A Hypersonic Attack Platform:
The S3 Concept
A Research Paper
Air Force 2025
Dr. John J. Bertin
Cadet John M. Boehm
Cadet Stephen B. Matthews
Cadet Thomas C. McIntyre
Cadet Brandon L. Rasmussen
Cadet Adam R. Sitler
Cadet J. Brett Taylor
Cadet Robert A. Williamson
Cadet George R. Wyse
2025 is a study designed to comply with a directive from the chief of staff of the Air Force to examine the concepts, capabilities, and technologies the United States will require to remain the dominant air and space force in the future. Presented on 17 June 1996, this report was produced in the Department of Defense school environment of academic freedom and in the interest of advancing concepts related to national defense. The views expressed in this report are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense, or the United States government.
This report contains fictional representations of future situations/scenarios. Any similarities to real people or events, other than those specifically cited, are unintentional and are for purposes of illustration only.
This publication has been reviewed by security and policy review authorities, is unclassified, and is cleared for public release.
In the Spring of 1995, Col Richard Szafranski (Air University, Maxwell Air Force Base) invited personnel from the US Air Force Academy to take part in the study: "2025." Col Randy J. Stiles, who was acting chairman of the Department of Aeronautics (DFAN), suggested that a section of the senior design course be dedicated to the support of that study. Their role was instrumental to the birth of this project.
This study was accomplished by the cadets of a Senior Design Class (AE481Z and AE 482ZS) at the USAF Academy during the Academic Year 1995-1996. The authors of this report received numerous briefings from leaders of the aerospace community. Those who briefed the class at various times during the Academic Year 1995-1996 include:
John Bode, Sandia National Laboratories, Albuquerque, N.Mex 87185 Ramon Chase, principal, ANSER Corporation, Arlington, Va 22202 Chuck Eldred, head, Vehicle Analysis Branch, Langley Research Center, Hampton, Va 23681-0001 Col Jae Engelbrecht, professor, National Security Studies, Air University, Maxwell Air Force Base, Ala 36112 Harry Hillaker, Consultant (Member of USAF Scientific Advisory Board), Fort Worth, Tex 76116 Dr Jim Horkovich, senior engineer, Science Applications International Corporation (SAIC), Albuquerque, N.Mex 87106 Dr Hans Mark, professor, the University of Texas at Austin, Austin, Tex 78712 Lt Col Rich Moore, HyTech Program Office/WL, Wright-Patterson Air Force Base, Ohio 45433 Don Rondeau, Sandia National Laboratories, Albuquerque, N.Mex 87185 Maj Bert Schneider, Wright Laboratory, Eglin Air Force Base, Fla 32543 Don Stava, Flight Dynamics Directorate/WL, Wright-Patterson Air Force Base, Ohio 45433 Dr Jim Trolier, technical director, Science Applications International Corporation (SAIC), Wayne, Pa 19087
In January 1996, the cadets traveled to the Wright Laboratory where they shared their ideas with and received briefings from: Val Dahlem, Peter Gord, Harry Karasopoulos, Don Stava, and Don Stull. They also received tours of the relevant research facilities at the Wright Laboratory. This exchange of information provided midcourse guidance to the project.
In April 1996, Dale Gay, Ron Kay, and Mary Dyster at the US Air Force Academy provided substantial graphical support that had a significant impact on the quality of the final product.
The authors would like to express their gratitude for all who gave of their time and of their talent to share their expertise. The visions they shared and the challenges they offered made significant contributions to the education of the cadet authors. The cadet authors and Dr Bertin thank you.
Place yourself into the future, into the world of 2025. Where will our nation be and what adversaries will we face? Possibilities include a resurgent Russia, a hostile China, or possibly a hostile Korea or Iraq. What capabilities will opposing nations have to our military? One thing is for certain, all of these possible adversaries will have access to high technology weapons. What capabilities will we need to counter these potential adversaries?
To counter these problems, we have identified three broad missions that the United States (US) military must accomplish in 2025. First, we must have the ability to deliver accurate lethal blows before or at the onset of hostilities. Second, we must be able to sustain our fighting potential without a large support infrastructure and logistical footprint. Third, we must be able to provide a routine, reliable, and flexible access-to-space capability. Based upon these three missions, we feel that our best option is the use of hypersonics.
