Defense Technology International - May 2008 - (Page 26)

DEFENSE STRATEGIC HYPERSONIC AND HEAT-RESISTANT The link between the Army’s Advanced Hypersonic Weapon (AHW) and Sandia National Laboratories is the hypersonic boost-glide vehicle (BGV), the core technology of the Prompt Global Strike program. BGV is an old technology, first tested more than 60 years ago, but one that has yet to ﬁnd an operational application. Ballistic missiles are long-range artillery. Operational reentry vehicles are unguided and do not generate aerodynamic lift. However, the German developers of the World War II A-4 (V-2) missile realized that the rocket’s descent velocity could be traded for lift by adding wings to the vehicle and extending its range, and experimented with winged A-4s. SANDIA NATIONAL LABORATORIES Ceramic composites developed by Sandia Labs are key to the Army’s AHW. In the late 1950s, USAF and McDonnell Aircraft tested the Alpha Draco boost-glide research vehicle (BGRV), designed to use aerodynamic lift at double-digit Mach numbers. Alpha Draco was a slender cone with a skirt of movable ﬂaps at the base, which made it possible to trim the vehicle with a nose-up angle of attack. McDonnell went on in the 1960s to design the Isinglass manned reconnaissance BGV for the CIA. A winged vehicle with a relatively high lift-todrag ratio, Isinglass offered nearglobal range and was designed to pass over targets at Mach 20, but was canceled before it ﬂew. Another closely held project from the 1970s was the McDonnell Douglas Advanced Maneuverable Reentry 26 Vehicle (AMaRV), designed to defeat missile-defense systems by performing pre-planned evasive maneuvers in descent. It was tested successfully three times. USAF’s current Conventional Strike Missile, by all accounts, borrows heavily from AMaRV. In the late 1980s, USAF sponsored work on a Hypersonic Glide Vehicle (HGV), a weapon that was possibly intended to attack mobile ICBMs. Its low trajectory and high speed would give the target much less warning time than a ballistic missile. Air- and ground-launched versions were studied. The project was publicly discussed in 1987, with a planned start in 1988, and thereafter disappeared. It was either canceled or went black. Nevertheless, multiple published references to such a program continued after 1988. Air-launched BGVs are exempt from the Strategic Arms Reduction Talks treaty. BGV designs vary, but heating due to air friction is often the driving issue. Conical shapes spin to spread the heat evenly (ﬂying with a small angle of attack, the “windward” side heats up more than the “leeward” side), but a pure cone is hard to package because the center of gravity is behind the center of pressure, which makes it unstable. AMaRV was a biconic shape, which places more volume and mass forward and is easier to package than a pure cone. A winged shape like Isinglass or the late-1980s HGV provides a high lift-to-drag ratio and potentially long range, but heating is concentrated on the sharp leading edges, and the longer the glide range, the more severe the heating challenge. Some designs use a skip-glide proﬁle to mitigate heating, performing repeated climbs above the atmosphere to dissipate heat. Thermal protection systems based on ablative materials can be used to some extent, but become less useful as the glide range increases; and this is where Sandia’s involvement in the AHW becomes a factor. Sandia pioneered the development of ultrahigh-temperature (3,000C) ceramic composite materials based on zirconium diboride and hafnium diboride, used in common with silicon carbide. Sandia reported a breakthrough in this area in October 2003, overcoming structural deﬁciencies encountered with earlier materials. ■ maneuverable reentry vehicle (RV) that could deliver a variety of payloads, from kinetic penetrators and scatterable munitions to air-deployed unmanned aerial vehicles. There is, however, a strong contingent of elected officials and staff members in Washington that have been skeptical of PGS. In 2005, under pressure from Congress, Darpa eliminated the acronym behind Falcon and the CAV test articles were renamed Hypersonic Test Vehicles. Congress remains steadfastly opposed to the simplest and most near-term PGS solution—putting a conventional warhead on a Trident sealaunched ballistic missile. Much of the technology required to do this has been demonstrated, and it was proposed in the FY2008 defense budget, with the aim of achieving initial operational capability (IOC) in 2010. Congress, however, rejected the proposal and instead directed money to a joint-service PGS project. No Conventional Trident Missile funding was included in the 2009 budget. Under the joint PGS project, the project closest to fruition is USAF’s Conventional Strike Missile (CSM). This is intended to hit targets deﬁned in a July 2006 initial capabilities document—e.g., a missile on a gantry, ships in port, an airﬁeld or hardened targets, including missile silos and bunkers. A CSM would be launched from the continental U.S. and strike within an hour. The basic concept deﬁned by USAF’s Space & Missile Center uses a Minotaur booster from Orbital Sciences Corp., an off-the-shelf system comprising boost stages from the retired Peacekeeper ICBM, carrying a biconic vehicle similar to a scaled-up version of the late-1970s Advanced Maneuvering Reentry Vehicle (AMaRV—see abutting story) weighing 3,800 lb. (1,723 kg.) overall and carrying a 2,000-lb. payload. The CSM would have near-global range from Vandenberg AFB, Calif. It would be distinguishable from a nuclear ICBM launch by its location, which is more than 1,500 km. from U.S. launch silos, and by a skip-glide flight profile. The system would have enough range and speed to cover likely targets while ﬂying an indirect route to avoid neutral nations. Boeing was awarded a study contract covering the CSM system in August 2007. One team member is Honeywell, which developed the guidance system for the original AMaRV along with McDonnell Douglas (now part of Boeing). The goal of the study, to be AviationWeek.com/dti DEFENSE TECHNOLOGY INTERNATIONAL MAY 2008 http://AviationWeek.com/dti

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Defense Technology International - May 2008

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