Coldstar was a freezer satellite, named after the company which ran it.
It was in orbit around Enyo and gained its ice from a nearby ice planet. The ice, however, contained frozen Ice Warriors from the Ice Warrior Wars. Once they unfroze, they planned to set Coldstar on a collision course to Enyo in revenge, but the Tenth Doctor and Rose Tyler stopped them by changing the course for the nearby sun instead. (AUDIO: Cold Vengeance)