If SpaceX managers are able to meet "even half of their mission goals, that would be a huge success, " according to Jeff Greason, chief executive of XCOR Aerospace, a space-transportation start-up.

WSJ: SpaceX's Pioneering Flight Plans

However XCOR Aerospace, an experimental rocket-development company based in Mojave, California, begs to differ.

ECONOMIST: Lost in space

Companies preparing for commercial suborbital passenger service include Virgin Galactic, a U.S.-based offshoot of Branson's Virgin Group of London, and XCOR Aerospace of Mojave, Calif.

MSN: Win a Free Trip to Space

California's XCOR Aerospace also is developing a reusable vehicle that will take a pilot and a front-seat customer to the edge of space -- for pleasure or to transport scientific payloads that would benefit from microgravity.

CNN: Private space pioneers: We're inheritors of Apollo legacy