The journey time from Earth orbit to Mars could be slashed from six months to less than six weeks if NASA’s idea for a nuclear fusion-powered engine takes off. The space-flight engine is being developed by a team led by Bill Emrich, an engineer at NASA’s Marshall Space Flight Center in Huntsville, Alabama. He predicts his fusion drive would be able to generate 300 times the thrust of any chemical rocket engine and use only a fraction of its fuel mass. That means interplanetary missions would no longer need to wait for a “shortest journey” launch window. “You can launch when you want,” Emrich says.