Update: The Dragon spacecraft is now scheduled for launch on 19 May. The berthing operation is set for 22 May.
Expedition 30 crewmembers André Kuipers and Don Pettit continue to train on the International Space Station for the arrival of the SpaceX Dragon spacecraft. Having started their training on a computer simulator in the Destiny lab, they are now training using the real robotic arm.
On 3 May, as the unmanned Dragon spacecraft approaches ISS, they will use the Station's Canadarm2 to first grab the spacecraft and then manoeuvre it into place to mate with the Harmony module's Earth-facing docking port.
The following animation from the Canadian Space Agency shows just how complex it is to catch a Dragon.