A deterministic approach is used to derive the total number of platforms, sensor elevation field of view, and sensor/space-object maximum range requirements for the preliminary design of space-based surveillance systems in polar orbits that provide continuous multiple global or polar cap above-the-horizon (ATH) viewing. These requirements are determined as a function of surveillance platform altitude, the minimum and maximum space object altitudes of interest, and the multiplicity of continuous global or polar cap ATH coverage desired. Example trade-offs are given for platform altitudes between 500 and 2500 km.
"Design Of Low To Medium Altitude Surveillance Systems Providing Continuous Multiple Above-The-Horizon Viewing," Optical Engineering 28(1), 280125 (1 January 1989). https://doi.org/10.1117/12.7976896