 Since the arrival of the first permanent crew to the ISS in 2000, the emergency return capability has been fulfilled by Soyuz spacecraft rotated every 6 months.In the original space station design, emergencies were intended to be dealt with by having a "safe area" on the station that the crew could evacuate to, pending a rescue from a U.S. Space Shuttle.However, the 1986 Space Shuttle "Challenger" disaster and the subsequent grounding of the shuttle fleet caused station planners to rethink this concept.