Update (Friday, 7:54 p.m. ET): SpaceX said that the Falcon 9's first stage did not successfully land on the at-sea drone ship. It was the fifth failed attempt to launch and land the rocket's first stage at sea.
Elon Musk, the company's CEO tweeted that, "Rocket landed hard on the droneship. Didn't expect this one to work (v hot reentry), but next flight has a good chance."
The company did not say when that next flight would be.
Update (Friday, 6:38 p.m. ET): SpaceX said that the Falcon 9 had a successful first-stage separation, and second-stage engine ignition.
Update (Friday, 6:36 p.m. ET): SpaceX's Falcon 9 launched right on time. It will take about ten minutes to determine if the rocket's first stage is able to land successfully.
Today at 6:35 p.m. EST, SpaceX hopes, at last, to make its fifth attempt to launch and then land, its Falcon 9 rocket on an at-sea platform. The launch attempt has been delayed for a multitude of reasons over the last nine days, including bad weather, heavy winds, and even a boat roaming into a safety zone.
Launching from Cape Canaveral Air Force Station, Florida, the rocket is set to deliver a commercial satellite into orbit. Shortly after liftoff, the first stage of the rocket will automatically attempt a landing on a so-called "drone ship" at sea, which SpaceX has named "Of Course I Still Love You."
The company’s four previous attempts to land the Falcon 9 at sea have ended without success, some in spectacular explosions, some in oh-so-close misses, and one in which the rocket blew up while still ascending. In February, the first stage made it back to the drone ship, but exploded when it fell onto the deck of the drone ship after one of its legs broke on impact.
In December, SpaceX did successfully return the the Falcon 9 first stage to Earth for the first time. But the company's ultimate plans are to be able to land it both on land and at sea, giving it maximum flexibility in the future.
About 10 minutes after launch, the first stage will attempt to return upright on the deck of "Of Course I Still Love You," a 100-foot-by-300-foot, unmanned floating platform currently off the coast of Florida. The rocket is meant to guide itself to the barge using GPS.
Those hoping for a successful landing, however, should temper their expectations. SpaceX said in a mission description (PDF) published ahead of time that because of the launch’s specific profile, "a successful landing is not expected."
When Elon Musk’s company eventually does complete an at-sea landing of the first stage, it will secure a key element of a future of affordable launches.
"SpaceX believes a fully and rapidly reusable rocket is the pivotal breakthrough needed to substantially reduce the cost of space access," the company says on its website. "The majority of the launch cost comes from building the rocket, which flies only once. Compare that to a commercial airliner—each new plane costs about the same as Falcon 9, but can fly multiple times per day, and conduct tens of thousands of flights over its lifetime. Following the commercial model, a rapidly reusable space launch vehicle could reduce the cost of traveling to space by a hundredfold."
Today's mission, of course, also has a scientific purpose beyond returning the rocket home. The launch is meant to deliver the SES-9 commercial communications satellite for SES, a global satellite company, to a geostationary transfer orbit (GTO). SES clients, who receive satellite-based communications from the company, include Internet service providers, broadcasters, business and governmental organizations, and mobile and fixed network operators. The company has a fleet of more than 50 geostationary satellites.
"SES-9 is the largest satellite dedicated to serving the Asia-Pacific region for SES," SpaceX wrote in the mission description. "With its payload of 81 high-powered Ku-band transponder equivalents, SES-9 will be the 7th SES satellite providing unparalleled coverage to over 20 countries in the region."
The new satellite will be co-located with SES-7.
Watch a live stream of the satellite launch above. We will update this article with news of the ocean landing attempt, or if weather impacts SpaceX's ability to launch.