The International Space Station is manned by a team of astronauts drawn from America, Russia and other countries and while their duration of stay is limited, plans are afoot to send an American and a Russia astronaut who will remain there for one year's time.

The reason for such an expedition is to study the effects on the human body of long term exposure to the environments in the space station in preparation of long-haul journeys to distant planets like Mars. The two astronauts will undertake the joint mission to test the physiological and psychological effects of long-term space flight.

The basic objective is to find out how the human body can adapt to the rigors of future voyages to a distant asteroid or Mars because such journeys could span several months. Incidentally, the two volunteers will not enjoy the benefits of artificial gravity.

Experts believe that when long periods are spent in microgravity they can lead to increased loss of bone and muscle apart from reduced heart and artery function and also impaired sensory motor performance.

The two astronauts Scott Kelly of NASA and Michael Komienko from the Russian space agency, Roscosmos, will lift off in a Russian Soyuz spacecraft headed to the ISS in March 2015. During their stay in the ISS, they will work alongside three European Space Agency astronauts - including the British former test pilot Timothy Peake.