WASHINGTON — Orbital Sciences Corp., one of two companies under contract with NASA to deliver cargo to the international space station, has rolled the core stage of its Antares rocket out to the launch pad for several days of fitting tests.

The first stage left the horizontal integration facility at NASA’s Wallops Flight Facility on Wallops Island, Va., April 11 for an hour-long trek to a launch pad that is “pretty much done” but still awaiting NASA certification, Baron Beneski, an Orbital spokesman, said. The pad certification is behind schedule and Orbital officials have identified it as a pacing item as they prepare for the vehicle’s debut later this year.

The pad is “certainly complete enough for us to do fit checks,” Beneski said. “So when we erect the first stage, there are interfaces that go between the launch pad and the first stage itself, and we just need to make sure everything fits up properly.”

On April 16, Beneski said, the first stage will be stood up vertically for the first time since Orbital moved into the Mid-Atlantic Regional Spaceport, the commercial corner of the NASA installation. The first stage will then undergo a series of tests in preparation for a hold-down test scheduled for this summer, during which the stage will be fired for about 30 seconds.

Orbital’s pad will need to be certified for that test, Beneski said.

If all goes as planned, the stage used for the hold-down test will be reconditioned for Antares’ maiden launch later this year.

Orbital will be updating its testing and launch schedule during its April 20 quarterly earnings call.

Dulles, Va.-based Orbital holds a $1.9 billion Commercial Resupply Services contract with NASA. The company must complete two flight demonstrations — one of just the rocket and one of the rocket and its Cygnus cargo capsule — before it can begin regular supply runs to the space station.

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.