Engineers have discovered orbits that allow satellites to harness forces that would disrupt other craft — making it possible for a four-craft constellation to monitor almost the entire globe at once.

Calculations in the 1980s showed that it is theoretically possible for four satellites to constantly observe all of Earth. But substantial amounts of propellant, an expensive resource, would be needed to maintain the required orbits, in part to correct for forces such as the gravitational pull of the Moon and the Sun.

Lake Singh at the Aerospace Corporation in Chantilly, Virginia, and his colleagues created an algorithm to look for orbits that maximize satellite coverage while taking into account forces that are usually disruptive. Sifting through five million simulated orbits, the algorithm found configurations that exploit these forces to keep a four-craft system in check. One such arrangement would cover 86% of Earth’s surface; another, 95%. Both would use 60% less propellant than existing systems with similar coverage.

The gains could allow mission operators to save money or to extend satellite flights, say the authors.