Earlier this month, 24th August 2011, saw the crash soon after launch from Kazakhstan of an unmanned Soyuz carrying food and fuel to the ISS, following the failure of one of the booster rockets. The Russian Space Agency Roscosmos has delayed the next manned mission by at least a month to allow time for safety checks to be carried out, and it is likely that at least two test launches of an unmanned rocket will be conducted before sending anymore astronauts up.
The delay means that replacement crew will not go to the ISS until late October at the earliest, assuming that all goes well with the testing. The station is currently manned by a team of 6, with 3 likely to return to Earth in mid September and a decision needing to be made about the remaining crew.
Alexei Krasnov, head of manned flights at Roscosmos recently indicated that: 'If for any reason we will not be able to deliver the crew before the end of November, we will need to review all possibilities including leaving the station unmanned.'
The ISS has been continuously manned for more than a decade. It can in fact be flown without a crew if needed, though this is not an ideal situation as repairs can be made and problems fixed faster with crew members onboard, reducing the possibilities of major damage occurring.