It has been a long-cherished dream of space enthusiasts, as well as lovers of science fiction, but now it seems that someone has finally come up with an ambitious – and some say realistic – plan to send two astronauts to Mars in just five years’ time.

Tomorrow at the National Press Club in Washington, multi-millionaire Dennis Tito – the world’s first space tourist – is expected to reveal how he hopes to launch a privately-funded mission to Mars in 2018, when the Red Planet makes its nearest approach to Earth.

Little is known about the “Inspiration Mars” mission accept that it is Tito’s brainchild and that he has garnered some high-profile supporters, including Jonathan Clark, the associate professor of neurology at Baylor College of Medicine who was the crew’s surgeon on six Space Shuttle flights.

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Dr Clark told The Independent that he is not supposed to talk about the mission until all is revealed at the Washington press conference this evening, but he dismissed suggestions that the plan is not a serious one.

“I wouldn’t be involved if I didn’t think that there was something to it. I don’t want to pre-empt the announcement, but it’s a very in-depth study that has gone into it,” Dr Clark said.

The Inspiration Mars mission will send two astronauts on a simple return trip to Mars, flying around the far side of the planet once but without going into orbit.

Scientifically, the 501-day mission will accomplish next to nothing. The probes, landers and robots that have already been sent to Mars have sent back far more interesting and useful information than this simple manned mission is ever going to be able to gather.

However, in terms of human endurance and psychology, the mission could set new precedents in space exploration. For 17 months, two people will experience what it is like to be cooped up together in a space module not much bigger than a small bathroom with the ever-present risk of something going fatally wrong.

Technically, it is known as a return fly-by, meaning that it will need the smallest amount of fuel to get there and back again. If anything goes wrong, the spacecraft should make its own way back to Earth – but with no possibility of any short-cuts home.

Anyone who knows anything about the immense problems of manned missions to Mars will want to hear about how Tito intends to raise the estimated $1.5bn-$2bn (£1bn-£1.3bn) that it will cost to send two people to Mars and back again.

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Tito, a former Nasa scientist who made his fortune in financial investment, is believed to be in contact with other self-made billionaires with an interest in space flight, including Elon Musk, the Paypal entrepreneur and founder of SpaceX, the private space company.

One possibility is that a privately-funded mission could raise money through TV rights and internet deals. The public could be invited to pay for exclusive access to on-board camcorders or the privilege of talking to the crew – some commentators have even suggested some kind of reality TV deal.

Anu Ojha, the director of the UK National Space Academy in Leicester, said that the global space community is agog at the thought that a group of extremely wealthy individuals could club together to fund a “quick and simple” manned mission to the Red Planet.

“I am more excited about this than any human spaceflight story I’ve seen or heard about being planned since I was a kid – but it all depends on the funding question,” Mr Ojha said.

“This could be the biggest space adventure since the Apollo programme. In fact it is Apollo 8 on steroids, but without the funding it’s dead in the water,” he said.

Apollo 8 was the first manned space flight that took astronauts beyond Earth orbit. It was a trailblazer mission in that, for the first time, men made a simple return trip to the Moon, orbiting the lunar landscape 10 times before coming back home.

With the Inspiration Mars mission, “the returns in terms of understanding human physiology and psychology in long-duration spaceflight would re-write the textbooks,” Mr Ojha said.

“As an exemplar of human endurance and exploration, it is totally unprecedented. This would be an Apollo 8 moment – but lasting a year and a half rather than six days and with no meaningful abort options once on its way.”

Professor Martin Rees, the astronomer royal, agreed that technically the mission is far simpler than sending a manned Mars orbiter and lander, but the physical and psychological issues faced by the crew would be formidable.

“The Mars trip would be more of an ordeal than a Moon-loop trip, though no more than what Ranulph Fiennes was trying to do, and would require more provisions. But it’s not technically crazy – and hugely simpler than a Mars landing,” Professor Rees said.

The Mars Inspiration mission plans to use the Falcon Heavy rockets made by SpaceX to launch the company’s Dragon space module, the first private spacecraft to dock with the International Space Station. Dragon, however, is little more than 14ft long and 12 ft wide, although extra living space could be made available with the addition of a Bigelow “inflatable” module.

But even so, the living conditions will be more Spartan than the recent Mars 500 ground mission in Moscow where six “astronauts” simulated in a scientific institute what it was like to live together in close confinement on a 520-day “space mission”, which ended in January.

A technical paper to be presented at the IEEE Aerospace Conference in Montana this weekend, co-authored by Tito and Clark, says that conditions on board the Dragon module will be testing. “Crew comfort is limited to survival needs only. For example sponge baths are acceptable, with no need for showers,” it says.

Apart from the psychological problems associated with claustrophobia and the limited room for exercise and other bodily functions, there will be the ever-present problem of a coronal mass ejection from the Sun, which could send out a stream of high-energy particles and radiation that could seriously harm the astronauts.

Although in 2018 the Sun will be going through a quiet phase of its 11-year sunspot cycle time, a coronal mass ejection is still possible, which would put the crew in serious risk of injury or even death.

But perhaps this will be the least of their worries on a journey where there isn’t much else to do but look at the stars and dream of home.