In August 1998, I attended the founding convention of the Mars Society. During that first gathering at the University of Colorado, society founder and President Robert Zubrin waxed poetic about the urgent need to send humans to Mars. Seven hundred attendees signed the group’s founding manifesto, which contended that it was necessary to journey to Mars so that we could extend scientific knowledge, advance human civilization and carry forward “as much of the best of [human] heritage as possible” while “leaving the worst behind.” Conference speakers talked about terraforming the red planet and establishing a new society that would exploit the planet’s resources to sustain human life.
At the time, the ideas struck me as slightly loopy. But now, nearly 20 years later, Zubrin’s mad dream seems tantalizingly achievable. In 2014, a working group of more than 60 experts from government, industry and academia released a joint statement concluding that “a human mission to Mars is both feasible and affordable.” The group also said that putting humans on Mars is “technologically feasible by the 2030s.”
Plans are already taking shape with NASA’s program to put humans on Mars — the target date is sometime in the 2030s. Although other agencies, including the Russian Institute for Biomedical Problems and the European Space Agency, are also studying the feasibility of a human Mars mission, NASA currently has the most advanced Mars program and remains the only group to have successfully landed a craft on the planet. (Several countries, including China, India, Japan and the United Arab Emirates, have sent or will send robotic missions to Mars by 2024.) The private companies SpaceX and Blue Origin are also aiming to send humans to the red planet, but these private plans remain mostly in the early stages. Some major challenges remain, however, before any of these programs can deliver people to Mars.
Challenge: Getting there
The first problem is simply getting off the ground. People venturing to Mars will require fuel and other supplies to last more than two years, and that means their spacecraft will be larger and heavier than anything we’ve ever sent into space. Bigger spacecraft require much bigger launch vehicles, said Robert Braun, a former NASA researcher who’s now dean of engineering and applied science at the University of Colorado (no matter what, he won’t be going to Mars himself — in his wedding vows, he pledged to his wife that he would stay on Earth).
To tackle the liftoff problem, NASA is developing the Space Launch System, dubbed the “biggest, most capable rocket ever built” to launch astronauts to Mars and other destinations beyond Earth’s orbit. In its first iteration, the rocket will have 8.8 million pounds of thrust (more than 31 times the total thrust of a 747 jet) and the capability to launch 77 tons of cargo into orbit. (For comparison, the space shuttle could launch about 26 tons.) The second-generation system is even more powerful and is designed to blast 143 tons of payload into space. If all goes as planned, the first-generation rocket will undergo its first test launch in 2018 from NASA’s Kennedy Space Center in Florida.
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While NASA works on SLS, Elon Musk’s company SpaceX is developing its own Interplanetary Transport System consisting of a large rocket booster and spaceship combo, and Amazon founder Jeff Bezos has gotten into the space business, too — his company Blue Origin is working on a rocket that could send astronauts into deep space.
Once the spaceship leaves the ground, you need a rapid and fuel-efficient way to propel it to Mars. The trip takes at least six months each way, and because of planetary alignments, you’re looking at a multiyear mission, said Walter Engelund of NASA’s Langley Research Center. Even with technological advances, engineers can squeeze only so much power from traditional chemical propulsion fuels.
Nuclear electric power is another option. It has a very high specific impulse (a measure of how efficiently fuel is used to produce thrust), which “means that it has very good gas mileage,” said Stephen Jurczyk, the associate administrator of NASA’s Space Technology Mission Directorate. “The downside is that it’s very low thrust.” A craft propelled this way would take longer to get to Mars, but it would travel more efficiently, so this type of system could be a good way to send supplies to the planet in advance of the astronauts’ arrival, he said. Given the dangers of spaceflight (more on that below), engineers want to limit the transit time for people. In the meantime, researchers are working on electric propulsion thrusters that could produce greater speeds and potentially shorten the trip.
Challenge: Supplying the mission
Forget the extra baggage fee, if you’re heading to Mars; you won’t have the luxury of hauling along much stuff. Storage space and weight will be at a premium, and there’s only so much skimping you can do when it comes to fuel, food, water and other vital supplies.
Sending some supplies in advance is an obvious solution, but if we expect people to stay on Mars for any length of time, we’ll have to become adept at “in situ resource utilization” — NASA’s term for living off the land.
There’s water lurking below the Martian soil, but it contains perchlorate (a salt that’s dangerous to humans), so it would have to be mined and purified before use. Materials from the planet’s surface might be usable for crew housing. Presumably this sort of resource extraction would begin with robotics before any people arrived, Braun said. The next logical step would be establishing a system for growing food. The first people sent to Mars would need to arrive with ample food supplies, but agriculture of some sort or another would probably be taking place by the time the second or third crew arrived, Braun said. Martian farming faces its own set of difficulties. The planet’s soil does contain the nutrients plants need to grow, but photosynthesis could be a challenge, since Mars gets only about half as much sunlight as Earth and the planet’s frequent dust storms could further diminish the amount of light reaching the ground.
