Russian announced on Wednesday a February mission to the International Space Station to pick up crew members left stranded after a strike damaged the capsule that was to take them home.

Didier Schmitt, the European Space Agency's head of human and robotic exploration, said it was not rare for tiny meteorites to hit the space station.

The micrometeorites can be traveling at speeds from 10 to 30 kilometers (6-18 miles) a second—"much faster than a shotgun bullet," Schmitt said.

That is why, when the space station's large observation window is not in use, it is shuttered with "very, very thick layers of protective materials," he said.

Here are some key facts about the orbiting laboratory set up to advance space exploration—and prepare to send humans to Mars—where Russians and Americans have worked together for a quarter of a century.

Size of a football field

The ISS is the largest man-made structure ever put into orbit.

Launched in 1998 by the United States, Russia, Canada, Japan, and members of the European Space Agency (ESA) it is the size of a football field and weighs about the same as a jam-packed Boeing 747.

Built at a total cost of about 100 billion dollars, mostly paid for by the US, it orbits the Earth every 90 minutes at an average altitude of 400 kilometres (250 miles).

It has been permanently occupied since November 2000 by Russian and American-led crews that usually stay for around six months to carry out experiments in microgravity (weightlessness) which have practical applications on Earth and help prepare for future Mars missions.