A SpaceX Falcon 9 rocket was being readied for launch from Florida on Wednesday on a mission to thrust a European satellite toward orbit and then attempt a return touchdown on an ocean platform, company officials said.
The 23-story-tall rocket, carrying a commercial communications satellite for Luxembourg-based SES SA, was scheduled to blast off from Cape Canaveral Air Force Station at 6:46pm EST/2346 GMT.
Meteorologists forecast a 60 percent chance that weather at the cape would be suitable for lift-off.
The flight would be the second of more than 12 planned this year by Space Exploration Technologies, the private rocket launch service owned and operated by high-tech entrepreneur Elon Musk.
It would also mark the fourth attempt at a return sea-based landing of the Falcon 9's main stage, a milestone in Musk's goal to develop a cheap and reusable booster.
The rocket's main section is supposed to separate from the second stage about 2 1/2 minutes after launch, turn around and attempt to land itself on a platform floating in the Atlantic about 400 miles (645 km) east of Cape Canaveral.
A returning SpaceX rocket successfully touched down at a ground-based landing site near the launch pad in December, but three previous attempts to land a returning rocket on an ocean platform failed.
The rocket flying on Wednesday, which will be carrying the 12,613-pound (5,721 kg) Boeing-built SES-9 satellite, will be traveling too fast to try to get back to a landing pad at Cape Canaveral, prompting SpaceX to try the ocean landing instead.
SES, which currently operates a constellation of 53 satellites, has three more under contract to fly on SpaceX Falcon rockets through 2017, SES Chief Technology Officer Martin Halliwell told reporters at a prelaunch news conference.
"SES would have no problem in flying a re-used (rocket's) first stage. If it's flight-worthy, we're happy," Halliwell said.
SES has started talking with SpaceX about buying a used rocket to fly a future SES satellite but they have not yet agreed on a price.
A new Falcon 9 costs about $61 million, the company's website shows.
"I did throw out a challenge to SpaceX that we would be the first satellite operator that would use the same rocket twice to get to ... orbit. That's something which I would really like to do," Halliwell said.