WASHINGTON — In less than five years, a married couple could be on their way toward Mars in an audacious but bare-bones private mission that would slingshot them around the red planet, under a plan announced Wednesday by a financial tycoon and his team.

The voyage to Mars and back would be a cosmic, no-frills flight that would take the husband-and-wife astronauts as close as 100 miles to the planet, but it would also mean being cooped up for 16 months in a cramped space capsule half the size of an RV.

The private, nonprofit project, called Inspiration Mars, will get initial money from multimillionaire investment consultant Dennis Tito, the first space tourist. The team would not say how much the overall flight would cost, but outsiders put it at more than $1 billion.

NASA will not be involved. Instead, the project’s backers intend to use a private rocket and space capsule and some kind of habitat that might be inflatable, employing an austere design that could take people to Mars for a fraction of what it would cost NASA to do with robots, officials said.

The crew members will have no lander to go down to the planet, and no spacesuits to go out for any spacewalk. They will have minimal food and clothing, and their urine will be recycled into drinking water.

“This is not going to be an easy mission,” said chief technical officer and potential crew member Taber MacCallum. “We called it the Lewis and Clark trip to Mars.”

It also involves a huge risk, more than a government agency like NASA would normally permit, officials concede.

As for why a couple will make the flight, “this is very symbolic and we really need it to represent humanity with a man and a woman,” MacCallum said.

The project aims to capitalize on the once-in-a-generation close approach of the two planets’ orbits. It calls for a launch on Jan. 5, 2018, a Mars flyby on Aug. 20, 2018, and a return to Earth on May 21, 2019.