Why can’t we put a space cadet from the newly formed Space Force in the nose of the interceptor, and have him shoot at the warhead as he zooms by? Intuition fails us with the speeds and acceleration. The space cadet would be mashed flat in the high-g blast-off. The speed of his bullets is 1/10 the speed of the target, almost as slow as the mail.

The hit-to- kill vehicle  is  devastating in head-on collision. The energy delivered to the target is the kinetic energy of the vehicle,   much large than the energy of an explosive charge. Purity of the concept is of no concern,  so one of the ways to turn a miss into a hit is an explosive charge that fragments the kill vehicle in front of the warhead.  Another enhancement, workable only outside the atmosphere, is an extensible “cow catcher”.  Both replace the head-on collision with smaller but sufficient mass to break  the target. Aerodynamics and the heat of air friction do the rest.

What kind of fragment, or other small object, is sufficient to destroy a warhead just from being in the right place at the right time? At collision speed, the kinetic energy is about the same as equivalent weight of TNT. But our study so far has been amenable to napkin calculations because of the binary definition of success, hit or miss. Materials lack that certainty. We don’t theorize about tank armor versus penetrating round; we try it out. The behavior of materials in extreme conditions is an experimental science.

Space junk and micrometeorites pose a threat to satellites. Shielding is thought to be practical up to an asteroid size of 1 cm. The shield is a double wall. The first wall shatters the asteroid into smaller pieces that cannot penetrate the second wall. But an asteroid is not engineered material. The toughest asteroids are nodular iron, which isn’t very tough.  Most are chondrites, made of small grains cemented together by pressure. A shield may be effective against the bulk of satellite debris. But a  titanium bolt, left over from an anti-satellite missile test, is an engineered material, with far greater penetrating power than a clod of dirt.

The small chance of a  pure hit-to-kill against a maneuvering target might be improved by release of a cloud of small engineered objects, with sufficient density  to insure destructive impact. The calculation of Part 4 can be repeated with a “hit” expanded  to the vicinity implied by the size of the cloud. This is standard with anti-aircraft missiles. But aircraft are the ultimate soft targets. It doesn’t automatically imply destruction of a warhead hardened against reentry. We have to think about it.

If a pack of high-tech BB’s were released in front of a hypersonic vehicle, would destruction result? Unlike the hit-or miss proposition, it depends upon details: shape, material, thickness, internal structure, and warhead vulnerability at point of collision. The BB’s could be the densest, meanest BB’s imaginable, tungsten with a depleted uranium center, yet success is not assured.

If a BB craters the surface, or puts a hole in it, it could disrupt aerodynamic control, or cause local heating, leading to destruction. Some obstacles to success:

• As soon as the BB’s are released, they are blown backwards in the air stream, losing kinetic punch.
• A hypersonic warhead has sharply sloping sides. Like the sloping glacis of a armored tank, the impact energy is reduced by the sine of the impact angle.
• The properties of carbon fiber plastics, of which Avangard is said to be made, can be vexing, as the Russians have discovered. But they also offer complex opportunities for manipulation, of strength and cleavage properties that vary sharply with angle.

Once the rivalry gets going, Avangard, or other hypersonic vehicles, could be equipped with “spare parts.” If there’s a lucky shot to the tip of the nose, it falls off, revealing — another nose. Unlike the original missile race, the Russians have plenty of throw-weight, which can be diverted to armor Avangard, and descendants, against threat.

A counter to plastic armor could be an ingeniously engineered micro-projectile.  A pointed shape, concentrating impact force, might be stabilized in the right orientation by a dispenser that imparts spin, or by a magnetic pulse.

Suppose we pass over the idea of a penetrating BB in favor of gumballs.  I’ve spent my life scraping these things off my shoes.  A gumball is a projectile with a soft core,  still very massive, to resist the aerodynamic forces of the slipstream.

When it hits Avangard, the gumball goes “splat!”, and  the soft, chewy core sticks on it, quickly setting to an adherent, thermally conductive ceramic. This disrupts the crucial thermal balance of the surface. Frictional heating does the rest, burning a hole, or causing thermal-mechanical stress fracture, a virtual guarantee of destruction.

Without frequent access to a test article, ie., a stolen Avangard, we’re working in the dark. But it is at least conceivable that a micro-projectile could,  by a chain of effects, be as damaging as a direct hit.

