An unmanned space freighter carrying a stash of precious medical samples from the International Space Station has parachuted into the Pacific Ocean, completing the first official shipment under a billion-dollar contract with Nasa.
The California-based SpaceX company successfully guided the Dragon capsule down from orbit to a splashdown a few hundred kilometres off the Baja California coast.
"This historic mission signifies the restoration of America's ability to deliver and return critical space station cargo," Elon Musk, the billionaire founder and head of SpaceX, said.
Nasa administrator Charles Bolden praised the "American ingenuity" that made the endeavour possible.
Several hours earlier, astronauts aboard the International Space Station used a giant robot arm to release the commercial cargo ship 410 kilometres above earth. SpaceX provided updates of the journey back via Twitter.
The supply ship brought back nearly 900 kilograms of science experiments and old station equipment. Perhaps the most eagerly awaited cargo is nearly 500 frozen samples of blood and urine collected from station astronauts over the past year.
The Dragon is the only delivery ship capable of returning items, now that Nasa's shuttles are retired to museums. Atlantis made the last shuttle haul to and from the station in July last year.
SpaceX - more formally Space Exploration Technologies Corp - launched the capsule three weeks ago from Cape Canaveral, full of groceries, clothes and other station supplies.
It's the second Dragon to return from the orbiting lab; the first mission in May was a flight demo. This flight is the first of 12 deliveries under a US$1.6 billion contract with Nasa.
A Russian supply ship, meanwhile, is set to blast off this week. It burns up upon descent, however, at mission's end. So do the cargo vessels provided by Europe and Japan.