The Land and Disassemble mission orders the ship's crew to disassemble the starship when it reaches an unowned or friendly planet. The crew will become colonists, and they will use the ship's parts to make supplies for the planet (after unloading any colonists, cargo, and fuel on the ship to the planet's surface).
Starships have a recycle rate of 75%. This is the percentage of the minerals that are recovered from a starship that colonizes a planet. The recoverable materials from those used to build the hull and weapon systems are transformed back into minerals and laid out on the planet's surface. Money spent to build a ship cannot be recovered, but some Supplies are generated. Fighters and torpedoes are also recycled.
(NOTE: Crew numbers have nothing to do with the number of colonists generated, which can vary from zero to about twenty per ship.)
See also: Out of Fuel.