"I call it the 'super-duper missile,' and I heard the other night 17 times faster than what they have right now, when you take the fastest missile we have right now. You've heard Russia has five times and China's working on five or six times — we have one 17 times, and it's just gotten the go-ahead..."
Donald Trump 19 May 2020
Putting the Hype into Hypersonic,
Feeling the need for speed
|2019 Approved Programs|
|USN||CPS||Conventional Prompt Strike|
|USA||LRHW||Long Range Hypersonic Weapon|
|USAF||HCSW||Hypersonic Coventional Strike Weapon|
|USAF||Lockheed||ALRRW||Air Launch Rapid Response Weapon|
|DARPA||TBG||Tactical Boost Glide|
|DARPA||HAWC||Hypersonic Air-breathing Weapon Concept|
|...||HACM||Hypersonic Advanced Cruise Missile|
|...||HCCW||Hypersonic Counter-Cruise Weapon|
"Hypersonic" describes any speed faster than five times the speed of sound, which is roughly 760 miles per hour at sea level. Multiply that by five and the product is a weapon that travels at least 3,800 miles per hour or more - a mile per second and faster. But is speed enough to change the game? Does a missile flying at Mach 7 outperform one at Mach 3 on metrics other than speed? Hypersonics have been spoken of as game-changers (whether because of their speed or their radar-evading low flight profile), though opinions vary across the defense community as to whether current hypersonic technology is advanced enough to be revolutionary.
China and Russia are pursuing hypersonic weapons because their speed, altitude, and maneuverability may defeat most missile defense systems, and they may be used to improve long-range conventional and nuclear strike capabilities. There are no existing countermeasures. Both the White House and Pentagon insist that the U.S. military needs enhanced capabilities to counter growing threats such as Russian hypersonic missiles. Some defense analysts are unconvinced that the United States needs a hypersonic strike and are skeptical of some technical claims made about hypersonic weapons, pointing out that there are other ways to hit fleeting targets, get into denied areas or strike a rogue nuclear facility--ways that cost less, and risk less.
Air Force Lt. Col. Jeff Schreiner wrote in a 2014 Stars and Stripes op-ed calling for a hypersonic test ban: "The tactical planner in me sees countless uses for hypersonic delivery platforms against a range of target sets. The strategic planner sees the ability to help offset other nations' strategic assets with a conventional versus nuclear strike. The pessimist in me sees a technology that has the potential to spiral out of control in many nations into deadly new nuclear delivery platforms."
Systems that operate at hypersonic speeds — five times the speed of sound (Mach 5) and beyond — offer the potential for military operations from longer ranges with shorter response times and enhanced effectiveness compared to current military systems. Effective defense against future air-to-surface missiles, on-the-deck attacks, and IRBM attacks will require major reduction in time-to-intercept of the defense missiles, compared with presently available surface-to-air missiles. For the foreseeable future, effective intercept of ballistic missile warheads, as well as air-supported attacks, will occur within the atmosphere, because the atmosphere provides the best means for distinguishing between the ballistic warhead which must be destroyed and extraneous re-entering material accompanying the warhead to which firepower must not be diverted. The margin of superiority of ramjet missiles to rockets increases rapidly as missile speed increases. To provide equivalent performance to a Mach 7 supersonic combustion ramjet vehicle at sea level, a rocket would have to have roughly three times as much weight.
Hypersonic flight is arbitrarily defined as flight at speeds beyond Mach 5 although no drastic flow changes are evident to define this. Several formidable problems are encountered at these speeds. First, the shock waves generated by a body trail back at such a high angle that they may seriously interact with the boundary layers about the body. For the most part, these boundary layers are highly turbulent in nature. Secondly, across the strong shocks, the air undergoes a drastic temperature increase. Aerodynamic heating of the body is a major problem. For sustained hypersonic flight most normal metals used in today's airplanes would quickly melt; therefore new materials or methods that can withstand the high-temperature effects are required. The temperature of the leading edge of the airplane wing may be reduced by using a high degree of sweepback. Additionally, to obtain a good lift-drag ratio, a flat-plate design wing is used. Control surfaces for hypersonic flight must be strategically placed so that they encounter sufficient dynamic pressure about them to operate. Otherwise, if shielded from the approaching flow by the fuselage, for example, they will be ineffective.
Hypersonic vehicles fly through the atmosphere at incredibly high speeds, creating intense friction with the surrounding air as they travel at Mach 5 or above – five times faster than sound travels. Developing structures that can withstand furnace-like temperatures at such high speeds is a technical challenge, especially for leading edges that bear the brunt of the heat. When an extremely fast vehicle, such as a so-called hypersonic missile, flies through the atmosphere, portions of the outer hull of the flying body are subjected to high heat loading.
For example, especially the leading edges of the wings and the nose of a hypersonic aircraft are subject to very high thermal loading. One known solution to this problem involves using so-called ablation materials, which distribute over a larger area the great amount of thermal energy arising at the critical locations, and which may also vaporize or otherwise deteriorate due to the heating, whereby a temperature reduction is achieved. Other possible solutions include the use of a heat shield consisting of temperature resistant tiles, or of locally applied cooling using liquid hydrogen, which is also used for the propulsion of the vehicle.
A disadvantage of using an ablative material is that a rather thick layer of the material must be applied in order to reliably protect the inside of the spacecraft from an unacceptably high penetration of heat. Furthermore, the aerodynamic outer surface of the ablative material changes as it vaporizes, so that it deviates from the precalculated optimum aerodynamic shape and results in an altered aerodynamic characteristic. A disadvantage of using tiles to form a heat shield, as is done in the Space Shuttle for example, is that a relatively thick layer of the tiles is necessary and thereby a substantial additional weight must be transported by the spacecraft.
A disadvantage of directly cooling the flying body's structure with liquid hydrogen is that it must be carried out at a very low temperature, because the liquid hydrogen is provided in a cryogenic state. As a result, reducing the temperature of the structure necessarily increases the reception of heat energy, whereby in turn the required amount of cooling medium increases. Moreover, this method of cooling requires a very good thermal insulation of the outer skin of the flying body, because the temperature of the pipes through which the hydrogen cooling medium flows cannot be allowed to become too high.
If a supersonic LACM requires around 17 minutes to reach a target at 1,000 km, a hypersonic missile reaches the target in less than 10 minutes—a difference of approximately eight minutes. Is this eight minutes critical for military outcome? Even if this timeline is critical, most militaries are neither equipped with necessary C4ISR systems nor the civilian and the military organisational structures are geared to respond in such a time critical manner.
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