Proposed is an integrated weapons platform approach, the S3 concept, which would accomplish these objectives. It involves three separate, but integrated, vehicles. These include the SHAAFT (supersonic/hypersonic attack aircraft), the SHMAC (standoff hypersonic missile with attack capabilities), and the SCREMAR (space control with a reusable military aircraft). SHAAFT, SHMAC, SCREMAR (S3) can accomplish the broad roles of Global Reach/Global Power, in-theater dominance, and access to space.
The SHAAFT is a dual stage hypersonic aircraft that fulfills future requirements for Global Reach/Global Power. It is a mach 12 hypersonic aircraft that uses a "zero-stage" flying wing to stage at mach 3.5. It is designed for compatible use with a hypersonic missile, the SHMAC, and a transatmospheric (TAV) orbiter, the SCREMAR. These two components combine with the SHAAFT to form the S3 concept and allow for the fulfillment of the in-theater dominance and access to space mission requirements, respectively.
The initial goal of this study was to investigate Air Force missions that are best accomplished by hypersonic vehicles and the technology required to support them. The identification of the three broad missions to be accomplished by military forces in the year 2025 led to the need for a hypersonic weapons platform. The diversity of these missions yielded a need for different platforms with different capabilities. However, with current military budget cuts and drawdowns, development of three different weapons systems is impractical. Instead, we opted for a fresh approach based on previous studies and our own research that integrated the necessary features for accomplishment of these missions. The result was the S3 concept: a highly survivable, lethal integrated hypersonic weapons platform that allows the US to accomplish a diverse set of missions and is capable of deterring and/or punishing adversaries anywhere in the world.
The clairvoyant who in 1996 gazes into a crystal ball with the intent of predicting the world of 2025 indeed faces daunting challenges. The economic, political, and military environment of the world is changing rapidly. Apparently, gone are the continued stress and tension associated with the confrontation between two superpowers. Gone also is the stability that resulted because the two superpowers developed alliances in which most of the other nation states of the world took a subservient role. Military strategists from one alliance could focus on a single adversary (or a single alliance of adversaries). Although regional military conflicts occurred, there was an absence of global conflict, since both of the superpowers recognized the substantial risks of MAD (mutually assured destruction).
Some vestiges of the cold war remain today (e. g., traditional alliances, such as the NATO alliance, continue to exist, albeit aiming for a membership expanded to include former adversaries). However, in addition to the traditional alliances, ad hoc alliances are developed in real time in response to regional conflicts, such as Operation Desert Storm, and to "internal" conflicts, such as the conflict in the Balkans. Rogue nations, no longer constrained by dependence on a superpower's military aid or financial aid, follow confrontational policies which threaten the peace and security, both of a region and of the world. Whether it is the desire of Iraq to dominate a region of the world or the desire of North Korea to develop nuclear weapons, these rogue nations are less likely to consider the downside of aggressive actions, before initiating hostilities.
While the level of economic and of political constraint diminishes, the potential for destruction grows. The military strategist of the twenty-first century can expect that most adversaries-whether a relatively traditional alliance of nation states, a rogue nation using military hostilities as a tool of national policy, or an ethnic army from a fragmented country-will have weapons of considerable destructive power, speed, and range. Many countries have nuclear weapons and other weapons of mass destruction (WMD). Theater missiles and high performance aircraft armed with sophisticated missile systems are available to all the countries of the world.
Thus, no matter what model one postulates to describe the world of 2025, it is very likely that the air and space forces of the United States (US) will have (at least) three broad roles in any conflict in 2025. They include
This paper proposes an integrated multistage weapon system, which is capable of performing a variety of missions, both strategic and tactical. The design of this weapon system would be based on technologies developed during a variety of previous and of existing programs. Furthermore, the design process would include consideration of mission planning activities, base operational support requirements, etc.
In addition to the three broad roles described above, the air and space forces of the United States of the twenty-first century will have many other tasks to perform, including: counter air, close air support, and air lift (including humanitarian relief). However, these missions are best accomplished by other air force assets, such as the F-15, the F-16, the C-17, or their twenty-first century replacements. The proposed weapons platform is designed to be a deterrent, used at the onset of hostilities to stop the war before it begins. In short, the SHAAFT, SHMAC, SCREMAR (S3) hypersonic weapons platform can deliver lethal blows quickly and without a large support infrastructure, is survivable with both the vehicle and the crew returning safely to their base in continental United States, and can provide routine, sustained access to space for a variety of scenarios.
