Watch SpaceX Launch its Falcon 9 rocket from Kennedy Space Center with a Korean communications satellite and land the first stage on the Of Course I Still Love You drone ship.

On June 3, the spacecraft approached within about four miles of the ISS — just barely outside its imaginary safety zone — and circled the orbiting research complex occupied by six astronauts.

The close encounters suggested the NRO mission, led by Ball Aerospace, might be testing technologies for observing the rendezvous and grappling of spacecraft in low Earth orbit.

“If the flyby was intentional, one has to wonder if targeting a high-profile object like the ISS was meant to send a signal,” wrote Marco Langbroek, a satellite tracker and member of the astronomy department at Leiden University in the Netherlands, in a June article in “The Space Review.”

“I readily admit, this all to a high degree remains speculation and wishful thinking of course,” Langbroek wrote to fellow satellite trackers of the potential connection between the Zuma and NRO missions.