The hypersonic (at least five times the speed of sound) velocities that the engine is striving for have until now only been feasible with single-use hydrogen- or hydrocarbon-fueled ramjet engines that in most cases would be destroyed by the end of the flight, making them suitable for missiles but not much else. Scramjet test engines -which improve upon ramjet performance and reliability but are much harder to engineer-have been around for decades, but their success rate has been dismal, and they have usually burned dangerous and unwieldy hydrogen for fuel. (Ramjets slow air traveling through them to subsonic speeds, while scramjets keep airflow above supersonic speeds-hence, the difficulty keeping them lit.) But this new engine, being tested at the cutting-edge facilities of aeronautical engineering firm GASL, runs on JP-7, a significantly more manageable kerosene-like jet fuel, and it has a unique cooling system that is key to its performance under hypersonic conditions. HyTech is slowly edging toward success, with several tests over the summer that have come close to a previously unattainable milestone: actually starting and sustaining combustion amid supersonic airflow.