Musk nonetheless characterized it as "a pretty good test" during a post-flight teleconference.

"We successfully reached space and really retired almost all the risk associated with the rocket, so I feel very good about where things are," said Musk, who stressed that it was a test flight and there was no satellite aboard.

Space Exploration Technologies' Falcon 1 is planned to be the first in a family of competitively priced launch vehicles from the El Segundo, Calif.-based company. Musk said he has two satellite launches scheduled this year, one for the Department of Defense and another for the Malaysian space agency.

Musk said the rocket had no anomalies during the first stage burn, stage separation and other events until late in the second-stage burn when a roll control problem prematurely shut down the stage after reaching an altitude of 186 miles.

"We feel that's something pretty straightforward to address," he said from El Segundo.

The launch was Webcast from Omelek island in the Kwajawlein atoll. The island quickly receded in a camera view pointing down from the rocket, and after a few minutes the sphere of the Earth became apparent.

Transmission was then lost, said SpaceX launch commentator Gwynn Shotwell.

It was the second Falcon 1 to be launched. The first, a year ago, failed due to a fuel leak fire.

Tuesday's mission, dubbed Demo-2, was designed primarily to gather flight data.

The launch shortly after 6 p.m. PDT followed an abort just over an hour earlier. The rocket's first-stage engine began to fire, then shut down before hold-downs were released.

The abort was caused by low pressure in the combustion chamber, Shotwell said. The pressure was 0.2 percent below normal, apparently because the fuel was colder than desired, she said. The fuel was replaced.

The rocket was designed to be held down for about 1› seconds after the first-stage engine ignites so that trends in performance can be quickly analyzed for problems such as the low pressure.

An attempt to launch on Monday was aborted when a split-second delay in communications with the vehicle was detected when there was a switch from a land line to radio. That occurred before engine firing.

Musk was a co-founder of the PayPal Inc. electronic payment system now owned by eBay.

His company, known as SpaceX, is trying to break into the orbital space launch market. The Falcon 1 is designed to carry up to 1,254 pounds to low orbit for $6.7 million.

A March 24, 2006, launch from Omelek failed when leaking fuel caught fire seconds into liftoff. An Air Force Academy satellite was lost in the accident, which an investigation linked to corrosion of an aluminum nut due to prolonged exposure on the launch pad.

Falcon 1 is a 70-foot-long, two-stage rocket powered by liquid oxygen and kerosene. Its first stage is designed to parachute into the ocean to be recovered and used again.

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