Private space firm SpaceX launched its Falcon-9 rocket from Cape Canaveral in Florida on Friday, carrying a resupply capsule to the International Space Station, NASA television showed.
The rocket rapidly reached orbital altitude where it deployed the Dragon vehicle, carrying 1,200 pounds (544 kilograms) of supplies, on what was the firm's third launch and second mission to the ISS.
"The Dragon has separated from the second stage," mission control announced during a live broadcast from space, watched by space fans on Earth and the crew of the space station awaiting their delivery in orbit.
This is the second of 12 planned trips in NASA's $1.6 billion contract with SpaceX, the private company owned by billionaire entrepreneur Elon Musk.
Their successful mission last October was the first ever commercial re-supply operation to the ISS, a milestone for US efforts to reduce costs by privatizing the space industry.
SpaceX had earlier completed a near flawless test flight.
"This unique vehicle has become a very integral part of how we operate and use the space station," NASA's ISS program manager Mike Suffredini said on Thursday, as he described plans for the 25-day mission.
SpaceX president Gwynne Shotwell said that among the equipment on board are two grapple bars that will be transported in an unpressurized compartment of the spacecraft, a first for SpaceX.
Also on board will be equipment for 160 experiments to be conducted by the space station crew, which currently consists of two Americans, three Russians, and a Canadian.
On the return flight, Dragon -- the only spacecraft able to bring cargo back to Earth for now -- will be loaded with just over a ton of materials, including results of medical research.
The capsule is scheduled for a splashdown landing off the coast of California on March 25.
NASA has bet on SpaceX and other commercial ventures to take over for its fleet of space shuttles, which last flew in July 2011.
Before SpaceX's successful mission in October, NASA had been relying on Russian spacecraft -- but the Soyuz craft does not have room for cargo on the return flight.
SpaceX says it has 50 launches planned -- both NASA missions and commercial flights -- representing about $4 billion in contracts.
So far, SpaceX has only sent unmanned flights into orbit, but the company aims to send a manned flight within the next three or four years. It is under a separate contract with NASA to refine the capsule so that it can carry a crew.
NASA also has a $1.9 billion resupply contract for the station with Orbital Sciences Corporation, which will run its first test flight in the next few months at a base in Virginia.