Tuesday, April 7, 2015

Star Trek Shields For Tanks

Last week we talked about shields for protecting
astronauts. This week shields against projectiles.
But they both can use plasma. The Star Trek
shields absorb or deflect energy, but a hunk of rock
would go right through. Read the post to find the
PASS plasma system – it might work better than
a Star Trek graviton shield.
Manny Pacquiao and Floyd Mayweather are going to have the next “fight of the century” on May 2, 2015 in Las Vegas. In "the sweet science" it’s all about hit and don’t get hit. But just as important is to minimize the damage when you do get hit.

We talked last week about how we are developing plasma shields to protect astronauts from space radiation. In a way, that’s the “don’t get hit” part in a nutshell. But space radiation isn’t trying to hit you; it’s just there, and so are you.

In Star Trek, the deflector shields were meant to avoid or minimize the damage of things meaning to destroy them. Like Mayweather’s right cross, photon torpedoes are sent with bad intentions.

Today let’s concentrate on emerging technologies to protect ourselves from things coming at us with bad intentions. In practical terms, using the technology we have right now, this would be most considered armor, but we are quickly moving to deflector shields. And some new armors now have deflecting capabilities.

One of the problems with plasma-based deflector shields is that you are relying on charges to deflect charged things away from you. Projectile weapons are often uncharged, although the metals in them can be charged. You would have to rely on destroying them with energy before they got to you rather than deflecting them away – and engineers are working on that.

Armor is designed to blunt the effect of some projectile, or an explosion + shrapnel. In most cases, the thicker the armor the better – like the traditional methods of shielding spacecraft from cosmic radiation. But newer types of armor are meant to protect in a more pro-active way.

Osmium is the densest naturally occurring
element. This makes it great as a contrast for
transmission electron microscopy. Here we see the
layers of myelin sheath around a neuron in the
brain. The dark lines are the lipid in each layer, as
fats pick up the osmium best.
After the refit of the Enterprise, Mr. Scott described a type of shield to be used that was more like armor. The replicator would produce a wall of very hard metal, I think they used a diburnium-osmium alloy. Then the transporter would project that alloy outside the ship’s hull, like a second layer of the hull. The Defiant had an ablative armor shield as well. Heck, so did Iron Man.

Ablative armor is a physical shield intended to be sacrificed. Its destruction dissipates much of the energy of the incoming projectiles or beam. We use ablative armor on returning vehicles from space. The heat shield tiles on the old Apollo missions were a form of ablative armor. The space shuttles had reusable tiles, but Orion is going back to an ablative system on the underside portion of the vehicle that will be hottest (4000˚ F).

A newer technology, called advanced ablative armor, will anticipate an attack and put additional armor where needed when needed. It's essentially a big catcher’s glove - stick it out where the pitch is coming.  Fullerene would be a good candidate for ablative armor – it is strong and light.

Real science has made more use of reactive armor than ablative armor. Reactive armor is also called active protection. This armor does something to protect the target, it doesn't rely on its material strength alone.

The earliest type of reactive armor was (and is) explosive. Explosive reactive armor (ERA) is meant to repel the killing mechanism of anti-tank missiles and rockets. High explosive armor piercing (HEAT) projectiles do their damage by breaking the outer hull by kinetic force, and then setting off an explosion that injects superheated copper through the hull and into the cab where the electronics and people are.

The army has been touting the effectiveness of ERA
since 2007, but the 2011 paper independently
confirmed it. This is a Bradley tank with the ERA
installed as an additive armor. It needs to be a certain
distance from the hull of the tank in order to protect it
maximally. Each individual box is an explosive unit, so
protection is precise to the area being struck.
ERA counters this by providing it’s own shape charged explosive. When the HEAT projectile pierces a thin metal plate on the outside of the tank, an explosion between it and the main hull of the tank throws a lot of energy out (away) from the hull. This counters the explosion and injection of liquid copper, repelling it away from the hull.

What you have to watch out for is tandem HEAT weapons, where one is fired right after the other at the same target point. The ERA charge which protects against the first won’t be there for the second.

ERA has been around since the late 1970’s, but there are new versions that actually sense the incoming round and set off the explosive armor BEFORE the rocket gets to the tank or the personnel carrier. Advanced ERA's been further improved by making the inside of the charge non-explosive, merely a rubber that turns to gas and expands the outer plate before the HEAT weapon hits. This is called bulge armor and is helpful against that second shot from a HEAT weapon, not just the first.

Electric reactive armors are being developed as well. One type uses two charged plates separated by an insulator. When a projectile penetrates the outer hull, the first plate touches the second. This completes an electrical circuit that releases a large electric charge and destroys the projectile.

A second type of electrical armor, developed by the British Defence Science and Technology Laboratory, uses a thin layer of a supercapacitor (a material that can store a large electrical charge over time) just internal to the outer armor. When a projectile is sensed by the radar/video/ESP of the armored target, it releases the charge from the capacitor onto the outer metal armor at the precise spot that is being targeted. This creates a huge EM field with flux lines spreading out from the target and acts as a temporary force field to repel/deflect/destroy the incoming projectile. Sounds a lot like a Star Trek deflector shield to me.

