While humans have dreamed about going to Mars practically since it was discovered, an actual mission in the foreseeable future is finally starting to feel like a real possibility.
But how real is it?
Nasa says it's serious about one day doing a manned mission while private companies are jockeying to present ever-more audacious plans to get there. And equally important, public enthusiasm for the Red Planet is riding high after the Curiosity rover's spectacular landing and photo-rich mission.
Earlier this month, scientists, Nasa officials, private space company representatives and other members of the spaceflight community gathered in Washington D.C. for three days to discuss all the challenges at the Humans to Mars (H2M) conference, hosted by the spaceflight advocacy group Explore Mars, which has called for a mission that would send astronauts in the 2030s.
But the Martian dust devil is in the details, and there is still one big problem: We currently lack the technology to get people to Mars and back. An interplanetary mission of that scale would likely be one of the most expensive and difficult engineering challenges of the 21st century. "Mars is pretty far away," Nasa's director of the International Space Station, Sam Scimemi said during the H2M conference. "It's six orders of magnitude further than the space station. We would need to develop new ways to live away from the Earth and that's never been done before. Ever."
There are some pretty serious gaps in our abilities, including the fact that we can't properly store the necessary fuel long enough for a Mars trip, we don't yet have a vehicle capable of landing people on the Martian surface, and we aren't entirely sure what it will take to keep them alive once there. A large part of the H2M summit involved panelists discussing the various obstacles to a manned Mars mission. "I've said repeatedly I'll know when we're serious about sending humans to the Mars surface when they start making significant technology investments in particular areas," engineer Bobby Braun, former Nasa chief technologist, told Wired.com.
The good news is that there's nothing technologically impossible about a manned Mars mission. It's just a matter of deciding it's a priority and putting the time and money into developing the necessary tools. Right now Nasa, other space agencies, and private companies are working to bring Mars in reach.
Here, Wired.com presents the most challenging obstacles we'll have to overcome to get to Mars and how to fix them.
Getting off the Earth
Before you can run you need to walk. And before you can do deep space exploration, you need to get off your own planet.
While we've been sending people and probes into space for more than 50 years, a manned Mars mission would be on a much larger scale than almost anything we've done before. There is no rocket in existence that can take off from the Earth's surface and escape its gravitational pull to reach space carrying the weight of a large spacecraft, astronauts and all the supplies and materials needed to get to Mars. Most likely, rockets would have to make several trips to drop off supplies and pieces for a vehicle into low-Earth orbit.
There astronauts would slowly build the vehicle over time and then rocket off to the Red Planet.
That still requires some heavy lifting. The largest construct assembled in space, the International Space Station, has a mass of 4,500 tonnes and required 31 spaceship flights to complete.
According to Nasa, a Mars vehicle capable of taking people to the Red Planet and back would be smaller than the space station -- around 1,250 tonnes. But our capabilities are hampered by the retirement of the Space Shuttle fleet, which was capable of carrying large masses to Earth orbit with relative ease.
Using existing rockets, aerospace engineer Bret Drake, who leads planning and analysis at Nasa's Exploration Missions and Systems Office, estimated it would take 70 or 80 launches to assemble a Mars mission spacecraft. Considering the ISS took more than a decade to complete, assembling a Mars vehicle would require a very long time.
But in the future, this task should be much easier. Nasa is hoping to have its Space Launch System ready by 2017, which will be the largest rocket ever flown, even bigger than the Saturn V that carried astronauts to the moon. The private spaceflight company SpaceX is also working on its new Falcon Heavy launch vehicle, which would have somewhat less cargo capacity than Nasa's big rocket but still much greater than anything around today. Falcon Heavy's first tests could begin later this year.
Nasa estimates it would need to fire at least seven of its new SLS rockets to deliver to orbit the people, supplies, and ships necessary for a Mars mission. And while SLS could help get to the Red Planet, it should be noted that there are other alternatives we could pursue.
