New Generation of Hypersonic Engines Harvest Oxygen Directly From Air: Can Hop From London to Sydney in 4 Hours
Innovative, reusable rocket engines are being developed that are so powerful, they could one day fly a suborbital spaceplane from London to Sydney in just 4 hours.
While Concorde cruised at Mach 2 - twice the speed of sound - with regular jet engines, these new engines are shooting for Mach 5 and beyond - a speed known as “hypersonic”.
Rocket-powered aircraft are capable of hitting far greater speeds than those with simple jet engines. But they are extremely expensive because they must be powerful enough to carry the mass of the liquid hydrogen and liquid oxygen fuel they need. Making them lighter would make them cheaper to fly, but how do you ditch weight?
The answer is obvious: the air the spaceplane passes through has plenty of oxygen. If you can suck up the air and burn it with hydrogen you can instantly slash the amount of on-board oxidant you would need to just that required to propel the spaceplane when it leaves the atmosphere.
That’s the idea behind Sabre, a hydrogen-and-air-burning engine that is being developed and tested by Reaction Engines of Culham in Oxfordshire, UK. It is designed to reach orbit in a future satellite-launching spaceplane called Skylon (illustrated above), and may be used suborbitally in a point-to-point Mach 5 passenger aircraft.
Sabre’s main advantage is that it could power a reusable spaceplane able to take off from a runway and climb to space with just one type of engine. That puts it well ahead of scramjets - engines with no moving parts that use the superfast motion of the plane to compress air into fuel. Scramjets only begin working at about Mach 4 and need boosting to that speed by a rocket. “If you need different engines for different parts of the trajectory, you’re carrying expensive dead weight,” says Ben Gallagher, business development manager at Reaction Engines.
Sabre’s key technology is a “precooler”, a superfast, lightweight chiller that processes air to burn with hydrogen. “Air entering the Sabre engine at Mach 5 heats up to over 1000 °C. That would melt a normal rocket engine,” says Gallagher. “So our precooler chills that air to -150 °C in one hundredth of a second.”
This frigidity means that when the air is compressed, in preparation for combustion with hydrogen, it does not get too hot. The precise details of how the precooler works are a secret - so secret that Reaction Engines has not even filed any patents on the technology. All we know is that it passes air over a great many thin, helium-chilled tubes that present a large surface area for cooling.