Microsoft millionaire Charles Simonyi plans to pay a second visit to the International Space Station in the spring of 2009. His first visit took place two years ago. Thus he will probably become a more frequent space visitor than most professional astronauts and the best customer ever.

Another devoted customer, Richard Garriott, 46, son of NASA astronaut Owen Garriott, is scheduled to launch to the space station October 12. His $30 million trip is in fact an agreement between Russia's Federal Space Agency and Space Adventures.

Vienna, Virginia-based Space Adventures did not say how much Simonyi will pay. However he paid $25 million to accompany two cosmonauts aboard a Russian rocket that went to the international space station in 2007. What they did say is that Simonyi, 60, will train with the Soyuz TMA-14 crew for the current trip.

Simonyi is a software engineer who helped develop Microsoft Word and Excel. He joined Microsoft in 1981.

"We congratulate Charles on his continued commitment to commercial spaceflight. We look forward to assisting him in preparation for the spring 2009 mission," Eric Anderson, president of the space tourism company, said.

Space Adventures, based in Vienna, Virginia, first launched a private client into space in 2001. Dennis Tito, an American businessman and former NASA scientist, became the first space tourist when he visited the ISS in 2001. He was followed by South African computer millionaire Mark Shuttleworth in 2002, and Gregory Olsen, a U.S. entrepreneur and scientist, in 2005. In 2006, Anousheh Ansari, a U.S. citizen of Iranian descent, became the first female space tourist. Richard Garriott was the sixth.