The events of 9/11 as they unfolded through actual audio.
DARPA's Hypersonic Spacecraft Concept
DARPA created its Experimental Spaceplane (XS-1) program to help create a new paradigm for more routine, responsive and affordable space operations. The program aims to develop a fully-reusable unmanned vehicle that would provide aircraft-like access to space and deploy small satellites to orbit using expendable upper stages. XS-1 seeks to deploy small satellites faster and more affordably, and develop technology for next-generation hypersonic vehicles.