The Daily Beast:
A trio of mysterious Russian government satellites
startled space experts when, shortly after blasting into low orbit between 2013 and 2015, they began dramatically changing their orbits, demonstrating a rare degree of maneuverability for small spacecraft.
Now after being idle for a year or more, two of the mystery-sats are on the move again. On April 20, 2017, one of them reportedly shaved hundreds of meters off its orbit in order to zoom within 1,200 meters of a big chunk of a defunct Chinese weather satellite that China smashed in a controversial 2007 test of an anti-satellite rocket.
By orbital standards, that's pretty close.