CAPE CANAVERAL, Florida (Reuters) - A Japanese businessman who trained for a 10-day flight aboard the International Space Station has sued to get his money back, claiming he was defrauded of $21 million by the U.S. firm that arranged the venture.

Space tourist Daisuke Enomoto of Japan, who is due to take off from the Baikonur cosmodrome this September, tries on his space suit at an undisclosed factory outside Moscow July 5, 2006. REUTERS/Sergei Remezov

Daisuke Enomoto, 37, had completed training in Russia and planned to fly to the station aboard a Russian Soyuz capsule in September 2006. But he was pulled from the three-member crew a month before liftoff, opening a seat for Dallas businesswoman Anousheh Ansari to fly instead.

Enomoto filed suit last month in the U.S. District Court in Alexandria, Virginia, against Virginia-based Space Adventures, the space tourism company that plans to send its sixth paying passenger to orbit next month.

In the lawsuit, which was posted on the Internet by Wired magazine, Enomoto says the medical condition cited for his removal from the crew -- kidney stones -- was well known by Space Adventures and the doctors who had monitored his health and suitability for space flight throughout the training.

Enomoto alleges he was pulled from the flight so Ansari, who had invested in Space Adventures, could fly instead. Ansari also was the primary backer of the $10 million Ansari X Prize awarded in 2004 for the first privately developed manned space flight.

In a response filed on Wednesday, Space Adventures’ lawyers said Enomoto’s contract did not entitle him to a refund if he became medically disqualified.

“That was a risk he undertook,” they said. “Even if Enomoto could prove his unlikely claim that he was somehow misled, he suffered absolutely no damage from any misstatement because ... the cause of his failure to fly was medical disqualification, not lack of authority.”

Enomoto claims Space Adventures persuaded Russian space officials to disqualify him under the pretense of medical issues.

“Mr. Enomoto’s ‘medical condition’ was no worse than it was just two weeks prior to his disqualification, when he was medically cleared by the Russian Government Medical Commission,” the lawsuit said.

Nor was his health any worse than it was seven weeks before his disqualification, when Enomoto was cleared by the group of five doctors charged with approving private citizen travel to the space station. They included doctors from the Russian Federal Space Agency, the U.S. National Aeronautics and Space Administration, and other space station partners, the lawsuit said.

The complaint also alleges that Space Adventures promised Enomoto he could conduct a spacewalk while aboard the station and collected $7 million in deposits, though the firm never had an agreement with Russia for the outing.

In all, Enomoto paid Space Adventures $21 million over two years, none of which has been refunded, the suit claims.