Nasa is hoping to build a nuclear propulsion system which would allow a spacecraft to travel to the nearest star. While humanity has explored large parts of our own Solar System, the distances to another star system are, literally, astronomical. Nasa"s Voyager 1 became the first spacecraft to venture into interstellar space in 2012. But even if the 10-miles-per-second probe were heading in the right direction, it would take it 70,000 years to reach our closest star Alpha Centauri, which is 4.37 light years away, or 25 trillion miles. However, Dr Thomas Zurbuchen, associate administrator at Nasa"s Science Mission Directorate, believes that it might be possible. Speaking to The Sunday Telegraph at the launch of the Solar Orbiter probe last week, Dr Zurbuchen said Nasa should move away from missions that could be handled by private companies and instead focus on answering the big...