NASA has made a commitment to send humans to Mars by the 2030s. This is an ambitious goal when you think that a typical round trip will anywhere between three and six months and crews will be expected to stay on the red planet for up to two years before planetary alignment allows for the return journey home. It means that the astronauts have to live in reduced (micro) gravity for about three years – well beyond the current record of 438 continuous days in space held by the Russian cosmonaut Valery Polyakov.