Navigational deflector
In the Star Trek fictional universe, the navigational deflector is a device found on many Starfleet ships capable of warp travel, generally noticeable by its foremost location on many ships' engineering hulls and its soft blue glow. The navigational deflector is used while moving at faster-than-light speeds to prevent damage to ships' hulls from micrometeoroids and friction from microscopic objects, space debris and gases found in interstellar space. Deflectors accomplish the first goal through the use of powerful deflector/tractor beams extending several thousand kilometers fore of their ships, aimed automatically through use of the ships' long-range sensors. The deflection of smaller objects and stray atoms is done by largely static low-power deflector shields generated by the deflector.
The beams and shields created by the deflector are often a source of subspace distortion and electromagnetic radiation, which can interfere with the operation of ships' sensors. Due to this, long-range sensor arrays are often placed circularly around navigational deflectors. This allows the sensors to look along the same axes of the beams and shields to reduce interference and also, because of their proximity to the deflector, allows for the speedy receipt of data from them by the computer in control of the device.
In combat, the navigational deflector forms the first layer of a starship's static defenses. It is almost useless against high-powered beam and missile weapons, but quite potent at blunting the assault of light and medium-powered weapons such as lasers.
The hardware used in navigational deflectors can be quickly reconfigured to produce a variety of particle streams and energy emissions, making them a sort of 'Swiss army knife' for Starfleet vessels (and a convenient deus ex machina for script writers). Such uses can be seen in Star Trek: First Contact, where it was used to travel into the past and, later, reconfigured into an interplexing beacon, a long-range communication device; in "The Best of Both Worlds" (TNG), as a weapon against a Borg cube ship; in "Scorpion", Pt. 2 (VOY), for travel between alternate universes; and, during the Klingon Civil War, for detecting cloaked Romulan ships.
Navigational deflectors are not seen on a few Starfleet craft, such as the Miranda, Soyuz, and Constellation classes. These classes perform the same functions by use of bow-mounted tractor emitters and low-power use of the deflector grid. Many alien ships also do not have deflector dishes and presumably operate similarly.
In the short online story Journey to Centauri[1], which provides background to the game Sid Meier's Alpha Centauri, the starship "Unity" has no navigational deflector, and due to a chance collision with a small space object, probably about the size of a fist, at near-lightspeed, the ship is badly damaged. Ostensibly, a functioning (not to mention present) deflector array could have prevented this fiasco.
In real life, similar technology would be needed to construct a Bussard ramjet, a promising means to achieve near-lightspeed travel. As well as protecting the ship from high-speed particles, it would funnel them into a reaction chamber to generate thrust. The Star Trek Starship Creator PC game has the Miranda class deflector dish sitting atop of the torpedo launcher. Although the device itself has never actually been seen in that location.