US and Russian space experts scramble outside to assess the 'very serious' ammonia leak.
An ammonia leak outside the International Space Station led to a series of events which will cause two astronauts to do a spacewalk and fix the issue.
"Indeed, they have a serious defect, very serious," Vladimir Solovyov, flight director for the Russian segment of the space station was quoted as saying by the Interfax news agency.
The ammonia leak had supposedly occurred in one of the radiator lines that cool the powers systems, and there's been a leak in that area previously too. "This is not critical," the state RIA Novosti news agency quoted Alexei Krasnov, head of manned flight programmes at the Russian Space Agency, said.
NASA claims that the six-man station crew is not in danger, and three of them will be returning to earth on Monday. Americans Chris Cassidy and Tom Marshburn will be doing the spacewalk to try and detect the source of the leak.
"We are going to get them outside and see if we can't lay eyes on the leak source," Michael Suffredini, International Space Station Program Manager told reporters.
Orbital debris or a meteorite is suspected to have hit the cooling radiator and cause the problem, according to Suffrendini.
The situation is expected to be under control, given that both Cassidy and Marshburn have prior experience in spacewalking. Marshburn has logged in 18 hours and 59 minutes of extra vehicular activity (EVA), while Cassidy has recorded 18 hours and 5 minutes back in 2009.
Also, their six and a half hour spacewalk will probably not interfere with their planned departure from the space station, according to NASA.
The space news website Spaceflight101 claims that the Mission Control already knows the source of the leak, and the astronaut's task will be to confirm it.
An official statement is yet to be obtained from the Russian Space Agency.
Previously, the capacity of the space station was only three people, but since 2009, there are six people abroad the station currently, all set to get back to Earth on May 14, 2013.
Though Russia has suffered a few setbacks in its space program, its manned missions have been flawless.