A SpaceX dragon cargo spacecraft is grappled by the station's robotic arm. Credit: NASA

WASHINGTON — A Space Exploration Technologies Corp. Dragon spacecraft arrived at the international space station April 20, delivering some two metric tons of cargo to the orbital outpost. Dragon’s arrival follows an April 18 launch aboard a SpaceX Falcon 9 rocket from Cape Canaveral Air Force Station, Fla.

Dragon was berthed with the Earth-facing port on the station’s Harmony node at 10:06 a.m. EDT. The spacecraft is scheduled to remain at station for about four weeks, according to a notice NASA posted on its website during the weekend.

The capsule is slated to bring back some 1,600 kilograms of cargo, including scientific experiments and medical samples, when it splashes down May 18. Dragon’s launch was delayed several times, most recently April 14, when a faulty helium valve on Falcon 9’s first stage prompted the company to abort liftoff and swap out the balky hardware.

On April 23, with Dragon still berthed with station, astronauts Richard Mastracchio and Steve Swanson will perform a spacewalk to replace an external computer — known as the External-2 Multiplexer/Demultiplexer — that failed April 11.

Now that Dragon has arrived, NASA’s other contract cargo hauler, Orbital Sciences Corp. of Dulles, Va., is set to launch its next cargo delivery mission in early June.

SpaceX, Hawthorne, Calif., and Orbital are delivering cargo to the ISS under Commercial Resupply Services contracts signed in 2008. SpaceX’s $1.6 billion deal calls for delivering at least 20 tons of cargo spread over 12 flights. The mission that launched April 18 is SpaceX’s third. Orbital, which has flown one delivery mission so far, has an eight-flight, $1.9 billion contract.

Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.