Nasa and the SpaceX rocket company are to study the feasibility of running a private astronaut mission to extend the life of the Hubble telescope. The orbiting observatory, one of the greatest instruments in the history of science, is gradually losing altitude. If nothing is done to re-boost it, the telescope will eventually fall into the atmosphere and burn up. Hubble was serviced on five occasions by astronauts in Nasa's space shuttle, the last time being in 2009. Since the