Orbital Sciences and Aerojet resumed testing of a Russian rocket engine for the Taurus 2 rocket this week, the first firing of the 40-year-old engines since one of the power plants caught fire on the test stand in June.

The AJ26 engine fired in Mississippi for about 54 seconds on Wednesday. Credit: Aerojet/Orbital Sciences

The AJ26 engine ignited Wednesday at NASA's Stennis Space Center in southern Mississippi, consuming rocket-grade kerosene and liquid oxygen for approximately 54 seconds in a perfect test, according to Frank Culbertson, senior vice president of advanced programs at Orbital Sciences Corp.

Orbital Sciences will use the AJ26 engines to power the first stage of the Taurus 2 rocket, a medium-lift launcher under development to haul cargo to the International Space Station. On a real flight, the engines will burn for nearly four minutes.

The first test flight of the Taurus 2 is scheduled for no earlier than December from a commercial spaceport at Wallops Island, Va. But officials say the launch will probably slip into the beginning of next year.

The engine fired in Mississippi on Wednesday is one of two power plants that will be on the test flight.

Engineers will fire another AJ26 engine at Stennis in October, then both engines will be shipped to Wallops for integration with the Ukrainian-built Taurus 2 first stage.

The test flight will carry a dummy payload with sensors to track how the rocket performs during the launch. Orbital's automated Cygnus spaceship will be aboard the second Taurus 2 mission, which will reach the space station.

"We take engines through Stennis for an acceptance test firing, and then if that goes well we bring them to Wallops and integrate them together into the thrust frame in the first stage," Culbertson said in an interview.

Wednesday's test was the first firing of an AJ26 engine since a mishap in June, when a weakened propellant line split open and spilled fuel, generating a fire on the test stand. After an investigation and some repairs, the AJ26 test campaign resumed on Wednesday.

"The root cause was stress corrosion cracking," Culbertson said. "These engines are 40 years old. They had been inspected, but I think there was some cracking that Aerojet didn't suspect and hadn't really tested for. It manifested itself by basically unzipping the line and that spilled fuel and caused a fire. The drop in pressure actually shut everything down, so there was very little damage. The engine itself probably could eventually be repaired if it needed to be."

Artist's concept of the Taurus 2 rocket. Credit: Orbital Sciences

The AJ26 is a kerosene-fueled engine modified by Aerojet from the Russian NK-33 powerplant. Each Taurus 2 rocket first stage will be powered by two AJ26 engines.

Kept in storage for four decades, the NK-33 engines were originally designed and built in the 1960s and 1970s for the ill-fated Soviet N1 moon rocket.

Aerojet converts the NK-33 to an AJ26 engine by removing some harnessing, adding U.S. electronics, qualifying it for U.S. propellants, and modifying the system to gimbal for steering, according to company officials.

Orbital Sciences has already received two AJ26 engines for a static test firing of the Taurus 2 on the launch pad later this year. The engine fired Wednesday, along with a second unit due for testing in October, will power the Taurus 2 into space for the first time.

The engines for the first flight were cherry-picked from Aerojet's inventory. Aerojet has 37 NK-33 engines under its control. Each engine can generate up to 370,000 pounds of thrust.

Culbertson said he expects the test flight to slip until some time in January, based on slowed progress readying the Taurus 2 launch pad at Wallops.

"We've had to go in and do things like certify the welds that hold the launch mount that holds the rocket during the testing and the launch operations," Culbertson said. "We had some problems so they're having to redo some of that. The tanks had to be recleaned for a variety of reasons, some of which were they had just been out there for a while."

Orbital says it could fly its Cygnus cargo freighter to the space station on the second Taurus 2 launch within two months of a successful test flight.