DID A SPY SATELLITE JUST VISIT THE ISS? On May 1st at Cape Canaveral, SpaceX launched a classified satellite (USA 276) for the US National Reconnaissance Office. Watching the spysat go into orbit, analysts around the world quickly realized something odd. The orbit of USA 276 was similar to that of the International Space Station and could theoretically make close approaches to the orbiting outpost.
On June 3rd, that’s exactly what happened. “USA 276 made a close approach and effectively circled the ISS,” reports Marco Langbroek of Leiden, the Netherlands. He prepared this diagram showing the circumstances of the encounter:
Amateur satellite watchers have been tracking USA 276 since late May, and their observations have resulted in ever-improving estimates of the satellite’s orbit. “With the latest data included, we can establish the moment of closest approach as 3 June 2017, 14:01:52 UT. It happened in daylight over the southern Atlantic north of the Falklands, near 43o.75 S, 45o.45 W, with a miss distance of only 6.4 ± 2 km.”
In the diagram above, the brick-colored box has dimensions of 4 x 4 x 10 km. Whenever an object looks like it is going to pass through that box, ISS mission controllers evaluate the possibility of a collision avoidance maneuver. “USA 276 remained just outside the 4 x 4 x 10 km box at closest approach,” notes Langbroek. “As a result, collision avoidance maneuvers were not required.”
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