NEW YORK (CNN/Money) - An attempt to have the first privately-financed manned space flight is set for June 21, backers of the effort announced Tuesday.

SpaceShipOne, which will attempt the first manned privately-financed space flight June 21.

SpaceShipOne, which has already successfully completed a flight 40 miles above earth, will attempt to exit the earth's atmosphere in a sub-orbital flight 62.5 miles, or 100 kilometers, above earth on that date.

The flight is another step along the way to try to win a $10 million prize, known as the "X Prize," that will go to the first privately-financed space craft to make two sub-orbital flights carrying three people within a two-week period. Beyond the prize money, the SpaceShipOne effort is aimed at opening up space travel to private citizens in the future.

"Since Yuri Gagarin and Al Shepard's epic flights in 1961, all space missions have been flown only under large, expensive government efforts," said a statement from Burt Rutan, who designed the space craft along with his research team at privately-held Scaled Composites. "By contrast, our program involves a few, dedicated individuals who are focused entirely on making spaceflight affordable."

The SpaceShipOne effort is backed by Paul Allen, one of the founders of Microsoft Corp.

"Every time SpaceShipOne flies we demonstrate that relatively modest amounts of private funding can significantly increase the boundaries of commercial space technology," said a statement from Allen.

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Rather than launch from a launch pad, SpaceShipOne will be take off from the Mojave desert in California underneath an airplane, which is to carry it to a height of 50,000.

Once it is released, plans call for it to fire a rocket motor for about 80 seconds, reaching a speed about three times the speed of sound. The pilot, who has yet to be named, will be weightless for about 3 minutes before starting back to earth.