Update April 18th, 2014 3:30pm: The Falcon 9 has successfully launched, and the capsule is headed towards the ISS for a Sunday docking.

After weeks of delays, SpaceX is preparing to launch its third supply mission to the International Space Station. The Falcon 9 rocket and accompanying Dragon capsule are expected to blast off from Cape Canaveral at 3:25 EDT, and the craft is set to rendezvous with the space station on the morning of Sunday, April 20th. A video feed of the takeoff will go live around 2:45PM. The CRS-3 mission, carried out through a partnership with NASA, comes almost two years after the Dragon capsule became the first commercial craft to ever dock with the ISS. This time, SpaceX is using the flight to test the next steps in its plan for a reusable rocket. The first stage of the Falcon rocket has been equipped with four landing legs. After launch, it will separate as normal, then attempt to slow itself and make a controlled return to Earth, which would allow it to be used again after being fished out of the ocean.

The odds of this happening successfully aren't great — SpaceX VP Hans Koenigsmann put them at between 30 and 40 percent earlier this month. SpaceX has previously managed to restart the first stage's engine after it separated, but it hasn't yet pulled off a landing. A reusable rocket would allow SpaceX to save millions, especially if it can eventually pull off the more difficult trick of recovering the second stage, which drops off at a higher altitude. But even if it fails, the central supply mission won't be compromised. As long as nothing else goes wrong, in fact, SpaceX and NASA will be breaking new ground on the ISS. The capsule is carrying red romaine lettuce and radishes in an experimental plant growth chamber, part of a test project meant to give astronauts a source of fresh food.

Since its original launch date on March 16th, though, the third supply mission has been delayed by technical snags. The first takeoff was aborted so SpaceX could resolve "remaining open items," and a second planned launch on March 30th was called off because an Air Force tracking radar system at Cape Canaveral shorted out. On the latest date, April 14th, the Falcon rocket's first stage sprung a helium leak. SpaceX maintained that its backup systems would have still made a launch successful, but it pushed the launch back to today despite weather concerns. This morning, NASA reported a 40 percent chance that weather would be amenable, so we'll be watching for confirmation that the launch is taking place.

Update April 22nd, 3:45PM ET: in a press conference following the launch, Musk said that SpaceX had been unable to recover the reusable rocket due to rough seas, according to Mother Nature Network. "I heard reports of 13- to 20-foot wave heights. It's really pretty crazy out there," Musk reportedly said. "In fact, the [retrieval] boats weren't able to get close because of the heavy seas. It's unlikely that the rocket was able to splash down successfully."