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. However, the amount of propellant needed to keep the satellites in place, and the ensuing cost, made the configuration unfeasible.

Now, a National Science Foundation-sponsored collaboration led by Patrick Reed, the Joseph C. Ford Professor of Engineering at Cornell University, has discovered the right combination of factors to make a four-satellite constellation possible, which could drive advances in telecommunication, navigation and remote sensing. And in an ingenious twist, the researchers accomplished this by making the forces that ordinarily degrade satellites instead work in their favor.

"One of the interesting questions we had was, can we actually transform those forces? Instead of degrading the system, can we actually flip it such that the constellation is harvesting energy from those forces and using them to actively control itself?" Reed said.

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