A key motivation driving the event of hypersonic weapons, which glide through the atmosphere at greater than five times the speed of sound, is the will to counter missile defenses. Evading terminal defense interceptors would allow these weapons to destroy missile- and air-defenses early in a traditional conflict, opening routes of attack for other weapons. It could also allow hypersonic weapons to pose a serious threat to ships.
A recent article, citing defense officials, warns that “Even probably the most advanced US warship within the South China Sea might be defenseless against a hypersonic attack.” In contrast, a March Pentagon press statement says that “Aegis ships equipped with the sea-based terminal [defense] capability can now engage some hypersonic threats.”
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What’s the truth? With prospects of a hypersonic revolution pushing U.S. spending and strategy, it is necessary to know what hypersonic weapons can and may’t do.
Our recent evaluation of hypersonic weapons and hypersonic defense looks on the physics of missile interception and shows that in contrast to common claims, hypersonic weapons may be intercepted by existing terminal defenses.
The hypersonic weapons currently being developed by the US, Russia, and China for conventional uses have maximum speeds below about Mach 10-12. We show that the atmospheric drag on these weapons as they glide and dive to targets on the bottom will slow them enough that they may be intercepted by defenses like advanced versions of the Army’s Patriot PAC-3 and the Navy’s Aegis SM-6.
This vulnerability was illustrated when Ukraine used PAC-3 to shoot down multiple incoming Russian Kinzhal missiles, despite their maneuvering flight at hypersonic speeds.
Which means that ships are less vulnerable to hypersonic attack than is incessantly claimed. Ship-based radars could detect approaching hypersonic weapons at distances of many a whole bunch of kilometers, which is greater than adequate to fireside interceptors at them. Ships with interceptors much like advanced PAC-3 and SM-6 systems should subsequently find a way to defend themselves from the hypersonic weapons currently being developed.
This finding is supported by a Missile Defense Agency animation showing a carrier group using ship-based interceptors against hypersonic weapons. The video shows a ship-based interceptor like SM-6 engaging hypersonic weapons detected by the ship’s radar.
Developing faster hypersonic weapons could help a rustic evade current interceptors, but would raise recent problems. Faster flight through the atmosphere would result in rather more intense heating of the vehicles, which stays the fundamental challenge in designing these weapons.
And at the identical time, countries can be working to develop increasingly fast and maneuverable interceptors to interact the subsequent generation of hypersonic weapons their adversaries might develop.
Our evaluation also shows that hypersonic weapons’ ability to maneuver during their glide phase—around defended regions, for example—is often exaggerated and comes at a big cost.
The very high speeds of those weapons means they require very large aerodynamic forces to show. Generating these forces increases drag and may significantly reduce the speed and range of the weapon.
For example, consider a Mach 10 weapon that turns by 30o to avoid overflying a selected location after which turns back by 30o to its original direction of flight. Under reasonable assumptions, the drag during this turn would cut back its speed from Mach 10 to about Mach 6 and reduce its total glide distance to lower than 60% of the space it could have flown with no turns.
Adding an engine, like a scramjet, could reduce the lack of speed and range during maneuvers, but adding an engine and fuel would increase the weapon’s size and mass, requiring a significantly larger booster to launch it. Since scramjets usually are not a mature technology and operating them is notoriously complicated, powered hypersonic systems will likely be less reliable and costlier than boost-glide weapons.
Ballistic missiles also fly at hypersonic speeds, and flying them on depressed trajectories can deliver missiles in equal or shorter times than hypersonic weapons, without the heating problems. Ballistic missiles delivering warheads that may maneuver within the atmosphere (using maneuverable reentry vehicles, or MaRVs) can use similar guidance technologies and have similar accuracy as hypersonic weapons. MaRVs also can use lift as they reenter the atmosphere to maneuver and re-target over a whole bunch of kilometers.
Typically, MaRVs launched by ballistic missiles on depressed trajectories out-perform hypersonic weapons in lots of scenarios. A recent evaluation by the Congressional Budget Office predicts they might be a 3rd cheaper than hypersonic weapons.
The hypersonic arms race is more likely to increase tensions and military spending internationally without enhancing national or global security. Hypersonic weapons don’t live as much as lots of the grandiose claims about their performance, and there are higher options for gaining the capabilities they do offer. The US must take a more realistic view of those weapons and the billions of dollars it’s spending on them.
David Wright is a visiting scholar within the Laboratory for Nuclear Security and Policy within the Department of Nuclear Science and Engineering on the Massachusetts Institute of Technology. He has a PhD in Physics.
Cameron Tracy is a research scholar within the Center for International Security and Cooperation, Freeman Spogli Institute for International Studies at Stanford University. He has a PhD in Materials Science and Engineering.