Characterization of the Proposed Weapons System
The proposed weapon system is an integrated multistage system, which
can perform all three roles defined previously, as indicated in figure
1-1. A two-stage configuration serves as the delivery system. The weapons
delivery system includes (1) an unpiloted flying wing, which is used to
accelerate the weapons system from the runway to a flight condition of
mach 3.5 at approximately 60,000 feet and (2) a piloted, aerodynamically
efficient, attack aircraft capable of sustained hypersonic flight, known
as the supersonic/hypersonic attack aircraft (SHAAFT). The SHAAFT cruises
at a nominal mach number of 12 at approximately 100,000 feet. The SHAAFT
could launch either: (1) a barrage of hypersonic cruise missiles (HCM),
which could deliver massive firepower to multiple targets, or (2) a transatmospheric
vehicle (TAV), which is capable of delivering new satellites to orbit,
repairing existing satellites, or attacking the enemy's space assets. The
cruise missiles will be referred to as standoff hypersonic missiles with
attack capability (SHMAC) and the TAV will be part of Space Control with
a Reusable Military Aircraft (SCREMAR). Since the hypersonic cruise missiles
have a range of over 1,000 nautical miles, the attack aircraft can stand
off from the targets, minimizing the risk of losing the delivery system
and its crew. Piloted and unpiloted versions of the TAV are under consideration.
Figure 1-1. Capabilities of the S3 Hypersonic Weapons Platform.
Note that the SHAAFT is the only one of the four elements that definitely has a crew. For the proposed integrated multistage weapons platform, both the flying wing and the SHMAC should be designed as unpiloted aerospace vehicles (UAV). As noted in the previous paragraph, piloted and unpiloted versions of the TAV are under consideration. Thus, referring to figure 1-1, the reader can view the SHAAFT as a mobile control room wherein the personnel who deploy and control the myriad of UAVs in their arsenal are transported closer to the action. Thus, using continually updated intelligence, the crew can make better use of the unpiloted assets by modifying the mission profile in real time.
The design of the two-stage delivery system would be such that the flying wing and the SHAAFT are capable of an unrefueled flight of 14,000 nautical miles. The elimination of the refueling requirement provides many benefits. First, the operational complexity required to support the mission is reduced. Second, by eliminating the prepositioning of tanker aircraft to refuel the weapons delivery system en route to the target, there is a considerable reduction of the communications-traffic/mission-signature that could alert the adversary of the impending mission. Third, the mission will cost less when tankers are not required. Finally, since there is no rendezvous with a tanker, it is easier to update the mission plan in response to intelligence updates. The integrated weapons system would operate from one of four bases within the continental United States (CONUS), essentially one at each corner of CONUS. By flying at hypersonic speeds, the attack aircraft (the SHAAFT) could reach any point in the world within approximately two to four hours. The exact mission duration depends on the mission routing and the exact speed range of the elements. Based on the present conceptual designs, the flying wing accomplishes the low-speed portion of the flight, from takeoff up to cruise at a mach number of 3.5, the SHAAFT cruises at mach 12 at which point the SCREMAR may stage or SHMACs may be launched, and the SHMAC flies at mach numbers up to eight.
Because there is no prepositioning of tankers to tip off the mission and because the elapsed flight time from take off from the CONUS base is relatively short, the adversary has very little response time. Furthermore, the SHAAFT operates at hypersonic speeds at high altitudes even when launching the SHMACs. Since the SHMACs, themselves, are standoff weapons with a range of over 1,000 nautical miles, the supersonic/hypersonic attack aircraft will not have to fly over heavily defended targets. Thus, it will be a very tough target for enemy defenses. The combination of hypersonic flight at high altitudes with standoff weapons makes the SHAAFT very survivable. The high altitudes and speeds also make it ideal to serve as a first stage to a small TAV. Thus, the weapons system would have the ability either (1) to deliver massive firepower to targets anywhere in the world from bases in the CONUS or (2) to provide reliable, routine, flexible access to space.
