The concept of phase angle as a variable of interest when reporting resident space object (RSO) brightness information is widespread throughout the community. Phase angle is the angle between the direction to the Sun and the direction to the observer, as seen at the object being observed. If the object were the Moon, a near-zero degree phase angle would be full moon. Phase angle is widely used in ... [Show full abstract] the astronomical community, and has been adopted by the satellite community as well. Phase angle is very useful for some objects (e.g., spherical objects with Lambertian reflectance properties), but rapidly loses its utility when applied to objects which have different properties.