb payload, field-supportable, unique fuel requirements.

• Tactical class: 10-12 hr endurance, 100 lb payload, multimission.

U.S. Army UAS requirements are similar to those of the Air Force, as presented, and are shown in Figure 2-3.

FIGURE 2-3 Army aviation modernization plan. SOURCE: Bolton (2005).

Of the roughly $5.7 billion per year that DoD invests in turbine engines, sustainment (62 percent), acquisition (22 percent), development (14 percent), and S&T (2 percent) are the main components (Richman, 2005). Improving future turbine engine efficiency and mitigating and decreasing aircraft sustainment costs will continue to be key economic drivers for the Air Force and DoD budgets. The rising

cost of fossil fuels, their availability and their dependence on them were a frequent theme throughout the study. For example, in FY03, the Air Force alone consumed 3.2 billion gallons of fuel at a cost of $5 billion, and fuel costs have doubled since September 11, 2001 (Sega, 2006). In addition, DoD spends approximately $50 billion to $75 billion per year on sustaining more than 49,000 turbine engines on more than 25,000 aircraft (Haven, 2004). These costs will likely continue to rise.

The Department of Defense Space Science and Technology Strategy is the exception proving the rule that DoD has not been able to articulate warfighter requirements. This document is very specific about future space propulsion requirements (DoD, 2004). Assured access to space focuses on providing responsive space support through the development and demonstration of technologies that enable the unimpeded rapid deployment of space systems using next-generation and generation-after-next launch systems. Access to space can be assured through sufficiently robust, resilient, and flexible launch vehicles; improved launch infrastructure; and ranges that support expanded space operations, including horizontal launch capability and/or mobile launchers. An ability to sortie into space to any desired altitude and orbit will enable truly revolutionary operational space concepts. Resources will also be focused on manufacturing and producibility to get improved reliability and lower cost (DoD, 2004).

Table 2-1 lists the requirements for assured access to space, responsive space capability, assured space operations, and enhanced spacecraft technology. In each case, requirements for the next 5 years and requirements for 2020 and beyond are shown.

First, assured access to space is defined as:

Second, responsive space capability is defined as:

Third, assured space operations is defined as:

Fourth, spacecraft technology is defined as:

The Air Force and the Air Force Space Command (AFSPC) further refine the nation of operationally responsive spacelift (ORS)to include the ability to provide launch within hours instead of days (with storable fuels), and airplanelike operations, and to be economical, survivable, interoperable, and flexible. The AFSPC spacelift roadmap is shown in Figure 2-4. Each bar in the figure represents planned incremental capability (spiral development). Additional capabilities needed are in-space maneuvering of satellites as well as microsatellites, replace and repair on orbit, and protection (defense) of U.S. and allied satellites.

The Air Force has identified another set of mixed systems for the future: maneuverable near-space vehicles that can operate for extremely long times and tat include lighter-than-air vehicles and gossamer aircraft. The Air Force also identifies a class of reusable orbital vehicles that possesses the following

characteristics: responsivity, extremely long range, single stage, horizontal takeoff and landing, and two stages, one of them air-breathing.

FIGURE 2-4 Spacelift roadmap. SOURCE: James (2005).

Given the paucity of clearly stated needed capabilities, the committee’s analysis for this report must be based on a great deal of informal and anecdotal information gathered through contacts with capabilities planners and the technical base managers who are attempting to satisfy the planners and from briefers to the committee from the services, DDR&E, DARPA, NASA, and various academic institutions and private companies. This is not to say that there are no documents that help define potential future technology developments. There are. In fact, one excellent example is discussed in Chapter 4. A space strategy was clearly defined in a recent document co-signed by the Undersecretary of the Air Force for AT&L and the DDR&E. However, in informal discussions with AFRL and AFSPC personnel, it became obvious that this strategy was not the sole determinant of their marching orders and was considered to be only one of several strategies in play. The conclusion, then, is that even when clear direction exists, it is not always followed. With a clearer understanding of the capabilities that are needed, the technical base managers can reassess their programs to identify the program elements that are needed to draw up technology transition roadmaps and funding profiles. Service leaders would then be in a much better position to assess capability alternatives. The committee’s judgments are derived specifically from data gathered about propulsion technology development and not from data on the broader aspects of technology development and transition. However the committee fears that basing important AoAs on less than fully considered cost and schedule realities does not serve decision makers well.

