Traveling light and living off the land whenever possible, Robert Zubrin says, humans could reach the Red Planet within a decade:
In the spring of 2014, a heavy-lift booster similar to Apollo’s Saturn V launches from Cape Canaveral and uses its upper stage to throw an unmanned payload weighing 40 metric tons onto a trajectory to Mars. The payload includes an Earth return vehicle (ERV) that will eventually bring a human crew home; it’s carried to Mars with its two methane-oxygen propulsion stages empty. Also on board are 6 metric tons of liquid hydrogen, a 100-kilowatt nuclear reactor mounted in the back of a truck that is also fueled by methane and oxygen, a set of compressors, an automated chemical-processing unit, and a few scientific rovers.Arriving at Mars eight months later, the payload uses atmospheric friction to brake its way into orbit and then lands with the help of a parachute. Next, the rovers explore and characterize the landing site while a human operator back on Earth telerobotically drives the truck a few hundred meters and then deploys the reactor, which powers the chemical-processing unit and the compressors. The chemical-processing unit begins to create a reaction between the bottled hydrogen brought from Earth and the Martian atmosphere, which consists largely of carbon dioxide, to produce methane and water. It electrolyzes the water, producing oxygen and hydrogen, and the compressors liquefy the methane and the oxygen, which are stored in the propellant tank of the ERV. The hydrogen, meanwhile, is recycled to produce more methane. Still more oxygen is produced by dissociating carbon dioxide in what’s called a reverse water-gas-shift reactor; some of that oxygen will go into the ERV’s tanks, and the rest will be stockpiled, both for breathing and for synthesizing water later on.
From start to finish, the process takes 10 months and yields 108 metric tons of methane-oxygen propellant. That’s 18 times as much as the amount of hydrogen brought from Earth. Of that, 96 metric tons will fuel the ERV for the flight back to Earth, and 12 metric tons will be stored for later use by human crews.
Two more rockets fly in 2016—the next good launch window. The first payload is another unmanned fuel factory and an ERV. The second is a habitation module containing a human crew of four, food and other provisions sufficient for three years, and a pressurized rover fueled by methane and oxygen. During the six-month trip, the habitat spins around the burned-out upper stage of the booster, attached by a tether. The spinning creates enough artificial gravity to counter bone loss and other physiological problems brought on by weightlessness.
Arriving at Mars, the manned craft drops the tether, aerobrakes, and lands at the 2014 landing site, where a fully fueled ERV awaits. The second ERV lands several hundred kilometers away, at landing site 2, and starts making propellant for the third mission, to take place in 2018. The third mission, in turn, will fly a crew to site 2 and an additional ERV to open up landing site number 3, and so on.
The first crew spends 18 months exploring Mars; they’ll have enough fuel to drive the pressurized rover a total of 24 000 kilometers. That should suffice: The circumference of Mars is about 21 000 km. Among other things, the crew will be able to conduct a serious search for evidence of past or present life.
By remaining on the surface, the crew will benefit from the planet’s natural gravity (about one-third that of Earth) and will be protected by the Martian environment against most of the cosmic rays and all of the solar flares. Thus there will be no need for a quick return to Earth, a problem that plagues conventional Mars mission plans that envision living aboard an orbiting mother ship that sends down landing parties for brief jaunts.
Finally, the crew returns to Earth in the ERV. Meanwhile, a second crew is on its way to Mars. Thus every other year, two heavy-lift boosters are launched: one to carry a crew, the other to prepare a site for the next mission. As the missions progress, they leave behind a string of bases that open up ever broader stretches of territory. At an average launch rate of just one booster per year to pursue a continuing program of Mars exploration, this plan is clearly affordable. In effect, it removes the manned Mars mission from the realm of megafantasy and reduces it to a task whose difficulty is comparable to that faced in launching the Apollo missions to the moon.