They can reduce drag, repel shock waves and make jet fighters vanish. Will plasmas start an aerospace revolution, or are they just another mirage? To look at, the test vehicle suspended in the hypersonic wind tunnel is little more than a cone. But inside is a small device that could revolutionise the way aircraft fly, saving fuel and heralding a new age of travel. It’s a generator that sends a beam of microwaves upstream into the Mach 6 flow, ripping apart the gas ahead of the model so that it is flying through a plasma–a boiling mix of positive ions and electrons–rather than ordinary gas.