A SpaceX Falcon 9 rocket that blasted off from Florida on a cargo run for the International Space Station has achieved a dramatic spaceflight first - its reusable main-stage booster landing itself on an ocean platform.
The liftoff at 4.43pm (local time, Friday - 8.43am AEST Saturday) from Cape Canaveral marked the resumption of resupply flights by privately owned Space Exploration Technologies for NASA following a launch accident in June 2015 that destroyed a different cargo payload for the space station.
About 2-1/2 minutes after Friday's launch, the main part of the 23-storey tall, two-stage SpaceX rocket separated, turned around and headed toward a landing platform floating in the Atlantic about 300km northeast of Cape Canaveral.
A live video feed broadcast on NASA television showed the rocket booster settling itself upright on the platform, roughly eight minutes after launch.
"We have a Falcon 9 on board," a crewman on a nearby recovery vessel radioed to SpaceX mission control.
Four previous at-sea landing attempts had failed. But a Falcon 9 main-stage rocket achieved a successful ground-based touchdown in December, the first during a commercial space mission. The latest feat marked another major milestone in the quest by high-tech entrepreneur Elon Musk, founder and chief executive of the private launch service, to develop a cheap, reusable launch vehicle.
"Looking forward to delivering the goods for you," Musk tweeted to the US space agency after the launch.
The rocket's cargo ship, dubbed Dragon, was due to arrive on Sunday at the International Space Station, the $100 billion laboratory flying about 400km above Earth.
The delivery vehicle was packed with about 3175kg of food, supplies and science experiments, including a prototype inflatable habitat, bound for the orbital outpost.
About a week after Dragon's arrival, ground controllers will use a robot arm on the space station to pull the 1400kg Bigelow Expandable Activity Module, or BEAM, from the capsule's trunk and attach it to a berthing port.
Built by Nevada-based Bigelow Aerospace, the lightweight fabric habitat will be tested to see how it compares with more traditional orbiting enclosures made from metal.
Bigelow Aerospace, operated by real estate billionaire Robert Bigelow, plans to follow BEAM with modules 20 times larger to serve as free-flying orbital outposts leased to companies and research groups.
NASA is interested in expandable habitats to serve as crew living quarters during three-year trips to and from Mars.
