It took four tries, but SpaceX’s CRS-3 mission is on its way to the International Space Station (ISS). Today at 3:25:21PM, EDT, the unmanned Dragon cargo spacecraft lifted off atop a Falcon 9 rocket from Space Launch Complex 40 at Cape Canaveral Air Force Station in Florida in rainy, overcast weather that NASA said only gave the launch a 40 percent chance of going ahead without delay. The successful launch is SpaceX’s third cargo mission to the ISS and its fourth visit to the station.

The Falcon 9 rocket lifted off on schedule from Cape Canaveral in the first step in a cosmic race. Because of the need to rendezvous with the ISS, CRS-3 had to launch in what is called an “instantaneous launch window.” If any holds had occurred during the launch, it would have required another delay until at least Saturday for the next launch window.

Despite previous delays, today’s launch went off without incident. Three minutes after the launch, the first stage of the Falcon 9 cut off as planned, followed by second stage separation and ignition. The second stage then fired until +10 minutes, when it shut down and separated from the Dragon spacecraft. Two minutes later, the orbiting spacecraft deployed its solar array while a worldwide audience watched over television and the internet.

What made this launch unusual is that it was a bit of a multitasking event. After separating from the Dragon cargo ship, the Falcon 9 second stage deployed a cluster of minisatellites. Meanwhile, the first stage, instead of passively falling into the sea, executed a re-entry burn, then deployed the landing legs that the rocket carried for the first time on an operational flight, before firing its engines a final time to simulate a powered landing on the surface of the Atlantic Ocean. SpaceX says that this landing maneuver is still experimental in anticipation of an actual landing on dry land, and gave it only a 30 to 40 percent chance of success. The company says that the entry burn went off, though the success or failure of the landing simulation has yet to be made public.

The Dragon spacecraft is currently coasting as mission control tests its systems in anticipation of a series of course correction burns that will put it on course for the ISS, and the opening the the guidance and navigation control bay door to expose navigational sensors.

This is the fourth attempt at launching the CRS-3 mission. The first delay was due to a contaminant found in the unpressurized cargo bay of the Dragon cargo ship, and the second occurred when a tracking radar was put out of action by a major malfunction. During Monday’s third launch attempt, preflight checks detected that a helium valve was leaking, resulting in another scrub.

The Dragon spacecraft is carrying 2.5 tons (2.26 tonnes) of experiments and supplies to the ISS, including a new spacesuit and parts to repair the spacesuits already on the station. It’s scheduled to rendezvous with the ISS on Sunday, when Expedition 38 Commander Koichi Wakata and Flight Engineer Rick Mastracchio will use the station’s 17.6-m (57.7-ft) robotic arm to secure the spacecraft and guide it to the Earth-facing docking port on the Harmony module, where it will be bolted into place for its stay.

Source: SpaceX