The European Union has launched in 2005 its Long-Term Advanced Propulsion Concepts and Technologies project (LAPCAT). Several companies worked on this €7 million EU-funded project. For example, Popular Science reports that Reaction Engines Limited has designed an hydrogen-powered hypersonic airliner simply dubbed A2. This plane would fly at Mach 5 (3,400 mph or 5,500 km/h) on very long distances, such as non-stop flights from Europe to Australia in less than 5 hours. And because it would be hydrogen-powered, it would not release any greenhouse gases over our heads. The A2 plane has been designed to carry about 300 passengers who would pay a price equivalent to current business class tickets. The question is: will this plane ever take off? But...