Beam weapons can affect the ability of the S3 system to successfully execute its mission. If the SHAAFT relies totally on external navigation inputs such as global positioning system (GPS) to accomplish its mission, an adversary with advanced space capabilities could attack those assets. Thus, the elements of the S3 system should have an onboard navigation capability. Laser weapons are currently under development to provide point defense against theater missiles, such as the Scud. It is conceivable that powerful adversaries could develop beam weapons to intercept (at least some of) the incoming SHMACs. The development of the S3 system will have to consider such possible threats to the successful execution of its mission.
Features of the Elements of the Proposed Weapons System
-The Flying Wing The flying wing serves as a zero-stage, launch platform. The use of a flying wing, (incorporating many of the technologies developed for the high-speed civil transport (HSCT), to accomplish the initial acceleration of the weapons system provides many advantages, especially in relation to simplifying the design of the second stage vehicle, the SHAAFT. For the outbound leg, the crew of the SHAAFT would pilot the mated configuration. Once staging occurs and the SHAAFT is on the way to the target, the flying wing will return to its CONUS base as a UAV. The second-stage SHAAFT can be much lighter, since it does not have to carry the considerable weight of fuel required to accelerate the vehicle to a mach number of 3.5 and carry it to the 5,000-nautical miles point, where it stages. The landing gear assembly for the second-stage vehicle can be relatively small, since it needs only accommodate the relatively light weight of the vehicle at the end of the mission (and the potential ferry missions to be described subsequently). Furthermore, since staging occurs at mach 3.5, the second-stage vehicle will not need propulsion cycles that operate efficiently at low speeds. However, such a decision means that the SHAAFT will land unpowered (as does the Space Shuttle Orbiter).
-Global Reach/Global Power Based on the computations presented in the proceedings from the Wave Rider Conference and reproduced in our research, a vehicle capable of flying at mach 12 would be capable of reaching any point on earth within two hours.1 Furthermore, to accomplish the objective of Global Reach, Global Power, the second-stage vehicle should be capable of 14,000 miles of unrefueled flight at a mach number of eight or of 12. The second-stage vehicle, a SHAAFT would be an aerothermodynamically efficient design incorporating technologies developed during the National Aerospace Plane (NASP) program and for waverider designs. The SHAAFT would deliver multiple SHMACs without slowing down. Thus, the entire mission would be accomplished at hypersonic speeds, greatly increasing the survivability of the SHAAFT and its crew. Furthermore, the SHMACs themselves would fly hypersonically to targets at a range of over 1,000 nm. Launching the SHMACs, which are HCMs, from a flight path which keeps the SHAAFT well away from heavily defended areas, further enhances the survivability of the weapons system. The ability to deliver a decisive suite of weapons to any point on earth within hours provides a permanent "presence" that does not require constant forward deployment of the United States' armed forces. The short time required to execute the operation will catch the adversary by surprise before critical elements of the opponents military strategy can be deployed or protected. Potential targets for the SHAAFT/SHMAC weapons systems include the adversary's space access complex, command and control centers, and other assets critical to the conduct of warfare in the twenty-first century. It is believed that the massive, sudden, and unexpected application of force on the first day of conflict will eliminate the opponent's desire and capability to wage war.
-In-Theater Dominance In addition to serving as the weapons to be launched from the SHAAFT, the hypersonic cruise missiles would have many uses in the case of protracted hostilities. The SHMACs would be sized so that two could be carried by and launched from an F-15E or from other conventional aircraft. Because the SHMAC has a range of over 1,000 nautical miles, the F-15E would be able to remain well out of the range of most defense systems. Furthermore, the hypersonic capabilities of the SHMAC accommodate its use against time critical, moving targets (e. g., mobile launchers, tank formations, etc.). Since the SHMACs would be launched from the (conventional) carrier aircraft at high subsonic speeds at an altitude of 35,000 feet, additional power would be required to accelerate the missile to hypersonic speeds and high altitudes (i. e., essentially the initial conditions from which the SHMACs are launched from the SHAAFT). As will be discussed in chapter 3 on the design characteristics of the SHMAC, the initial acceleration from the subsonic speeds associated with a conventional aircraft launch would be accomplished by a rocket located within the dual-mode ramjet/scramjet combustor flowpath. After the rocket fuel has been expended, the rocket casing is ejected, leaving a clean flowpath.
