Contributions of the OH Airglow to Resident Space Object Irradiance

Abstract : A goal of space situational awareness is the detection and characterization of resident space objects. An around-the-clock capability depends on the ability to observe the space object under a variety of illumination conditions. In this report, we focus on space-based sensors operating in the visible, near-infrared and short-wave infrared where reflected light sources are the dominant signature components. of particular interest is the ability to observe space objects from above during nighttime in a moonless sky. A promising illumination source is the hydroxyl radical airglow. It is the most dominant illumination source under these conditions. A further advantage is the location of the airglow between 80 km and 90 km. By being well above the ground. it illuminates surfaces that are pointing upward and hence are observable from above. We predict surface irradiance of space objects as a function of surface orientation for a number of spectral bands, using SAMM2 to compute LOS radiances. A few sample calculations of sensor irradiance for nadir and limb viewing of a space object (modeled as a flat plate) illustrate the ability to observe a space object from above. The requirements of an arnund-the-clock modeling capability are briefly outlined.