This story was updated  April 3 at 4:39 p.m. EDT.

WASHINGTON — Orbital Sciences will roll Antares out to the pad early April 6 in preparation for the rocket’s debut launch less than two weeks later, the Dulles, Va.-based company announced April 3.

Orbital was planning to roll out the first Antares to fly in space April 5, but forecasts of lightning near the launchpad forced a delay, Orbital spokesman Barron Beneski said in an email.

Antares will roll out of its Horizontal Integration Facility at 4:45 EDT on April 6. The rocket will be vertical on the pad later that morning, an Orbital press release said.

Antares is slated to launch April 17-19. Orbital plans to set an exact day once Antares is installed at its launch pad at the Mid-Atlantic Regional Spaceport at NASA’s Wallops Flight Facility in Wallops Island, Va. The launch window opens at 5 p.m. EDT all four days. Orbital aims to launch Antares to the same low Earth orbit it will target when it starts launching the unmanned Cygnus spacecraft on cargo delivery missions to the international space station under an eight-flight, $1.9 billion NASA contract awarded in 2008. Before the company can begin regular service under that contract, it must prove that Antares and Cygnus can safely deliver supplies to the orbiting outpost.

In its mid-April debut, Antares will carry a dummy payload that weighs the same as Cygnus. This mass simulator will carry sensors to monitor Antares’ performance throughout the flight.

If the upcoming flight is successful, a full-up demonstration cargo run to the space station will follow this summer. That would clear the way for routine cargo deliveries to begin late this year or early next.

Orbital is one of two companies NASA contracted with in December 2008 to deliver cargo to the space station. The other, Space Exploration Technologies Corp. (SpaceX), on March 26 completed the second of 12 cargo runs it is expected to make under its $1.6 billion contract.

Antares was supposed to have launched Cygnus on a demonstration flight to the space station by December 2010 under the schedule Orbital and NASA agreed upon in 2008. Three years later, NASA added several milestones to Orbital’s demonstration effort, including the upcoming Antares test launch, which was supposed to have happened by October 2011.

Orbital has blamed the holdup on the state of Virginia, which built and operates Pad-0A — the only launch pad at the Mid-Atlantic Regional Spaceport capable of supporting liquid-fueled rockets. Antares is Orbital’s first liquid-fueled rocket.

SpaceX, which got started on its NASA-subsidized Falcon 9 rocket and Dragon cargo capsule two years earlier than NASA tapped Orbital to begin work on its rival system, completed its first demonstration mission to the space station last May — 32 months later than originally planned.

Meanwhile, a NASA-chartered safety panel on April 3 gave Orbital and Wallops high marks for making progress toward a safe launch.

“We’ve been to Orbital … and note with pleasure and excitement the progress that they’re making [toward] their not-too-distant launch, and their progress at Wallops,” retired Navy Vice Admiral Joe Dyer said at the Goddard Space Flight Center in Greenbelt, Md., during a meeting of NASA’s Aerospace Safety Advisory Panel, which he chairs.

Dyer called Wallops “a remarkably and impressively different place” than it was two years ago when the panel last visited the facility. “We were impressed with the cooperation and work between the NASA and contractor team,” he said.

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.