Takeoff has been set for April 25, cosmonaut training center spokesman Andrei Maiboroda said. The crew is to leave Saturday for the Baikonur cosmodrome in Kazakhstan to prepare.

The Interfax news agency said an interdepartmental commission that must approve all those who fly on Russian rockets found Shuttleworth had not met ``certain conditions'' for the flight but that he had plenty of time to do so. The report did not elaborate, and officials in the commission could not be reached for comment Monday evening.

A 28-year-old economist, who made a fortune with an Internet business, Shuttleworth said he would conduct gene engineering studies while on the space station using animal stem cells. He said he hoped his research could be used to help find cures for Alzheimer's and Parkinson's disease.

He said he and Gidzenko had been trained by Russian and South African biologists to conduct the experiments.

Shuttleworth confirmed that he is paying $20 million for the trip _ but in installments that will be complete only when the mission is over. That's the same sum American Dennis Tito paid Russian space agencies last year to fly to the international station, becoming the world's first space tourist.

``We have a staggered series of payments covering the training, covering the preparation, covering the launch, covering the completion _ a successful completion of what we all hope will be a very good scientific program of flight,'' Shuttleworth said.

Shuttleworth said he might be interested in one day taking a trip on a U.S. space shuttle.

He also said that during training in Star City, his Russian colleagues had fun with the ``shuttle'' in his last name, nicknaming him ``Buranov'' after the Russian-made Buran space shuttle.