Hypersonic airliners
Hypersonic airliners are already being researched and developed, and could enter commercial service within the next 25 years.*
These aircraft would have a cruising speed of Mach 5 - or 3,800 mph - allowing them to fly from Europe to Australia in less than four hours. With a range of more than 20,000 km (12,000 miles) they could perform this journey without refuelling. They would have excellent subsonic and supersonic fuel efficiency, avoiding the problems inherent in earlier supersonic aircraft. Furthermore, and perhaps more importantly, hypersonic airliners will be environmentally friendly. Powered by liquid hydrogen, their only waste products will be water vapor and small levels of nitrous oxide.
Another advantage is that, while the 150m-long designs will be larger than previous jets, they will actually be lighter than Boeing 747s and could utilise conventional airport runways. They will have moderate take-off noise, too.
In many ways, they will be the spiritual successor of Concorde.
The craft will likely be windowless, however. The heat generated by traveling so fast will make it difficult to install windows that are not too heavy. One solution to this problem might be the installation of flat screen displays projecting images of the scene outside.