Fuel storage
Humans aren't the only things you want to send on a manned Mars mission.
In order to stay alive in space, people need lots of things: food, oxygen, shelter, and, perhaps most importantly, fuel.
Somewhere around 80 percent of the initial mass launched to space for a human Mars mission is going to be propellant. Trouble is, storing that amount of fuel in space is hard.
Objects in low-Earth orbit (the place you'd park your Mars spaceship while you built it) travel around the world every 90 minutes. During half that time, they experience the intense heat of the sun and then the unheated blackness of space. That difference causes liquid hydrogen and oxygen -- rocket fuel -- to vaporise.
Unless tanks are regularly vented, containers holding these materials are liable to explode.
Hydrogen in particular is susceptible to leaking out of its tanks, resulting in a loss of about 4 percent per month. This means that if a Mars mission required a year to assemble in low-Earth orbit, it would lose more than half of its propellant before even departing to the Red Planet. At a cost of around $10,000 (£6,600) to send a kilogram to space, that would be an expensive waste.
Nasa is actively pursuing new technology that would allow them to store propellant in space for long periods of time. Starting this year, the agency hopes to demonstrate the capability for large, in-space cryogenic loading and transfer. Such technology would be extremely valuable for a manned Mars mission and could one day lead to the equivalent of a Space Age gas depots waiting to top up a rocket's fuel.
Advanced propulsion
While you want to get people to Mars as fast as possible to minimise exposure to the hazards of radiation and weightlessness in space, their supplies can leave Earth earlier and travel at a more leisurely pace.
A relatively low-power engine could push along a large ship carrying astronauts' supplies for their time on Mars. In its interplanetary plans, Nasa would like to send such things on ahead of a crew and have them waiting on the Martian surface when the people arrive.
The agency is currently working on advancing solar electric propulsion, which shoots ionised gas behind a craft to move it forward. Previous missions, such as Nasa's Dawn and the Japanese Hayabusa spacecraft, have used this method. A Mars mission would need much larger solar electric thrusters than have been used before. The agency currently has plans for a mission to collect a small asteroid and tug it back to Earth, which could be helpful in moving this technology forward.
Landing on Mars
We currently don't have the capability to land people on Mars, plain and simple. This is a fairly recently recognised problem, having only been understood through calculations made in the early 2000s.
As engineers began to build larger and larger machines to land on the Martian surface, they realised they were reaching a limit. The thin Martian atmosphere can't quickly inflate very large parachutes, such as those that would be needed to slow a spacecraft big enough to carry humans. But the atmosphere is just substantial enough that a lunar-style vehicle using downward-facing rockets couldn't land without creating too much turbulence.
The 0.9 tonne Curiosity rover, which arrived on Mars in 2012, is the largest object our current technology can place on the ground.
Human-scale missions, according to Nasa, will require landing at least 36 tonnes. Even the bare bones one-way manned mission proposed by Mars One would bring around 9 tonnes of material to the surface. "Landing Curiosity was landing a small nuclear car," said engineer Bobby Braun, former Nasa chief technologist and currently a professor at the Georgia Institute of Technology. For a human-scale mission, "We're talking about landing perhaps a two-story house, and then another two-story house with fuel and supplies right next to it." "That's a fantastic challenge," he added. Though Curiosity's landing was a truly remarkable achievement, it "pales in comparison to what might be required one day to land humans."
Landing things at that scale will require new technologies that have to be invested in, matured, and tested over and over to make sure that they don't kill their crew. "The one thing we do not want landing for humans to be characterised as is 'Seven Minutes of Terror'," said engineer Kendall Brown of Nasa's Marshall Spaceflight Centre.
Curiosity also had a relatively large landing ellipse. That is, researchers could be reasonably sure where the rover would touch down, but only within an ellipse seven by 20 kilometres. Imagine if a human descent vehicle touched down on Mars and then the astronauts' supplies came down 20 km away. It would be quite a schlep just to go pick up your extra oxygen.
