Only recently have smaller, nimbler companies like SpaceX, some of them run by billionaires who proved themselves in other fields, started trying to compete as equals with NASA and its major contractors. (Mr. Musk, for example, is an Internet entrepreneur who founded PayPal.)

“SpaceX is attempting to build the same class of vehicle, to my mind, only with modern manufacturing techniques and management techniques to reduce the cost,” said Jeff Greason, chief executive of XCOR Aerospace, which is building a two-seat rocket plane to take tourists to the edge of space.

Since the end of the space shuttle program, NASA has relied on Russia to take its astronauts to space in Soyuz rockets, but now it is looking to hire commercial companies for space taxi services. So there are incentives for commercial companies both to build the transportation and to offer it at competitive prices. SpaceX, for one, says that it could provide rides to NASA astronauts at $20 million a seat, a third of the Russian price.

But the new space companies are relying on taxpayer dollars to finance their research and development. The Obama administration requested $830 million for next year to finance the development of passenger-carrying spacecraft. Proponents argue that the investments will jump-start a vibrant new business that dwarfs NASA; Congress has so far remained skeptical. A report by the House committee in charge of NASA’s budget said the program ran the “risk of repeating the government’s experience from last year’s bankruptcy of the solar energy firm Solyndra.”

Despite the ambivalence on Capitol Hill, the new space competition has drawn both entrepreneurs and the old aerospace giants.

Alliant Techsystems, better known as ATK, manufactured the solid rocket boosters for the space shuttles and had the contract to build a longer-range version as the first stage for NASA’s next-generation rocket, the Ares I. That was before the Ares I was canceled in favor of the space taxi approach.

ATK has now teamed up with Astrium, a European rocket company, to come up with what is essentially a commercial version of the Ares I, which it called the Liberty. Last week, ATK announced that it was developing its own capsule — based heavily on the Orion capsule that was originally going to sit on top of the Ares I — to carry astronauts for NASA one day. ATK says it, too, would charge less than the Russians.