An artist's conception shows SpaceShipTwo during descent. The space plane uses a unique "feathering" reentry system. The wings are rotated into vertical positions to increase drag and reduce speed.

SpaceShipTwo will require the assistance of WhiteKnightTwo, a carrier craft that was unveiled on July 28, 2008, to reach the edge of space. However, it will return to Earth under its own power.

The first SpaceShipTwo is about 70 percent complete, and Virgin Galactic officials say that passenger flights could begin as early as 2009.

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