2nd Update: According to SpaceX founder Elon Musk the first stage of the SpaceX booster "landed hard" on the droneship, which was the expected result of a rocket coming back from a high velocity with limited propellant to slow down.

Musk said the company will have a better chance to nail a sea-based landing with the next Falcon 9 launch, which likely will be a cargo delivery mission to the International Space Station. A launch to the station will leave more rocket fuel for a return to Earth, increasing the odds of success. That launch is presently scheduled for no earlier than March 30.

Update: The Falcon 9 rocket launched successfully, however it was not immediately clear that the first stage was able to land safely on the barge about 600km off the Florida coast. Images from the drone ship, before the video feed died, were not entirely promising.

About 30 minutes after launch the second stage of the Falcon 9 fired, successfully delivering the satellite into orbit. It will now essentially coast to an altitude of 36,000km.

Original story: Here we go again. Four times SpaceX has attempted to launch the SES-9 communications satellite, and four times the rocket company had to scrub. For today's launch attempt, at 6:35 pm ET (11:35pm UK) weather does not appear to be a constraint, so we will again be watching primarily for fuel-loading issues.

The most dramatic of the four scrubs came on Sunday when, just as the launch countdown reached zero, flight computers on board the rocket halted the launch due to a low thrust detection. Elon Musk, the company's chief executive, said that issue was partly due to a 35-minute delay caused by a boat that strayed into the safety zone off the coast of Florida.

With its new, more powerful variant of the Falcon 9 rocket, SpaceX is having to handle this super-cold, dense propellant more carefully, and one of the things it is trying to do is deliver the right amount of fuel just before launch. Issues related to propellant loading caused the first two scrubs. The most recent scrub, on Tuesday, came due to high winds. SpaceX has been waiting for them to die down, and they now have.

As with other recent launches, SpaceX will try yet again to fly its booster back to an automated ship in the Atlantic Ocean off the coast of Florida. However, because this is a high orbit (about 36,000km above the equator) and will require a heavy vehicle with more fuel and more speed, returning safely back to Earth is far from a sure thing. Additionally, at 5,300kg, this is the heaviest payload SpaceX has attempted to deliver to a geostationary orbit. Still, the company says it will make another attempt at a historic first, landing an orbital rocket on a sea-based platform. "The first stage of the Falcon 9 will attempt an experimental landing on the 'Of Course I Still Love You' droneship," SpaceX said in its press kit. "Given this mission’s unique GTO profile, a successful landing is not expected."

The live video below should begin about 20 minutes before the launch window opens at 6:35pm ET.

The company's previous tries to successfully land a rocket at sea have failed, but the last attempt in January came close. One of the rocket's four landing legs failed to lock out, even as the Falcon 9 booster made a feathery touchdown on the drone ship in high seas. Today's landing attempt should occur about 10 minutes after launch.