A US federal judge is allowing a Japanese millionaire to go ahead with his lawsuit against a Virginia company he says unfairly denied him a ride into outer space.

Daisuke Enomoto had planned to be the world's fourth "space tourist". He paid $21 million to Space Adventures, the company known for brokering such deals with the Russian space agency.

Space Adventures, which is based in a Virginia suburb of Washington, DC, says Enomoto was medically disqualified in 2006 because of kidney stones. But Enomoto says the kidney stones were a pretext to boot him off the mission, because he refused demands from Space Adventures for more money.