WASHINGTON — Government investment in commercial space transportation will be a good investment because it will be cost-effective and end NASA’s reliance on Russian spacecraft to get crews to low-Earth orbit, executives of private space companies told a House committee on Wednesday.

The business leaders urged the lawmakers to support NASA’s commercial crew development program, but committee members questioned the long-term viability of the business model, which promotes commercial spaceflight in addition to transporting crew to the International Space Station.

Rep. Mo Brooks, R-Ala., expressed concern that a market for spaceflight doesn’t exist beyond NASA.

“It does not seem to me that there’s really a commercial market in the sense that you might have with airline flights,” he said, adding that if NASA is the private sector’s only customer, the cost per launch might end up increasing.

But representatives from Space Exploration Technologies, Boeing, United Launch Alliance, Sierra Nevada Space Systems and ATK said the market extends beyond the government.

“The depth of it is difficult to estimate,” John Elbon, Boeing’s vice president of space exploration, acknowledged. . But, he added, “we have chosen a system that will be affordable if the only transportation we do is government transportation to the ISS.”

SpaceX CEO Elon Musk had more confidence in the commercial market, noting that non-spacefaring nations are interested in space research and would buy seats on American commercial spacecraft.

Musk said that with the current lack of competition and supply, the U.S. is paying too much — $56 million per seat — for transportation via the Russian Soyuz.

“Should the U.S. space industry lower the cost to between $20 and $30 million per seat, it will be possible for research scientists to visit the ISS for shorter periods of time, conduct dedicated research and return to Earth,” Musk said in his written testimony. “Less costly, more regular access to ISS will enable more scientists to do more research in the same about of time, with the same amount of dollars.”

Musk said SpaceX plans to have spacecraft available for crew transportation to the ISS within the next three years, well ahead of NASA’s projection that commercial crew vehicles won’t be available until 2017 — provided that the proposed funding is available for commercial development to continue at current pace.

NASA leaders said that if the agency’s $850 million budget request is not fully funded, it will have to continue to rely on sending astronauts into space on Russian Soyuz vehicles beyond 2017.