WASHINGTON — Once again, Orbital Sciences Corp. of Dulles, Va., is preparing to fire the core stage of the NASA-subsidized Antares rocket the company is building to service the international space station. The test is set for Friday (Feb. 22).

Word of the test came not from Orbital itself, but from a Feb. 20 alert from the public affairs office at NASA’s Wallops Island Flight Facility on Virginia’s eastern shore. The NASA range is home to the Mid-Atlantic Regional Spaceport, which is leased and operated by the state of Virginia. Antares launches from the spaceport’s Pad 0A, the only liquid fueled pad on the range.

NASA’s Wallops Flight Facility will provide launch range support for an Orbital Sciences Corp. Antares rocket engine test scheduled for Feb. 22 at the Mid-Atlantic Regional Spaceport’s Pad-0A.

The test is a key milestone leading up to the first flight of the Antares rocket, which is preliminary scheduled for about four to six weeks following the completion of the engine test.

Orbital attempted an Antares hot-fire Feb. 13, but the rocket’s computer aborted the test less than two seconds before ignition. Orbital chief David Thompson, in a Feb. 14 conference call with investors, said the shutdown happened because the computer detected lower-than-acceptable pressure in a nitrogen-purge tank. The anomalous pressure level was blamed on a wonky valve.

Antares, like the Cygnus space tug it will one day send to the international space station — assuming Orbital’s system works as intended — is an international piece of hardware. The rocket, billed as a Delta 2-class launcher, uses a Ukrainian-built core stage, surplus Soviet-vintage liquid engines refurbished by Sacramento, Calif.-based Aerojet, and a solid-fueled upper stage from ATK Aerospace.

The rocket is years late in making its maiden flight, but so was Space Exploration Technologies Corp.’s (SpaceX) Falcon 9 — the other NASA-subsidized rocket chosen for cargo resupply missions to the international space station under the agency’s Commercial Resupply Services program.

Orbital got a $1.9 billion resupply contract in 2008. SpaceX got a $1.6 billion contract in 2007. Per NASA, aspiring cargo haulers cannot start flying their contracted flights until they prove that their rockets and spacecraft can safely reach the space station. SpaceX finished the development program in May and flew its first contracted resupply flight in October.

In Orbital’s case, an Antares core-stage hot-fire would clear the way for Antares’ maiden flight, which itself is a prerequisite for the demonstration cargo mission Orbital has to complete before it, too, can start fulfilling its station resupply contract.

Orbital’s demonstration cargo run is scheduled for this summer.

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...