I mis-spoke. 4.5 hours: "U.K.-based Reaction Engines is developing technology for Synergetic Air-Breathing Rocket Engines (SABRE), which could one day allow ai

I mis-spoke. 4.5 hours: "U.K.-based Reaction Engines is developing technology for Synergetic Air-Breathing Rocket Engines (SABRE), which could one day allow aircraft to fly up to five times faster than the speed of sound — that’s Mach 5 or 3,836 miles per hour. At that speed, hypersonic flights between London and Australia could be over in just four-and-a-half hours." https://www.cnbc.com/2019/04/08/hypersonic-flight-technology-passes-a-hugely-significant-milestone.html https://www.cnbc.com/2019/04/08/hypersonic-flight-technology...