Since the SHMAC is to be a weapon that would be launched from conventional aircraft and, therefore, to be deployed to forward bases around the world, simplicity of operations is a driving factor in the design of this weapon. The handling of cryogenic fuels under these conditions was believed to introduce undesirable operational complexities and expense. Therefore, since the maximum mach number associated with the use of endothermic hydrocarbon fuels is eight, that established the maximum flight mach number for this weapon.
-Access to Space Should the objective of a very short war not be achieved, the weapons described in the previous paragraphs can play significant roles in the military strategy for a protracted war. In this case, any nation that possesses the ability to launch nuclear weapons into space poses a serious threat to the command control, communications, and intelligence (C3I) operations of our armed forces. A relatively small orbiter-roughly similar in size to the Black Horse or to an F-15 could replace the HCMs carried as the payload for the SHAAFT.2 Using multistage concepts similar to the Beta3 or the Saenger,4 the flying wing and the SHAAFT would deliver the orbiter to efficient initial conditions for its "Access-to-Space" mission. The multiple-stage system would provide flexible access to space from conventional military runways, which would be a most valuable characteristic in the event that the adversary had destroyed the facilities at Cape Canaveral and at Vandenberg. Using rocket propulsion and aerodynamic forces to achieve the desired orbits, the SCREMAR would be able to place as many as three to four satellites (nominally six feet by six feet by six feet and weighing 1,000 pounds) into low earth orbit (LEO). The same TAV could also be configured to repair satellites on-orbit as well as perform sophisticated antisatellite (ASAT) missions.
Utilization of the Proposed Weapons System
The proposed integrated multistage weapons system is capable of performing
a variety of missions, both strategic and tactical. Consider the scenario
where an adversary threatens to invade (the threat may include nuclear
blackmail) or has just invaded a neighbor state. Based on recent headlines,
the adversary in this scenario could be Iraq or North Korea. Future headlines
might include China or a resurgent Russia. Despite negotiations at the
highest levels, the adversary shows no signs of backing down or retreating
from the occupied territory. Plans are made for a mission that would strike
at the key war-fighting infrastructure of the adversary. The targets include
the command, control, communications, computer center(s), the space launch
facilities, critical supply depots, massed formations of enemy tanks, etc.
An ultimatum from the president of the United States suggests that, if
the enemy does not act responsibly, massive force will be applied, suddenly
and without further warning. Authority is given to plan a mission that
would seriously damage the adversary's ability and will to fight.
Figure 1-2. Standoff Capabilities of SHAAFT/SHMAC.
The next day the mission is launched. One to four SHAAFT weapons systems are launched. The number depends on the size of the adversary (specifically, the number of and distance between the targets) and the operational philosophy (whether the mission objectives include total destruction of the enemy's war-fighting capabilities or merely a very strong attention-getting strike at selected targets). The range of the "zero" stage, the flying wing, allows it to take the attack aircraft approximately halfway to the target (for purposes of discussion, 5,000 nautical miles). Staging occurs at mach 3.5 at an altitude of approximately 60,000 feet. The supersonic/hypersonic attack aircraft, the SHAAFT climbs to approximately 100,000 feet, where it flies at a mach number of approximately 12. Soon after staging from the flying wing, the crew of the SHAAFT is given final instructions: continue on to the target and execute the full-scale operation, continue on to the target and execute a modified plan (change the targets or change the degree of destruction), or abort the mission altogether. The fact that the SHAAFT is a crewed vehicle provides a great deal of flexibility. Assuming that the instructions are to continue the mission, the SHAAFT proceeds to the area where the SHMACs are to be launched. Since the SHMACs have a range of over 1,000 nautical miles, the launch point, which is 10,000 nautical miles from the SHAAFT's home base, may not even be over the hostile country. To see an example of the standoff capability of the SHAAFT/SHMAC weapon system, refer to figure 1-2. Without slowing down, the SHAAFT launches a barrage of SHMACs from a point well out the enemy's threat zone. Since the SHAAFT does not slow from its cruise mach number of 12, the SHMACs will decelerate to their design cruise mach number of eight. The SHMACs themselves may strike the target or they may deploy submunitions, which further prioritize and diversify the targeting philosophy. The suite of weapons may be nuclear, conventional, or ray devices.
