If they only pull as many Gs as any other missile, then their turning radius will be larger proportional to the square of the velocity ratios. For example a Mach 10 missile pulling the same Gs as a Mach 2 missile will turn in a circle 25 times larger.
Or, to put it differently, if the missile is approaching its target and X seconds before impact decides to change the impact point, or perhaps evade a countermeasure, a Mach 10 missile will be only able to make 4% of the correction a Mach 2 missile with the same transverse acceleration would be able to make from the same distance.
Turning radius doesn't matter though. What matters is being able to outmaneuver interceptors and cause them to lose energy. What matters for that is only Gs.
The turning radius is completely irrelevant if you want to evade a countermeasure. All that matters is how far you are from where the countermeasure is going. That's measured in Gs.
Similarly, there's not going to be any issue changing impact points, the only issue is changing targets, but I don't see where that would be useful.
> The turning radius is completely irrelevant if you want to evade a countermeasure. All that matters is how far you are from where the countermeasure is going. That's measured in Gs
The problem here (for the hypersonic missile) is that the countermeasure is mirroring this: it's interested where the hypersonic missile is going to be X seconds from now. And a high velocity target shrinks that circle of possibilities - very substantially, as I've noted, inversely proportionately to the square of velocity.
As for Gs, today we have missiles like Python 5 than have no problem pulling something like 40 Gs. One reason for that is that they're optimized for maneuvering, not for extreme velocities. Just getting to and maintaining extremely high velocity is difficult enough so it seems unlikely that the incoming hypersonic vehicle would be capable of both, especially in terminal flight regime for which it isn't optimized.
Also, one obvious problem with your reasoning is that your hypersonic missile isn't likely to be equipped or capable of evading whatever your target is throwing at it. An antimissile is going to be small, most likely much smaller than your hypersonic missile. That alone will make the antimissile hard to detect. Furthermore, assuming that your hypersonic missile will be hypersonic in the terminal phase, issues of aerodynamic heating etc. will quite likely make it difficult for any kind of sensor to operate. Especially the need to separate the antimissile from the background of the target won't make it any easier. So "wanting to evade a countermeasure" is nice but perhaps not as feasible as one might think. We're generally not even doing it today when it's easier. Not quite sure why it should work for a vehicle for which it will be substantially harder.
You said it yourself, the interceptor is interested in knowing where the missile will be in X seconds.
Let us think about this mathematically. Let us use the following coordinate space - the missile travels along the X axis.
The missile may accelerate on the ZX plane by, say, 20Gs.
This means that after x seconds the missile may be in a circle 98m * x^2 in radius = 20G * 9.8m/Gs * 1/2 * t^2 which is the basic kinematic equation.
So if we want to answer the question, how much uncertainty is there in where the missile will be in X seconds, the correct metric is actually lateral G force, not turning radius.
The interceptor missile cannot simply have a higher lateral G than the target and be assured it will hit it. Indeed, the Python 5 missile you mentioned wouldn't be able to hit the hypersonic missile.
Why? It's too slow. The Python 5 will hit Mach 4 shortly after launch and impact around Mach 2 or so. Meanwhile the hypersonic missile will maintain Mach 7+ throughout.
This means that despite higher lateral G forces, the Python simply will not have the energy to maneuver with the hypersonic missile. Consider the following scenario, as an example that is simple to understand. The Python missile, going at Mach 3, will go towards where the missile seems to be going. This is hugely problematic for the Python 5, it means that every movement the hypersonic missile does will be amplified by the pursuant missile as it has to "get in the way". So if the missile, 150km away, increases pitch by 4 degrees, the Python 5 might have to immediately pitch up almost 30 degrees, bleeding of a lot of energy.
Then if the hypersonic missile pitches down to -4 degrees, it will seem to impact now a full 13km lower. Now the Python, already slowed down, has to maneuver down 50 degrees!
So because of the speed difference, the interceptor now has to engage much more G force than the hypersonic missile, because it has to position itself in the path of the hypersonic missile due to its speed being too low to pursue it.
This is made even worse by the fact that this very maneuvering is going to reduce the speed of the interceptor, which can't make it back up because it doesn't have an air breathing engine!
This is the reason why the Radar Warning Receiver made the early long distance missiles ineffective. Despite in this case the missiles being faster than the planes and despite being able to pull off more Gs, their inability to regenerate kinetic energy meant that fighter could bait them into losing their energy, reducing their speed and shaking them off.
Now the same problem repeats itself, except that the hypersonic missile is now faster than the interceptor and the maneuvrability gap is much lower.
That's all to say, if you want to evade intercepting missiles, what matters is : lateral G forces, speed, and energy regeneration. Nothing else!
> So if we want to answer the question, how much uncertainty is there in where the missile will be in X seconds, the correct metric is actually lateral G force, not turning radius.
I'm sure that if you draw the situation for yourself on a paper, it will be more readily apparent to you how the two are basically the same thing.
> So if we want to answer the question, how much uncertainty is there in where the missile will be in X seconds, the correct metric is actually lateral G force, not turning radius. The interceptor missile cannot simply have a higher lateral G than the target and be assured it will hit it. Indeed, the Python 5 missile you mentioned wouldn't be able to hit the hypersonic missile. Why? It's too slow. The Python 5 will hit Mach 4 shortly after launch and impact around Mach 2 or so. Meanwhile the hypersonic missile will maintain Mach 7+ throughout.
I don't see how what you wrote makes sense. You've limited yourself to the transverse plane. For point defense, that makes perfect sense. But it also makes the longitudinal Mach 7 meaningless, except for the dynamics of the encounter and impact, since that movement doesn't happen in the transverse plane.
> So if the missile, 150km away, increases pitch by 4 degrees, the Python 5 might have to immediately pitch up almost 30 degrees, bleeding of a lot of energy.
You wouldn't be hitting it in this phase of flight. I was speaking solely of terminal defense. Therein might lie your confusion.
Hypersonic get their claim for manoeuvrability by comparison with their faster cousins the ballistic missiles, not short range (less than 60 km) air-to-air missiles that have sort bursts of Mach 4.
This is wrong. Hypersonic vehicles are thought to have maneuvering accelerations over 15Gs. That's more than most cruise missiles.
Of course they will not be as maneuverable as A2A missiles. But what's the point? If you want to evade A2A missiles already going slower than you you're using energy to your advantage so 10Gs is more than enough.
As it stands hypersonic missiles are more maneuverable than all other missiles including cruise missiles short of specialized A2A missiles. So for the purpose of evading interceptors and penetrating defence systems it's more than enough.
The X-15 was able to sustain G forces in excess of 15Gs. The limit was that its chassis would break apart.
Maneuvrability works very differently for high-trust, vectored, supersonic vehicles. That's why A2A missiles can pull of 50Gs despite very low L/D ratio, speed helps a lot.
Hypersonic flight magnifies this even further. I mean, look at the X15, it was able to do more than 15Gs despite having lower relative thrust and non-vectored engines, at higher altitudes!
The X-15 to my knowledge was not under thrust when maneuvering in the hypersonic regime, so I don't understand the connection here. And because of being unpowered and hypersonic, it would still be losing speed more rapidly than even an unpowered airplane or missile flying at a lower velocity.
> That's why A2A missiles can pull of 50Gs despite very low L/D ratio
No, they can do this because they're small, and being small means a low ballistic coefficient because your mass shrinks faster than the aerodynamic-force-generating area. But a 100kg missile is not what you use to strike very remote targets on the ground.
Hypersonic missiles pull just as many Gs as any other missile, they are not any less maneuverable.