Last week's loss of an unmanned Russian supply ship may be a bigger problem than first believed.  NASA officials say keeping crews on the International Space Station now depend on finding and fixing the problem that caused the crash.

With the space shuttles now retired, American and Russian crews have to  use the Russian Soyuz space vehicle to get to and from the the International Space Station.

ISS Program Manager Mike Suffredini says they're now concerned about the safety of the Soyuz vehicle, because it uses a launch system very similar to the system that launched the unmanned spacecraft which crashed.

Suffredini says if the problem isn’t resolved by November 16, and if a manned Soyuz cannot be launched and flown safely by then, the space station will have to be "de-crewed" temporarily.

This would be a huge blow to NASA, which just completed construction of the ISS earlier this year, and has continuously occupied the station for 11 years.

In the meantime the planned Sept. 8 return of three of the six members aboard the space station, who will ride home in a Soyuz already attached to the station, will be put on hold for about week.

Without the arrival of a replacement crew, this will give the station an additional week to conduct a full amount of research.

Then the three remaining astronauts aboard the space station can remain on board the station until mid-November before they would need to come home.

That’s because their Soyuz, also presently attached to the station, is only rated to stay on orbit for six months and will be near the end of that time frame.

Suffredini says losing that unmanned vehicle could be a blessing in disguise.  He says it's a learning opportunity for space agencies in both countries.

After all, he says, it could have been manned Soyuz that was lost.