Having delivered massive firepower to the targets, the next consideration is the safe recovery of the SHAAFT. The optimum scenario would have the SHAAFT return to its CONUS base. However, if there is not sufficient fuel to reach the CONUS, the SHAAFT would proceed to an alternate, preselected recovery base. Depending on the mission, Hawaii or Diego Garcia seem natural selections for the non-CONUS recovery base. The recovery base will be within the 14,000 nm overall mission capability of the flying wing/SHAAFT. Once it releases the SHAAFT, the flying wing would proceed directly to Hawaii or Diego Garcia, where it would await the SHAAFT to complete its mission.
Procedures by which the SHAAFT returns safely to its CONUS base from other recovery bases, such as Diego Garcia, will be evaluated through further study. One possibility is sending a flying wing to retrieve the SHAAFT. The mated configuration would be flown home using the engines of the "zero" stage, the flying wing, and fuel added at the recovery base. Fuel and supplies would be brought to this base so that the SHAAFT could be serviced for its flight back to its home base in the CONUS. Because the technology base for the flying wing is that of the HSCT, the logistics infrastructure at the alternate recovery bases is relatively conventional.
Considerable savings can be realized through the elimination of the constant forward deployment of the more conventional forces to provide a "presence" of US armed forces. For those regions of the world where our forces do not have a permanent physical presence, the deployment of forces for a regional conflict is a very expensive and time-consuming project. Recall that Desert Shield took longer than Desert Storm. Furthermore, it is not likely that a future adversary will leave in place a near-by base infrastructure and then allow us the luxury of several months to build up our forces in the region. The savings described in the previous sentences could pay for most, if not all, of the design and of the development costs for the proposed, integrated hypersonic weapons system. The total fleet would consist of (approximately) five vehicles, deployed from four bases in the CONUS, two on each coast. By having an integrated weapons system strategy, the cost of the technology programs required to design and to develop the system would be greatly reduced. Furthermore, technology programs relevant to the various elements of this integrated weapons system (the flying wing, the supersonic/hypersonic attack aircraft, space control with a reusable military aircraft, and the standoff hypersonic missile with attack capability) have been in various stages of development for more than a decade.
Consider next the application, where the weapons delivery system (the flying wing and the SHAAFT) would serve as the first stage of a multi-stage access-to-space system. A transatmospheric vehicle would replace the SHMACs as the payload carried by the weapons delivery system. In a mission concept similar to that of the Beta System5 or to that of the Saenger,6 the two elements of the first stage would carry the TAV/orbiter to its launch point. Although the exact conditions for launch of the TAV/orbiter would be the subject of design trade studies, obtaining a high speed for staging appears to be more important that obtaining a high altitude.7 Preliminary calculations indicate that the orbiter would be lighter or the payload would be greater, if staging occurred at mach 12. Since the proposed system is to be an integrated, multipurpose weapons system, the results of the staging trade studies will influence decisions relating to the maximum velocity capabilities of the SHAAFT (in addition to the constraints placed on the SHAAFT as a result of its mission as the delivery system for the SHMACs).
It is assumed that the armed forces of the United States will have a constellation of satellites (on the order of hundreds) in place at the outbreak of hostilities. Using a variety of launch vehicles, these satellites (some large, others small) will have been placed in space over the years, as part of an evolving, strategic military strategy. However, at the outbreak of hostilities, the military leaders identify the need for additional satellites (perhaps to fill a gap in coverage, to provide additional information using special sensors, etc.) or the need to repair existing satellites. The situation becomes more critical if our adversary has disabled and/or destroyed a considerable fraction of our satellites. The armed forces of the United States have become very dependent on military/commercial satellites for communication and reconnaissance and are becoming increasingly dependent on other systems, such as GPS and Milstar. The elimination of a significant fraction of these assets by an enemy would paralyze our C3I . Rapid replenishment of lost assets is critical to the successful execution of our military operations. The flying-wing/SHAAFT combinations take the TAV/orbiter to mach numbers near 12 at 100,000 feet, where it stages. The TAV is a rocket-powered vehicle, approximately the size of an F-15, capable of carrying three or four small satellites (6 feet x 6 feet x 6 feet, weighing 1,000 pounds) into LEO. Thus, after a handful of missions, the country's military leaders could have a minimum of a dozen new satellites in place within days of the outbreak of hostilities. These satellites would provide communication links, intelligence information, etc.
