Can You Stop a Hypersonic Missile? | Christian Engel<br>Post<br>Cancel<br>Can You Stop a Hypersonic Missile?<br>Contents Can You Stop a Hypersonic Missile?
The headlines say yes. Patriot crews shot down a Kinzhal over Kyiv on the night of May 4, 2023. Arrow-3 batteries killed Iranian ballistic missiles over Tel Aviv in April and October 2024. A pair of THAAD batteries in Israel emptied something close to a quarter of the US national inventory across twelve days of war in June 2025. The headline word in every one of those engagements was hypersonic. The headline is wrong.<br>No maneuvering boost-glide hypersonic vehicle has ever been fired in combat against a defended target. Every “hypersonic intercept” the press has reported in the last three years was a different class of weapon: an air-launched aeroballistic missile, a quasi-ballistic short-range ballistic missile with a maneuvering reentry vehicle, or in one case a MIRV bus on an intermediate-range ballistic missile that the press could not stop calling hypersonic. The Avangard, the only Russian vehicle that meets the strict definition, has sat in silos in Orenburg since 2019 without being touched. The Chinese DF-17 has never been used. The American Dark Eagle has not yet been ordered to fire.<br>So when we ask “can you stop a hypersonic,” we are partly asking “what would happen if anyone fired one.” The honest answer to that question, in June 2026, is that we do not know, because the kill chain we would use against one has not been tested against a true target in a real engagement, and the dedicated interceptor designed to do the job will not exist for at least three more years.<br>The rest of this essay is about why that is harder than the press understands. And about a second problem hiding underneath it: even before the glide vehicle shows up, the defender is already running out of interceptors, against the weapons it knows how to stop.<br>What “hypersonic” actually means<br>“Hypersonic” is a marketing word that does a lot of work in the press and very little in engineering. The official definition is faster than five times the speed of sound. By that definition every ICBM warhead is hypersonic on re-entry. A V-2 rocket from 1944 was hypersonic. A meteor is hypersonic. The Space Shuttle was hypersonic.<br>The Mach 5 threshold is not arbitrary, though. It is the line where the textbook aerodynamics most engineers learn stops working. Above it the air gets so hot that nitrogen and oxygen molecules start to break apart, the heat-capacity ratio γ stops being constant, and what was a fluid problem becomes an aerothermochemistry problem. Below it you are doing high-school physics. Above it you are running a small particle accelerator with a missile attached.<br>Mach number M 8.0 Airliner Concorde Rifle bullet SR-71 X-15 Zircon Avangard ICBM re-entry
1 km of ground, in real time target speed shown vs walking pace (3 km/h)
Velocity
Time to cross 1 km
London → Berlin (930 km)
The reason any of this matters for missile defense is that a small number of modern weapons do three things at once that no previous weapon did:<br>They sustain hypersonic speed for thousands of kilometres, not just for the brief terminal arc.They maneuver in flight, which earlier fast weapons could not.They do both at low enough altitude (20 to 60 km) to hide under the horizon of legacy ground-based defenses.As of 2026, only three weapon classes in the open-source literature meet all three criteria: Russia’s Avangard, China’s DF-17 / DF-ZF, and the United States’ Dark Eagle. Most of what the press calls hypersonic fails at least one of these tests.<br>The Kinzhal is an air-launched Iskander on a MiG-31. Russia claimed Mach 10. A Ukrainian Patriot operator measured Mach 3.6 and shot it down.1 The Oreshnik is an intermediate-range ballistic missile with a six-warhead MIRV bus. It comes down very steep and very fast on a lofted ballistic trajectory. It does not glide. The Zircon is a scramjet that climbs to about 28 km, cruises at Mach 8 to 9, and dives. It does not glide either. Iran’s Fattah-1 is a maneuvering-RV MRBM. None of them is what this post means by “hypersonic.”
Showing observed figures (independent measurements)<br>SystemCountryTypeSpeedRangeManeuvering HGV?
First you have to see it<br>Ground radar is line-of-sight. The Earth is round. Anything below the horizon is invisible.<br>How far is the horizon? Imagine a radar on the ground, looking up. The line of sight grazes the surface tangentially and then leaves into space. Anything above the line is visible. Anything below is hidden behind the curve. Over-the-horizon radar is the exception, not the rule, and I set it aside here.<br>The distance from radar to the horizon, when the target is at altitude $h$, is given by simple geometry:<br>\[d \;\approx\; \sqrt{2 \, R_e \, h}\]The square root is the part that matters. Doubling altitude only multiplies horizon distance by about 1.4.<br>A ballistic warhead at 1,000 km altitude is visible from 3,570 km away. At Mach 20 closing...