MOSCOW/HOUSTON, May 16: The three crewmen aboard the International Space Station (ISS) drew from emergency oxygen on Thursday after the main oxygen generator shut down, but US and Russian space officials said the situation was not serious.

Two Americans, Carl Walz and Dan Bursch, and Russian commander Yury Onufriyenko activated reserve systems as they worked to repair the “Elektron” unit which extracts oxygen from water.

“The cosmonauts are now using oxygen cartridges as a back-up,” Valery Lyndyn, spokesman at the Korolyev flight control centre, told Russian NTV television. There was no acute danger to the crew, he stressed.

“It’s not a problem, we have oxygen supplies for three more months on board,” said John Ira Petty, spokesman for the US space agency NASA.

Petty said it was not clear whether the problems were caused by hardware or computer software defects in the equipment. Spares could be sent to the ISS on the space shuttle Endeavour which is due to arrive with a new crew and fresh oxygen supplies in early June.

The crew has some bottled reserves and can also burn stocks of special chemical cartridges that produce oxygen.

But these systems can also pose a threat. In Feb 1997 an oxygen stick used on the Mir space station burst into flames and filled the interior with smoke. Only courageous action by cosmonauts aboard prevented damage to the outer skin of the module that would almost certainly have amounted to a death sentence for the crew.—dpa