SpaceX's Dragon spacecraft has completed its fly-by of the International Space Station, and has begun a battery of engineering tests ahead of the planned docking early on Friday morning. Dragon crossed under the ISS at a distance of 2.4km within the past few hours; look close in this image SpaceX tweeted earlier, shot from the ISS itself, and you can just see the Dragon capsule visible as a small dot.
Some of the tests on the roster today include the UHF radio link between Dragon and the ISS, which will be used to remotely control its docking process. Dragon is unmanned, and will be guided into place by astronauts and cosmonauts onboard the orbiting space station.
Initial tests worked out as expected, with the ISS able to remotely turn on and off a strobe light on the capsule. Still, there are plenty more to go before Dragon is allowed to come closer and perform a test-dock with the station; that's essential if SpaceX is to carry out its twelve trip resupply mission contracted with NASA.