Saucer separation is a maneuver where a Federation starship separates its saucer section from its stardrive section. In 23rd century ships, this would be used only in emergencies, whereas 24th century vessels could redock the two sections unaided. Prometheus-class ships, as well as most late 24th-century Hydran ships, take the concept further with their multi-vector mode.
Classes capable of saucer separation Edit
Constitution-class starships could separate their saucers by means of explosive bolts at the joint between the neck and the saucer. Reattaching the saucer required a shipyard. (TOS comics: "'Til Death", "None But the Brave"; Bait and Switch: "The Universe Doesn't Cheat")
In Galaxy-class starships the maneuver was reversible and was intended for use to allow the ship's civilians to escape. In practice it was also used as a combat tactic, such as during the USS Enterprise-D's 2367 confrontation with Locutus' Borg cube in the Sol system, as it allowed the stardrive's forward dorsal phaser array to be employed. (TNG: "Encounter at Farpoint", "The Arsenal of Freedom", "The Best of Both Worlds"; Star Trek Online)