Orbital Sciences has delayed the scheduled "hot-fire" of its Antares launch vehicle due to a fault in one of the two Aerojet AJ-26 engines. The fault was discovered when the engine automatically shut down seconds before ignition.

"After a preliminary overnight review of the data from the hot fire test attempt on February 13, Orbital's Antares team has identified low pressurization levels of a "nitrogen purge" of the aft engine compartment as the reason the Antares flight computer, acting as designed, aborted the test with about 1.5 seconds left in the countdown," says a statement from the company. "All other aspects of the countdown procedure, from the ground fueling system of the MARS [Mid-Atlantic Regional Spaceport] launch complex to the Stage 1 test article, performed nominally."

The hot fire test, also called a hold-down test, involves momentarily igniting the engine to ensure its functionality before flight.

Gaseous nitrogen is commonly used in liquid-fueled engines to purge the engine of its liquid fuels and other gasses that may be within the fuel lines. If the nitrogen fails to fully purge the engine, the liquid fuels -- in this case, liquid oxygen and a form of highly enriched kerosene called rocket propellant (RP-1) -- may react with the stray gasses, potentially causing an unintended combustion.

While no date has yet been given for the new test, Orbital chief executive officer, speaking during a phonecall with investors, suggested that less than a week would be needed to reset and try again.

The hot flow test is the last ignition test before flight. The long-delayed launch, nominally scheduled in April but possibly further delayed due to the nitrogen purge mishap, will be the first for the Antares launch vehicle.

Antares is intended launch the Cygnus cargo capsule to the International Space Station for NASA. Orbital Sciences could not be reached for comment.

Source: Flight International