Satellite constellations harvest energy for near-total global coverage

Think of it as a celestial parlor game: What is the minimum number of satellites needed to see every point on Earth? And how might those satellites stay in orbit and maintain continuous 24/7 coverage while contending with Earth's gravity field, its lumpy mass, the pull of the sun and moon, and pressure from solar radiation? In the mid-1980s, researcher John E. Draim proposed what is generally considered to be the ideal solution: a four-satellite constellation. More

(Source: Phys.org - Jan 11)