WALLOPS ISLAND, Va. — Orbital Sciences Corp. has been cleared to launch the Antares rocket April 17 on its inaugural flight, but bad weather headed for the Virginia coast could delay the mission, a NASA official said here.

“It looks like we have about a 45-percent chance for favorable weather for launch because of the low cloud ceiling, and the possibility for precipitation and thunderstorms,” John Dickerson, test director for the Wallops Flight Facility Research Range said here during a media briefing.

If the April 17 launch is scrubbed, Orbital would try again the next day. After that, the outlook gets murkier.

“We will almost definitely take a shot at the first few days,” said Michael Pinkston, Antares program manager for Orbital. However, “the weather on Friday [April 19] looks really, really, really unbearable.”

Aborting a launch once the rocket has been fueled at the pad “makes for a very long day for our team,” Pinkston said. “If we do that two days in a row, we’ll be looking at trying to get a day of rest in there, somewhere.” 

Backup launch opportunities identified so far range from April 18 to April 21, Orbital spokesman Barron Beneski said. 

For now, Orbital is aiming to launch Antares April 17 between 5 p.m. and 8 p.m. EDT, per the official go-ahead issued April 16 by NASA Wallops Flight Facility Site Director Bill Wrobel. The so-called Authority to Proceed followed a launch readiness review “at which Orbital managers gave a ‘go’ to proceed to toward launch,” NASA said in a statement.

Bad weather would be the second hiccup Orbital has dealt with since April 6, when it installed Antares at Pad 0-A — a liquid-fueled launch pad on the Wallops range that is owned and operated by the state of Virginia.

On April 13, the company aborted a countdown rehearsal because of a faulty valve in one of the two Aerojet-supplied AJ-26 liquid kerosene engines that power the Antares’ first stage. The valve was replaced April 14.

Antares is a big part of Orbital’s plan to win new business from NASA, the U.S. Air Force, and the National Reconnaissance Office. 

In its maiden flight, Antares will attempt to park a dummy payload in the same orbit where it would drop off its companion Cygnus cargo capsule during resupply flights to the international space station.

If the inaugural Antares flight is a success, a demonstration cargo delivery to the space station would follow in June or July, said Frank Culbertson, a former astronaut who is now executive vice president and general manager of Orbital’s advanced programs group. When both of these flights are completed, Orbital can begin paid cargo runs to the station.

If all goes according to plan, the company will make at least one contracted run this year. 

“After the demo, we’re in a position where we can deliver two full-up missions to the space station before the end of this year,” said Mark Pieczynski, Orbital’s vice president for space launch strategic development 

But there are other factors that affect the pace at which Orbital can launch. The biggest of these is the availability of docking space at the international space station, which is set to be visited this year by spacecraft from Europe, Japan and Russia.  

Orbital is the second of NASA’s Commercial Resupply Services contractors to attempt a flight to the space station. Space Exploration Technologies Corp., Hawthorne, Calif., completed its own demonstration cargo run to the space station last May and has flown two contracted cargo runs since. The second wrapped up March 25.

Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...