At the time, in 1964, he was only 23.

Tito's former colleague Norm Haynes recalls, "We were all right out of school. It was incredible. Nobody had ever done this stuff before."

That was particularly true four years later, when Tito collaborated with Bourke and Haynes to design the Mariner 9 mission, the first attempt to put a spacecraft in orbit around another planet.

Although Mariner 9's goal was to photograph the entire planet at relatively close range, the craft only carried enough fuel for a highly elliptical orbit. To complicate matters, only one giant antenna, the 210-foot (64-meter) dish at Goldstone, California, would be available to receive the spacecraft's signals as it circled Mars.

Tito helped devise a 12-hour-long orbit for the craft that would allow controllers at Goldstone to receive new data twice each day, enabling Mariner 9 to carry out its mission in half the time originally anticipated.

What most amazes Haynes, looking back, is how quickly the trio of planners accomplished their complex task.

"[Dennis] and Roger and I designed the Mariner 9 mission on my blackboard in my office one afternoon," Haynes recalls. "And that's the mission we flew."

Three years later, in 1971, their planning bore fruit when Mariner 9 arrived at Mars and revealed giant volcanoes, huge canyons and ancient dry river valleys.

"Not only was it the first time we did it," Bourke said, "but we did it well."

By that time, however, Tito was nearing the end of his space career.

In the early 1970s he left JPL for the world of finance, a move that Haynes believes was in character.

"He was always interested in the stock market," Haynes said, recalling that Tito and another engineer spent their off hours working on new ways to analyze the market.

By the time Tito went on to found Wilshire Associates, his Santa Monica-based investment firm, Bourke and Haynes had already lost track of their former collaborator. But in the years that followed, Tito occasionally appeared in the business pages of the Los Angeles Times.

"Somebody at JPL would always bring [the article] in," Haynes said, "and wed kind of chuckle about it."

The paper's coverage of Tito also included his 30,000-square-foot hilltop mansion. "He's got a master bedroom bigger than my house," quips Haynes. "So somewhere along the line, I realized he'd hit the big time."

And Tito also gained visibility as a philanthropist.

"Hes been a major supporter of the opera in Los Angeles," said Bourke. "Hes supporting medical work at UCLA. Hes done things with his wealth that are very socially admirable."

But Tito never lost his sense of connection to JPL, or the space business, as Bourke and Haynes learned a couple of years ago when Tito came to the lab to give a talk about his new life.

Tito told his colleagues that his success in business came from applying the analytical skills he'd learned at JPL. During that visit, said Bourke, "We had a little reunion of a few of us who worked together in the '60s. Half a dozen folks around the table."

And it was clear, said Bourke, that "Dennis is extremely proud of his JPL background and the things he did there."

So proud, said Haynes, that he seemed to long for returning to the space business. Tito even came by once to ask whether he could obtain copies of the plans for Mariner 4, and other spacecraft he had worked on, so that he could have full-scale replicas made for his office.

"He was very interested in going back into that world," Haynes said. "He knew he couldnt do it on an active, day-to-day basis like he did before, but I think he just wanted to go back into that world."