In 1985, J.E. Draim wrote the article "Three- and four-satellite continuous-coverage constellations" (paywalled, sorry) for the Journal of Guidance, Control, and Dynamics. The article described using four satellites in a tetrahedral configuration of inclined, elliptical orbits to provide complete surface coverage of Earth at all times, as the minimal number of satellites necessary to do so. Draim was subsequently awarded patentson the idea. A couple months ago, a discussion in the IRC chann