Private US firm SpaceX launched its unmanned Dragon capsule to the International Space Station on Friday, its third trip carrying supplies and equipment to the orbiting lab.

After three delays, the Falcon 9 rocket and its Dragon capsule finally blasted off as planned at 3:25 pm (1925 GMT) from Cape Canaveral in Florida.

About 10 minutes after liftoff, the capsule separated from the second stage of the rocket before going into orbit. The capsule deployed its solar panels shortly after, ensuring a continuous power supply.

"THAT. WAS. AWESOOMEEE," someone using the handle Petar Le Grand wrote on SpaceX's website after watching the launch live.

Dragon is due to meet up with the space station on Sunday at 2314 GMT.

SpaceX has a $1.6 billion contract with NASA for a series of future supply missions.

It marks the California-based company's third commercial resupply mission and fourth visit to the ISS, where it is due to deliver 2.2 tonnes of cargo, including food, new spacesuits, components to replace those aboard the ISS and equipment for 150 scientific experiments.

One of the experiments will be the Vegetable Production System, or Veggie, which would allow the production of salad-type crops to safely feed the astronauts.

SpaceX owner and Internet entrepreneur Elon Musk was positive about the start of his company's latest space mission.

"Orbit insertion and Dragon deploy all good. Falcon reentry burn also good. Waiting for landing data from tracking plane," he wrote on Twitter.

If all goes to plan on Sunday, two of the six astronauts aboard the ISS will use the station's robotic arm to grab the capsule and dock it at the Harmony module, a US utility hub.

The mission had originally been scheduled for mid-March but did not go ahead because of technical issues.

It then was delayed because of a US military radar issue earlier this month, then again due to a helium leak in the Falcon rocket's first stage this week.

- Fresh vegetables in space -

Another experiment at the ISS seeks to determine why astronauts' immune system weakens in microgravity.

NASA is also sending an experiment system that can more rapidly transmit data using a laser communication system, in a first from space.

In all, SpaceX is due to complete 12 missions for the US space agency.

SpaceX became the first commercial entity to reach the space station with its Dragon cargo ship in May 2012 in a trial run. The company's first cargo mission took place in October that year.

The last mission involving a Dragon capsule was completed in March 2013.

Shaped like a gumdrop, the Dragon capsule was designed to be reusable.

SpaceX plans to try to bring Dragon back to Earth this time and have it land in a controlled manner in the ocean using thrusters during re-entry into Earth's atmosphere.

To stabilize and slow the spacecraft, huge parachutes each measuring 116 feet (35 meters) in diameter will deploy at about 10,000 feet in altitude.

SpaceX will then use a 100-foot boat equipped with a crane and two inflatable boats to recover the spacecraft. About a dozen SpaceX engineers and technicians, along with a four-person dive team, will be aboard.

The company has admitted the odds are not on its side but it wants to try anyway to learn from the experience.