Space Exploration Technologies Corp., or SpaceX, conducted a full mission duration firing of its new Merlin Vacuum engine, the company announced.

That test, at the SpaceX Test Facility in McGregor, Texas, saw the engine fire for six minutes, consuming 100,000 pounds of liquid oxygen and rocket grade kerosene propellant.

The new engine, which powers the upper stage of SpaceX’s Falcon 9 launch vehicle, demonstrated a vacuum specific impulse of 342 seconds, which SpaceX stated was the highest efficiency ever for an American hydrocarbon rocket engine. Thrust was measured at approximately 92,500 pounds of force in vacuum conditions and the engine remained thermally stable over the entire run.

"Specific impulse, or Isp, indicates how efficiently a rocket engine converts propellant into thrust," said Tom Mueller, SpacX vice president of propulsion. "With a vacuum Isp of 342 seconds, the new Merlin Vacuum engine has exceeded our requirements, setting a new standard for American hydrocarbon engine performance in space."

Based on the Merlin 1C engine that boosted the SpaceX Falcon 1 rocket to orbit in 2008, the Merlin Vacuum engine uses a regeneratively cooled combustion chamber. However, the vacuum engine features a larger exhaust section than the Merlin 1C and a much larger radiatively cooled expansion nozzle, in order to maximize performance in the vacuum of space.

The Merlin Vacuum engine provides the final push that delivers customer spacecraft into their desired orbits. A redundant ignition system ensures the engine can shut down and restart multiple times. The engine can also operate at a reduced thrust to achieve optimum performance. During recent tests, the engine was successfully throttled down to 75 percent of maximum thrust, and upcoming tests will demonstrate throttling to approximately 60 percent of maximum thrust.

SpaceX’s Falcon 9 launch vehicle and Dragon spacecraft were recently selected by NASA to resupply cargo to the International Space Station after the shuttle retires in 2010. The inaugural flight of Falcon 9 is scheduled for later this year from SpaceX’s launch pad SLC-40 at Cape Canaveral, Florida.