The American Defense labs have a version of reactive armor as well, called the American Iron Curtain. It's termed an Active Protection System (APS – because the military is the best in the world at creating initialisms). In this system, highly sophisticated radar and optical systems detect incoming projectiles and even classifies them as to their type and danger.

Projectiles are then fired down from the top of the targeted vehicle to intercept the incoming round and render it a dud. It doesn’t make them blow up early, it deactivates them with a projectile so they can’t blow up. They then just bounce of the hull. Iron Curtain was integrated into several different vehicle defense system in 2012 and 2013.

The left image is the vehicle based PASS system
ready to be deployed by the US Army as a nonlethal
crowd control device. On the right is the plasma
clouds produced by the primary laser. In the near
future, there will be hundreds of plasma cloud spots
and they will be able to form three dimensional shapes.
There is even a plasma-based shield weapon on the way. The United States Army Armament Research, Development and Engineering Center has developed a system called PASS (plasma acoustic shield system). Originally designed in 2007 to be a deterrent by creating a disorienting flash bang, the technology has come far in the past couple of years.

PASS uses a couple of high power lasers. The first creates an intense energy beam that strips the air molecules of their electrons, creating a plasma cloud. The plasma creation (very hot at the point of plasma, but dissipating rapidly as you move away, creates a small explosion, more like a loud bang.

A second laser then hits the plasma cloud just milliseconds later. The plasma absorbs the energy, expands rapidly which creates a shockwave and an even bigger bang. You can set this system up to fire repeatedly in a pattern, creating a wall of light and sound. Depending on the energy levels of the lasers, the wall will appear at various distances from the source.

Increase the energy of the wall (or whatever shape you want to project) and PASS can go from purely disorienting to lethal. Or it could disrupt incoming fire. This was the aim of the US Navy Plasma Point Defense System that was abandoned on the 2000’s, but advances present in PASS have made it feasible again. The PASS wall can’t be seen through and is impenetrable to infrared waves, but it carries some of the same drawbacks as Star Trek shields; you can’t see out either, and you couldn’t fire through it.

Finally, metamaterials may act as a defense shield some day. Structure in three dimensions gives metamaterials their characteristics instead of just the molecules of the material that makes them up. To give an example, cotton T-shirts have certain characteristics based on being made of cotton (soft, stretchy, can be dyed, shows off my guns, etc.). But a metamaterial T-shirt made from cotton might be able to deflect sound waves or do some other amazing things with EM waves, based on the shape that the cotton fibers are given in the shirt.

A soundproof room is a pretty good model for a absorbing metamaterial. 
The quietest room in the world is in Minneapolis. The cones at high 
angles bounce the sound into the other cones at 90˚ from the
first. Sound checks in but doesn’t check out. Metamaterials that absorb 
EM radiation do the same thing, they are just a billion times smaller, 
smaller than the wavelength of the light they absorb.
Recent papers have shown that certain metamaterials can act as energy absorbers. A group from Poland published a study in 2014 that used S-shaped metamaterials cells can absorb low frequency energy. The energy waves enter the S-shaped cells and bounce around until there energy is dissipated. Right now the potential use is for shielding electronics from EM pulses, but they could expand.

For an invisibility cloak, you would want the metamaterial to bounce the light around like a prism and then let it go after it passes around the object. But a cloaked object using an absorbing metamaterial would look black; the absorber doesn’t reflect the light so none returns to your eye. This would make for a bad cloak but a great shield - if you can find a way to keep the absorbed energy from destroying the shield.

Right now, the absorbers work in the low gigahertz range, so they absorb radio and microwaves, but a new study shows that some are being developed that absorb in the terahertz range. This is within infrared and visible light frequencies, the types of light used in high-energy laser weapons. Go a bit higher and perhaps we could absorb ultraviolet waves. But wouldn’t that just be sunscreen?

Next week – Mr. Data was an android, but at his most basic he was a robot with artificial intelligence. We’ve got rudimentary robots, but that AI thing is tougher.

Contributed by Mark E. Lasbury, MS, MSEd, PhD

Mayseless, M. (2011). Effectiveness of Explosive Reactive Armor Journal of Applied Mechanics, 78 (5) DOI: 10.1115/1.4004398

Yoo, Y., Zheng, H., Kim, Y., Rhee, J., Kang, J., Kim, K., Cheong, H., Kim, Y., & Lee, Y. (2014). Flexible and elastic metamaterial absorber for low frequency, based on small-size unit cell Applied Physics Letters, 105 (4) DOI: 10.1063/1.4885095

Grześkiewicz, B., Sierakowski, A., Marczewski, J., Pałka, N., & Wolarz, E. (2014). Polarization-insensitive metamaterial absorber of selective response in terahertz frequency range Journal of Optics, 16 (10) DOI: 10.1088/2040-8978/16/10/105104

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