Prior to the Galaxy ClassEdit
Numerous Starfleet ship classes, such as the Constitution class and Galaxy class, consist of two sections: the stardrive section, also known as the battle section, engineering section, engineering module, or secondary hull, where the warp nacelles are located; and the saucer section, also known as the primary hull or command module. Nearly every starship design that follows the saucer/secondary hull pattern has had some ability to separate into two autonomous sections during extreme emergencies: for example, an imminent warp core breach or the failure of antimatter ejection systems. However, even if the two sections could later be reconnected, it was only possible at drydock facilities. The idea of routinely separating and reconnecting the two starship sections was a 24th century innovation in starship design.
At least twice before TNG debuted, the idea of separating the saucer section was mentioned. In the episode of the original series The Apple, Kirk mentions the possibility of jettisoning the warp nacelles and saucer and using the saucer to escape. In early drafts of Star Trek: The Motion Picture, the USS Enterprise was to separate its saucer section while confronting V'ger, and the separation line indicated in concept art is clearly visible on the connecting dorsal of the finished model, but this scene was scrapped.
Galaxy-Class saucer separationEdit
In times of battle, it was intended that the saucer section of a Galaxy class ship (which contained the bulk of the ship's crew and support systems) would separate from the ship's stardrive section (which possessed the bulk of the ship's armaments). Carrying all the non-essential personnel, the saucer section could depart the battle area; meanwhile, the stardrive section (controlled from the battle bridge, an auxiliary command centre in the stardrive section) could engage the enemy with a minimal complement.
In extreme emergencies, protocols allow for the saucer to de-orbit and make a forced landing on a habitable planet; the craft is not designed for this maneuver, and severe damage was expected to result. Until the crash of the Enterprise-D saucer in Star Trek Generations, however, this procedure was not tested beyond computer simulation; as such, Starfleet engineers were uncertain that a Galaxy class saucer could survive such a forced landing.
While the Galaxy class was built with saucer separation in mind, the saucer section only had impulse engines and no independent warp capability, making it vulnerable to enemy attack. About the only way to safely perform the separation was for the docked vessel to withdraw to a safe haven, and separate the saucer away from the battle; the stardrive section could then return to the battle. However, most situations developed so quickly that there was no time to separate at a safe distance, nor was there usually time during battle to withdraw to separate the saucer.
Saucer separation generally takes place at impulse (sublight) speeds. While the crew of the Enterprise-D proved that separation at warp was possible, to do so is very dangerous and entails no margin for error. Such dangers included collision between the two sections and problems with warp field integrity/geometry. In situations where a saucer successfully detached at warp speeds, the saucer module would usually drop out of warp within two minutes.
The operation was observed on screen four times during the Next Generation : in the pilot Encounter At Farpoint, the first season episode The Arsenal of Freedom, and in the third season/fourth season two-parter The Best of Both Worlds. It was not seen again until the Star Trek Generations movie, when the ship separated shortly before the warp core exploded.
The maneuver was also performed in the course of at least two novels: Foreign Foes and Rogue Saucer (which introduces a new and improved saucer section for the Enterprise D).
It is believed that saucer separations would also occur during maintenance layovers at starbases. According to Star Trek: The Next Generation Technical Manual, one such instance was sometime after the first season of TNG, when a new battle bridge module was configured and installed atop the stardrive section of the Enterprise-D (on deck 8) (an explanation for why the Battle Bridge looked different in later appearances than it did in the first season).
Despite the procedure's rarity, Starfleet has not entirely abandoned the concept of separable starships. Around 2373, the Sovereign class was designed for saucer separation (like the Galaxy class); however, this ability has not yet been observed on screen. It is featured in the Post-Nemesis novel Resistance by J.M. Dillard. At the same time, the USS Prometheus – an experimental warship design – featured "multivector assault mode," whereby the ship separated into three sections that could engage targets independently (Star Trek: Voyager: "Message in a Bottle"). Each section – designated Alpha (command module), Beta (dorsal engineering module), and Gamma (ventral engineering module) – also possessed independent warp capability.
- The original model of the Enterprise-D built for TNG could be separated (and was also unwieldy to film), yet a follow-on smaller, more detailed model built after the first season could not be separated. As a result, the larger, original model was used to film various scenes during "The Best of Both Worlds", where the saucer and battle sections were separated while fighting the Borg.
Saucer separation was seldom used in large part because the original filming model was so difficult to handle. In future episodes such as in Voyager, CGI models are one reason more ships are seen to separate.