WASHINGTON — Orbital Sciences Corp. successfully launched its Antares cargo rocket to space for the first time April 21, bringing the Dulles, Va., company a big step closer to making routine cargo deliveries to the international space station for NASA.

Antares heaved itself slowly off Pad 0-A at the Mid-Atlantic Regional Spaceport on Wallops Island, Va., at 5 p.m. EDT. About 10 minutes later, the vehicle dropped off its main payload — a sensor-equipped, dummy satellite with roughly the same mass as the Cygnus space tug Orbital will use for cargo deliveries — in a 51.64-degree inclined orbit about 250 kilometers above Earth’s surface. This is the same orbit where the real Cygnus would be dropped off at the start of a cargo run.

Also carried aloft by Antares were four experimental cubesats, all of which made it to their intended orbits, according to Orbital officials. The hitchhiker payloads were Dove-1, a commercial imaging triple cubesat, and three single-unit cubesats with consumer smartphone cores, which were built at NASA’s Ames Research Center in Mountain View, Calif.

The Antares configuration that flew April 21 can send 5,000 kilograms to low Earth orbit.

It took Orbital three tries to get its new rocket off the ground. The first launch attempt April 17 was scrubbed about 10 minutes before the scheduled liftoff because a data cable linking ground computers with Antares’ second-stage flight computer disconnected prematurely. Orbital said the cable was hung too tautly to tolerate a sudden movement of a hydraulic arm on the Transporter Erector Launcher vehicle that holds Antares at the pad.

An April 20 attempt was scrubbed due to wind conditions.

With the inaugural Antares flight in the books, Orbital has one more mission to perform before it can begin delivery service under the eight-flight, $1.9 billion Commercial Resupply Services contract it got from NASA in 2008. This mission, a demonstration cargo delivery mission to the space station, is scheduled for June or July, said Frank Culbertson, executive vice president and general manager of Orbital’s Advanced Programs Group.

For the Commercial Resupply Services program, Orbital is under contract to haul 20,000 kilograms of cargo to the space station by 2016. Back in February, Garrett Pierce, Orbital’s chief financial officer, said on an investor conference call that the company has already recognized about $1 billion in revenue from the $1.9 billion CRS contract. However, NASA has paid only about $750 million of these costs back to Orbital. The other 25 percent are being held pending successful completion of contracted cargo runs.

From 2007 through 2012, Orbital’s research and development expenses for Antares were $235 million, according to the company’s 10-K filings with the U.S. Securities and Exchange Commission.

By the time Orbital completes its second demonstration flight for NASA this summer, the company estimates it will have spent $513 million developing the Cygnus cargo freighter. That figure includes a $288 million NASA contribution, which the agency provided to Orbital under a Commercial Orbital Transportation Services contract signed in 2008. Cygnus costs through 2012 were $480.5 million, according to Orbital’s financial disclosures.

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...