Next: Beyond kinetics: directed energy, nukes, and hybrids.

 

 

 

 

 

Let’s put another nail in the coffin for kinetic-kill vehicles. An EKV (exoatmospheric kill vehicle) has a  chance only if the adversary warhead climbs above the atmosphere for some portion of flight, and Avangard may never do so. If a hypersonic warhead descends enough to maneuver in flight, that contest is over.

There is a little bit of high school level math. If this turns you off, Part 5 will return to a qualitative presentation.

At lower altitudes, a winged interceptor missile, like the hypersonic adversary, can convert some forward motion into maneuvering energy. The DARPA RFPs will naturally include enhancements to winged interceptors. The logic: To intercept a hypersonic warhead requires a hypersonic interceptor missile. This means bigger, faster boosters, and a missile shape with more aerodynamics  than the vestigial fins found on today’s interceptors. Something like the Boeing Waverider on top of a Sprint booster.

There is  a major fly in the ointment. Suppose that after some years, both sides have squeezed all they can out of air frame  propulsion, and guidance. Missile development, like everything that depends on physics, is subject to the law of diminishing returns. Novelties can only delay the inevitable. It then becomes an even match,  except for one thing. The warhead knows its evasion plan. The interceptor has to observe, and estimate.

The interceptor, combined with ground-based tracking, estimates (I did not say knows) the position of the warhead. To figure it out, the interceptor thinks that:

• Position is anticipated by velocity, which is  combination of speed and direction. So we need the velocity of the warhead.
• Velocity is anticipated by acceleration.(The accelerator pedal in a car, and turning the steering wheel both produce acceleration.)
• Acceleration is anticipated by “jerk“, which corresponds with how your foot is jiggling the accelerator pedal and twisting the steering wheel.

“Jerk”, corresponding to the warhead’s next move, is known only to the warhead. What goes on in the warhead’s little brain cannot be eavesdropped. All other things equal, the warhead has the advantage.

A typical mutual closing velocity is 10,000 meters/second, split between the warhead and the interceptor. Suppose a hypersonic warhead makes this maneuver:

• Change of course  100 milliseconds before impact, when separation is 1000 meters.
• Converts 1% of its forward velocity, 5000 meters/second, into lateral  velocity, 50 meters/second, over 75 milliseconds.
• A change of 50 meters/second in 75 milliseconds is an average acceleration of 66g’s. For comparison, a Sprint missile accelerated at 100g’s, impossible for humans, but comfortable for a compact, hard warhead.

Without a course change by the interceptor, it misses by about 5 meters. To correct course requires an accurate prediction. It has a camera on the front,  and a computer to interpret the images. The computer runs a program, an algorithm, to figure out the new anticipated intercept point  from a mess of data.

Now here’s a WAG of the prediction problem, where for clarity I have made certain simplifications about “filters”:

• Position, velocity, acceleration, and jerk are coupled together.  For this problem, we need them all to get one.
• To get all four variables requires a minimum of 4 observations. Remember your simultaneous equations from high school: 4 equations for 4 unknowns. Call each of these an observation set.
• To get decent accuracy, we need at least 3 sets, probably more. A total of > 12 observations.
• When a sensitive sensor, CCD or CMOS, images a point of light, it blooms, with expanding bright halos that fuzz the position of that point. Allow 10 milliseconds for the bloom to fade before another observation can be taken. Total time to observe: >120 milliseconds.
• Time to run the program to come up with the new position and compute how the interceptor should respond by actuation of thrusters and control surfaces: 80ms.
• Total time: 200 milliseconds.

Now the interceptor alters course,  by adjustments that require more time, to signal actuators, such as control surfaces and thrusters, which require more milliseconds. A thruster needs 2 ms just to start, and more to stabilize.

In that 200+ ms, the warhead and interceptor, moving at  closing velocity of 10,000 meters/second, have moved a further 2000 meters, 6000 feet. In the blink of an eye. And the warhead may change its mind again while all this is going on.

The above describes a scenario where the interceptor almost works, but not reliably enough to save a city. How much money do you lay on the interceptor? It has to hit to win. The warhead only has to miss.

To the above, we can add a corollary of Murphy’s Law:  Everything works a little worse than designed.

Next: Is there a game-changer?