WASHINGTON — The launch of Space Exploration Technologies Corp.’s third contracted cargo run to the international space station was scrubbed April 14 and reset for April 18 because of a helium leak on the first stage of the company’s Falcon 9 rocket.

NASA spokesman Trent Perrotto said the next launch attempt will be at 3:25 p.m. eastern time April 18, assuming SpaceX can resolve the leak issue.

“A fix will be implemented by the next launch opportunity on Friday April 18, though weather on that date isn’t ideal,” SpaceX wrote on its website shortly after the scrub.

SpaceX had been set to launch the mission at 4:58 eastern time, despite the recent failure of an external space station computer that will require replacement by spacewalking astronauts, a NASA official said during an April 13 press briefing. The so-called External-2 Multiplexer/Demultiplexer, a computer that controls station’s solar arrays, among other things, failed April 11.

A backup unit has been activated, and even a failure of the secondary system does not pose an unacceptable threat to the SpaceX mission, Michael Suffredini, space station program manager at the Johnson Space Center in Houston, said during the press conference.

NASA has a spare for the failed computer onboard the station. It will be installed during a spacewalk scheduled to take place after SpaceX’s Dragon cargo capsule berths with the station two days after the launch. NASA astronauts Richard Mastracchio and Steve Swanson will perform the spacewalk, according to slides shown April 14 to the NASA Advisory Council’s Human Exploration and Operations Committee by Joel Montalbano, deputy ISS program manager for research at NASA headquarters here.

One of the two astronauts tapped for repair duties will don the same spacesuit that nearly drowned Italian astronaut Luca Parmitano back in July, when his helmet filled with fluid. NASA has since determined that a clogged filter was the cause, and the spacesuit, or Extravehicular Mobility Unit has undergone repairs to make it safe, Suffredini said.

SpaceX’s third contracted station cargo launch was delayed once before, by problems with a radar used to track launches from the Cape. The slippage — and the possibility of another — may have implications for Orbital Sciences Corp., NASA’s other commercial cargo hauler.

Dulles, Va.-based Orbital is working toward a May 6 launch of its Antares rocket from Wallops Island, Va. However, the mission will not launch until after June 9, unless SpaceX misses its April 18 launch opportunity, William Gerstenmaier, NASA’s Associate Administrator for Human Exploration and Operations, told SpaceNews here April 14.

Orbital, in an April 7 note on its own website, said there is a traffic jam brewing at the space station. SpaceX’s Dragon is required to remain at station for about a month following its arrival, and the Russian Federal Space Agency, Roscosmos, is scheduled to launch new crew members to the station May 28.

SpaceX’s commercial manifest might also be affected by the delay. The Hawthorne, Calif.-based company is scheduled to launch half a dozen data-messaging satellites for Fort Lee, N.J.-based Orbcomm in late April.

Hans Koenigsmann, SpaceX’s vice president of mission assurance, said during the April 13 press briefing that the Orbcomm launch was still on for the end of April, but Orbcomm said in an April 11 note on its website that “due to the recent delays with [SpaceX’s station cargo] mission, our new target launch window is May 10-15.”

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.