As US firm SpaceX prepares for its third launch to the space station Friday, NASA said there was nothing "particularly challenging" about a mission that a few months ago was unprecedented.

Liftoff is set for 10:10 am local time (1510 GMT) in Cape Canaveral, Florida, to launch the unmanned Dragon capsule into orbit carrying some 1,200 pounds (544 kilograms) of supplies to the International Space Station.

Forecasts give an 80 percent chance of favorable weather conditions.

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 to the ISS.

As NASA's ISS program manager Mike Suffredini described plans for the latest 25-day mission, he emphasized that the process has become routine.

"This is not a particularly challenging event," Suffredini said of the launch and berthing at a televised pre-launch press conference Thursday.

"This unique vehicle has become a very integral part of how we operate and use the space station," he added.

SpaceX president Gwynne Shotwell, also speaking at the press conference, said the final pieces of cargo and supplies were being loaded for the trip, which was scheduled to take less than 24 hours from launch to berthing.

Among the equipment on board, she added, 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.