Russian cosmonaut Oleg Kotov(center), U.S. billionaire Charles Simonyi (l), and Russian cosmonaut Fyodor Yurchikhin (r) gesture after a news conference at the training center in Baikonur, Kazakhstan, 06 Apr 2007

That was long before he left Hungary for the United States, where he eventually made his fortune working as a designer at U.S. software giant Microsoft.

The 58-year-old paid over $20 million for his flight into space, making him the fifth so-called "space tourist".

But Simonyi insists the mission will be far more than a pleasure ride.

He says he wants to boost interest in space exploration, and during his stay at the international space station, he will conduct some medical experiments.

He will also write a blog about the experience aimed mostly at getting more children on earth interested in space exploration.

"I think it's to advance civilian space flight, and to assist in space station research, to involve kids, to communicate the experience of space flight, and of course it's a personal experience too that I will enjoy tremendously," said Simonyi.

Simonyi began working at Microsoft in 1981 when the company was still young.

He helped to design both Microsoft Word and Excel programs before leaving to form his own company in 2002.

Simonyi has long been a pilot of airplanes and helicopters, and has undergone training for the flight at Russia's Star City space complex outside Moscow.

He and his two Russian companions head into space in a Soyuz spacecraft launched from the Baikonur Cosmodrome in Kazakhstan.