For the second time in a week, SpaceX's upgraded Falcon 9 rocket fired its engines on a new California launch pad Thursday in one of the final steps before the 22-story launcher is cleared for liftoff on a test flight no earlier than Sept. 29.

Credit: SpaceX

The slender two-stage rocket, towering more than 220 feet over its hillside launch complex, ignited its engines Thursday afternoon at Vandenberg Air Force Base, Calif. The brief engine firing, known as a "static fire" in SpaceX parlance, includes an ignition and burn of the rocket's nine first stage engines for several seconds while the launcher is held on the launch pad by restraints.

SpaceX CEO and chief designer Elon Musk posted an update on his Twitter account late Thursday: "Completed rocket static fire with all systems green this time. Launch window opens in 10 days."

The rocket's Merlin 1D engines, arranged a new "octaweb" configuration, generate 1.3 million pounds of thrust at sea level.

Musk tweeted last week engineers saw several anomalies during the Falcon 9's first static fire Sept. 12, forcing a delay in the launch from its Sept. 15 target date to resolve the problems and wait for the U.S. Air Force to complete Minuteman missile testing nearby.

Launch of the Falcon 9 rocket, fitted with more powerful engines and enlarged fuel tanks, is expected from Vandenberg's Space Launch Complex 4-East on Sept. 29. SpaceX has a backup date Sept. 30 on the Air Force-run Western Range, which provides tracking, safety and communications support for launches from California.

The upgrades give the launcher about a 50 percent increase in lift capability over the Falcon 9's previous version, which flew five times on test flights and resupply missions for the International Space Station with SpaceX's Dragon cargo capsule.

The Sept. 29 launch, considered a test flight by SpaceX, will carry several satellites to orbit. The largest payload is the 1,100-pound Cassiope space weather research satellite, a joint program by the Canadian Space Agency and MDA Corp., a Canadian aerospace contractor.

The new version of the Falcon 9 - named the Falcon 9 v1.1 - will be SpaceX's workhorse for the coming years, launching logistics to the space station and lofting commercial, scientific and military payloads to orbit.

SpaceX has a backlog of 40 launches of the Falcon 9 rocket and the Falcon Heavy booster - a behemoth 27-engine rocket that has not yet reached a launch pad.

The backlog, worth more than $2 billion, includes geostationary communications satellites waiting for launch on SpaceX at discounted prices compared to the commercial market leaders, such as Arianespace and International Launch Services.

SpaceX has not launched a satellite into geostationary transfer orbit, the drop-off point for communications satellites heading for operating posts 22,300 miles over the equator.

The Falcon 9's next launch after the Sept. 29 test flight is scheduled for this fall from Cape Canaveral, Fla., with the SES 8 communications satellite. In the SES contract with SpaceX, the Luxembourg-based telecom satellite operator stipulated the launch firm demonstrate the Falcon 9 v1.1, including its unflown 17-foot-diameter payload fairing, before putting SES 8 on the next Falcon 9 mission.