process that leads to gradual decrease of the distance between two orbiting bodies at their closest approach (the periapsis) over many orbital periods
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If left unchecked, the decay eventually results in termination of the orbit where the smaller object strikes the surface of the primary; or for objects where the primary has an atmosphere, it burns, explodes, or otherwise breaks up in its atmosphere REF: 'Orbital decay'. Wikipedia, https://en.wikipedia.org/wiki/Orbital_decay [21.12.2016]
During its last 13 months of operations, as its orbit decayed and it spiraled into lower altitudes and eventual re-entry into Earth’s atmosphere, C/NOFS satellite captured a unique set of comprehensive observations as it traveled through the very space environment that can directly cause premature orbital decay.
