CRS-2 nearly failed in orbit. Shortly after Dragon separated from the rocket, three of its four thruster pods failed to pressurise, leaving the spacecraft able to control its attitude but not to manoeuvre — and a capsule that cannot manoeuvre cannot reach a space station.
The cause was blockages in the oxidiser pressurisation lines, most likely a stuck check valve. Engineers on the ground worked the problem in real time, commanding pressure cycles that hammered the valves repeatedly until they freed, and restored all four pods within a few hours.
The rendezvous slipped by a day and the mission proceeded normally, delivering supplies and hardware and returning experiment samples and equipment. Two grapple fixtures were also carried up for future use on the station's exterior.
It was the last flight of the original Falcon 9 configuration and the last of the first Dragon design. Both were substantially revised afterwards, with the thruster valve issue among the specific items addressed.
The episode is a good illustration of what a crewed station gains from having spacecraft that can be talked to. An automated vehicle with the same fault and no ground intervention would simply have been lost.
