Last year, China tested a hypersonic missile that circumnavigated the globe before hitting its target. It surprised the world, and it was a sign of just how advanced its military has become.  So amid calls for the US and its allies including Australia to develop better missile capabilities in response, how big is the threat?  Today, aerospace engineer and former NASA employee, Professor Iain Boyd, on the hypersonic arms race Beijing seems to be winning.   Featured:  Dr Iain Boyd, professor of aerospace engineering sciences, University of Colorado Boulder