It is feared that the International Space Station's (ISS) oxygen generator might break up - the generator had a lot of problems lately.
The crew of Discovery will stop off at the International Space Station, which is capable of housing only three persons. Additionally, if Atlantis were required to set the rescue mission into effect, it would return with a crew of 11 members. This scenario is a nightmarish one for all concerned.Discovery is planned to launch in the first half of May. NASA said it will not launch the Discovery shuttle if the rescue shuttle Atlantis can't be launched a month later. A rescue mission will be very dangerous as it will need to be launched without all routine tests and precaution procedures.
Source: Earth Times