Aerospace designer Burt Rutan yesterday announced he will try to win $10 million as the first civilian to put the equivalent of three people into space twice within two weeks in September and October.

Rutan, who won national attention June 21 when Michael W. Melvill used SpaceShipOne in a trial run to become the first commercial pilot ever to reach space, plans to launch the ship at least two more times to win the Ansari X Prize.

Under the terms of the competition, his team will win $10 million if it can become the first private company to fly the equivalent of three people -- determined to be about 600 pounds -- into suborbital space twice with the same equipment within two weeks, and do it by the end of 2004.

The first attempt would come Sept. 29, over the Mojave Desert, Rutan said yesterday. A second flight could come as early as Oct. 4, and in case one flight fails, Rutan said he will be prepared to fly one more time before his window closes Oct. 13. The weight includes the pilot, equipment and ballast. Rutan said he has not chosen a pilot for any of the flights.

"It is now eight years since we announced the competition," said Peter H. Diamandis, chairman and president of the nonprofit X-Prize Foundation. "We are within arm's reach of the Ansari prize being won."

SpaceShipOne is a stubby rocket plane released by a wispy mother ship at an altitude of 50,000 feet. SpaceShipOne's rocket engine then burns a combination of nitrous oxide (the same thing as dentists' laughing gas) and hydroxy-terminated polybutadiene (a clear rubber) to get into space.

Near the top of its arc, the engines cut off and the spacecraft coasts upward then comes down, its angle of descent controlled by "feathering" its wings to maximize drag and keep the spacecraft pointing properly until it glides to a landing.

Rutan said the extra weight will require him to tweak the performance of the spacecraft's rocket engine to get the whole load above 328,084 feet: "The amount of weight we need is a lot closer to one person than two people," Rutan said in a telephone news conference from California's Santa Monica Airport. He said that the spacecraft on June 21 had carried a video camera, altitude recording equipment and other extra weight apart from Melvill.

Rutan also said he had determined that a jammed servomotor that briefly balked control of the spacecraft's stabilizers on June 21 and caused trim problems for Melvill on reentry was not as serious as it first appeared: "We've decided not to do anything about it," Rutan said. "If we try to 'fix' it, we may add too many moving parts and make it more complicated than it needs to be."

Rutan is bankrolled for more than $20 million by Microsoft co-founder Paul G. Allen and has been the competition's front-runner since it began, but there are other serious contenders among the 26 enrolled teams.

At Rutan's heels is Canada-based Orva Space Corp., whose Da Vinci Project aims to use a gigantic helium balloon to lift a bullet-shaped spacecraft to 80,000 feet, then light a rocket to put it into space.

Brian Feeney, president, pilot and co-owner of Orva, said yesterday in Santa Monica that he plans to present Da Vinci to the public next week and will fly as soon as he scrapes up the $350,000 he needs for final preparations. Da Vinci has been built with 150,000 hours of volunteer help from experts around the world and in-kind corporate contributions.

"We will definitely fly," Feeney said. "I've never let -- and will not let -- the lack of money stall this project."

Diamandis designed the competition to promote space tourism and patterned it after the Orteig Prize won by Charles Lindbergh for his 1927 transatlantic flight. "We are excited at the chance to revitalize interest in space travel," Diamandis said, "and to show that space travel is possible for the rest of us, not just governments."

Beside a model of SpaceShipOne in Santa Monica, Calif., designer Burt Rutan announces his timetable for winning the Ansari X Prize.