Missions to the ISS had the advantage of delivering the crew to a place where they could wait for a subsequent mission to retrieve them or go home via the Soyuz. Assuming an injured shuttle could dock to the ISS, its crew could await a rescue mission for ninety days or more. This “safe haven” capability was one of the key factors that led NASA to approve the resumption of shuttle flights.5 The issue was more problematic for servicing missions to the Hubble Space Telescope, which is in a different orbit than the ISS.6 Because of the laws of orbital mechanics, the amount of fuel needed to move
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