Here’s an article describing the pre-rendezvous testing that it will go through. This is misleading, though:
“This is pretty tricky. And also, for the public out there, they may not realize that the space station is zooming around Earth every 90 minutes, and it’s going 17,000 mph,” said SpaceX CEO Elon Musk. “This is something that is going 12 times faster than a bullet from an assault rifle. So it’s hard.”
The velocity relative to earth isn’t really relevant, and doesn’t make it harder. All that matters is the relative velocity between the spacecraft and the ISS. And that, of course, is what they have to demonstrate their ability to control.
[Update a while later]
More thoughts from Tom Jones.