It is envisioned that the flying-wing/SHAAFT/SCREMAR system would be routinely used during peacetime to place military satellites in space, to repair and to reposition existing military satellites, etc. This would be done to develop mission planning and operational experience, so that our armed forces could easily shift to the wartime pace of operations in the event that hostilities cannot be avoided.
Furthermore, the TAV/orbiter of the SCREMAR could perform the ASAT role should our adversary also have significant space assets. Finally, once sufficient technology for the TAV/orbiter is developed, it could be modified to fulfill other missions: it could deliver weapons in a strategic attack on the enemy for a suborbital profile or serve as a space-based laser (SBL) or airborne laser (ABL) weapons platform.
It is quite possible that, despite the severity of the strike described in previous paragraphs, the enemy will choose to continue to fight a war. One enemy may view the conflict as a Holy War and would consider early surrender unthinkable. Another enemy may have the resources (large population and widely scattered assets) to absorb such a blow and continue the fight. A third possible scenario would be the case where the United States was confronted with two Regional Conflicts and the strike described above would be used to eliminate one enemy, allowing us to focus on the other. In each case, our forces are involved in a protracted war.
For the protracted war, the elements of the integrated weapons system
could serve as significant elements of our arsenal. For instance, in addition
to serving as the weapons to be launched from the SHAAFT, the hypersonic
cruise missiles would have many uses in the case of protracted hostilities.
The SHMACs would be sized so that two could be carried by and launched
from an F-15E or some other conventional aircraft. Because the SHMAC has
a range of over 1,000 nautical miles, the F-15E would be able to remain
well out of the range of most defense systems. Furthermore, the hypersonic
capabilities of the SHMAC accommodate its use against time critical, moving
targets (e. g., mobile launchers, tank formations, etc.).
Figure 1-3. Aerospace Roles and Missions Fulfilled by S3.
Indicated in figure 1-3 are some of the basic aerospace roles and missions that can be performed by the S3 integrated weapons system. The missions that the S3 can accomplish by itself are highlighted in gray boxes while other missions that are fulfilled as a result of the capabilities of the S3 are indicated in plain boxes. A schematic of the fully mated S3 concept can be seen in figure 1-4. The integrated weapons system that has been described can perform counterspace tasks for aerospace control, tasks of strategic attack, of C2 attack, and of interdiction for force application, aerospace replenishment and space lift tasks for force enhancement, and on-orbit support for force support. It is an integrated hypersonic weapons platform capable of accomplishing a diverse set of missions in a variety of situations.
Figure 1-4. Schematic of Mated S3 Platform (with SCREMAR).
Numerous technological challenges will have to be met before the proposed integrated, multistage weapons system can be built. However, none of these challenges presupposes that a breakthrough in technology is an enabling requirement. The zeroth-stage flying wing is a UAV with a maximum mach number of 3.5. While that is slightly above the mach number for the current high-speed civil transport design, it should not be difficult to solve the problems unique to this application, given that the proposed system would be fielded in the twenty-first century.
The design of the SHAAFT offers the greatest challenges because there exist no vehicles that have flown at sustained hypersonic speeds while powered by an airbreathing system. Furthermore, the aircraft should have global range with a payload of approximately 50,000 pounds. The use of a flying wing to transport the SHAAFT to the one-third point of its global range mission at a mach number of 3.5 greatly simplifies the design of the SHAAFT. Considerable weight savings occur because the flying wing will carry the fuel required for takeoff, acceleration, and flight to the one-third point. The SHAAFT won't need heavy landing gear to support the takeoff weight. Furthermore, it does not need a zero-speed or a low-speed propulsion system. It appears that a dual-mode ramjet/scramjet combustor8 could be used to accelerate the vehicle from mach 3.5 to its cruise mach number of eight or of 12 and to sustain flight in this speed range. The decision as to whether to limit the vehicle design to mach 8 flight or to extend its capabilities to mach 12 flight is dominated by the propulsion system. Assuming reasonable development of the technologies of hypersonic-airbreathing propulsion systems and their fuels, it is assumed that mach 8 is the upper limit for the use of endothermic hydrocarbon fuels. One will need cryogenic fuels to extend the maximum cruise speed to mach 12. Some of the pros and cons of this problem are presented in the Critical Technology Requirements chapter, tables 5-1 and 5-2. Based on the survivability and on the range of the SHAAFT as a weapons platform for delivering SHMACs and as the initial stages for the SCREMAR, mach 12 flight would probably be preferred. Based on considerations relating to ground operations and support, especially if a recovery base is needed as an intermediate host, the endothermic fuels support a decision to limit the vehicle to a maximum mach number of eight. In any case, a serious trade study (including the effect on the design of the TAV/orbiter and its payload) should be conducted at the outset of the SHAAFT program.