The next generation of landers will need accuracy on the order of hundreds of metres and make sure they don't come down on top of some other vital piece of equipment, like a nuclear power plant.
Scientists at Nasa are currently working on hypersonic inflatable systems. These are basically gigantic balloon-like objects that would expand and stiffen to become something like a super-rigid parachute, helping to slow a landing vehicle down. But the key technology to landing people on Mars is something called supersonic retropropulsion.
A spacecraft comes into the Martian atmosphere at a screaming 24,000 kph. Even after slowing down with a parachute or inflatable, it would be traveling well above the speed of sound. Simply sparking a rocket flame would be something like trying to light a candle while someone is blowing on the wick the entire time. And once you had your thruster going, it would be injecting that flame into an extremely dynamic environment, something our technology has never had to handle before.
Nasa has done wind tunnel tests to look at this problem before, once in the 60s and 70s for the Viking landers, and again more recently. The good news is the testing shows that supersonic rockets are theoretically possible. The bad news is that Nasa is not working on this program anymore.
While Nasa may yet pick up testing for this again, a member of the private spaceflight business may be leapfrogging them. SpaceX is working to create reusable rocket tanks that descend from orbit and land back at their launch pad. The company is planning to test supersonic retropropulsion later this year, which could be used both on Earth and in an eventual Mars mission.
Keeping the crew healthy
Space is a dangerous place to send complicated, delicately tuned systems, and "perhaps the most complex system of them all is the human body," said health specialist Saralyn Mark, president of SolaMed Solutions, which consults with Nasa's health and medical office.
Ironically, the thing responsible for powering most life on Earth, the sun, is also the most deadly part of space travel for living organisms.
Once outside the protective magnetic field of our planet, solar radiation would accumulate in an astronaut's body, raising his or her risk of cancer. Recent data from Nasa's Curiosity spacecraft have helped quantify just how risky background radiation levels are. Massive explosions like solar flares or energetic particle events could throw potentially lethal doses of radiation right at a spaceship.
That's why the private manned mission to flyby Mars in 2018, Inspiration Mars, is planned for a time of low activity from the sun, when the chance of a solar outburst is lowest. Though, lowering solar activity increases levels of radiation streaming in from the galaxy, which would also be hazardous.
The trip out to Mars would probably take between seven and nine months, and humans would need to be protected the entire time.
Currently, the most feasible solution is to line a spacecraft with water, which would absorb radiation and provide some amount of shelter during a solar storm. But water is heavy, and any added weight on a mission is an added cost. In the future, the capability to create a mini-magnetic field to protect a crew could be developed, but this is years or possibly decades away.
Aside from radiation, the biggest challenges for a manned Mars trip will be microgravity, which causes a host of odd medical conditions, and isolation, which can bring on a range of psychological issues.
The record for continuous time spent in space is held by a few pioneering Russians, who remained aboard the Mir space station for periods up to a year or longer. "That's pretty much the limit of our understanding," said Richard S. Williams, Nasa's chief health and medical officer. "And when you're talking about going to Mars, that's up to 30 months for a round-trip."
What we do know is that extended stays in zero-g cause bone and calcium degradation, muscle loss, and a recently-identified issue that may stem from swelling of the optic nerve. If left unchecked, astronauts arriving on Mars could be weak, brittle-boned, and possibly blind.
Medical advances and regular exercise seem to help some of the biological problems of space travel. Nasa is currently planning to have its astronauts undergo long stays of up to a year on the International Space Station to better understand these factors.
But the psychological issues that a crew en route to Mars will face are largely unknown. With the ISS, Earth is a relatively short Soyuz ride away, and astronauts can gaze down upon it. But crewmembers on a Martian trip would have no way to abort their mission and would suffer an ever-increasing time delay in communication with home.
There have been other isolated group experiments that offer some insight into how a Mars crew might fare. The Biosphere-2 experiments of the 1990s had seven or eight people stay in a large simulated environment for two years at a time. "All crewmembers in Biosphere-2 agreed that the psychological issues were the biggest issue," said Taber MacCallum, co-founder of Paragon Space Development and a participant in Biosphere-2.
