No human has ever left Earth's orbit. Armstrong, Aldrin and the who visited the Moon as part of the 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 . His 1952 book, , 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 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 , 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.
That's a long time to spend in space. The longest single spaceflight in human history – 's stay aboard the – 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 , 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.
As the 21st century dawned, more space agencies started getting excited about Mars. In 2001, the European Space Agency (ESA) proposed the – a long-term vision for the exploration of the solar system. It began with robotic exploration, followed by simulations on Earth and eventually a manned mission in 2033.
Disagreements among the largest contributors to the ESA's budget have, however, set back that timetable substantially. Missions featuring robotic explorers have successfully launched in the last decade, such as 2016's , and these are likely to continue over the next decade.
But it's an open question whether the European Space Agency will develop its own human spaceflight missions in the future, or merely follow behind its international competitors, partnering on specific missions and sharing knowledge without taking a leading role.
To date, many of those partnerships have been with ROSCOSMOS – the Russian space agency. While a number of Mars mission concepts have been proposed by Russian scientists, and some research has been done on the psychological effects of isolation on a long space mission (most notably the ), the country has mostly stayed out of the race to Mars and concentrated on low-Earth orbit instead.
That has left something of a vacuum, which newer space agencies like China's National Space Administration (CNSA) and India's Space Research Organisation (ISRO) have jumped to fill. Japan's Aerospace Exploration Agency – JAXA, if you're wondering – is , sending robots towards Venus and Mercury, and the occasional astronaut to the International Space Station.
To date, China has seemed more focused on lunar rather than Martian exploration, but that's beginning to change. The country partnered with Europe and Russia on the Mars 500 study, and launched the in 2011 which, unfortunately, failed to make it out of the Earth's orbit.
But in early 2016, CNSA announced the – a plan to put an orbiter, lander and rover on Mars, delivered on a Chinese rocket. It's planned to be a demonstration mission for the technology necessary for a robotic sample return mission in the 2030s.
On the manned side of things, China has sent five crews into space since 2003 and has a space station in orbit, but – perhaps recognizing that the country has a lot of catching up to do – has to send humans beyond the Moon yet. That said, don't count China out – it's got the resources, the cash, the technology, and the desire to prove themselves to a watching world.
Another new entrant worth watching is India. ISRO launched a Mars mission, , in 2013 and successfully entered the orbit of the Red Planet in 2014, making it the first country to succeed on its first attempt to send a probe to Mars, and only the fourth space agency to do so at all.
Like Russia, ISRO's current focus is chiefly on low-Earth orbit, and on launching satellites for other countries (which it's getting very good at), but is planned for the coming years, while an that could carry humans into space is under development. Its is due in 2024, and the country's future appetite for manned space missions will no doubt be heavily influenced by the results.
Don't forget Nasa
Then, of course, there's international space flight's biggest player: Nasa. In 2004, US President George W. Bush announced a manned space exploration programme, titled the . Released in the wake of the Columbia Space Shuttle disaster, its express goal was to "inspire, innovate and discover" public enthusiasm for space policy.
It shifted Nasa's focus away from the space science missions it had been concentrating on (like the ) and back towards exploration, with the ultimate objective of a manned mission landing humans on Mars in the 2030s.
When Barack Obama ascended to the presidency in 2009, he came with his own set of priorities, set out in a at the Kennedy Space Centre. His proposals increased Nasa funding, signed off on the development of a new heavy-lift rocket, and predicted a crewed orbital Mars mission by the mid-2030s. However, it also scrapped the behind-schedule , which was the United States' foremost plan to get humans back to the Moon and eventually to Mars.
That 2010 speech was a major turning point for Nasa, and saw the beginning of a shift towards relying on commercially-operated launch vehicles, rather than its own rockets, to put its equipment into space. Mere weeks later, SpaceX successfully launched its Falcon 9 rocket for the first time, heralding a totally new era of spaceflight.
SpaceX founder Elon Musk has about how his ultimate plan is to colonize Mars, and the firm has a comprehensive vision to achieve that goal. Its (formerly known as the Mars Colonial Transporter) includes a launch vehicle, spaceship and tanker that would allow a to be build at a site named . How soon? According to an "optimistic" schedule, the first crewed flight, carrying "about a dozen people", could launch as early as 2024.
While that all might sound like pie in the sky, the plans released by the company are long-term in scope, and extremely detailed. With Musk's deep pockets and total commitment to the cause, and despite the company's relatively short history compared to its competitors, SpaceX is perhaps the closest of any space-going entity to landing on Mars.
Musk does have some commercial competition, though none has as well-developed plans. Lockheed Martin is working on its project, which would supposedly send astronauts to Martian orbit as early as 2028. Amazon CEO Jeff Bezos' Blue Origin spaceflight venture is .
The much-maligned project, however, is barely worth discussing, nor American space tourist Dennis Tito and his , both of which have been pretty quiet of late. Meanwhile engineer Robert Zubrin reckons his concept – a mission that's been in the planning stages since at least 1990 – could be delivered on board cheap SpaceX rockets, so that's an outside shot.
No, really, don't forget Nasa
But amidst all the private firms rushing to the Red Planet, Nasa has its own proposals. In 2015, Nasa's then-administrator Charles Bolden the agency's goal of sending humans to Mars, picking 2030 as the date of a surface landing, with robots arriving beforehand to prepare an underground base for astronauts.
The spaceship carrying Nasa's astronauts will be the Deep Space Transport, in March, which will dock with a space station in lunar orbit (built by Boeing) called the . Nasa's human exploration administrator, William Gerstenmaier, said the gateway "could move to support robotic or partner missions to the surface of the moon, or to a high lunar orbit to support missions departing from the gateway to other destinations in the solar system".
The future of Nasa's plans for manned Martian exploration are now, however, in the hands of Donald Trump, a man whose space policy is – like many of his other policies – tough to glean. The Trump administration has said very little about its plans for human spaceflight, so Nasa seems to be .
All we know for now is that Trump's space advisors , that Elon Musk sits on Trump's advisory board of business leaders, and that there's . The latest dates from Nasa set a humans-to-Mars mission for 2033.
So, where does that leave us? Europe is too divided, Russia and Japan too uninterested, and India too far behind to compete. That means a strong likelihood that the first person on Mars will be American (but with no clear idea if they'll be working for the government or not), and an outside chance that they might be Chinese.
Beyond that, there are too many sources of uncertainty. Changing relationships between China, Russia and the United States – three of the biggest players in space exploration – could dramatically shift global geopolitics, and the timelines for space exploration along with them. A new could spark a new , rapidly accelerating technological development, while Elon Musk does his own thing in the background.
But one thing is for sure – for Mars enthusiasts, the coming decades will be very exciting indeed. And if you'd like to fire your imagination in the meantime, we'll leave you with this video from SpaceX showing how Elon Musk sees his own dreams unfolding…