The Australian test flight of a hypersonic “scramjet” engine which researchers believe will one day allow people to fly at 8,000 km (5,000 miles) per hour or more has been set back several months. Originally due for its maiden launch in the Australian outback on August 13, the prototype engine — built by the University of Queensland’s Center for Hypersonics — will now be fired off into the upper atmosphere on October 23, a university spokesman said.