This paper presents the design evolution of a military transatmospheric aerospace plane, considerations of options, and the formulation of a single transatmospheric aerospace plane. The design concept started with requirements, an operational concept, a set of design choices, a technology base, and a close look at the factors that determine orbital closure performance requirements. Several unique factors are considered in the design formulation. The baseline mission is a once around and return to the base from which the takeoff occurred. The flight profile to minimize energy requirements is a boost-glide-skip-glide trajectory. The configuration is based on recent work at the University of Maryland on waverider optization across a range of Mach numbers. Engine selection is based on both specific impulse and engine thrust to weight for a rocket-based combined cycle engine. The Aerojet “strut rocket” combined-cycle engine is baselined. Technology portfolio readiness is evaluated using NASA technology readiness criteria. A comparison of rocket and air-breathing concepts is presented. In addition, design choices with respect to piloted versus automated remote guidance and control and vertical versus horizontal takeoff are presented. Lastly, the benefits of a military aerospace plane are discussed.