By Dr David Whitehouse BBC News Online science editor

Supplying the ISS without the shuttle is a problem

It is said Nasa let the launch go ahead even though some engineers had raised concerns about the safety of the platform's air cleaning system.

The unnamed engineers also questioned whether medical and other supplies were at an appropriate level.

The incoming ISS commander Michael Foale said he was aware of the issues.

Safety not in doubt

Nasa (the US space agency) says that the safety of the mission was never in doubt. Spokesman, Robert Mirelson, said there was a full discussion by engineers who decided that the launch could proceed safely.

Mr Mirelson said that at a series of pre-launch meetings in the US and Russia, officials had considered the concerns of some engineers about the air-cleaning equipment and supplies on the ISS (International Space Station).

The latest crew arrive safely

But the Washington Post reports that two officials overseeing health and environmental conditions on the platform would not consent to the blast-off.

Responding to these points, Nasa Administrator Sean O'Keefe said that, as he understood it, there was no immediate hazard to the crew, but that conditions could deteriorate in the next six months and force the crew to abandon ship.

"If there is any indication whatsoever that this situation is hazardous to their continued existence, or to their health longer term, the answer is: 'Get aboard the Soyuz, turn down the lights and leave'," he said in an interview.

Headaches and dizziness

The dissenting scientists were reported to say that the 1 February disaster of the shuttle Columbia and the subsequent grounding of the shuttle fleet had made it impossible to repair or replace faulty equipment on the ISS.

They said there was a growing array of hardware problems that were preventing Nasa from assessing the quality of air, water and radiation levels aboard the ISS.

Some medical officials have said that equipment problems had been growing for more than a year, with ISS astronauts complaining of headaches, dizziness and, according to one official, "an inability to think clearly."

Speaking during a press conference on board the ISS, Michael Foale said he had been made aware of the issues several weeks earlier by his flight surgeon.

Return home

He emphasised that it had been raised at a "sub-meeting" and was not considered important enough to discuss at the full-flight readiness review for his mission.

Astronaut Ed Lu said that the monitoring equipment problems began about six weeks ago and were limited to measuring minor trace gases on the ISS.

Michael Foale, Russia's Alexander Kaleri and Spain's Pedro Duque entered the space station on Monday, two days after their Soyuz transport craft blasted off from Kazakhstan.

Mr Duque is to remain aboard the station for eight days before returning to Earth with American Ed Lu and Russian Yuri Malenchenko, who have been aboard since 28 April.