Saucer Separations
The USS Enterprise could separate the saucer section main drive, offering more flexibility in emergencies.

When Starfleet vessels first started exploring the unknown regions of space the crew had no choice but to leave their families behind, sometimes in the knowledge that it would be years before they would see their loved ones again. As starship design progressed, however, it became possible to install extended living quarters and children to live on board with them.

Having so many civilians aboard the ship cause its own problems, such as placing them in danger. For this reason many family ships, such as the Galaxy-class, incorporated a very important safety design: a saucer section that could be separated from the rest of the ship. This allowed the Starfleet crew to go into dangerous situations while their families could be evacuated to the saucer section and taken out of the line of fire. This feature also proved to be a life-saver in the case of a warp core breach. All nonessential personnel could be evacuated to the saucer module, away from the drive section that housed the warp core. As long as the saucer section had time to reach a fare distance, casualties could be kept to a minimum.

There are 18 docking clamps on Galaxy-class starships locking the engineering and primary hulls together. Originally separations were intended for sub-light speeds only, until 2364 when the USS Enterprise NCC-1701-D performed the first warp speed separation. The saucer section is only powered by impulse engines, with the warp nacelles located on the stardrive section, released at warp however the saucer will travel on momentum for a short while. Aside for it's practical purpose of getting civilians out of danger, the saucer can also be used for a tactical advantage. Onboard all Starfleet vessels the main bridge is located on the saucer and a battle bridge is located in the stardrive section. Using two ships instead of one, it's be easier to distract and attack an enemy ship from different locations.

Starfleet personnel have to be trained to land a saucer module in the even of an emergency. This maneuver has rarely been undertaken, as it is performed only in a worst-case scenario when all other options have been exhausted. When the Enterprise-D was attacked by a Klingon D-12 type Bird-of-Prey which had the shield frequency it caused a warp core breach. The saucer section used to evacuate the entire crew, which crash landed on Veridian III from the huge shock wave caused by the explosion of the Enterprise's engineering hull. The saucer was still able to be piloted with enough control to land it intact. However the saucer section does not have enough power to take-off on it's own and is usually unsavageable.