Deflector shield

A deflector shield is a fictional technology commonly found in science fiction. Typically, deflector shields (often referred to as simply "shields") are some form of energy field that is projected along the surface of, or into the space around, a starship, space station, planet, moon, or building. The concept goes back at least as far as the 1920s, in the works of E.E. 'Doc' Smith and others; and William Hope Hodgson's The Night Land (1912) has the Last Redoubt, in which the remnants of humanity shelter, protected by something very like one. Although fictional, deflector shields have some resemblance to real devices such as magnetic field generators.

The abilities and exact functionality of deflector shields vary; in some works (such as in the Star Trek universe), deflector shields can stop both energy beams (e.g. phasers) and physical projectiles, both natural and artificial; in others, such as the Star Wars universe, there are multiple types of deflector shields -- so-called ray shields which are designed to stop energy beams (such as laser and blaster weapons), and particle shields which are designed to stop kinetic projectiles, missiles, bombs, etc.

Deflector shields usually work by absorbing or dissipating the energy of the incoming attack; prolonged exposure to such attacks weakens the shield and eventually results in the shield's collapse, making the ship's hull (or building's walls, or planet's surface) vulnerable to attack. Larger deflector shield systems, or those powered by bigger energy sources, can absorb/dissipate more damage before failing -- so that larger starships, for example, can mount much stronger shields than a small, single-person starfighter, much in the way that a sea-going battleship has much thicker armor than a tiny patrol boat.

Deflector shields in Star Trek

Main article: shields (Star Trek)

This part is fictional, but within the scientific logic of Star Trek. Sources: The book Star Trek: The Next Generation Technical Manual by Rick Sternbach and Michael Okuda, as well as Star Trek: Deep Space Nine Technical Manual by Herman Zimmerman, Rick Sternbach, and Doug Drexler.

The Star Trek deflector shield creates areas of highly focused space distortion containing a field of gravitons. The shape of this shield resembles the ship's shape. If the shield is being hit - no matter if it's a subatomic particle or a massive object - the field energy is being focused on that particular point, creating a small but powerful spatial distortion. For an observer on board of the ship, it looks as like the object bounced off the shields; for an observer on the object itself it would look as if the trajectory never changed - just like it would be with a regular space distortion.

Shielding the ship from the whole spectrum of electromagnetic radiation is almost impossible because it would take too much energy and conflict with the sensors. In normal flight, shields are on 5% of the maximum possible output, the only exception being the frequencies of the EM spectrum from which the crew needs to be protected. In battle situations, the shields are brought to at least 85% of the maximum possible output.

The frequency modulation and spectrum of the shields is varied randomly, so it is possible to set weapons to pass the shields unaltered. On the other hand, knowledge of the modulation and spectrum of an enemy weapon can be used to increase the efficiency of the shields.

To use weapons, sensors, and shuttles through the shield, electromagnetic shield windows can be opened temporarily. This is usually done via EM-window transponders present in shuttles and photon torpedoes.

Deflector shields in Halo: Combat Evolved

In Halo: Combat Evolved, deflector shields are worn by certain Covenant personnel, placed as stationary defences (much like a physical shield), and equipped by the human SPARTAN-IIs as a core component of their MJOLNIR powered armor. The shields may be literally "force fields", as a bullet moving at high speed has less force than a vehicle moving at a relative crawl, but the vehicle will almost always penetrate the shield while the bullet almost never does so. The shield may project a physical field, like that of an energy bridge. According to Newton's laws of motion, every action must have an equal and opposite reaction. The second law states that force equals mass times acceleration. One of the equations for energy in pgysics is E=1/2 M V^2 where E is energy, M is mass and V is velocity. Shields of differing strengths affect projectiles differently. Whereas the visible shield will deflect a grenade, the personal shield will not; while the visible shield will deflect a ultrahigh-velocity bullet, the personal one will attempt to do so but fail. The shield mechanism may work to counter a force, or energy not beyond a certain threshold.

There are two core types of shielding, each with their pros and cons.

The first (and most common) type of shielding generates a visible energy field. The field generated, and is usually worn like a buckler or placed as a static defence. It is as of yet unknown what powers the shields, but what is known is that they deflect all kinetic attacks (i.e bullets, grenades) and absorb energy attacks (plasma, explosions). This means that a grenade thrown at a shield will bounce off, but the explosion will deplete the shield. Rockets are an exception; they explode upon contact, which further lends weight to the theory that the shield works by acting a force upon the projectile, triggering the rocket's impact fuse. Plasma weapons deplete the shield faster, and cause a change in the shield color where they impact (from a higher frequency color of the electromagnetic spectrum to a lower frequency one) and are not deflected.

The benefits associated with these shields are that they are generally far stronger than the other form of shielding. Bullets will never penetrate/deplete these forms of shielding, and far more energy damage is required to deplete them.

The drawbacks to these forms of shielding are that they are extremely obvious. Because they emit visible light, they are very obvious during covert operations. Possibly because of that, they are far less efficient and take longer to recharge. Also, if worn, they cause a hindrance to the wearer and hinder mobility.

The second form of shielding is the personal body shield. Worn only by the Covenant Elites and human SPARTANs, these shields project an invisible field around the user. The shield shimmers visibly (at the low-frequency range) when it is attacked. It is worn as part of a powered combat suit. The field's frequency and wavelength can be altered to disrupt energy fields, including phase pulse generators. These shields do not visibly deflect bullets and may instead just greatly reduce their velocity, as tracers disappear when they impact these shields, but visibly deflect when they impact the other form of shielding. Also, these shields may be programmed to deflect projectiles above certain velocities only; grenades are not deflected (and continue as though there were no shield, nor visible sign of the shield being activated) but bullets visibly affect the shield. Plasma grenades, which stick to their targets due to some unknown mechanism, are deflected off visible shielding but go past personal shielding. The low-velocity needles launched by the needler deflect off visible shielding but do not visibly trigger personal shielding. These shields are generally weaker than their visible counterparts, as bullets will eventually deplete the shield and plasma will do so even faster. One difference of note is that for a small difference in the number of plasma shots to deactivate a shield (~20:~8 visible:personal) there is a huge difference in the number of kinetic projectiles from the MA-5B rifle deflected (<1320:~40 visible:personal).

Some benefits associated with these shield types are that they are invisible when not in use. This greatly facillitates covert operations. Secondly, they are built into combat suits. The user is not encumbered by an additional generator mounted on the arm. Most importantly, these shields are designed to cover the whole area of the body. An attack from any direction will trigger the shield. This may have neccesitated the velocity threshold of activation, as walking does not activate the shield, but falling from a height will. Additionally, these shields recharge quickly relative to visible shielding, and are efficient enough to be mounted on combat suits. They are also compatible with modifications such as active camouflage and overshielding.

However, they are not without their disadvantages. The greatest is their low strength. Ultrahigh-velocity rounds will instantly penetrate most personal shields, while they deflect indefinitely off visible shielding.