Nasa is mulling the worst-case scenarios of leaving the $100 billion International Space Station unstaffed for a period of time following the crash of a Russian rocket, said US astronauts.

Two Americans aboard the ISS, Ron Garan and Mike Fossum, told reporters in a video press conference from space that they have begun minimal preparations, namely taking video of some tasks in order to quickly train future station staff.

However, Nasa mission managers in Houston are hard at work on contingency plans after both Russia and the US admitted that abandoning the research outpost, at least temporarily, is a possibility.

“You have to start working right now to say ‘what if?’” Mr Fossum said. “There are a lot of efforts going on to look at all of the different options that could possibly come into play.”

Six people – three Russians, two Americans and one Japanese astronaut – typically staff the research station on six month rotations.

But last month’s failure of a Russian Soyuz rocket to lift its unmanned Progress cargo vehicle into orbit has raised questions about the ability of Russia to tote people to the ISS.