Hypersonic flight: A new fuel for jets and missiles is on the cards
economist.com
economist.com
1) Boron Carbide and Boron Nitride particles form in the exhaust. These are extremely abrasive, destroying downstream engine components. They also make the exhaust plume highly detectable over long distances - think of the particles like soot from a coal burning ship.
2) The fuels are extremely corrosive, and thus you can't leave a tank full with them, and even when you do fuel up, you can't run on pure boranes, you need to mix them with other fuels. This means you can't keep a boron fueled missile on standby, so its speed advantage is rendered moot except for surprise first strikes. Further, in diluting the fuel the performance gains are reduced.
3) Boron based fuels suffer from incomplete combustion, dramatically reducing real performance below theoretical values.
4) Manufacturing and storing these chemicals is incredibly dangerous and expensive. One of the major reasons for the initial program's abandonment was that a production plant exploded. These safety concerns were damning in the age of atmospheric nuclear tests, one can imagine the difficulty of production in a modern regulatory environment.
In short, boron based fuels offer only questionable performance gains at very high economic, technical, and human costs. I won't say there is no future at all for them, but the idea that they are the fuel of the future is laughable.
The combination is diborane (B2H6) and hydrazine (N2H4). These react to form boron nitride (BN) and hydrogen. This reaction is exothermic and by itself would give an Isp of maybe 250 s, IIRC. The gas is hydrogen rich, and would be great for feeding into the air turborocket, or into a scramjet, for combustion with air.
>Fifteen years ago people used to ask me "What is an exotic fuel any- way?" and I would answer "It's expensive, it's got boron in it, and it probably doesn't work." I had intended, originally, to entitle this chap- ter "The Billion Buck Boron Booboo," but decided against it on two grounds. The first was that such a title might conceivably be consid- ered tactless by some of the people who authorized the programs con- cerned. The second reason is that it would not be completely accurate. Actually, the boron programs did not cost a billion dollars. It just seemed that way at the time.
In order to achieve the same goals while avoiding the safety issues of boron fuels, the Decilin-M fuel for the Zircon missile is thought to use engineered hydrocarbons (the exact composition is unknown) with polyethylene to thicken the solution with aluminium nanoparticle added.
Railguns are a lot more likely, but I think we still don't have "barrels" that survive firing more than a couple shots before replacement.
If you use a satellite, you might as well put a larger concave mirror on it to focus sunlight. A nearly 100 year old weapon concept that luckily never happened [1]
Also, flight at Mach 9 can be done at low altitudes. Just not for very long and only once.
Also, I don't think you appreciate the amount of energy in a 5 ton missile going at hypersonic speeds. For it to slow down within 200m, it needs to basically stop in 0.075 seconds.
For non-aerodynamic fragments, this is not very difficult. Furthermore 0.075 seconds for a 200m braking distance seems too short unless you're flying at something like Mach 15. But you're not flying at Mach 15 if you're 200 m from a ground target because you can't fly at Mach 15 at a 0-200m altitude -- certainly not with something powered and guided and equipped with sensors. Maybe a solid metal rod could do that but this ain't it. So it seems quite reasonable to assume that 200 m off the target, the vehicle will be at a significantly slower speed, much like ICBM RVs don't impact their targets at Mach 25 either.
Instead of hydrocarbon use hydrosilicon. Thought to be unstable (like "big bada boom" unstable) Peter Plichta discovered that "Silanes with chains of seven or more atoms of silicon per molecule are stable and can be pumped and stored very much like gasoline and other carbon-based liquid fuels."
http://www.rexresearch.com/plichtasilane/plichta.html
They burn nitrogen and are said to make lightning instead of flames.
> The combustion process of hydrosilicons is fundamentally different from the exclusively oxygen based combustion we know from burning hydrocarbons. In a sufficiently hot reaction chamber, silanes separate into atoms of hydrogen and silicon, which immediately mix with the oxygen and nitrogen of the air. The hydrogen from the silanes and the air's oxygen now burn completely leaving only water vapor, bringing the temperature of the gases close to 2000 degrees C.
> Since there is no more oxygen, no silicon oxide can be formed in the following phase. What happens instead is an extremely energetic reaction of the 80% nitrogen in the air with the silicon atoms present, that forms a fine powder called silicon nitride (Si3N4).
This means that to hit a moving target at Mach 9 (or about 3 km/s) you need to launch your 11m long rocket within either 9 or 120 km depending on the desired probability for a kill.
As a reference, an aircraft carrier can go over 50 km/h, the Chinese hypersonic weapons go about 1.7 km/s and have a range of at least 1000 km. How does that work out you wonder? Simple, they put nukes on their hypersonic missiles.
I'm assuming you mean km/h there? I'd love to see a boat going that fast.
A 50km/s vessel carrying hypersonic missiles would be like bringing turtles on a transatlantic flight!
Hypersonic missiles pull just as many Gs as any other missile, they are not any less maneuverable.
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.
Considering the mediocre L/D ratio of hypersonic vehicles, this seems extremely optimistic to me.
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!
> 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.
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.
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 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!
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.