【讀者分享🛰️】難以捉摸的軌跡、而不是速度，才是「超高音速導彈」的最大突破 (Patreon)

【按：日前訪問了Neo Hong Kong 軍武器研Larry談論俄羅斯的「超高音速導彈」，一位匿名讀者希望分享以下回應。Larry表示在其平台已詳細解釋，有興趣的網友可以重溫參考。】

There are some misconceptions on Larry@Neo Hong Kong regarding hypersonic missiles and ICBMs. He mentioned that the longer the range, the slower the speed. That is a misconception I don’t know where he picked up from. 

ICBMs reach the speed easily over Mach 23 at reenter phase (ICBMs’ trajectory goes to space, cruise, before reenter to gain speed). Hypersonic weapons is less than Mach 10. The main difference is that ICBM’s B means ballistic - basically a parabola that allows minor adjustments only. So once you have spotted its launch origin, angle, and basically you can calculate its trajectory and the time it will reach its target. So it is relatively easy to intercept. 

“Hypersonic missiles”, however, are traveling at suborbital altitudes, thus gaining less speed from the orbital mechanics. But the catch is that it can steer significantly from its trajectory in the middle of the flight to strike its target. So instead of a parabola, it has too many possibility to change course in middle and interception becomes impractical.

And since the earth is a sphere, the curvature of the earth’s surface hide distant objects behind. So radar cannot detect distant objects behind the curvature. And since the parabola of an ICBM travels rather high up onto orbital altitude before reenter, that means it shows up earlier on the radar screen of the defender’s side (higher altitude, breaking through the horizon earlier). Since hypersonic missiles stay at suborbital altitude, it can stay behind the horizon for longer. 

I suspect that current missile defense systems depend more on satellites instead. So regarding detection and calculation of basic trajectory, this is not a big advantage anymore.

Another advantage for hypersonic missiles is that it is traveling at suborbital altitude and not a parabola. They do not have the problem of “impossible trajectories”. Parabolas connecting two points on a sphere have limitations. For example, famously, ICBMs launched from northern hemisphere to a target in northern hemisphere, say from Russia to the US, will not take an Antarctic route since it’s limited by the parabola.

These are actually about physics.

Many people are misled by the name hypersonic and think that it’s the speed that gives it it’s edge. Comparing to cruise missiles flying within the atmosphere, yes. But not to ICBM. You may ask Neil deGrasse Tyson to make an explainer on this on Star Talk. Lol

Actually, hypersonic missiles, from what I read from open sources, are pretty much like the Fractional Orbital Bombardment System developed by the USSR. Striking so short range targets with hypersonic missiles is not so meaningful I would say. Hypersonic missiles are useful in a sense that it can swerve and avoid being intercepted. But at such a short range, I wonder how many swerves they could have performed before hitting the targets. Since the US has almost certainly monitored the data of the launch and maybe even got some data regarding their trajectories, it may give out some intelligence about the weapons’ readiness.

Speed, manoeuvrability, and accuracy are like a trilemma. I think it is hard to not sacrificing at least one to achieve the other two.

▶️Neo Hong Kong 軍武器研主持Larry：俄羅斯以秘密武器「高超音速導彈」攻擊烏克蘭，能改變戰局嗎？
https://www.youtube.com/watch?v=bCyz7ZtV6FU