Finding 2-1. Space strategy is clearly defined by the Department of Defense Space Science and Technology Strategy. However, it is not being followed except as part of a broader set of strategies deriving from other considerations. There appear to be no similar OSD-level documents that define strategies for achieving capabilities in other important areas, such as aircraft systems and UASs.

Recommendation 2-1. The DoD should prepare strategy documents containing clear guidance on future required capabilities in all system development areas and seek funding to achieve those capabilities.

(Note: this opinion was derived specifically from data gathered about propulsion technology). For example, the specification of propulsion capabilities for assured access to space—survivable, low-cost, and reliable launch systems to enable on-demand launch of payloads to any orbit and altitude required— would be sufficient to focus propulsion R&D.

Burdeshaw Associates, Ltd. 2004. White Paper on Long-Range Strike. June.

CRS (Congressional Research Service). 1999. Defense Research: A Primer on the Department of Defense’s Research, Development, Test and Evaluation (RDT&E) Program. Washington, D.C.: Library of Congress. July 14. Available online at http://www.globalsecurity.org/military/library/report/crs/97-316_990714.pdf. Last accessed on April 21, 2006.

DoD (Department of Defense). 2004. Department of Defense Space Science and Technology Strategy. Washington, D.C.: Defense Research and Engineering. July 31.

Etter, Delores. 2002. Defense science and technology. Pp. 167-181 in AAAS Science and Technology Policy Yearbook 2002. Albert H. Teich, Stephen D. Nelson, and Stephen J. Lita, eds. Available online at http://www.aaas.org/spp/yearbook/2002/ch18.pdf. Last accessed on April 21, 2006.

NRAC (Naval Research Advisory Committee). 2002. Science and Technology Community in Crisis. Available online at http://www.onr.navy.mil/nrac/docs/2002_rpt_st_community_crisis.pdf. Last accessed on April 21, 2006.

NRC (National Research Council). 2006. Identification of Promising Naval Aviation Science and Technology Opportunities. Washington, D.C.: The National Academies Press. Available online at http://www.nap.edu/catalog/11566.html. Last accessed on August 30, 2006.

Sega, Ron. 2006. Air Force Energy Strategy. Washington, D.C.: Office of the Undersecretary of the Air Force. April 19. Available online at http://www.desc.dla.mil/DCM/Files/Dr%20Ronald%20Sega%20%2019%20Apr%2006-V2.ppt. Last accessed on August 13, 2006.

Claude Bolton, “Army Rotorcraft Modernization Plan Progress,” Presentation given by Assistant Secretary of the Army for Acquisition, Logistics & Technology on plans for Army Aviation Modernization. Available online at https://acc.dau.mil/simplify/ev.php?ID=68994_201&ID2=DO_TOPIC. Last accessed on June 4, 2006.

Gary Butler, “Rotocraft Propulsion Technology,” Presentation to the committee on May 24, 2005.

Charles Gorton, “NAVAIR Presentation,” Presentation to the committee on May 24, 2005.

Brenda Haven, “Turbine Engine Technology: An Air Force Perspective,” April 23, 2004.

Larry James, “ARES Industry Day AFSPC,” Presentation to Air Force Space Command on March 7, 2005.

Darphaus Mitchell, “Capabilities-Based Planning: The Road Ahead,” Presentation to the Military Operations Research Society on October 19-21, 2004. Available online at http://www.mors.org/meetings/cbp/presentations/Mitchell.pdf. Last accessed on April 20, 2006.

Karen Ray, “Defense Science and Technology Reliance,” Presentation to the committee on August 16, 2005.

Michael Richman, “Department of Defense Propulsion Science and Technology,” Presentation to the committee on March 1, 2005.

Lynda Rutledge, “Air Armament Capability for the Future,” Presentation to the Precision Strike Summer PEO Forum on July 28, 2005. Available online at

http://www.dtic.mil/ndia/2005precision_strike_peo/rutledge.ppt#316,17,LONG RANGE STRIKE. Last accessed on July 11, 2006.

Ron Sega, “Department of Defense Propulsion Science and Technology,” Presentation to the committee on May 24, 2005.

U.S. Air Force. “Rotocraft Propulsion Technology,” Undated.