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October 1987 Air Force Monthly


Apr 21, 2009
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Boost-Glide Vehicles

DARPA and NASA have been in­volved in the NASP program since its inception. Now the Air Force is pursuing a joint program with DAR­PA to develop hypersonic boost-glide vehicles and build a prototype. These would be quite different from the runway-takeoff aircraft/ spacecraft that the NASP program is expected to bring about. The boost-glide vehicles would be un­manned weapons and breathtaking ones at that. They would almost certainly rev­olutionize strategic warfare. The Air Force sees them as capable of reaching speeds up to fifteen times that of sound, of ranging farther than ballistic missiles, and of ap­proaching targets at relatively low altitudes. It is possible that a prototype could be built and test-launched by the early 1990s. Initial plans involve launching the prototype atop a Min­uteman ICBM booster, now in stor­age, for a test flight from Vanden­berg AFB, Calif., to the Kwajalein Missile Range in the Pacific Ocean.

The hypersonic vehicles would not go into space. They would level off in the upper atmosphere and head toward their targets oceans and continents away. They are being designed to be so maneuverable on their approaches that they would be difficult to bring down—even if it were possible to detect and track them in the first place. There is a passing similarity be­tween the boost-glide vehicle and the X-20 Dyna-Soar, which was conceived by AFSC in the late 1950s as a manned, winged craft to be launched into space by a Titan booster and then to glide back through the atmosphere. That proj­ect was dropped in the early 1960s, but the work done on it led to the development of the Space Shuttle in the 1970s, most especially with re­gard to advanced materials for ab­sorbing the heat of reentry. The concept of the hypersonic boost-glide vehicles was promoted by Forecast II and is an outstanding example of how research in mate­rials, propulsion, electronics, and optics has progressed to the point where the Air Force can pull it all together to begin developing—with confidence—a full-blown system for testing.

Materials for Tomorrow

On the wings of Forecast II, re­search on advanced materials is fly­ing high. In the offing are light­weight, highly ductile, superstrong materials of supreme resistance to heat. New processes have been in­troduced in rapid solidification rate (RSR) powder metallurgy for pro­ducing awesome alloys. Extremely strong and heat-resistant "intermet­als"—for example, titanium alumi­nide—are coming forth, as are ad­vanced carbon/carbon materials and ceramic composites. ASD's Materials Laboratory is learning how to rearrange the mole­cules and atoms of a broad range of materials to endow them with prop­erties that greatly improve upon those offered by nature itself. Forecast II calls these "ultra-structured materials." Some are al­ready in existence. Whatever their compositions, these highly advanced materials are destined for optical computers and switches and for high-performance turbine engines. Capable of holding up under ter­rific heat, those engines will not need the complex cooling tech­niques required by today's turbine engines and, in consequence, will be far smaller, lighter, more power­ful, and more reliable. It is increasingly likely that such advanced engines will come to pass by or around the turn of the century, thanks to Forecast II's having un­derscored their research.

They are expected to double—at least—the thrust in relation to the weight of the ATF's advanced en­gines. This would be a startling—even revolutionary—advancement. The ATF's engines will improve upon the performance of power-plants in modern fighters in many ways, particularly by providing the capability for supersonic speed and persistence without using after­burners. But in terms of thrust to weight, the ATF's engines will be only about twenty percent—one-­fifth—superior to the best of the cur­rently operational fighter turbine engines. With the exceptionally high thrust-to-weight engines in Fore­cast II's future, the Air Force will be able to build Mach 4 aircraft and—by converting thrust into lift—V/ STOL aircraft for a wide variety of missions. Most likely, the ATF will have en­tered production—in the mid-1990s, if all goes well—before the turbine engines foreseen in Fore­cast II are ready to be flown. How­ever, the ATF will undoubtedly evolve into increasingly capable variants as it goes along, so it is possible that those engines will be­come available for it as its produc­tion approaches or crosses the cusp of the centuries.

Smaller Boosters, Bigger Loads

Rocket engines are also in for a big shot of change as a result of re­search rallied by Forecast II. Such research is generating a new class of fuels—"high-energy-density pro­pellants"—that are expected to dou­ble the thrust of existing solid and liquid propellants in space boosters. Their energy density—thrust per unit of mass—may be ten times or more that of current propellants. This will make them amenable to containment in boosters of dwarfish dimensions and of puny poundage in comparison with the boosters that now loom like skyscrapers on planetary launchpads. The implications for the US space program are profound. It has always been plagued by the extraordinarily high cost of boosting payloads into orbit. Smaller boosters capable of carrying larger and more numerous payloads at the same total system weight will translate into far greater cost-effectiveness, capability, and versatility for the US space pro­gram, which is currently short on all such attributes. Forecast II sees the advanced fuels as powering the heavy-lift launch vehicles of the future. USAF has a crying need for such lifters. The Space Shuttle fleet has a limited and uncertain future, and the Stra­tegic Defense Initiative program, the Space Station program, and oth­ers to involve outsize payloads will make strong demands on US spacelaunch capabilities in the 1990s and beyond. The first of the heavy lifters—the Advanced Launch System (ALS)­is being developed and will be op­erational well before Forecast II's futuristic propellants come on the scene—but maybe not all that long before.

The Air Force plans to demon­strate the technologies of such fuels by 1990. Experiments on them be­gan this year, and researchers be­lieve that the technologies will be under control in relatively short order. Such work stands as yet another example of going nature one better in Forecast II research. It involves exciting the outer-shell electrons of such inherently stable chemical ele­ments as argon and krypton to make them unstable. Once this state is reached, the agitated electrons are "bound" in ionic or covalent com­pounds that expend enormous, pent-up energy upon combustion. Air Force Astronautics Labora­tory (formerly Rocket Propulsion Laboratory) and AFOSR have awarded twelve contracts to univer­sities to master the chemistry and the "excited-state physics" in­volved in producing the powerful propellants. Forecast II officials are confident that such mastery is well within reach. Supercomputer calculations have told them so.
Bolding mine - Did this happen? Where are these high energy density fuels. Probably too damaging to the environment or something :eek:

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