SpaceX successfully fired the Falcon 9 rocket's nine Merlin engines on a Florida launch pad Saturday, completing a key preflight test before the privately-developed booster is cleared for launch in April.

The Falcon 9 rocket fires its nine Merlin 1C first stage engines Saturday afternoon. Credit: Chris Thompson/SpaceX

The 15-story rocket's first stage engines ignited at 12:30 p.m. EST (1730 GMT), sending a plume of smoke out of the flame trench at Cape Canaveral's Complex 40. The nine engines ramped up to more than 800,000 pounds of thrust and burned for a handful of seconds, meeting all the company's test objectives, according to SpaceX.

"Today, SpaceX successfully completed a test firing of the inaugural Falcon 9 launch vehicle at Space Launch Complex 40 located at Cape Canaveral," the company said in a written statement. "Following a nominal terminal countdown, the launch sequencer commanded ignition of all 9 Merlin first stage engines for a period of 3.5 seconds."

Steam and exhaust gushed from the pad's flame trench and was quickly dispersed by strong winds. Four swing arms held the rocket firmly to Earth.

The engine test punctuated several hours of countdown preparations, including loading of kerosene and liquid oxygen propellants into the rocket. About 30 launch controllers managed the operations from the SpaceX Launch Control Center at the southern perimeter of Cape Canaveral Air Force Station.

Engineers tried to light the Falcon 9 first stage Tuesday, but a high pressure helium valve did not open during the ignition sequence. The helium is used to spin up the turbopumps in each of the nine Merlin 1C engines.

Thunderstorms and high winds prevented SpaceX from trying a countdown on Thursday and Friday.

Founded in 2002 by Internet mogul Elon Musk, SpaceX is competing for rights to carry NASA astronauts to orbit under the agency's new policy of procuring commercial crew transportation services. SpaceX is headquartered in Hawthorne, Calif.

The company has released detailed updates on the cause of Tuesday's aborted engine test and other progress, but SpaceX was unable to announce when it would make static fire attempts. Officials did not give reports on the status of the Falcon 9 countdown, despite multiple requests for information.

The real-time information vacuum is a departure from typical rocket operations at Cape Canaveral. The high profile of the first Falcon 9 launch is garnering more interest than most unmanned missions departing from the spaceport.

The nine Merlin 1C engines fired for 3.5 seconds and produced more than 800,000 pounds of thrust. Credit: SpaceX

Officials say Saturday's ground test was one of the final steps before launch of the Falcon 9, which is scheduled for no earlier than April 12. The static fire verified all of the launch pad's ground systems are ready to support the mission.

Between now and launch, engineers will install the rocket's flight termination system charges that would destroy the vehicle if it flew off course and threatened the public.

SpaceX took residence at Complex 40 in 2007, taking over the historic launch pad that hosted more than 50 Titan rocket launches between 1965 and 2005.

The Falcon 9 reuses the Titan-era concrete flame trench and water deluge systems, but SpaceX built its own assembly hangar and transporter/erector, which also serves as an umbilical tower.

"Just prior to engine ignition, the pad water deluge system was activated providing acoustic suppression to keep vibration levels within acceptable limits," the SpaceX statement said. "The test validated the launch pad propellant and pneumatic systems as well as the ground and flight control software that controls pad and launch vehicle configurations."

The so-called hotfire also exercised the launch team and the Air Force Eastern Range.

The Falcon 9's first launch will be a demonstration mission destined for a low-altitude orbit about 155 miles above Earth.

"The completion of a successful static fire is the latest milestone on the path to first flight of the Falcon 9 which will carry a Dragon spacecraft qualification unit to orbit," officials wrote in a statement Saturday.

The Dragon is the space component of SpaceX's end-to-end transportation system. Once launched by the Falcon 9 on future flights, the Dragon will fly to the International Space Station to deliver supplies to the orbiting lab.

The Falcon 9 rocket fires its engines Saturday on Complex 40 at Cape Canaveral. Credit: Chris Thompson/SpaceX

NASA awarded SpaceX a $1.6 billion contract to fly 12 operational Falcon 9 and Dragon missions to the International Space Station beginning in 2011.

SpaceX plans a shakedown flight of the Dragon in July, followed by a rendezvous demonstration with the space station in November. But those schedules hinge on a timely and successful Falcon 9 test flight in April.

Orbital Sciences Corp. is designing and building a competing system using the Taurus 2 rocket and Cygnus cargo freighter. Orbital will launch the Taurus 2 from Wallops Island, Va., starting in March 2011.

The Falcon 9 and Dragon are positioned to carry future astronaut crews to the outpost under NASA's proposal to solicit commercial providers for human transportation to low Earth orbit.

Other rockets, including the Atlas 5, Delta 4 and Taurus 2 vehicles, could also bid for commercial crew contracts.

SpaceX says the Falcon 9 and Dragon can be modified to safely deliver astronauts to space by 2013, or about two-and-a-half years after winning a contract.