A good place to start is Iain Boyd’s understated article, (CBS News) U.S., Russia, China race to develop hypersonic weapons.  It may be the only article in the popular press that offers measured assessment. But the most important statement, somewhat overshadowed by the depiction of U.S. inferiority, appears towards the end as a tentative suggestion. It’s worth highlighting with a quote:

“It is not clear if the types of interceptors that have been developed for defense against slower weapons will be effective against hypersonic missiles. Entirely novel approaches may be needed to defeat this new threat. Examples include high-power lasers and beams of electromagnetic energy.”

The article concludes with the catch-all,

“I believe that to avoid an important gap in U.S. defensive capabilities, American efforts in defense must at least keep up with the progress of other nations in developing hypersonic weapons.”

This nonspecific conclusion, descending to common sense, is the weakest point, because we are resource limited.

DARPA has initiated the proposal process for Glide Breaker, with the goal of impact-hard-kill against a particular category of hypersonic vehicles, boost-glide. This is problematic in several ways:

• While China strategic weapons appear to fall in the category of boost-glide, Russia’s Avangard system  is not; see Russia’s Hypersonic Missile; Reverse Engineering Secrets of Avangard.
• Boyd’s first quote, to which I add emphasis of certainty, implies that physical interception-hard-kill is (a) probably impossible. (b) If it is possible, changes to the adversary design would make it impossible.
• The hypersonic threat has such potential variation, and interceptors have such specificity, that the effort to counter is likely to end in resource exhaustion.
• Theodor Postol spent half a lifetime arguing the impossibility, on solid physical grounds, of effective ABM defense. He came as close to mathematical proof as one can  in the strategic realm. Supporters of missile defense found it unnecessary to refute, because decision makers don’t understand proofs. Now we have a second proof. As hypersonic vehicles are more difficult in all ways to intercept than ballistic missiles, interception is also impossible.

Decision makers are confused because, in tests, interceptors occasionally work. Some systems, such as THAAD, have performed remarkably well in tests, but are technically limited in ways the civilian policy-maker is unlikely to understand. Each interceptor is rigidly designed for a particular regime of altitude and velocity. The PAC-3 Patriot, specialized to ballistic missiles,  missed drones powered by the equivalent of  lawnmower engines, on multiple occasions. (Times of Israel) IDF: Patriot missile fired at incoming UAV from Syria, which retreats.

DARPA Glide-Breaker aspires to counter a new threat that is technically far more difficult than ballistic missiles, against which there is no practical defense. DARPA employs the services of engineers and scientists to solve strategic problems. These two fields,  engineering and strategy, employ  different modes of logic and habits of thought. When  engineering ventures into strategic thinking, and vice-versa, expensive errors of national policy can result.

The 1991 Gulf War provided early warning of this conundrum. SCUD missiles were so poorly engineered that they broke up in flight, with irregular trajectories that could not be matched by the Patriot system of that era. Frontline summarizes:

Such a Scud therefore came down with a relatively heavy warhead and a heavy motor, separated by the light empty fuel tank. It was structurally unstable and often broke up in the upper atmosphere. That further reduced its already poor accuracy, but it also made the missile difficult to intercept, since its flight path was unpredictable.

Simple randomization of the trajectory, which Avangard does in spades, was enough to defeat antimissile defense. Bad engineering defeats the specificity of good engineering.

One of the characteristics of the PAC-3 version is increased maneuverability  at high altitude, which resulted in reduced maneuverability at low altitudes. This improvement is vastly outclassed by the real or potential maneuverability of hypersonic vehicles, except in a specific part of the trajectory, which is specific to the adversary.

This implies that the adversary could, at relatively reduced cost, produce a core missile with different clothing aerodynamics. (The AIDS virus defeats the immune system by this strategy.) By varying the fuselage structure of a compatible core, flight characteristics become randomized. Which vehicle are we shooting at today?

To be a productive engineer, one has to stay focused on the problem. There are little problems and big ones, and a different focus on each. But the engineering mindset seldom extends to, “Should we be doing this at all?” Instead, the engineer offers a metric of success for the given specifications of a limited goal. Should we always buy? How are we thinking about this? This is strategy.

Part 1 ends with a joke quoted from Reddit.