Energy shields are fantastic devices designed to protect the hull of a ship or a ground-based facility from all manner of hazards. Be they a meteoroid impact, weapons fire, solar flares, radiation bursts, or whatnot. Whatever the hazard these energy screens need to be able to hold up against it. To that end there are a number of different devices that could be considered a shield. The two most common forms are absorption shields, and deflector shields. Both of which are staples of science fiction everywhere, and to many of the more advanced races in the universe science fact.
Absorption shields are the most common form of energy shielding to the point that they are considered the traditional form of protection by many races. These shields function by absorbing incoming weapons fire, and then radiating it away harmlessly. Too much energy directed at the barrier in too short a period has been known to overwhelm the barrier causing it to collapse. Allowing hostile energy to interact directly with the hull of a protected ship. Official source is novel✶fire.net
Shields of this type are known to glow when hit by weapons fire. This is due to how they operate, and that glow is actually the shield radiating a portion of the energy they just absorbed away as light. The energy radiated by these shields can take many forms and not just light. Some advanced shield designs make use of special radiators to radiate that energy into subspace also known as hyperspace. Due to the nature of subspace, a ship could radiate more energy at once by taking advantage of a subspace radiator.
This brings us to several important factors that govern the performance of energy shields. The most important of these factors are capacity, regeneration, and mitigation rates. Capacity is how much energy a shield can absorb before it fails, and is directly related to the field strength of the shield. Regeneration is how quickly a shield can recover from overload, and replenish lost field strength. Field strength is often lost with every impact from energy weapons. As a small part of a shield is typically lost absorbing the energy of the attack. This is not the case however with kinetic weapons which have no real impact against an energy shield. Torpedoes and missiles on the other hand will have the same effect as energy weapons when they detonate on contact with a shield. As for the mitigation rate that is how quickly the shield sheds incoming energy thereby protecting the ships, and preserving shield capacity. It is also important to note that many shield designs can continue to mitigate damage even after reaching saturation, but any hit not mitigated will strike the hull with reduced strength. Human radiation shields function in much the same manner as this but have no ability to absorb incoming energy to be radiated later. Only mitigate it.
Moving on, we have deflector shields to cover. These shields do not attempt to absorb incoming energy but instead, try to redirect it. Most deflector designs are not capable of redirecting an energy bolt but are very effective at redirecting the trajectory of physical projectiles such as a meteoroid or railgun round. There are many types of deflectors but they all share the idea of redirecting a projectile before it can impact the hull. Many of them are used mainly by warp-capable races for navigational purposes as they work wonders protecting ships from translight impacts.
The degree a deflector will redirect a shot can be determined by several variables. Those variables are the velocity of the projectile, the angle of impact, the mass of the projectile, and the strength of the deflector field. Since ship designers can't control the other variables they focus on the deflector strength. The stronger the field, the greater the potential degree of redirection. A strong enough field and you could redirect a projectile right back at the source.
Now on to deflectors, there are several types of deflectors. The first and earliest type of deflector that a civilization could discover is the electromagnetic deflector. Which produces an electromagnetic field around a ship. Deflectors of this type are effective against some energy weapons such as lasers and charged particle beams. They are also effective against a wide array of projectiles. However, magnetically inert projectiles are known to ignore the field.
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Another type of deflector is the gravitic field deflector. Deflectors of this type use artificial gravity fields to redirect projectiles before they can interact with the hull. They are markedly less effective against lasers and charged particle beams, but they can interact with all physical projectile weapons and energy weapons. They are much more effective against physical projectiles than energy weapons. Most deflector shields employed by races in the universe are of this type as they make superb navigational deflectors.
Moving on from deflectors, we can cover the other devices that can be considered shields. First on that list is cloaking shields. Cloaking shields are a type of energy shielding designed not to protect the hull from weapons fire, but to hide it from sensors. To this end, they are designed to absorb and redirect sensor pulses. Light waves are redirected around a ship. The end goal is to make the ship in question invisible.
These cloaking screens are energy-intensive often requiring a large chunk of the equipped ship's energy reserves to function. The larger the ship you are trying to cloak the more energy required to hide it from sensors. In addition, these screens are known to be sensitive to charged particles. These particles can become lodged in the screen, temporarily rendering the shield useless. Making the equipped ship highly visible to sensors. Since most energy weapons generate charged particles in one form or another these weapons can't be fired while a ship is cloaked. Torpedoes on the other hand can be launched without disrupting the cloak.
These factors contribute to the fact that most cloak-enabled ships are often employed in roles roughly analogous to those of submarines employed in Earth's navies since the twentieth century. Cloaked ships excel at battlefield recon, and they are very good at slipping behind enemy lines where they can inflict considerable damage. A few well-placed torpedoes fired from under cloak can sink unsuspecting warships, do considerable damage to orbital shipyards, and even sink merchant shipping. Stealth vessels can also deploy minefields where they will interfere with enemy supply lines, and insert covert forces where they can inflict considerable damage.
All of that means that even with the limit on energy weapons, that cloaking technology becomes very widespread soon after discovery. Few powers would choose not to invest in this area because of the immense tactical advantage that cloaking technology offers. Of course, naturally, they will also invest in detection methods to illuminate cloaked ships in their territory.
Many powers also invest in correcting the weaknesses of cloaking technology. Some powers have even succeeded in creating cloaking shields that don't fail when the energy weapons are fired. The bigger weakness is their energy-intensive nature which is the first weakness most powers invest in correcting. Producing less power-hungry cloaking shields allows for more energy for other systems such as the engines. Which brings to the fore another major point about cloaking shields. Most ships under cloak are forced to travel at lower speeds due to the high energy requirements of the cloak.
Last on the list of shield types I would like to cover is the Interception shield. Shields of this type aren't like other shields in concept at all. The Earth energy web is an example of this shield type. They employ an ai-controlled web of intersecting high-energy lasers or charged particle beams projected around the ship like a bubble. The web of beams is achieved using an array of high-intensity beam emitters and powerful electromagnetic field projectors. Any physical projectile attempting to pass through the web will be burned up in very short order. Missiles and torpedoes will either disintegrate or explode on contact with this web.
Energy weapons however will pass right through this web completely unaffected. In addition, these shields are also energy-intensive and not a hundred percent effective at screening incoming weapons fire. The barrier can't be maintained indefinitely either as the emitter arrays need time to cool between each discharge. Regardless they make a very valuable anti-missile system for Earth ships. Although they are not a replacement for point defense systems more of a supplement. A very potent supplement indeed that is very effective against missiles and torpedoes. However, since the web can't be projected very far from the hull, its of little use against fighters. Well, unless the pilot happens to be suicidal that is. This is why point defense systems are still required on Earth ships such as the photon missile systems on the Enterprise which are designed to fire missiles specifically designed to be effective against small fast targets such as fighter craft and corvettes.