New York — A U.S. Air Force official says the service still plans to use Space Exploration Technologies (SpaceX) to launch the Tacsat-1 satellite in September, despite the second failed launch of the company’s Falcon 1 rocket in as many tries.

The March 20 Falcon 1 launch ended when the rocket’s second stage malfunctioned at an altitude of about 300 kilometers and failed to place its demonstration payload in orbit. The mishap occurred almost a year to the day after the inaugural Falcon 1 launch failed shortly after liftoff.

U.S. Air Force Col. Thomas Doyne, an action officer for operational experimentation in the director of defense research and engineering’s Rapid Reaction Technology Office, said the Pentagon is “extremely pleased” with SpaceX’s work thus far on the Falcon 1 rocket. Despite the second-stage issues, SpaceX made a “tremendous amount of progress” after its inaugural launch failure, and met most of the criteria that the Pentagon had wanted to see with the second launch, Doyne said in a March 23 interview.

Doyne said that while he was not intimately familiar with the details, preliminary reports indicate that SpaceX will not have difficulty addressing the issues with the second stage.

Prior to the March 20 Falcon 1 demonstration launch, the Pentagon had anticipated that TacSat-1 would launch in September and still expects to launch around that same time, Doyne said, adding that the Air Force does not plan to ask SpaceX to conduct another demonstration launch in the interim.

The two-stage Falcon 1 rocket lifted off from its Pacific Island launch site March 20 at 9:10 p.m. EDT , but suffered a roll control malfunction before completing its flight plan, SpaceX officials said. The rocket had been expected to place its demonstration payload into orbit at an altitude of about 685 kilometers above the Earth’s surface.

“We did encounter, late in the second burn, a roll control anomaly,” SpaceX Chief Executive Officer Elon Musk told reporters about five minutes into the launch. “But that’s something that’s pretty straightforward to address.”

The roll control glitch affected how the Falcon 1 booster’s second stage controlled itself in flight, sending the vehicle on a path that likely re-entered the Earth’s atmosphere over the Pacific Ocean without completing a full orbit, Musk said. The malfunction could have been due to a range of issues, such as helium leak or a roll control jet glitch, but only a subsequent analysis will root out the cause, he added.

The off-nominal spaceflight capped a drama-filled countdown that included payload communications glitches and one pad abort a half-second after the Falcon 1 rocket’s engine ignited. Each of those issues was eventually resolved, and the rocket — initially scheduled to lift off March 19 at 7:00 p.m. EDT — was readied for launch the next day within the same four-hour flight window.

“This was a pretty nerve-wracking day,” Musk said. “The rocket business is definitely not a low-stress business, that’s for sure, but I don’t think I’m disappointed. In fact, I’m pretty happy.”

The fact that the Falcon 1 rocket lifted off from its Kwajalein Atoll launch site in the Pacific Ocean, experienced successful first-stage and payload fairing separations — as well as the ignition of its second stage — proved that hundreds of booster improvements incorporated into the vehicle since its March 2006 failure were a success, Musk said. “We successfully reached space, and really retired almost all of the risk associated with the rocket.”

J.P. Stevens, vice president for space systems at the Arlington, Va.-based Aerospace Industries Association, said SpaceX — a dues-paying member — was right to be pleased with what it has accomplished between its first flight and the March 20 demo. “It shows they are well on their way to becoming another member of the launch community,” he said.

Several launch industry veterans, however, dismissed Musk’s happy talk as spin.

“It’s a binary business. You either put the payload in orbit or it’s a failure,” one vet said the day after the launch. “There are no partial successes.”

SpaceX launched the Falcon 1 rocket primarily as a demonstration for the U.S. Defense Advanced Research Projects Agency to prove the booster’s capabilities, though the rocket also carried a 50-kilogram set of experiments, including an automated flight safety system, low-cost satel lite communications transceiver and mechanical payload adapter ring.

“We, in the Washington office are celebrating with champagne,” Gwynne Shotwell, SpaceX vice president of business development, told reporters after the launch. “Falcon 1 clearly got to space.”

SpaceX’s first Falcon 1 test flight failed in March 2006 after a fuel leak and fire led to the failure of its inaugural space shot last year. Initially attributed to human error, the failed launch was ultimately found to be the result of a corroded aluminum nut, prompting the El Segundo, Calif. -based firm to institute a host of rocket and ground facility improvements.

“It didn’t take us one year to build the new rocket,” Musk said before the March 20 space shot. “The delay of one year was used to allow us to develop the Falcon 1, version two.”

Standing about 21 meters tall, SpaceX’s Falcon 1 rocket is a two-stage booster designed to carry satellite payloads of up to 570 kilograms into low Earth orbit for a flat price of about $7 million per space shot, according to the company. The rocket’s first stage is designed to be reusable, and carries parachutes to slow its descent and make a splashdown landing in the Pacific Ocean for later retrieval and refurbishment.

Musk has said repeatedly that he firmly believed that any serious glitch to afflict the second Falcon 1 test would not prompt another one-year delay in flights.

SpaceX plans to launch at least two more Falcon 1 rockets this year, including a summer space shot to orbit the U.S. Naval Research Laboratory’s TacSat-1 satellite and a third mission to launch Malaysia’s Razaksat Earth-observation satellite. Both customers have pledged to stand by SpaceX, with the Razaksat team offering a hearty congratulations following the March 20 liftoff, SpaceX officials said.

“We feel like there’s really no need for an extra test flight,” Musk told reporters.

That was still the sentiment two days after the launch.

“Unless something has changed, and I don’t think it has, our next launch will be TacSat-1,” Lawrence Williams, SpaceX vice president for international and government affairs, said March 22 .

Staff writer Brian Berger contributed from Adelphi, Md.