Some proposed plans are purposely one-way, leaving people there without a return trip. If Martian visitors want to return to Earth, they’ll need fuel. Launching from Mars would be easier than leaving Earth, because in addition to its thin atmosphere, the planet has about one-10th the mass of Earth, which means less gravity to overcome. But still, a return trip requires fuel, and fuel is heavy, and if you have to haul it to Mars from Earth, that means you’ll have a lot less room for other supplies. One likely solution would involve sending robots to Mars first so that they could take carbon dioxide from the planet’s atmosphere to extract oxygen and methane that could be turned into fuel for the trip home. “If you don’t have to bring all the return fuel with you, you can save a lot of money,” Engelund said.
Challenge: Keeping astronauts safe
Living in space inflicts a variety of insults on the human body. First, there’s the lack of gravity, which weakens bones and causes muscles to atrophy. Experience with the International Space Station has shown that exercise can help with, though not entirely solve, these problems.
A more worrisome issue is radiation, which could cause cancer, acute radiation sickness or even cognitive problems. While astronauts on the International Space Station are exposed to more radiation than they’d get on the Earth’s surface, they’re still protected from deep space radiation by the Earth’s magnetic field, Braun said. After space travelers pass the Van Allen Belts, collections of charged particles that protect the Earth from the most damaging incoming radiation and reach 400 to 36,000 miles above the Earth’s surface, they’ll have to mitigate deep cosmic radiation, too.
NASA is working on the problem by developing advanced materials to deflect space radiation. “The goal is to minimize mass while maximizing the protective effects,” Engelund said. At Brookhaven National Labs in New York, researchers are testing candidate materials such as plastics and metallic shielding. But shields may not entirely solve the problem, because the materials in them have a tendency to emit secondary radiation (radiation released when a substance absorbs outside radiation), Jurczyk said.
Space travelers will continue to require radiation protection when they arrive on Mars, because unlike Earth, Mars does not have a global magnetic field to shield against radiation blasting it from space. Probably the easiest solution here, Engelund said, would be for astronauts to live underground or coat housing structures with protective materials.
Challenge: Entry, descent and landing
Before you buy your SpaceX ticket to Mars (Musk aspires to get the price down to about $200,000), consider this sobering statistic: In the history of Mars missions, only eight craft have landed successfully.
Just reaching Mars is only the start — then you have the difficult task of landing. Vessels returning to Earth use friction created when entering the planet’s thick atmosphere to slow down, but the Mars atmosphere is very thin, so it can’t create the drag needed to reduce a space vehicle’s speed in preparation for landing.
One promising solution is supersonic retro propulsion, which essentially uses rockets firing in the direction opposite of the spacecraft’s travel to counter its forward motion.
But slowing down isn’t enough; you also have to stick the landing. “We know how to land small robotic payloads on the Mars surface — things the size of a child’s toy or, in the case of the Curiosity rover, a small car,” Braun said. But landing a spaceship will be more like landing a two-story house next to another two-story house that’s already there, Braun said. Not only do you need to nail the touchdown, you need to get the position just right.
“Landing with precision — and by that I mean within a few kilometers — is a big challenge,” Engelund said. “On Earth, we have this great thing called GPS, which we can use to steer and navigate things with fairly high precision.” Mars doesn’t have that global positioning system, so astronauts would have to rely on terrain maps and other forms of navigation. Touching down in the right spot is crucial to ensure that any supplies sent in advance are within reach — and it’s also important for avoiding hazards like cliffs and other potentially dangerous features.
Challenge: Sustained political will
Give NASA’s Mars program steady funding for a few decades, and it’s almost certain to solve the remaining technical barriers to putting humans on Mars, Engelund said. But therein lies the biggest barrier in the U.S.: NASA and the space program are politically charged topics. “Almost without exception, whenever a new administration comes in, we get a change in priorities,” Engelund said. Sending humans to Mars will require sustained support, and that means politicians who are willing to fund NASA and prioritize its Mars program.
Although private companies have entered the race to Mars, a successful journey will almost certainly rely on cooperation or technology from NASA. If NASA’s Mars program is going to have any chance of proceeding on its planned timeline, it will need ongoing support that outlasts multiple administrations and elections.
It’s too soon to know what the new administration will hold for the Mars program. President Donald Trump has, at least once, pledged not to cut space funding, but he also said at a town hall rally in New Hampshire in August that he wants to “rebuild our infrastructure” before sending people to Mars.
Sending people to Mars will take a lot of infrastructure too, and whether Robert Zubrin’s dream is fulfilled in his lifetime (he’s 64) will largely depend on money and politics.