The May 1 Space-X launch of a classified satellite mission was considered very unusual after amateur satellite watchers realized it was being put into the same orbit as the International Space Station (ISS).
(ISS resupply missions aren’t classified.)
We now know that not only was “USA 276” put into the same orbit, but it actually buzzed the ISS as it gradually “orbited” around the space station.
Here’s a simulation from the SatTrackCam blog, showing the new spy satellite just outside the box representing the safe distance for objects to pass near the ISS without an orbital avoidance maneuver:
Over time, the spy satellite then circled the ISS, just several kilometers away.
This does not happen by accident. To accomplish this you have to launch the satellite into a precise orbit with the same altitude and inclination angle with the equator. Then, you have to use on-board propulsion to fine tune the orbit and “catch up” to the ISS. To then “orbit” the ISS at a safe distance is even trickier.
So, what could this classified mission of USA 276 be?
The most logical explanation is that DoD is testing a capability to rendezvous with and spy on spy satellites, up close and personal. Such a capability would no doubt include high resolution imagers, electronic surveillance, and whatever else they can think of to investigate other countrys’ spy satellites and better figure out what they are doing up there.