The longest simulation approximating a Mars trip so far has been the Mars 500 mission, which had six men stay for 500 days in a sealed room while researchers monitored the results. The participants in this experiment became lethargic and bored. One of them became depressed. Only two out of the six crewmembers experienced no real problems and only one kept busy and active, with no deterioration of cognitive performance.
A Mars mission would test the limits of isolated human groups.
Crewmembers would probably have to pass through long-term screenings to make sure they are fit both physically and mentally.
Living off the land
With freezing temperatures and an arid environment, Mars may not seem like the best place to set up camp. But there is a wealth of materials on the Red Planet that astronauts could use to their advantage.
Nasa and other space agencies call this in-situ resource utilisation (ISRU) and it basically means living off the land. A machine could be sent to Mars ahead of astronauts that might extract oxygen from the carbon dioxide atmosphere. Or elements in the soil could be isolated and then used for building materials or rocket fuel.
As has been recognised in recent decades, Mars has a lot of water locked up in ice. In certain places, there are enough ice crystals in the soil that a robot could simply scoop up a heap. "Prior plans [to go to Mars] said we have to bring all this water," said space physicist Jim Green, Nasa's director of planetary exploration. "Now we say, bring a straw."
Though often discussed, ISRU technologies are something that have never been developed. Nasa would have to demonstrate that living off the extraterrestrial land is feasible.
Human missions to Mars also often call for some sort of crop growing capabilities. At first blush, the idea of farming on Mars seems like a reasonable plan. Your astronauts are going to want fresh vegetables and a farm could lessen the amount of freeze-dried food they might have to take.
[Quote"]We currently don't have the capability to land people on Mars, plain and simple[/pullquote]
But growing crops on another planet is tricky. You wouldn't want your crew to rely on the food they produce, said Taber MacCallum, co-founder of Paragon Space Development, which makes life-support systems for space. Plants are finicky. If the crew makes "one mistake, they all die," he said.
Looking at the amount of food you'd get out of farming for the amount of energy you'd have to put in, and considering all the temperature controls and other systems technology necessary, MacCallum estimates it would take 15 to 20 years of continuous habitation on Mars before it would be worth putting in an agricultural system.
Protecting ourselves and the planet
Earth is the only place we know of with life. But that doesn't mean something else isn't out there.
Because of this possibility, Nasa and other spacefaring nations have agreed to follow strict planetary protection standards. When the Apollo 11 astronauts came back from the moon, Nasa quarantined them for three weeks just to make sure they weren't harboring some terrible space virus that would destroy mankind. The procedure was repeated until Apollo 14, when scientists felt confident that there was no harm.
The moon is sterile. Mars is another case altogether. Evidence suggests that the Red Planet may have once been capable of supporting life. There is a slim but non-zero chance that something is still alive on the planet and could potentially be virulent.
Alongside the possibility of destroying mankind with Mars microbes, we also want to avoid the opposite problem. Humans come with their own smorgasbord of bacteria and fungi (your body has 10 microbial cells to every human cell in it) and right now there's nothing we can do to prevent some human contamination from leaking out onto Mars. Future technologies will have to improve our ability to seal ourselves from the dangers of Mars and Mars from the dangers of us.
To adhere to the strictest planetary protection protocols, perhaps the best course would be to spend a few missions without humans on the surface of Mars. People could park in orbit or set up camp on one of Mars' moons and teleoperate rovers and other robots on the surface in near-real time. They could pick over the surface for evidence of life and perhaps uncover areas that might be safer to land in. Future technologies could also help prevent Earth contaminants from infecting Mars for when we actually land people.
Dealing with dust
"The number one problem on the surface of Mars is going to be dust," said Grant Anderson, chief engineer of Paragon Space Development, which makes life-support systems for space.
