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DARPA's hypersonic scramjet achieves successful flight

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Re: DARPA's hypersonic scramjet achieves successful flight

#131

Post by rand846633 »

burkaman wrote: post #111
corndoge wrote: post #87

Is it just me or has the Pentagon and the complex largely replaced the word "soldier" with "warfighter"? Feel like I've seen it a lot lately and I'm not sure what the change implies

I assume someone thought it sounds cooler and will help them recruit. It's an awful term, although maybe it will make it slightly harder for people to claim that the US military is a force for good because "our warfighters are global peacekeepers". Really highlights the absurdity.

We as people should start refereeing to them as “nation state murder for hire professionals”.

Re: DARPA's hypersonic scramjet achieves successful flight

#132

Post by sudosysgen »

JumpCrisscross wrote: post #121
jhgb wrote: post #118

Earlier quoted context omitted.

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.

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.

Re: DARPA's hypersonic scramjet achieves successful flight

#133

Post by sudosysgen »

jhgb wrote: post #117
jack_pp wrote: post #110

Earlier quoted context omitted.

Isn't the point of these weapons that even if you can detect them they are too fast to intercept?

They're too fast to catch up with (i.e., from behind). But if someone sprints straight into your fist, that person will be hurt even if your fist itself is fully stationary. In fact this probably makes them somewhat more vulnerable to an interceptor's warhead's shrapnel: even lesser damage, survivable for a slower target, might be much more serious for a target flying at high Mach speeds (not the mention the imminent…

That only works if your rate of tangential acceleration is quite low. The reason why you'd make an airbreathing hypersonic instead of a ballistic missile is so it could manoeuvre.

Re: DARPA's hypersonic scramjet achieves successful flight

#134

Post by jhgb »

sudosysgen wrote: post #123
jhgb wrote: post #84

Earlier quoted context omitted.

> The missile you're hitting them with is going to be heating up the air around the camera probably at the same temps as the missile it's intercepting That would only apply if it were to hit it at comparable speeds. That's not necessary in many cases, especially in point defense when the target is heading towards you. Furthermore the limited time of flight of the interceptor might also allow for active cooling of the…

Interception against an actively manoeuvring target is a question of kinetic energy. If the intecepting missile is smaller all the hypersonic missile has to do is zig-zagging randomly and you're toast. If you're going to wait for the hypersonic missile to be close enough that this isn't a problem, you have the issue that your missile won't be able to manoeuvre right and might still be building up velocity. Plus there…

> Interception against an actively manoeuvring target is a question of kinetic energy. If the intecepting missile is smaller all the hypersonic missile has to do is zig-zagging randomly and you're toast.

What you're describing is not a matter of kinetic energy (clearly if it were about kinetic energy, this would be defeated by making the interceptor weigh 30 tonnes) but a matter of transverse acceleration. On that matter, as far as I understand it, current AAMs/SAMs are somewhere in the 50g region. I strongly suspect that hypersonic vehicles due to their lower L/D are nowhere near that -- hell, many of them seem to have a hard enough time flying straight, if US military's experience is of any relevance here.

Also, due to low L/D ratio in the high Mach region, if your missile is zig-zagging randomly, it won't stay fast for long. And if it's not zig-zagging randomly, then the question is how it gets the information how to zig-zag, since the nose of a hypersonic vehicle seems to be an extremely poor sensor platform -- which you admitted yourself. It's virtually certain that it won't be able to see the interceptor.

> The issue isn't the IR window, it's the air directly in front of the interceptor missile, which has to target from the frontal aspect.

It seems unlikely that the interceptor will have to fly at a comparable speed in a frontal aspect interception situation (considering that it doesn't need to catch up).

But as for terminal interception, I suspect that here the inverse-fourth-power-of-distance operation of an active radar homing solution might help you if all else fails -- at a small enough distance this will work even better than the inverse square applicable to passive optical/IR detection.

> would be unable to resolve any detail about the missile, so it would have no way of telling the difference between a missile and a flare of the same brightness and color.

It would seem that the easiest way to distinguish a flare would be to look if it's in a controlled flight? Unlike a flare, the hypersonic vehicle will continue flying, and the difference is readily apparent. Besides, you can't have that many flares on it, so you can't keep firing them continuously -- again, the only thing that's available to you if you can't see the incoming interceptor.

Re: DARPA's hypersonic scramjet achieves successful flight

#135

Post by rsj_hn »

burkaman wrote: post #111
corndoge wrote: post #87

Is it just me or has the Pentagon and the complex largely replaced the word "soldier" with "warfighter"? Feel like I've seen it a lot lately and I'm not sure what the change implies

I assume someone thought it sounds cooler and will help them recruit. It's an awful term, although maybe it will make it slightly harder for people to claim that the US military is a force for good because "our warfighters are global peacekeepers". Really highlights the absurdity.

It is politicians that keep insisting the job of the army is to get Afghanis to read and adopt liberal values.

Peacekeeping is not popular in the army, for good reason. They are there to fight wars, not deliver social programs, build nations, or referee conflicts.

If using language like "warfighter" can get the politicians to lay off on using the army for things other than fighting wars, then the clumsiness of the phrase is worth it.

I suspect, though, that this is just more corporate-speak infiltrating the military bureaucracy.

Re: DARPA's hypersonic scramjet achieves successful flight

#136

Post by sudosysgen »

jhgb wrote: post #118
JumpCrisscross wrote: post #113

Earlier quoted context omitted.

> even if you can detect them they are too fast to intercept? No. They still travel far slower than ballistic missiles. Their advantages are in being able to fly low and (theoretically) manoeuvre to avoid interceptors. They’re an evolution of cruise missiles, not strategic ballistic missiles.

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.

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.

Re: DARPA's hypersonic scramjet achieves successful flight

#137

Post by sudosysgen »

dgregd wrote: post #73

How a such hypersonic missile locks a target? Does it use a radar or some optic system? I guess that plasma around the body might disrupt conventional guiding systems.

Ionization applies starting at a given frequency depending on heat. You have to reduce the heat around the radar or move the radar somewhere where the air is less hot. You also have to use a radar of a higher frequency.

Re: DARPA's hypersonic scramjet achieves successful flight

#139

Post by [deleted] »

jhgb wrote: post #84
sudosysgen wrote: post #79

Earlier quoted context omitted.

Plasma stealth is an existing approach to radar stealth that is made easier by hypersonic speeds. Infrared targeting of multiple hypersonic missiles is easier said than done. The missile you're hitting them with is going to be heating up the air around the camera probably at the same temps as the missile it's intercepting, and a base station wouldn't have enough resolution to guide a missile accurately from 100+km aw…

> The missile you're hitting them with is going to be heating up the air around the camera probably at the same temps as the missile it's intercepting That would only apply if it were to hit it at comparable speeds. That's not necessary in many cases, especially in point defense when the target is heading towards you. Furthermore the limited time of flight of the interceptor might also allow for active cooling of the…

[deleted]

Re: DARPA's hypersonic scramjet achieves successful flight

#140

Post by jhgb »

sudosysgen wrote: post #136
jhgb wrote: post #118

Earlier quoted context omitted.

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.

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 pa…

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.
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