Deflector shield

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Deflector shield status display aboard a Constitution class.

A deflector shield (also called deflector screen, or referred to simply as shields) are a type of force field that surrounds a starship or space station to protect against natural spatial hazards or enemy attacks.

Deflector shields operate by creating a layer of energetic distortion containing a high concentration of gravitons around the object to be protected. Shield energies can be emitted from a localized antenna or "dish" (such as a ship's navigational deflector), or from a network of "grid" emitters laid out on the object's surface (such as a ship's hull). On modern starships, deflector shields are essential equipment. They are raised to full power in anticipation of environmental hazards or in combat situations.

Neither matter nor highly-concentrated energy (i.e., weapons fire) can normally penetrate a shield. When shields are "up," or energized at a high level, most matter or energy that comes into contact with the shields will be harmlessly deflected away. In contemporary starship combat, shields are essential for hull protection. When shields are up, only minor hull damage can be expected during combat. Without deflector shields, modern weapons are capable of causing catastrophic damage to starship hulls almost immediately.

Continuous or extremely powerful energy discharges can progressively dissipate the integrity of a shield to the point of failure. Shield capacities vary according to many variables, from the power available to environmental concerns (such as nebulae), making definitive and universal calculations of how much damage they can take difficult to estimate (there is no way to know exactly how many phaser hits will cause a failure, for instance). Therefore, during combat, tactical officers continually report on shield strength. Usually, the officer reports shield strength as a percentage of total effectiveness, with 100% meaning that the shields are at full capacity, and lower percentage scores indicating weaker shield conditions. Often, specific sections of the shield grid (e.g. aft or starboard) will take more damage than other sections, so tactical officers will report on the health of any section that needs reinforcement with additional power reserves. Shields are said to be "holding" if damage is not sufficient enough to allow a compromise, while if the shields are "buckling" or "failing," then a total loss of shield protection is imminent.

Shields operate within a range of shield frequencies to allow certain specific types of energy and matter to pass through (such as visible light), or to make them more effective at blocking them. The frequencies of shields are not usually discernible without examining the controls on board the ship deploying them, meaning that it is very difficult to tune weapons to the exact frequency of an opponent's shields to bypass them. In combat situations, starships match their own shield and weapon frequencies so their shielding does not interfere with their own weapons. Some weapons technologies, including those commonly used by the Borg, have rapidly adjustable frequencies, meaning that they will more rapidly penetrate shields with static frequencies. An effective counter is to repeatedly and randomly alter the shield mutations to minimize the effectiveness of the weapon's retuned frequencies.

Impacts on the shield cause Cerenkov radiation to be released, often perceived as a flash of colour which "lights up" the shield, rendering it briefly visible. To an observer it appears that the intruding object bounces off the shields - in fact the spatial distortion becomes so great that the path of the object is radically altered, and to a zero dimensional observer on the incoming object it appears that it is the starship which has suddenly changed location while his/her course is unchanged.

Certain starships have a shield system advanced enough to allow protection of only specific areas of the ship while leaving other areas unprotected. This is useful in times when power reserves are low. Lowering portions of the shields also allows usage of transporters without completely sacrificing the protection that shields provide.

Shields may be "extended" to encompass another vessel, which is often accomplished by matching the ships' shield emitter frequencies. While the extended shielding can provide some protection in the event of a shield failure on one ship in a convoy, this technique can put a strain on ship systems, and the overall strength of the extended shields is generally not as strong as two independent shield systems.

Shields and Transporters

For over a century after the invention of the shield it was impossible to use transporters to beam to or from a shielded location, but to an extent this limitation has now been circumvented. In general sensor and weapon windows are insufficient to allow beaming; whilst technically there is nothing to prevent a ship opening a window in its own shields of sufficient size to allow transport, in practice such windows are almost always large enough to be detected and exploited by enemy vessels and it is far simpler just to drop the shields briefly altogether. The more modern Star Fleet shield designs have now reached a point at which transporters can be operated via a large wide frequency window which is briefly opened over the hull emitters. This gives greater flexibility in using the transporter during high threat situations, but it remains a somewhat risky proposition - should an enemy score even a near miss on such a window the effects on the ship would be considerable.

Beaming through an opponents shields is an altogether more difficult proposition, but this can be accomplished successfully if the transporter operator has a detailed knowledge of the shield configuration s/he is attempting to beam through. Such operations remain the exception rather than the rule, however - and against the unknown shield configuration of an enemy vessel, beam through remains impossible.