Astronauts prepare for one-year mission

What's the one thing astronauts Scott Kelly of the US and Mikhail Kornienko of Russia can't do without when they move into space this week for a year?

For Kelly, it's a belt. Kornienko must have his vitamins.

Kelly went beltless during his five-month mission at the International Space Station a few years back, and he hated how his shirt tails kept floating out of his trousers. So this time, the 51-year-old retired Navy captain packed "a military, tactical-style thing" capable of supporting a tool pouch.

For Kornienko, three bottles of vitamins will be on board when their Soyuz rocket blasts off from Kazakhstan on Saturday.

After more than two years of training, Kelly and Kornienko are eager to get going. It will be the longest space mission ever for Nasa, and the longest in almost two decades for the Russian Space Agency, which holds the record at 14 months.

Medicine and technology have made huge leaps since then, and the world's space agencies need to know how the body adapts to an entire year of weightlessness before committing to even longer Mars expeditions. More year-long missions are planned, with an ultimate goal of 12 test subjects. The typical station stint is six months.