An aircraft running on hydrogen that races through the upper atmosphere at speeds exceeding twelve times the speed of sound might seem like a fantasy reserved exclusively for science fiction. That, however, is the promise behind the Australian Hypersonix Launch Systems’ DART AE demonstrator, a small and uncrewed vehicle that is built around the SPARTAN scramjet, a completely new kind of engine. The immediate objective of this development program is not to make this aircraft a vehicle for passenger travel.