The launch window for the mission opens on Jan. 5, 2018. The next opportunity is not until 2031.
"If we don't make 2018, we're going to have some competition in 2031," Tito told Reuters.
"By that time, there will be many others that will be reaching for this low-hanging fruit, and it really is low-hanging fruit," said Tito, who set up the nonprofit Inspiration Mars Foundation to organize the mission.
Project chief technical officer Taber MacCallum said U.S. industry is up for the challenge.
"That's the kind of bold thing we used to be able to do," said MacCallum, who also oversees privately owned Paragon Space Development Corp.
"We've shirked away from risk. I think just seriously contemplating this mission recalibrates what we believe is a risk worth taking for America," he said.
The spacecraft will be bare-bones, with about 600 cubic feet (17 cubic meters) of living space available for a two-person crew. Mission planners would like to fly a man and a woman, preferably a married couple who would be compatible during a long period of isolation.
The capsule would be outfitted with a life-support system similar to the one NASA uses on the space station, which recycles air, water, urine and perspiration.
"This is going to be a very austere mission. You don't necessarily have to follow all of NASA's guidelines for air quality and water quality. This is going to be a Lewis and Clark trip to Mars," MacCallum said, referring to the explorers who set out across the uncharted American Northwest in 1803.