Yes BUT WHY? when MBDA swears by the Aster with a 12g lateral acceleration what was the reason for something like the Barak-8 (I mean 80g seems exorbitant, in fact I had a nice talk with folks from the IWI and they said they were happy to trade range and speed in the design for said figure)?
Depends on the philosophy of design and intention, specifically what kind of targets are you going after.
These are
SOME of the target factors at the philosophical level:
- Aircrafts are highly unpredictable in their behaviors. Unpredictability does not equate to maneuverability. It simply means the missile have no way of knowing with any degree of certainty what the target is going to do next. Fighter aircrafts are the most difficult for any missile designer because a fighter aircraft have high maneuverability and is unpredictable in its behavior.
- Ballistic missiles have low maneuverability and are quite predictable in their behaviors.
- Helos have high maneuverability and are unpredictable in their behaviors but because they often operate at altitudes below 1000 meters, they have high Z axis constraints, meaning how much up/down they can go and the rate of that change, thereby limiting how unpredictable they can be.
- Ships have the lowest maneuverability quotient and have the most predictable behaviors. Same as with tanks or any other target types limited to 2D space.
So let us take ballistic missiles as targets for now...
A ballistic missile operate in 3D space but by virtues of its own philosophical design based on its own targeting philosophy, its x-y translation capability is quite limited by design. Its targets are practically fixed ground locations so why should it bother to maneuver other than to compensate for atmospheric interference ? Once launched, its flight behaviors are pretty much mathematically fixed. Its own body -- a mostly empty tube -- also limits its maneuverability.
If you are going to design an interceptor against ballistic missiles, ask when are you going to launch this interceptor and where.
If the interceptor is going to be launched in line-of-sight situations, as in the interceptor can 'see' the target -- the ballistic missile -- within its own sensor view, you would want an immediate orientation capability to your interceptor, as in if the sensor says the target is x-y degrees from boresight (center), the interceptor must reorient as fast as possible. In this situation, you want a high G capable flight controls system for your interceptor. High G as in double digits. You want your interceptor to acquire initial target resolutions as soon as possible so it can begin to calculate where the target is going to be based upon the target's own design philosophy. Against an ascending ballistic missile, those calculations are not going to be complex.
If the interceptor is going to be launched in non LOS situations, there is less to no need at all for a high G capable flight control system. You do want your interceptor to arrive at the ballistic missile launch point as soon as possible, of course. So you would give it high acceleration and cruise speed capability. You would want a wide area view for your sensor or combination of sensors. For example, wide area view staring IR sensor for initial target acquisition, then pencil beam radar for constant target focus and trajectory prediction. By the time the interceptor arrive at the ballistic missile launch point, that ballistic missile will most likely be at altitude and/or in its course correction arc, aka 'gravity turn', which is gradual, making trajectory prediction simple. There is no need for a high G capable flight control system here.
But you do not have the luxury of designing so specific an interceptor, one for LOS situations and one for non. Your customer specified portability to compensate for either situation. What if the interceptor is launched from a non LOS situation but acquire the target in only a few seconds ? How quickly do you want your interceptor to reorient itself ? What kind of flight control systems available ? The more capable, the higher the cost, and most likely more physically complex, which will demand more volume space in your interceptor. If your customer specified that he will never be able to get into an LOS situation, then your design task will be much easier, correct ? For a customer like the US military, what are the odds of that request ?
Now you must determine what kind of navigation-guidance laws for your interceptor, for example...
Proportional navigation - Wikipedia, the free encyclopedia
Proportional navigation (also known as
PN or
Pro-Nav) is a
guidance law (analogous to
proportional control) used in some form or another by most homing air target
missiles.
[1] It is based on the fact that two vehicles are on a
collision course when their direct
Line-of-Sight does not change direction. PN dictates that the missile velocity vector should rotate at a rate proportional to the rotation rate of the line of sight (Line-Of-Sight rate or LOS-rate), and in the same direction.
Anti-radiation missiles have beamrider navigation laws. First generation air-air missiles have simple Pure Pursuit laws, which demands only tail chase situations.
This gent seems to know a lot about missile guidance laws...
http://in.linkedin.com/pub/gaurav-sharma/27/601/a51
Missile Guidance and Control"
Project deals with the preparation of preparing a model and then writing code for guiding missile to the target. Specifically proportional navigation law is chosen out of the four commonly known laws ie. Velocity pursuit law, proportional navigation, command to line of sight & beam riding to guide the missile. The commanded acceleration of the missile was found out on the basis of this law and the simulations are performed on 3 degrees of freedom model & 6 degrees of freedom missile model.
If your targets are going to be the 2D type, as in ships and land vehicles, then the only z axis consideration you need is going to be for the interceptor itself, as in its orientation to the target, not if the target is going to change its own altitude. Ships and tanks do not fly. This will greatly simplify your navigation-guidance laws.
What kind of flight control system you chose directly affects what kind of laws you can install, which in turns will affect your interceptor's capability.
Aerodynamic exploitation give higher feedback as to what the flight control surfaces are doing than rocket thrust to make heading changes. Higher feedbacks means more precision in interceptor orientation towards targets, whether that target is a ballistic missile or a fighter aircraft. For the Aster using rocket thrust, I guess any feedback are going to be in the form of rate of fuel burn during that heading change to be correlated by accelerometer readings. That is a rather primitive system, in my opinion. I prefer direct mechanical feedback from the flight control surfaces themselves, via transducers at those surfaces, and correlated by accelerometer readings. On the other hand, if the interceptor is going to be used in distances of less than 150 km and with the speed of the interceptor itself, the feedback precision preferable in mechanical flight control systems are less or not needed at all. But then I know of no air-air missile uses lateral rocket thrusts to make heading changes against highly maneuverable and unpredictable targets like a fighter aircraft.
Another consideration is sensor capabilities. The higher the sophistication level of the sensor package, the greater the need for precision in everything else, from Propulsion to Flight Controls to Navigation-Guidance laws. The higher the precision and integration of these sub-systems, the less the need for an explosive warhead, which reduces weight and in aviation weight is a penalty. If your target type is 2D, as in ships and tanks, then you have to deal with ground clutter, IR or radar, which may give false z axis readings about the targets. So now may be your navigation-guidance laws are not so simple as previously thought because what if your sensor correct itself to give a new target location that have a new z (elevation) coordinate, now your navigation-guidance laws must recalculate to compensate as if your interceptor is going after a fighter aircraft instead of a tank because that tank just have a 10 meters elevation difference in a few micro-seconds of interceptor flight.
What I gave is just a small taste of what are needed to design an interceptor. This is why designing these weapons systems literally take years of constant hard work and budgeting maneuverings. While one company is busy working on a design under a set of philosophical constraints, another company in another country that may be hostile to your own is working on a different interceptor design with newer technology that widen those philosophical constraints. You probably do not know of those advantages. Or may be while you are well into the R/D process and entering production, you became aware of the newer technologies. Now what ? The contracts are already signed and the military establishment is already making changes to its own defense doctrines based upon your product -- as you claimed whatever it does. You claimed your missile can do collision course intercept so now your country's air force is going to tell its pilots that they can do collision course dogfights. If you failed or if the other guy's missiles are better, your country's pilots are going to die based upon your words and work.
