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Hypersonic Air-breathing Weapon Concept (HAWC)

Systems that operate at hypersonic speedsfive times the speed of sound (Mach 5) and beyondoffer the potential for military operations from longer ranges with shorter response times and enhanced effectiveness compared to current military systems. Such systems could provide significant payoff for future U.S. offensive strike operations, particularly as adversaries capabilities advance. HAWC uses the technology of scramjet engine, which enables hypersonic flight by taking in air at hypersonic speed and burning it without reducing the speed to below the speed of sound

The Hypersonic Air-breathing Weapon Concept (HAWC) program is a Joint DARPA / Air Force effort to develop and demonstrate technologies to enable transformational changes in responsive, long-range strike against time-critical or heavily defended targets. HAWC will pursue flight demonstration of the critical technologies for an effective and affordable air-launched hypersonic cruise missile. These technologies include advanced air vehicle configurations capable of efficient hypersonic flight, hydrocarbon scramjet-powered propulsion to enable sustained hypersonic cruise, thermal management approaches designed for high-temperature cruise, and affordable system designs and manufacturing approaches.

HAWC technologies also extend to reusable hypersonic air platforms for applications such as global presence and space lift. The HAWC program will leverage advances made by the previously funded Falcon, X-51, and HyFly programs. This is a joint program with the Air Force, and HAWC technologies are planned for transition to the Air Force after flight testing is complete.

On 23 September 2016 Lockheed Martin Corporation was awarded $171,191,252 under Solicitation Number: DARPA-BAA-16-07. Fiscal 2015 ($12,163,224) and 2016 ($7,193,252) research and development funds totaling $19,356,476 are being obligated at the time of award. The Defense Advanced Research Projects Agency, Arlington, Virginia, is the contracting activity (HR0011-16-C-0110).

The ramjet and supersonic ramjet (scramjet) propulsion cycles for supersonic (less than Mach 5) and hypersonic (Mach >5) engines are well-known within the art of aerospace propulsion. These engines are typically defined by an external compression device or forebody, and internal compression device such as an inlet including an isolator and/or diffuser, a combustion device or combustor, and an expansion device or nozzle. All surfaces wetted by flow streamlines ultimately passing through the engine are considered to be a part of the engine flowpath since they contribute to the engine cycle performance. Consequently the integration of the airframe and the propulsion systems for vehicles or projectiles employing these propulsion cycles is critical for high performance.

In the ramjet propulsion cycle above about Mach 5, the static temperature at the combustor entrance approaches the stagnation temperature and dramatically impacts fuel combustion. At such extreme temperatures, an appreciable amount of the energy which would be released due to combustion is bound in dissociated air and combustion product molecules such that the temperature rise due to combustion is reduced. The energy contained in dissociated gases is largely unavailable for the expansion and acceleration of the exhaust mixture. Thrust, therefore, is lost as a result.

For Mach numbers above 5, scramjet engines generate high propulsion efficiency. Above Mach 5, the main advantage of scramjet propulsion is that supersonic velocities within the combustion chamber are accompanied by lower static temperatures, lower pressures and reduced total pressure losses. These lower temperatures, pressures and losses thereby reduce combustion product dissociation, and the reduced temperature gases when expanded yield increased cycle efficiency. Above Mach 5, the scramjet engine has reduced pressures which decrease loads on engine structure and reduced total pressure losses (entropy gains) which increase the flow energy available for thrust production (i.e., increased efficiency).

War fighting capabilities and methods have slowly evolved over the period of the twentieth century. One of many improvements has been a significant advance in the ability to deliver a weapon with great accuracy. Weapon delivery with zero or near zero circular error of probability [also referred to as circular error probable ("CEP")] is almost the norm when the weapon is equipped with precision guidance capabilities.

In the military science of ballistics, circular error of probability is a simple measure of a weapon system's precision. The impact of munitions near the target tends to be normally distributed around the aim point with progressively fewer munitions located about the aim point at a greater distance away. A mathematician might characterize this pattern by its standard deviation, but a more intuitive method is to state the radius of a circle within which 50 percent of the rounds will land.

This movement for greater accuracy has been encouraged by the war fighter communities and has been made possible by technology growth. The World War I, World War II, Korean and Vietnam era warfare witnessed the application of massive use of unguided weapons with large chemically based explosive warheads. This approach was permitted because the size of the boundaries of the total set of acceptable targets was virtually unlimited (i.e., unlimited war) and the zone impacted by the chemically based warhead blast and shrapnel was normally within the CEP.

The geopolitical nature of warfare, however, has significantly evolved throughout the twentieth century and continues into the twenty first century. More specifically, changes in the set of all features that may form the list of acceptable targets has been driven by various influences.

A strong contribution to the reduction of the target region has been the great improvement in guidance with the associated pin-point accuracy of the weapons (i.e., the exceedingly smaller CEP). The results of the blast and shrapnel region generated with a typical chemically based explosive often extends beyond the CEP. In contrast, there are some lightly defended targets which are not "hard," but are simply of too little value to merit an individual attack. For example, a single tent would not be targeted in most of the conflicts of the twentieth century, unless it was associated with some other target such as an observation position or a command and control post.

As non-state enemies have emerged as a threat, it has become necessary to target small soft targets such as individual automobiles or a single tent. This boundary shift has increased the target region somewhat, but the absolute number of targets that can be attacked has not been strongly influenced.

Another factor is the need for flexibility. The nature of war has become much more dynamic and ad hoc as it applies to strike missions. In recent conflicts, the majority of strike platforms (e.g., ships, aircraft, troops, armored vehicles) did not know what specific targets with which they were to engage at the time of selecting munitions loading. Thus, the weapons carried to the conflict had to be general purpose, and it was highly desirable to have the effects of the weapons selectable to match both the target characteristics and the rules of engagement. In the process of prosecuting a campaign, matching weapons, targets, and rules of engagement is often impossible.

Placement of the warhead significantly influences the results achieved. The greater the precision of placement of a warhead with respect to the target, the smaller the warhead that can be employed to achieve acceptable levels of destruction or neutralization of the target. Increased precision of warhead placement also reduces the opportunity for collateral damage. Political demands, ethical considerations, social influences and economic constraints on the rules of engagement are such that collateral damage is undesirable. Likewise, a large class of targets that are now encountered in current scenarios can be successfully defeated with smaller warheads with improved placement provided that the target detectors and warhead fuzing can suitably interpret target information such as location, motion and physical characteristics.

Previous missile designs have relied in high altitude flight on stability mechanisms of dubious reliability, performance constraints, and cost penalties. The previous approaches to stabilizing missiles include large aerodynamic flares. All these aero-stabilizing mechanisms are costly, heavy, complicated to the point that successful operation was questioned, and significantly degrade the kinematic performance of the interceptor. Other more passive options proposed included nosecone aero-spikes, enlarging the airframe flare to mate with a larger diameter booster, and shifting the interceptor center of gravity with ballast. None of these passive control ideas has proven successful. Accordingly, it will be appreciated that improvements in missile design would be desirable.

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