An aerothermodynamically efficient vehicle having a hypersonic lift-to-drag ratio of five, or better, will be a long, slender body with relatively small leading-edge radii (the nose radius, the cowl radius, and the wing leading-edge radius). Thus, the heating rates in these regions will be relatively high. Controlling the vehicle weight will have a high priority. Therefore, the development of high-strength, lightweight materials and the ability to efficiently use them for the load-carrying structure and for the thermal protection system are high-priority items. Researchers at the National Aeronautics and Space Administration's Ames Research Center (NASA) are developing advanced Diboride Ceramic Matrix Composites (CMC), including Zirconium Dibirode and Hafnium Diboride materials which are reportedly able to withstand repeated exposure to temperatures of 3660 degrees fahrenheit and of 4,130 degrees fahrenheit, respectively. Materials for thermal protection systems developed for Shuttle derivatives, for the NASP, for the X-33, and for the X-34 should be reviewed for use in the proposed weapons system.
Major problems facing the aerothermodynamicist include the determination of boundary-layer transition criteria and the complex viscous/inviscid interaction associated with the multiple shock waves that occur, when the payloads (either the SHMACs or the SCREMAR) are released from the SHAAFT. The problem of developing boundary-layer transition criteria challenged the developers of the first reentry vehicles; it challenged the developers of the NASP; and it will challenge the developers of the SHAAFT. In the end, most likely, a criteria will be selected (with a degree of conservatism appropriate to the acceptable risk) and the design will proceed. The problem of shock/shock interactions associated with two objects flying in close proximity at hypersonic should be solvable. Some work has already been done, for on the staging of the Saenger.9
The decision to limit the SHMAC to a maximum flight mach number of eight was straight forward. Since a variant of the SHMACs will be launched from conventional aircraft, such as the F-22 or the F-15E, simplicity of ground operations, of fuel handling, and of weapons loading at forward bases dictates against cryogenic fuels. By limiting the SHMAC to a maximum mach number of eight, hydrocarbon fuels can be used. Use of hydrocarbon fuels instead of cryogenics greatly simplifies in-theater logistics, ground-support operations, and training requirements for base personnel. However, the SHMAC design must accommodate the transient loads associated with the short-duration overspeed when being launched from the SHAAFT.
Technology developments will be needed in the areas of guidance, navigation, and control (GN&C) and sensors for both the SHAAFT and SHMAC. Large changes in weight and in weight distribution will occur during the flight of the SHAAFT. Control of an aircraft flying at hypersonic speeds over great ranges requires advances in the state of the art. Collection and interpretation of data (threats, targets, political considerations at the brink of war) and decisions as to how to react must be continuously incorporated into the mission plan.
The design of the TAV/orbiter, a.k.a. the SCREMAR, should make use of the large number of access-to-space programs continuing around the world, including international programs, such as, the Japanese HOPE, as well as US programs, such as the X-33, the X-34, and the XCRV (currently under development at NASA). Since the SCREMAR is all rocket powered and operates in a similar manner as the Space Shuttle once separated from the SHAAFT, it should use as much of the current technology incorporated by the Space Shuttle as possible.
The technology programs used to develop the SHAAFT can be transferred directly to the SHMAC and SCREMAR, and vice versa. This is another application of the term integrated weapons system. The development of the S3 concept as a single weapons platform with several similar and fully compatible vehicles will be much easier on the technology demands as well the development costs than attempting to fulfill the same roles with different weapons systems.
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