"It's entirely possible that we wake up one day and the Russians say, 'We're not taking your astronauts up anymore,'" said Marco Caceres, director of space studies at Fairfax, Virginia-based consultant Teal Group. "NASA's anticipating this possibility. That's why they want to move as quickly as possible with this program."

Funding two ventures may raise development costs while also fostering competition and giving NASA an alternative if one vehicle encounters technical difficulties, said Marco Caceres, director of space studies with Teal Group, a Fairfax, Virginia-based consultant.

Congressional opposition to a similar arrangement for the crew contract has waned as the fraying U.S.-Russia relationship focuses attention on NASA's dependence on Soyuz rockets to put astronauts into orbit, Caceres said in a telephone interview.

"The Russians have done NASA a favor in terms of funding," Caceres said.