A US software engineer has become the fifth space tourist after blasting off on board a Russian Soyuz spacecraft.
Billionaire Charles Simonyi, 58, who led development of Microsoft's Word, lifted off from the Baikonur space station in Kazakhstan at 1731 GMT.
He is the 450th person to enter orbit and the $25m ride makes him, by his own admission, "the first nerd in space".
American businesswoman and lifestyle guru Martha Stewart was there to wave her friend off on the 12-day trip.
She selected a gourmet meal of roast quail and duck breast, which Mr Simonyi and his Russian colleagues will enjoy once they reach the International Space Station (ISS).
The Soyuz TMA-10 took off on schedule and entered orbit a few minutes later.
Inside the spacecraft, Mr Simonyi and two Russian crew members smiled into an onboard camera; he then gave the thumbs-up sign.
"The power of the ignition of those engines and the feeling on the ground gave such a sense of what space flight is, and it fills you with awe," said Mr Simonyi's spokeswoman, Susan Hutchison, who attended the launch.
Martha Stewart said goodbye separated by a glass wall
Dr Simonyi and the two cosmonauts - Fyodor Yurchikin and Oleg Kotov - will spend two days reaching the ISS.
Once there, he will spend 10 days onboard, completing 200 orbits of the Earth, covering 8 million km (5 million miles).
The return journey, accompanied by the 14th ISS crew already onboard, will take just two hours and will land on Earth on 20 April.
Dr Simonyi began training for the flight six months ago at the Yuri Gagarin Cosmonaut Training Centre in Star City, Russia and at the Baikonur Cosmodrome in Kazakhstan.
He underwent a gruelling physical programme, including strict medical tests, to prepare him for the ride to escape the Earth's atmosphere and his time on board the ISS.
Once on the space station, Dr Simonyi will carry out a series of experiments including measuring the amount of radiation that he is exposed to while on board the ISS.
The aim is to help to generate an accurate map of the radiation environment on the space station.
He will also take part in a series of ceremonies and rituals, including a viewing of Russian film White Sun of the Desert, a tradition for cosmonauts spanning many years.
Dr Simonyi's once-in-a-lifetime trip was arranged by US-based Space Adventures. The company has previously sent four private explorers to space.
In 2001, American Dennis Tito became the first space tourist. He was followed by South African Mark Shuttleworth the year after, and American Greg Olsen in 2005.
Iranian-born US businesswoman Anousheh Ansari became the first ever female space tourist in September 2006.
She was a last-minute replacement for Japanese businessman Daisuke Enomoto who failed his medical tests.