David Wolf was due to blast off from Cape Canaveral in Florida in the early hours of this morning on board the Atlantis space shuttle for his long-planned rendezvous with Mir. He will replace the British-born astronaut Michael Foale when the shuttle docks tomorrow.
The US space agency had been under mounting pressure from Congress to collect Mr Foale without replacing him because of the serial mishaps that have recently afflicted the Mir station.
"We move forward not only because it is safe, but for the important scientific and human experience we can gain only from Mir," Nasa's administrator, Daniel Goldin, said in a statement.
The decision was based on the findings of three separate reports completed by Nasa on the viability of Mir, which has suffered from myriad technical problems following its collision earlier this summer with a Russian cargo craft. The announcement also brought relief to Russian space agency officials, who have always insisted that the station is safe.
Members of Congress have raised concerns that the US astronauts have been exposed to unacceptable risk by being on board the ailing station. Anger has been growing that the American astronauts have increasingly found themselves playing a "Mr Fixit" role on board the ship.Reuse content