Dspiral writes "At the Canadian publication, The Globe and Mail, they write about the scramjet. A jet engine, with theoretical speeds over 8000 Kph, and pollution free!" Zero pollution because its fuel is hydrogen (a scramjet takes its oxygen from the air). The HyShot homepage is amazing; the beast has been built on a shoestring, barely over a million dollars Australian, and my favorite part is their planned test: "...shooting an engine into the atmosphere on a rocket, and hoping it will ignite as it plunges back down to Earth. Mr. Paull's speed objective is Mach 7.6, and the engine should ignite 23-35 kilometres off the ground."