This is a fascinating story about global supply chains and advanced weapons development. But I can’t get past one irksome detail. https://www.washingtonpost.com/national-security/china-hypersonic-missiles-american-technology/2021/04/07/37a6b9be-96fd-11eb-b28d-bfa7bb5cb2a5_story.html

It’s a small thing in the context of the overall story, and I certainly don’t mean to pick on this particular reporting team, but it keeps coming up, so let’s talk about “hypersonics.”

China’s DF-17 carries a hypersonic glide vehicle, or HGV. Here’s the thing about any HGV: it will fly *more slowly* than a ballistic missile payload, other things being equal.

So when I saw this, it lit up my pet peeve detector.

An HGV might be tough for a defensive system to handle, but not because of its speed - which, again, is relatively *low.*

Why is it relatively slow? Two points. 1) Both HGVs and ballistic missile reentry vehicles (RVs) are mounted on rocket boosters. When the booster burns out, the missile has reached its top speed, regardless of what it carries.

2) After that, the RV sails on an arc through space, slowing as it rises, accelerating as it falls back to earth. It’s only in the atmosphere briefly before it reaches its target, at which point it’s going about as fast as it was at burnout. But the HGV...

But the HGV doesn’t sail through space. It dips right back into the atmosphere after boost and glides all the way to its target, *continuously slowing the entire way.*

So if *speed* is the most important variable—and it definitely seems like *the* big selling point for HGVs with Congress and the public—then it bears repeating that there is nothing, nothing faster than a ballistic missile.

Threading error. Continue here: https://twitter.com/joshua_pollack/status/1380169911725654021