Orbital Sciences Corp. has installed its Antares medium-lift launch vehicle on the pad built for it at the Wallops Flight Facility in Virginia, in preparation for a hot-fire test of the new rocket later this spring.

The test article, one of two Antares vehicles taking shape at the state-owned Mid-Atlantic Regional Spaceport (MARS), was moved from his horizontal processing facility to the seaside launch pad earlier this week and erected for fit checks, according to former shuttle astronaut Ronald Grabe, Orbital’s executive vice president and general manager of the launch systems group.

The test vehicle will be returned to the processing building while work preparing the propellant-delivery systems at the pad are completed, according to Grabe. After the hot-fire test, a second vehicle will be launched to fulfill a milestone under NASA’s Commercial Orbital Resupply Services (COTS) seed-money effort to gain a private U.S. route to the International Space Station.

“Everything was verified, so it’s really the final step as far as checking out the interfaces of the vehicle,” Grabe said of the fit tests this week.

Still to be completed is certification of the pad itself, which has delayed on-pad testing and eventual launch of the first Antares. Grabe says the remaining tasks are essentially “punch-card” inspection jobs in the tank farms and plumbing that deliver kerosene fuel and liquid oxygen to the rocket after it is erected on the pad.

Orbital’s progress also was slowed by a test-stand fire at Stennis Space Center triggered by a kerosene leak in one of the AJ26 engines destined for Antares. Subsequent checks of the remaining AJ26s by Aerojet, which produced them by modifying surplus Russian NK-33 engines, have turned up no additional cracks as serious as the one that caused the fire, Grabe said during the National Space Symposium here, and the engine supply for Antares is adequate to support operations.

Ultimately the Antares is under contract to boost Orbital’s Cygnus commercial cargo carrier to the ISS as one of two competing systems developed with a mix of COTS funding and private investment. The other competitor, Space Exploration Technologies Inc. (SpaceX), is on track to launch its Dragon cargo carrier to the ISS on a Falcon 9 rocket on April 30, according to Gwynne Shotwell, the SpaceX president.