Deep Space 3 began its life as an Epic Class heavy cruiser (The USS Ozark). Its engines eventually shut down in orbit of Gamma T'serata a planet nicknamed Dilithia (for its rich deposits of dilithium crystals) Eventually ships came to ferry crewmen away, but being a remote planet with numerous mining possibilities, it was decided that the ship would not be repaired but rather refit into a space station. The only part of the Ozark that still remains is the upper dome / saucer. The nacelles and engineering section were retooled and reworked into mining, and heavy transporter arrays.
DS3, being in a strategic location has faced several threats from Rogue Gorn or Klingon ships, but the 30 phaser banks and over 1,000 photon torpedoes keep most marauders away. While the USS Ozark had a crew capacity of 500, DS3 can house up to 1500.
There are facilities on the planet below, but conditions are somewhat inhospitable to human life.