This is part of IEEE Spectrum's Special Report: Why Mars? Why Now?
Wernher von Braun would be so disappointed. The German-born rocket pioneer accomplished great things in his life, including overseeing the design of the Saturn rockets, the most powerful launch vehicles ever built. But he never saw the thing he yearned for most: people walking on Mars.
He did try mightily to make it happen. Shortly after World War II, when he was living at Fort Bliss, Texas, he wrote his only novel, Project Mars , about an expedition to the Red Planet. The book is packed with detailed explanations of orbital physics and unintentionally hilarious mission directives: ”The landing is to be carried out, if possible, with avoidance of any hostile contact with the inhabitants of Mars.” Ultimately, the lead spaceship ski-lands onto the Martian snow, and its crew of 18 befriends the underground-dwelling Martians. The year is 1985.
Through the 1950s and ’60s and into the ’70s, von Braun tirelessly propounded his Mars vision, in a group of articles for Collier's Weekly and later in a series of television specials for Walt Disney. During the Nixon administration, he was still pleading for a Mars landing by 1982.
Most of the other pieces of the von Braun dream eventually came to pass: A permanent space station orbits Earth, for example, and 12 men have walked on the moon. And yet, a Mars trip seems no closer now than it did in 1977, when von Braun died.
Turns out that going to Mars is a lot harder than he let on. It’s expensive, for one. In his novel, von Braun figured that a Mars expedition would cost US $2 billion—about $18 billion in today’s dollars. By 1989, NASA estimated such a trip would come to half a trillion dollars; if you correct that figure for inflation, you get the current U.S. fiscal stimulus package, give or take a hundred million.
Spooked by those numbers back in 2007, when a trillion dollars still seemed like a ridiculous amount of money for even the U.S. government to spend, Congress stipulated in a NASA appropriations bill that ”none of the funds...shall be used for any research, development, or demonstration activities related exclusively to the human exploration of Mars.” The Red Planet has undeniable cachet, but nowhere near the geopolitical punch that the moon had in the early 1960s, in the frigid depths of the Cold War. It’s hard to imagine a Mars project ever getting a presidential exhortation on the order of John F. Kennedy’s 1961 speech launching the Apollo program. And with the global economy on life support, you have to wonder if we’ll even get there before the century is out.
If going to the moon is a day hike, going to Mars is the Lewis and Clark expedition—a journey too long and too complex to carry everything that’s needed. Earth and Mars ride along in their concentric orbits, getting within striking distance of each other only for a brief window every two years. The shortest one-way trip, using conventional chemical propulsion, would take six months. If you include the time spent on Mars waiting for the two planets to move back into optimal alignment and also the trip home, the total mission would last at least two and a half years. The crew would have to endure extremes of boredom, isolation, and radiation, and they would require a vast amount of fuel and rations packed into a vessel sturdy enough to shield them from the harshness of space. Simply landing a spacecraft safely on a planet with an atmosphere and substantial gravity poses stunning challenges. And then there’s the matter of keeping the crew alive on the Martian surface.
In other words, the physical, technical, and economic demands of a Martian mission are too great to be overcome in a decadelong, Apollo-like sprint. The only solution is to chip away at the problems. And that’s just what’s happening.
Despite the congressional directive, NASA engineers have continued to move the agency slowly but inexorably in the general direction of Mars. Along with its counterparts in Europe and Asia and legions of academic researchers around the world, the space agency has spent years laying the groundwork for such a mission. The International Space Station, for example, hasn’t yielded much in the way of basic science, but it’s letting astronauts learn how to deal with issues like weightlessness, equipment failures, and the day-to-day routine of life beyond Earth. A lunar base will teach spacefarers and mission planners lessons about running an extraterrestrial outpost and will also push the development of NASA’s Ares V booster, which will likely be needed to loft the capsules, crew, and supplies for a Mars mission, unless better alternatives come to fruition.
Meanwhile, orbiters, landers, and rovers continue to gather vital information about the Red Planet, including the best places to find water and minerals. Upcoming sample-return probes to Mars, like Europe’s ExoMars and Russia’s Phobos-Grunt, will let researchers back on Earth touch Martian soil for the first time. All of these efforts will help set the stage for an eventual human mission.
When that happens—if it happens—it will be the most difficult and complicated undertaking in human history.
The list of challenges is long and sobering, and it starts with propulsion. Chemical rockets are only marginally capable of getting people to Mars and back, but the main alternative, the plasma drive, is at least a couple of decades away from the day when it’ll be ready to ferry folks to that red dot in the sky [see ”Rockets for the Red Planet,” in this issue].
Even after the propulsion problem is solved, there are at least five other really big ones: cosmic rays, muscle and bone loss, psychological stress, landing on the planet, and feeding the crew for the long haul. All of those challenges are harder with chemical rockets, because a chemically fueled trip would last much longer than one with a more advanced propulsion technology.
That time sensitivity is acute with cosmic rays, the combination of energetic protons ejected by the sun during solar storms and gamma-ray bursts from distant galaxies. You’re not at risk on Earth’s surface, because you’re shielded by the planet’s atmosphere and magnetic field. But out in space, you don’t have that protection. Of particular concern are solar storms, which can toss out deadly particle showers that can kill you quickly or slowly, depending on the storm’s severity. And both types of cosmic radiation can damage DNA, raising your long-term risk of cancer. Gamma rays might even make you stupid; regular doses can wreak havoc on brain cells, among other things.
Apollo astronauts were fortunate in not encountering a solar storm during their missions, none of which lasted longer than 12 days. But a Mars crew would almost certainly experience at least one solar storm and regular doses of gamma rays. Scientists estimate that astronauts on a 1000-day mission will be exposed to just over 1 sievert of radiation, equal to about 26 000 dental X-rays.
Nobody really knows exactly what such a dose would do to a crew or to what extent high-energy particles correlate to cancer rates. Officially, NASA rules dictate that any manned mission have a fatality risk below 3 percent. On paper, at least, a Mars mission isn’t too far off: For a 40-year-old male astronaut, the space agency puts the mean fatality risk due to cancer at 4 percent. But few physiologists put much stock in that number, and besides, variation among individuals makes it impossible to say who will develop cancer and who won’t.