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Comment by superkuh | Hacker News Reader

Correct. No one has "real" hypersonic missiles that travel in the atmosphere for extended periods(*1). The heating problems for shock impingment in non-"simple conicals" has *not* been overcome and won't be. "Hypersonic" missiles are mostly just ICBMs with a very brief passage through the dense lower atmosphere where there's enough lift. And if they try to go higher up to escape the heat flux there's not enough for lift. See, https://exrocketman.blogspot.com/2022/06/about-hypersonic-ve...

Tangential: the USA had a mach 5 phoenix missile back in the 1970s on the F-14 and now they're re-fitting them with new guidance/etc to make a hypersonic test bed.

*1: Of course, when you're going hypersonic you only need tens of minutes to travel to the other side of the Earth.

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"Sprint accelerated at 100 g, reaching a speed of Mach 10 (12,300 km/h; 7,610 mph) in 5 seconds. Such a high velocity at relatively low altitudes created skin temperatures up to 6,200 °F (3,430 °C)"

This is in 1975.

But sprint did not have an airbreathing engine and was intended for close range interception and not long range missions.

https://www.youtube.com/watch?v=YZZV464z9g8

That's a pretty fast missile...

(RV zips by at 3x the speed)

Mach 10 is almost too fast to be hypersonic! Hypersonic is the range around Mach 5-8.

There are various types of ballistic missiles that go faster than this (and have been doing for decades) but since they are old they aren't as sexy as "hypersonic missiles".

The new thing is trying to go hypersonic in the atmosphere for more than a couple minutes so you can use it for lift. But either there's too much heat or not enough lift.

No, this is in fact not categorically new. MaRV and related demonstrated 60 G pull up to horizontal glide maneuvers.

The technology of a HGV and a maneuverable re-entry vehicle are essentially the same. The main reason for talking about "hypersonics" as a separate category today is to emphasize flight profiles that would not be interpreted as nuclear strikes.

As I understand it, it's not about “not being interpreted as nuclear strike” — since almost every Russian missile (including anti-ship missiles like Kh22 and the likes) could potentially carry a nuclear warhead, they explicitly don't care about the ambiguity, while the Western doctrine is diametrically opposite, explicitly aiming for as little ambiguity as possible to keep the escalation risk low. And your interpretation basically goes against both doctrines. — But more about keeping a low trajectory so that the missile stays below the early-warning radar horizon for most of its flight, striking without warning, where a ballistic missile gets within the LOS of radars quite early due to its trajectory.

Yeah, ICBMs have slightly glidy, menuevering entry vehicles. But these don't fly. It's more like falling with style. And they certainly don't have shapes that aren't simple conicals. Otherwise the heat from compression and where the shockwaves impinge on the complex structure completely overcomes materials tech and any possible heat soak or re-radiation.

You beat me to it! This timecoded link shows the launch sequence of the Sprint with a tracking shot of the vehicle itself. Pretty remarkable watching it start to glow white:

https://www.youtube.com/watch?v=3dl9Ovwmnxw&t=220s

I think this is the first video on that channel where the subject can match the guy's cadence. It's a great overview of the development of the Sprint though, worth watching if it's of interest.

Ah yes, Sprint - for when having a 5kt bomb go off over your city is the good outcome.

Terminal ballistic missile defense is hard!

Seems like you almost wouldn’t even need explosives if you could push that through an aircraft carrier at that speed.

Who could build something like that today?

Low altitude air breathing hypersonics are unlikely to ever be practical. That speed at low altitude is just a fire ball.

Air breathing hypersonics at altitude are real though. The US has successfully tested scramjets in the past. And currently has the HAWC program which has successfully flown twice now.

Like the Pershing IIs the US deployed in 1983. https://en.wikipedia.org/wiki/Pershing_II

What about scram jets though?

they have to go high for reasons mentioned in parent. Their launch altitude is normally 40,000ft to begin with. then they climb from there.

the Standard Missile "SM-3" goes Mach 8 we have had hypersonic weapons since the 1930s. This is a goalpost shift to say they have to cruise AND be hypersonic which is impossible due to the curvature of the earth which is really the premise of the entire argument is that russiaboos think the earth is flat and Nato isnt like 100 years ahead of Russia in military technology.

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