SpaceShipTwo, the suborbital spaceplane designed for Virgin Galactic's commercial space tourism venture, crashed today during a test flight over California's Mojave Desert. This is the second such event this week, after the Antares rocket carrying science experiments and supplies to the International Space Station crashed on Thursday.

There were two pilots on board the rocket. White Knight Two, the jet-powered mothership that launches the spaceplane, is reported to have landed safely. The rockets are part of billionaire Richard Branson's Virgin Galactic empire.

The California Highway Patrol is reporting that one person is dead and another seriously injured, according to the AP.

Witnesses on the ground are sending out tweets about the incident, with one space blog called ParabolicArc.com saying the aircraft broke up almost immediately after rocket burn. It's reported that the spaceplane, which was on its 55th test flight, was trying a new type of rocket fuel that would enable it to reach higher altitudes. 

Virgin Galactic officials will hold a press conference at 5 p.m. EST. 

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