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Comment by jhgb | Hacker News Reader

But maneuvering at high velocities won't be that easy. As far as I understand it, your lift/drag ratio decreases appreciably with increasing Mach numbers. So either you'd have to limit your maneuvering, or you'd have to have a propulsion unit with ridiculous amounts of thrust - at a situation when any amount of useful thrust is hard to obtain, since we still don't know really well how to do propulsion in this regime.

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As a former aerospace engineer, I’m sceptical of the strategic value of hypersonics. Tactical? Sure. They’d have a better chance of taking out SAMs, light radar, et cetera. But the talk about these being carrier killers is, based on everything we’ve seen, off the mark. (Spending the cost of one hypersonic on a swarming attack would probably do more damage.)

The biggest difference between hypersonics and swarms of slow missiles is that the hypersonics can get there fast enough that you might not need high-quality targeting information. That's definitely a strategic advantage!

Also the 3M22 is estimated to only cost around 2 million dollars.

> hypersonics can get there fast enough that you might not need high-quality targeting information

The strategic systems hypersonics are hyped to hit have been hardened against ballistics. Hypersonics are slower than ballistics. (Their plasma envelope also makes them easier to track by satellite.)

This is a tactical evolution. Meaningful. Helpful. But not a strategic shift.

The big issue is that a ballistic missile may not be able to deviate as much from the expected position as it can search away from it.

I agree that they're not that different from ballistics but they still have considerable advantages.

> that you might not need high-quality targeting information

I don't see how this would work, unless of course you're talking about nuclear weapons. With a conventional warhead you still need to hit your target.

You can locate your own target if it's close enough - say 10-30 miles or so - from where you expected it to be. With a slower missile your target will have drifted a lot more.

I think taking out SAMs is huge thing. Or I am wrong?

Thrust is not the issue, the issue is net thrust. Essentially the missile/engine is compressing so much air that trying to get more air to produce more thrust doesn't work, you have to manage to increase efficiency, by increasing compression, without melting or blowing apart your engine

Once you manage to make significant net thrust making a bit more isn't that big of deal, it's really a critical point you have to pass.

Yes, that's what makes it even worse. Flying as fast as you can means you have very little reserve for velocity losses from extensive maneuvering.

> once you manage to make significant net thrust making a bit more isn't that big of deal

You’re still limited by your fuel and flight envelope. The latter which bleeds the former.

Hypersonic missiles will be harder to intercept than cruise missiles. Due to their novelty, they’ll also be harder than ballistics. (Ballistic projectiles don’t continuously illuminate their flight path. That permits for subterfuge options an air-breathing missile forfeits.)

These maneuvers are in the terminal phase. Knowing the reaction speed and the moment at which LOS is achieved as well as estimating the speed of the missile and it's acceleration one can calculate a relatively short period under which interception is possible. Outside of that there is basically no risk and thus no need for any maneuvers.

As for flight envelope we know from the X-15 that not that much is required to pull 10Gs at hypersonic speeds. There is no need for much more.

> maneuvers are in the terminal phase

One, this leaves the missile, which is screaming through the atmosphere, vulnerable in a way ballistics are not. (And visible in a way cruise missiles aren’t, either.) Two, if you have a carrier strike group in the middle of the ocean, this strongly restricts how much manoeuvring can be done. The target knows where you’re ultimately headed—if you tactfully manoeuvre into a blank patch of ocean, the strike group is fine.

> flight envelope we know from the X-15 that not that much is required to pull 10Gs at hypersonic speeds

The flight envelope restriction isn’t a structural one. If you have a known target, there is only so much manoeuvring the vehicle can aerodynamically do without slowing down to sub-scram speeds. Yes, you could supercharge the engine, but that cascades through another host of factors.

By the time that you're close enough to the strike group that you have a serious risk of seriously missing, it's already too late for the faster interceptors to be effective.

As far as only so much maneuvering you can do before being too slow for the engine, yes that's probably an issue for the HAWC, but scramjet missiles have been demonstrated to achieve Mach 9 in atmospheric flight which allows a lot of energy to bled out before you drop out below Mach 4.

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