International Space Station concern

Difficult decisions lie ahead over the ISS

By Dr David Whitehouse BBC News Online science editor

With the shuttle fleet now grounded, concern is being voiced about the future of the International Space Station (ISS), which currently has a three-man crew on board.

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Two American astronauts and one Russian cosmonaut - referred to as Expedition Six -have been on the platform since November.

Just how long they will have to stay there is unclear, but they will not return for several months.

The next visit had been planned for 1 March, when the shuttle Atlantis was due to take a relief crew to the outpost (Expedition Six would have come back on the return flight).

If necessary, this crew could come down to Earth aboard a Soyuz "lifeboat" vehicle that is attached to the ISS and reserved for emergencies. But for the present, the US space agency (Nasa) wants the station crew to sit tight until decisions are made.

'Not be there for awhile'

Ron Dittemore, Nasa's shuttle programme manager, said US officials had been in touch with their Russian counterparts to ensure the supplies sent up to the ISS on Sunday on an unmanned Progress supply craft were suitable.

"Those contents are appropriate given the fact that we will not be there for awhile," he said.

Expedition Six commander Ken Bowersox is set for a long stay in space

"[The crew] have enough consumables and supplies to go through the latter part of June without having a shuttle visit. So there's some time for us to work through this."

But what of the future for the ISS if the space shuttle fleet remains grounded for a long time?

"It's absolutely obvious that shuttle flights will be stopped, possibly for some years, until the final determination of the cause of the Columbia accident," Sergei Gorbunov, a spokesman for the Russian Space Agency (RSA), was quoted as saying by the ITAR-Tass news agency.

Russian Soyuz rockets currently ferry up Russian crews to the ISS for short visits (in addition to their emergency role).

RSA spokesman Vyacheslav Mikhailichenko said it was possible the Expedition crews could also take this route in the near future.

But Soyuz carries fewer people and far less cargo than the space shuttle. And although supplies regularly go up on Progress vehicles, the US is reluctant to rely on them. Now, however, it may have no choice.

Alarmingly, another RSA spokesman told ITAR-Tass that Russia's space agency only had two Soyuz rockets capable of carrying crews to and from the space station, and urged US and Russian officials to help the space agency build new rockets.

Space co-operation

Another major factor is that the ISS requires frequent re-boosting to raise its orbit and keep it stable.

This is usually done by the space shuttle. It is possible to do this with the rocket motors on a Progress re-supply craft but the vehicle is less powerful.

Space officials know that the shuttle programme does not have the option of a lengthy wait, like the two-year grounding after the 1986 Challenger disaster.

One thing they desperately want to avoid, if at all possible, is leaving the ISS unmanned.

If the ISS has to be abandoned then there is the slim chance that onboard malfunctions could lead - in the worst case scenario - to the platform tumbling out of control, posing perhaps insurmountable problems for spacecraft wanting to dock at a later date.

Tass also quoted James Newman, Nasa's director of human space programmes in Russia, as saying that space co-operation between Russia and the United States was bound to intensify.

"It is vital to analyse what happened and eliminate problems in order to ensure safe flights for ISS crews," Mr Newman, who flew aboard Columbia last year, said.

What is certain is that all construction work on the platform will come to an immediate halt - the shuttle has been the mainstay for getting new components up into orbit to extend the station.