Barring a turn in the weather or in his good health, he is leaving on a regularly scheduled eight-day mission aboard a Soyuz rocket, for which only two cosmonauts are needed–and there is a third seat. Russia sees this as a business opportunity, and with its economy in collapse, hopes there are other tourists willing to pay a fortune for a glimpse of Earth through a porthole. The Russians seem to adore Tito, treating him the way they still treat their space travelers, with demands for autographs and copious toasts with shots of vodka. But since he joined the mission in January, NASA and the other partners in the International Space Station have fought the move, arguing that the ISS is too new to accommodate nonprofessionals. Last Friday they changed their minds. “They came to me and asked me to sign a contract saying if I broke anything I’d have to pay for it,” says Tito, the diminutive, inconspicuous mogul who founded Wilshire Associates and runs Wilshire 5000. He signed, and NASA withdrew its objections.

“I spent most of last year of my life working on getting this accomplished,” he says in one in a series of interviews detailing his history-making quest. “I don’t want to gloat, but now all I have to face is the flight itself.”

But exactly why is he doing it? This, Tito is unable to articulate clearly. He simply believes in the majesty of space. “I just have to do this,” he says. “It’s probably the ultimate human adventure.” Upon his return to Earth, he would like to serve his friend George W. Bush as a goodwill space ambassador, getting children excited again about the wonders of space. He intends to promote the commercialization of space for manufacturing and tourism. He may commit his fortune–estimated at well over $200 million–to funding a museum or investing in the first generation of suborbital transportation vehicles.

The space bug first bit Tito as a teenager growing up in a small row house in Queens, N.Y., the eldest son of a sweatshop seamstress and a printer. He was standing outside a Carvel ice-cream stand when he saw his first satellite blinking overhead one early evening in 1961, at the dawn of the space race. He decided then and there to join this skirmish in the cold war. Ultimately he earned degrees in aerospace engineering and designed flight trajectories for three historic Mariner missions to Mars in the ’60s.

But after five years at NASA’s Jet Propulsion Laboratory earning $670 a month, he grew restless and began toying with the stock market in his spare time. With his wife, Suzanne, he built Wilshire Associates into the country’s third largest pensions-consulting firm, which now controls $1 trillion in assets. His riches bought him the sprawling 30,000-square-foot stone-and-marble manse, believed to be the largest in Los Angeles, which he built atop a Pacific Palisades mountain.

It is Tito’s other dream come true. Walking along the manicured jogging track that threads past the pool house and tennis court, guest cottage and eight-car garage, Dennis Tito calls his enormous home “my own little space station, in a way.” His enthusiasm is completely American. He lives there alone. “I lived there for six months after we finished it,” says Suzanne Tito, “and then I said, this is not the way I want to live, this is not me.” The couple, who raised three children, have divorced amicably.

But space was never far from Tito’s fantasies. A few years ago he entertained the idea of joining the hunt for the X Prize, a $10 million purse for the person who builds the first reusable passenger-rocket (it must make two round trips to space to win). He hired engineers, but eventually abandoned the project as out of reach. In his spare time he has sketched out schematics for a suborbital spacecraft that might rocket from Los Angeles to New Zealand, where his daughter lives, in just 45 minutes. But personally going to space? Tito has never been bungee-jumping or skydiving, and though he owns a titanium-colored Ferrari F355 Spider, he rarely slides it into the passing lane. “In so many ways, Dennis is not the typical type of person to do something like this,” says Wilshire’s senior managing director, Thomas Stevens. “He shocked us with this trip idea.”

Tito first looked into a space vacation in 1991 on a trip to Moscow. While there, Tito made an appointment to talk to the directors of Energyia, the state company managing the Russian space lab Mir. But then came the fiery putsch that nearly overthrew Mikhail Gorbachev, and Tito went home. “I thought my chances were shot then,” he says. He was 50 at the time. “I figured I would never be as healthy again.”

Eventually Tito came upon Space Adventures, a private company promoting space tourism. The company’s 27-year-old founder, Eric Anderson, wants to book the first space safari–already he has deposits from 100 people and a few corporations (Dole Foods, Taco Bell) that want to take part. He was the first person to realize the tourism value of the third seats on the Soyuz rockets, and helped Tito book passage on Mir. When Russian space officials decided late last year that Mir’s flying days were over, it nearly broke Tito’s heart. To his surprise, his reservation instead was transferred to the ISS in January. “That’s the Ritz, compared to Motel 6,” he said at the time.

Tito has since undergone 900 hours of cosmonaut training in Russia, where he has lived for most of the past eight months. He passed the cosmonaut exams with flying colors. “We are very happy to accompany you to space,” Yuri Baturin, the crew’s flight engineer, told Tito over drinks during a recent trip to Houston. “We like your mathematical mind. And we more like your romantic soul.”

But Tito has asked them to not cut him any slack. “I don’t want the white-glove treatment,” he said. “I don’t want to be your baby-sitting problem.”

“I have different opinion, Denny,” said Talgat Musabayev, the flight’s commander. “You are not baby. I am not babysitter. I am commander. You are ‘first cosmonaut tourist,’ an ’engineer in education.’ It is very important for mankind.” After the Tito mission, he explains, Russia will fly another tourist, and another.

“Oh, new designation!” Yuri Baturin, the flight engineer, interrupted. He held aloft a glass of Puligny-Montrachet 1997. “Denny is ‘first test passenger.’ A drink!”