How can we get to Mars - and back again?
Would you leave everything behind to start afresh on Mars, knowing you would never return to Earth?
More than 150,000 people would be willing to make the one-way trip, according to Mars One, an organisation that has been calling for applicants to make such a journey in 10 years' time. The Mars One plan may never come to fruition - people have been eyeing the red planet for decades and yet it remains unsullied by human footprints. But the one-way nature of the scheme does highlight one of the biggest barriers to visiting Mars - it's not getting there that's hard, it's coming back.
Humans could have visited Mars or Venus in the 70s or 80s using variations of the Apollo spacecraft that went to the Moon. The catch was that they couldn't land. An Apollo-based interplanetary mission would have just flown by or possibly spent a few weeks in orbit, because landing would require a much heavier spacecraft and a lot more fuel. Because of this the spacecraft would have to be launched in several pieces and assembled in orbit, and demand the development of a lot of new technology and infrastructure (one of the original purposes for the International Space Station was as a kind of shipyard for interplanetary craft). As such, a Mars mission would be extremely expensive.
Or would it? In 1989, the United States first president Bush tried to put the US on the road to a Mars landing but quickly pulled back when Nasa worked out the staggering cost. Yet 15 years later, when his son tried the same thing, the idea received more traction, in part thanks to a development from 1991 called Mars Direct.
Mars Direct is a scheme championed by American engineer Robert Zubrin and the Mars Society which he leads. It pulls a cunning trick to knock out one of the assumptions in my reckoning above. Yes, you need a lot of fuel and equipment to take off from Mars. But who said you had to take it all with you?
Mars Direct proposes sending two spacecraft to land on Mars. The spacecraft that the astronauts will fly home in goes first, empty and unfuelled. Once it lands it automatically converts chemicals in the Martian atmosphere into rocket fuel which will power its ascent from the surface and voyage back to Earth.
Then the astronauts depart Earth in a spacecraft designed for a one-way journey, but safe in the knowledge that they have a ride waiting for them when they get to Mars.
It's still a complicated endeavour, but it doesn't require any orbital construction or infrastructure in space, just two independent launches from Earth - and it makes a mission to Mars much cheaper than previously thought.
America's Martian plans were halted by the credit crunch, but the existence of organisations like Mars One and the Mars Society show that there is a lot of enthusiasm for Martian exploration. If we ever do mange to send people to Mars - and unlike Mars One's volunteers, they want to come home again - Mars Direct will make it possible.
F or more info, check out: marssociety.org