Pangram verdict · v3.3
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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.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.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.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.What “hypersonic” actually means“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.
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. Mach number M 8.0 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: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.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)SystemCountryTypeSpeedRangeManeuvering HGV?First you have to see itGround radar is line-of-sight. The Earth is round. Anything below the horizon is invisible.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.The distance from radar to the horizon, when the target is at altitude $h$, is given by simple geometry:\[d \;\approx\; \sqrt{2 \, R_e \, h}\]The square root is the part that matters. Doubling altitude only multiplies horizon distance by about 1.4.A ballistic warhead at 1,000 km altitude is visible from 3,570 km away. At Mach 20 closing speed, about ten minutes of warning.A glide vehicle at 30 km altitude is visible from 618 km away. At Mach 8 closing speed, about 260 seconds.This is the central reason the 20 to 60 km band is the strategic sweet spot. Lower and the vehicle melts. Higher and it becomes visible from a thousand kilometres out.There are two ways out. Push the radar back, or push the sensor up.Pushing the sensor up is what the Hypersonic and Ballistic Tracking Space Sensor was built for. Two competing prototypes launched on a Falcon 9 from Cape Canaveral on February 14, 2024. L3Harris’s prototype works. Northrop Grumman’s does not. The Missile Defense Agency confirmed both in April 2025. The Space Development Agency’s Tranche 1 Tracking Layer, which is supposed to put another 28 fire-control-quality satellites in low Earth orbit, has slipped past its early 2026 deployment target because the optical inter-satellite links between satellites are not yet talking to each other reliably.2Even on the ground, the glider is hard to track once you see it. The plasma sheath around the vehicle in flight scatters and absorbs radar pulses.
The standard Swerling models that ground radars use to track ballistic re-entry vehicles do not work against a target whose radar cross-section depends on plasma state.3The good news, from the defender’s perspective, is that the same plasma that breaks radar makes the glider visible in the infrared from low Earth orbit. SBIRS and the new HBTSS prototypes see the glide vehicle as a bright dot in the 2 to 3 micron band for most of its glide. The future of hypersonic defense is in low Earth orbit. The future just is not here yet.Then you have to track itOnce a sensor sees the target, a defender’s job runs the same loop for every weapon: detect, track, discriminate, commit, fly out, intercept. Each link takes time:StageTypical budgetTrack convergence (need several radar returns)~30 sDiscrimination (is it a warhead, decoy, or chaff?)~30 sFire-control commit (compute solution, slew launcher)~15 sInterceptor fly-out (Mach 4–5 missile)~75 sThat is about 150 seconds of fixed budget before the interceptor is anywhere near the target. The defender needs the target’s flight time from radar acquisition to impact to be longer than 150 seconds, by enough margin to actually maneuver onto a hit.For a ballistic warhead at 1,000 km, this is easy. Ten minutes of warning. Plenty of time to run the chain twice if you miss once. For a glide vehicle at 30 km, this is brutal. 260 seconds of warning. After the 150-second kill chain the defender has about a hundred seconds left to maneuver onto a target that is itself maneuvering. Target altitude 40 km Closing Mach M 8.0 Radar horizon vs altitudeDefender's clock from radar acquisitionHorizon distance·Flight time to impact·Engagement window·When the bar in the chart above goes to zero, the defender cannot intercept from this radar with this kill chain.
The way out is to change the inputs: push detection further back with space-based sensors, forward-deploy the launchers, or build a faster interceptor with a shorter fly-out. Every modern hypersonic-defense roadmap is some combination of these three.The single completed counter-HGV engagement in US history was on March 24, 2025. The destroyer USS Pinckney, sitting off the Pacific Missile Range Facility in Hawaii, ran the kill chain end to end against an air-launched MRBM with a Hypersonic Target Vehicle-1 front end. HBTSS provided fire-control-quality tracks. Aegis baseline 5.1.5 took the cue. The SM-6 Block IAU got an engagement solution. The test was named Stellar Banshee.4No SM-6 was actually fired. The engagement was simulated. The press covered it as a successful counter-hypersonic test. That was half true. The kill chain ran. The interceptor did not.A live test, designated FTM-43, is on the schedule. As of May 2026 it has not occurred.Then you have to hit itSuppose the kill chain ran fast enough to get an interceptor in the air with seconds to spare. What happens next?The interceptor does not fly straight at the target. It uses a guidance law called proportional navigation, invented in the 1950s and still the standard. The idea is simple: turn at a rate proportional to the rate at which the line-of-sight to the target is rotating. If the target is non-maneuvering, this converges on perfect lead pursuit. The interceptor cuts the corner and arrives where the target will be. The engineering, against airliners and cruise missiles and ballistic re-entry vehicles, is by now a solved problem.But if the target maneuvers, two things go wrong simultaneously.The first is the acceleration-advantage rule. As a rule of thumb, to reliably intercept a target pulling $g_t$ of lateral acceleration, the interceptor needs to pull roughly $3 g_t$ of its own. The exact multiple depends on the geometry and how late the target jinks, but the direction is fixed. A glide vehicle in a casual 3-g turn wants a 9-g defender.
A 6-g turn wants 18-g. A 10-g turn wants 30-g, near the structural ceiling of many interceptors. Past that the airframe breaks before the geometry closes.The second is what fighter pilots call the stern chase. If the target’s velocity component pointing away from the interceptor exceeds the interceptor’s own speed, the interceptor cannot catch up. Once that condition holds, the gap only grows. A Patriot at Mach 4.5 chasing a Zircon at Mach 8 from behind has the same problem as you trying to chase a car at 200 mph on a bicycle. No amount of cleverness fixes it. speed Target track Interceptor Closest approach hit marginal miss Miss distance·Single-shot Pk·Interceptor TOF·Outcome·The single-shot probability of kill in the simulator above uses a Gaussian model around the miss distance, calibrated so a miss inside about 30 metres gives a high kill probability. Real air defense fires layered shots from multiple interceptors, and the cumulative kill probability rises with each one. But each interceptor costs millions of dollars against a target that may cost less. The wallet was supposed to be the constraint. It turns out, as we will see, that the wallet is the constraint after all.What’s actually flyingThe defensive catalog as of June 2026 is shorter than the press suggests, and most of it is not built for glide vehicles at all.