The arid Martian environment has created ultra-tiny dust grains flying around the planet for billions of years. These fines are not quite like anything we have on Earth.
The only similar situation we have faced before was the moon dust that the Apollo missions encountered. The ultra-sharp and abrasive moon soil was recognised as something that could clog up machinery and damage basic functions. "We spent $17 million (£11 million) trying to solve dust problems and I don't know of one that worked," said Anderson. "John Young [commander of Apollo 16] was out on the moon brushing thermal panels with a pig-hair brush and it didn't work well."
For a human crew on the surface, living on Mars will be like living in a giant salt flat. The dust will be caustic and the crew's tools will need to be extra-hardy. During Apollo 17, astronaut Harrison Schmitt threw his geologic hammer away because the handle corroded off after just three days.
Keeping the crew as free of dust as possible will be even more important because Martian sand is thought to be toxic. Though little is known at this point, Curiosity and a previous mission, the Mars Phoenix lander, proved that the Martian soil is chock full of chemicals called perchlorates. These substances, which are basically highly chlorinated salts, can cause problems in the human thyroid gland. The issue is not well understood but researchers have labelled perchlorate "an emerging chemical of concern" in Earth water supplies.
The dust on Mars may also contain carcinogenic material and produce allergic reactions or pulmonary problems in humans, similar to the lunar hay fever experienced by Apollo astronauts. Missions will need to know how the Martian dust will interact with the humidity in a human habitat or else it could burn human skin like lye or laundry bleach.
Curiosity is helping scientists understand the extent to which Mars dust poses a hazard to human health. But "precursor missions should have some test of how dust is going to kill you," said Anderson. His company has been developing seals that they think can keep the dust out but they will need extensive experimentation to make sure they work.
Making the plan
In the grand scheme of things, engineering challenges are easy.
It's the social and political aspects of a manned Mars mission that are likely to be toughest.
Currently, many different plans are floating around. Nasa has its Design Reference Architecture (.pdf). SpaceX and Inspiration Mars have their visions. Other space agencies are weighing in with their own ideas. But at some point, one of these will have to be chosen as the plan.
No one knows exactly how much a human mission will cost but it is likely to run to tens or even hundreds of billions of dollars.
Adjusted for inflation, each Apollo landing cost roughly $18 billion (£12 billion), and a Mars mission would be an order of magnitude greater in difficulty. It seems most likely that an undertaking of that scale will be led by an international partnership. That requires everything to be outlined in formal commitments between participating countries. The only similar space mission, building the International Space Station, required about five years for the countries involved to hammer out their deals.
The plan would also have to be flexible. The world is complicated and multi-year missions need to cope with changing political landscapes and economic downturns.
We often have a vision for beautiful machinery in space, says Sam Scimemi, Nasa's director of the ISS: Something like the majestic wheeled space station in Stanley Kubrick's *2001:
A Space Odyssey*. "What we got with the ISS is not as pretty or sexy as a big rotating wheel," Scimemi said. "But this is what the politics, budget, and technical capability all provided for. After all the dreaming, this is what was built."
There are many that wish for a new Space Race to spur on the US to Mars. But the future is not going to be like the past and the very unique set of circumstances leading to the Apollo project are not likely to be repeated.
There are certainly new players that did not exist in the previous Space Age. Private companies have set their sights on the Red Planet, in particular Inspiration Mars and SpaceX, and there are probably many who believe commercial industry should go it alone. "But at current levels of technology, governments are going to play a big role," said space policy expert Scott Pace of the George Washington University. "Human space exploration is driven by visions and hopes, but they must be grounded in facts and analysis. Fantasies don't get you to space."
Pace outlined the best ways to get countries to sign off on an ambitious plan like a manned Mars mission. "Destinations are really just symbols, proxies for skills, inspirations, values," he said. "The US is not going beyond low-Earth orbit without international partners. Apollo isn't going to happen again. I think our partners are willing to go to the moon and Mars with us, but I don't think they're going to go without us."
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