The US National Aeronautics and Space Administration (Nasa) announced on Tuesday that it was collaborating with the US Defence Advanced Research Projects Agency (Darpa) to build and demonstrate in space a nuclear thermal rocket engine. The joint programme is designated the Demonstration Rocket for Agile Cislunar Operations (Draco). This technology, once proven, would be used to propel crewed interplanetary space craft, needed to voyage to and from Mars. A nuclear thermal rocket engine would use …