Elon Musk’s SpaceX will make a second attempt to deliver one of two docking rings to the International Space Station, a crucial step in enabling US commercial space taxis to ferry astronauts to the orbiting lab, NASA says.

Space Exploration Technologies, or SpaceX, tried last year to deliver a ring for the first time, but the equipment was destroyed during a launch accident.

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A SpaceX Dragon cargo spacecraft loaded with materials for the orbiting laboratory and its crew will also deliver the key docking adaptor, a metallic ring big enough for astronauts and cargo to fit through.

“I know how critical this is for NASA,” Hans Koenigsmann, SpaceX’s vice president for mission assurance, said during a press conference on Saturday. SpaceX’s Falcon 9 rocket and Dragon cargo ship are scheduled for launch at 12.45am EDT (1445 AEST) on Monday from Cape Canaveral Air Force Station in Florida.

The Dragon spacecraft is loaded with about 5,000 pounds of experiments and materials for the International Space Station.

Docking Adapter-2 to be sent to the International Space Station. Photo: NASA

About 2.5 minutes after liftoff, the rocket’s main section will separate, turn around and attempt to land on the ground a few miles from the launch site.

Landing the rocket is a secondary goal. The main mission is placing the Dragon capsule into orbit and sending it on a two-day trip to the station.

Re-useable rockets

Owned and operated by Musk, the technology entrepreneur who founded Tesla Motors Inc, SpaceX is developing rockets that can be refurbished and re-used, potentially slashing launch costs.

So far, it has successfully landed a Falcon on the ground once and on an ocean platform in three out of its last four attempts.

The metal docking ring, built by Boeing Co, is 2.4 metres in diameter.

After its attachment to a berthing port on the station, it will serve as a parking space for commercial spaceships under development by SpaceX and Boeing. The manned craft are scheduled to begin test flights next year.

The spacecraft also carries hardware and experiment elements needed for dozens of research investigations that will take place in orbit.

A second docking ring is due to be delivered in 2017, the National Aeronautics and Space Administration said.