|Quoting Thorny (Reply 3):|
Endeavour probably could have been ready to fly STS-117 in February, but that mission is almost identical (mirror image) to the just-flown STS-115 and is very heavy, so NASA wants to fly it on the lightest of the three Shuttles, Atlantis
|Quoting DfwRevolution (Reply 4):|
But I'm suprised the last off the line Endeavour is heavier than Atlantis. Is this because it was built mostly from spare parts and wasn't able to match the optimal mass of a factory-build like Atlantis?