Visible Signatures of Hypersonic Reentry

Aerothermal heating of hypersonic reentry bodies can generate significant radiation of visible light. This study investigates the conditions for ground-level visibility and what the authors term noticeability of that radiated light to the unaided human eye. This study considers radiated visible light, transmission to ground level as a function of relative observer position, sky background contrast, human contrast perception limits, and psychophysical considerations for attention capture. Considering both pure ballistic trajectories and lifting-body trajectories, this study presents examples of spatial and temporal viewing zones for both detectability and noticeability. In some cases, viewing zones extend a significant distance from the impact location and/or include the impact location for a potentially significant period of time before impact.