Stargate Atlantis: Season 4, Episode 1

4 - 1: Adrift

When Rodney McKay realizes Atlantis has started shutting down artificial gravity and collapsing protective shields to compensate for a damaged power system, he turns off all non-essential systems. But when the problem persists, McKay is forced to collapse the shield to the point where it is only protecting Atlantis' main tower, leaving the rest of the city exposed to space.