Jeff Greason, the president of XCOR Aerospace, a company that makes rocket engines for suborbital craft, worries that the X Prize, with its attached conditions, may not in practice lead to the right sort of craft being built.
It marks his first space venture since the partnership with Rutan and his colleagues to build the prize-winning SpaceShipOne rocket plane, which became the first privately developed craft to reach outer space in 2004.
Flying at roughly 30, 000 feet, the craft would climb sharply just as it released the rocket, which would use a cluster of four or five engines to boost itself into orbit.