No human has ever left Earth's orbit. Armstrong, Aldrin and the 22 other Americans who visited the Moon as part of the Apollo program may have been further than anyone else, but even they remained within our planet's gravitational influence.
But that may not remain the case for long. Space agencies around the world are slowly gearing up for a manned mission to Mars. But who's going to get there first?
Mars has been a target for human exploration since the 19th century, and the first person to make a detailed technical study was German aerospace engineer Wernher von Braun. His 1952 book, Das Marsprojekt, envisioned a fleet of 10 spacecraft assembled in low-Earth orbit with landing vehicles that would descend like aircraft to the surface.
Soviet rocket pioneer Mikhail Tikhonravov also came up with a manned Mars expedition proposal for the USSR in studies between 1956 and 1962. This featured a six-cosmonaut crew who would land on Mars for a one-year expedition, spending two and a half years in space in total.
In 1962, Nasa conducted its own studies, analyzing what it would take to accomplish a human voyage to Mars. Their researchers concluded that a Mars mission could be done with eight rockets assembling an interplanetary spacecraft in low-Earth orbit, or perhaps even with a single launch of an enormous hypothetical future rocket.
From there on out, and especially following the successful Moon landings, proposals for crewed Mars missions came thick and fast. Von Braun developed new mission concepts, this time for Nasa, suggesting that multiple space shuttle launches could ferry the parts necessary for a larger spacecraft into orbit.
Between 1981 and 1996, a series of conferences were held at the University of Colorado titled The Case for Mars, working through the different problems that a manned mission would encounter, and much of their work is still influential today. In the 1990s, Nasa also developed several conceptual human Mars missions, including the habitats that people would live in, as a way of spurring further thought and discussion.
Problems to solve
A couple of major problems that still need solutions are a big reason why we haven't been to Mars already. The first is that Mars is more than a hundred times more distant than the Moon, meaning the journey would take a lot longer, about seven or eight months – and that's one way.
But the cosmic ballet of orbital dynamics means you can't come straight back again – you need to wait for the planets to align. Taking the most efficient route would result in a mission duration of a little under three years.
That's a long time to spend in space. The longest single spaceflight in human history – Valeri Polyakov's stay aboard the Mir space station – lasted 14 months, from January 1994 to March 1995. We have no data on what the effects might be on humans of prolonged exposure to both physical factors like microgravity, cosmic radiation and freeze-dried food, as well as mental factors like isolation from Earth, and having to spend a lot of time in cramped conditions with a very small number of people.
The other big reason why we haven't been to Mars is the cost. In Fredric W. Taylor's 2010 book The Scientific Exploration of Mars, he low-balls a figure of 500 billion US dollars, saying the actual costs are likely to be even higher. That kind of funding – about the same amount that the United States spends on defence annually – simply isn't available for space exploration, especially as the benefits to humanity are somewhat nebulous. There's no question we'll gain a lot out of such a trip, but it's tough to say exactly what.
