An Aerojet AJ-26 engine, the main propulsion system for one of NASA’s commercial space-cargo haulers, shut down prematurely during a test firing at the Stennis Space Center June 9.

NASA disclosed the failed test a day later in a statement.

The AJ-26 is the main engine for Orbital Science Corp.’s Taurus 2 rocket, which will launch the company’s Cygnus capsule for commercial resupply missions to the international space station.

Barron Beneski, a spokesman for Orbital, and Glenn Mahone, a spokesman for Aerojet, both confirmed the premature shutdown.

“As we speak, we are looking into why it shut down early,” Beneski said June 10.

Mahone declined additional comment, pending an investigation of the failed test.

NASA spokeswoman Rebecca Strecker referred requests for details to Orbital and Aerojet.

The AJ-26, based on the Russian NK-33 engine, burns liquid-oxygen and kerosene.  Each Taurus 2 rocket uses two AJ-26 engines. Three AJ-26 engines have been successfully test-fired to date.

The first Taurus 2 test flight is still slated for early October. The rocket will launch from NASA’s Wallops Flight Facility on Wallops Island, Va.

Orbital is under contract with NASA to fly 10 cargo missions to the international space station through 2015, all from Wallops. The Cygnus capsule is scheduled for a test flight in December.