I. Introduction

Hypersonics is, and for the foreseeable future will be, the domain of both national defense and civilian space access and exploration/utilization. These categories are not mutually exclusive; defense applications obviously include space access as a necessary enabler for space war fighting. Civilian hypersonic applications include reducing the costs of access to space for both sensitive and not-so-sensitive (high g tolerant) cargo/payloads and planetary entry/reentry/aerocapture. We have executed these civilian hypersonic missions for decades; the current major requirement is for large improvements in affordability. Military hypersonic applications are multifarious and include hypersonic penetrators, affordable and "flexible" space access, endoatmospheric interceptors, flexible space war fighters, tactical and strategic missiles (ballistic/boost glide/cruise) propelled by rockets, air breathers, and various synergistic combinations with a broad range of fueling options. Military metrics include affordability and, for some applications, raw capability and mission enablement. Missions include protection/defense; strike; intelligence, surveillance, and reconnaissance (ISR); and asset placement. New hypersonic military requirements and metrics include rapid response for time-critical moving targets, penetration of hard and buried targets, reconstitution of command, control, communications, computing, and intelligence (C4I) assets, tactical ballistic missile (TBM) interception, and...