The Mars Direct Plan

How to Go to Mars

Why Go to Mars?

The Mars Direct Plan

To Mars by Way of Its Moons

A Bus Between the Planets

"Space is there, and we're going to climb it." These words from President John F. Kennedy in 1962 set forth the goal of sending an American to the moon within the decade. But for most of the 30 years since the Apollo moon landing, the U.S. space program has lacked a coherent vision of what its next target should be. The answer is simple: the human exploration and settlement of Mars.

This goal is not beyond our reach. No giant spaceship built with exotic equipment is required. Indeed, all the technologies needed for sending humans to Mars are available today. We can reach the Red Planet with relatively small spacecraft launched directly to Mars by booster rockets embodying the same technology that carried astronauts to the moon more than a quarter of a century ago. The key to success lies with the same strategy that served the earliest explorers of our own planet: travel light and live off the land. The first piloted mission to Mars could reach the planet within a decade. Here is how the proposed plan--what I call the Mars Direct project--would work.

Image: SAIC; Pat Rawlings Image: Ian Worpole Image: Robert Murray Pioneer Asronautics HUMAN MISSION TO MARS would allow astronauts to search for signs of life on the Red Planet (top inset). Under the Mars Direct plan, an unmanned Earth Return Vehicle, or ERV, would land on the planet first and lay the groundwork for the arrival of the astronauts two years later (middle inset). New missions could occur every two years, leaving behind a string of base camps similar to the one depicted here (bottom inset).

At a not too distant date--perhaps as soon as 2005--a single, heavy-lift booster rocket with a capability equal to that of the Saturn 5 rockets from the Apollo era is launched from Cape Canaveral, Fla. When the ship is high enough in Earth's atmosphere, the upper stage of the rocket detaches from the spent booster, fires its engine and throws a 45-metric-ton, unmanned payload on a trajectory to Mars.

This payload is the Earth Return Vehicle, or ERV, which, as the name implies, is built to bring astronauts back to Earth from Mars. But on this voyage no humans are on board; instead the ERV carries six tons of liquid-hydrogen cargo, a set of compressors, an automated chemical-processing unit, a few modestly sized scientific rovers, and a small 100-kilowatt nuclear reactor mounted on the back of a larger rover powered by a mixture of methane and oxygen. The ERV's own methane-oxygen tanks, which will be used during the return trip, are unfueled.

Arriving at Mars eight months after takeoff, the ERV slows itself down with the help of friction between its heat shield and the planet's atmosphere--a technique known as aerobraking. The vehicle eases into orbit around Mars and then lands on the surface using a parachute and retrorockets. Once the ship has touched down, scientists back at mission control on Earth telerobotically drive the large rover off the ERV and move it a few hundred meters away. Mission control then deploys the nuclear reactor, which will provide power for the compressors and the chemical-processing unit.

Inside this unit, the hydrogen brought from Earth reacts with the Martian atmosphere--which is 95 percent carbon dioxide (CO₂)--to produce water and methane (CH₄). This process, called methanation, eliminates the need for long-term storage of cryogenic liquid-hydrogen fuel, a difficult task. The methane is liquefied and stored, and the water molecules are electrolyzed--broken apart into hydrogen and oxygen. The oxygen is then reserved for later use; the hydrogen is recycled through the chemical-processing unit to generate more water and methane.

Ultimately, these two reactions, methanation and electrolysis, provide 48 tons of oxygen and 24 tons of methane, both of which will eventually be burned as rocket propellant for the astronauts' return voyage. To ensure that the mixture of methane and oxygen will burn efficiently, an additional 36 tons of oxygen must be generated by breaking apart the CO₂ in the Martian atmosphere. The entire process takes 10 months, at the end of which a total of 108 tons of methane-oxygen propellant has been generated--18 times more propellant for the return trip than the original feedstock needed to produce it.

The journey home will require 96 tons of propellant, leaving an extra 12 tons for the operation of the rovers. Additional stockpiles of oxygen can also be produced, both for breathing and for conversion into water by combining the oxygen with the hydrogen brought from Earth. The ability to produce oxygen and water on Mars greatly reduces the amount of life-supporting supplies that must be hauled from Earth.

With this inaugural site on Mars operating successfully, two more boosters lift off from Cape Canaveral in 2007 and again hurl their payloads toward Mars. One of these is an unmanned ERV just like the one launched in 2005. The other, however, consists of a manned vessel with a crew of four men and women with provisions to last three years. The ship also brings along a pressurized methane-oxygen-powered ground rover that will allow the astronauts to conduct long-distance explorations in a shirtsleeve environment.

The Astronauts Arrive

During the trip, artificial gravity as strong as that found on Mars can be produced by first extending a tether between the inhabited module and the burned-out booster rocket's upper stage; the entire assembly is then allowed to spin at a rate of, say, one revolution per minute. Such a system would eliminate any concerns over the health effects of zero gravity on the astronauts. The crew's exposure to radiation will also be acceptable. Solar flare radiation, consisting of protons with energies of about one million electron volts, can be shielded by 12 centimeters of water or provisions, and there will be enough materials on board the ship to build an adequate pantry storm shelter for use in such an event. The residual cosmic-ray dose, about 50 rems for the entire two-and-a-half-year mission, represents a statistical cancer risk of about 1 percent, roughly the same as the risk from smoking for the same amount of time.

On arrival at Mars, the manned craft drops the tether to the booster, aerobrakes and then lands at the 2005 site. Beacons at the original location should enable the ship to touch down at just the right spot, but if the landing is off course by tens or even hundreds of kilometers, the astronauts can still drive to the correct location in their rover. And in the unlikely event that the ship sets down thousands of kilometers away, the second ERV that was launched with the manned vessel can serve as a backup system. If that, too, should fail, the extra rations on the manned craft ensure that the crew can survive until a third ERV and additional supplies can be sent in 2009.

Image: Ian Warpole HOME SWEET HOME in interplanetary space and on Mars might look like this. The upper deck of the habitat, shown here, would have sleeping quarters for four people as well as a laboratory, library, galley and gym. A solar-flare storm shelter would be located in the center. The lower deck (not shown) would serve as a garage, workshop and storage area. During the trip to Mars, a tether system could produce artificial gravity.

But with current technology, the chances of a misguided landing are small. So assuming the astronauts reach the 2005 location as planned, the second ERV touches down several hundred kilometers away. This new ERV, like its predecessor, starts making propellant, this time for the 2009 mission, which in turn will fly out with an additional ERV to open up a third Mars site.

Thus, under the Mars Direct plan, the U.S. and its international partners would launch two heavy-lift booster rockets every other year: one to dispatch a team of four people to inhabit Mars and the other to prepare a new site for the next mission. The average launch rate of one a year is only about 15 percent of the rate at which the U.S. currently launches space shuttles. In effect, the live-off-the-land strategy used by the Mars Direct plan removes the prospect of a manned mission to Mars from the realm of megaspacecraft fantasy and renders it a task comparable in difficulty to the Apollo missions to the moon.

The men and women sent to Mars will stay on the surface for one and a half years, taking advantage of the ground vehicles to conduct extensive exploration of the surface. With a 12-ton stockpile of fuel for these trucks, the astronauts can travel more than 24,000 kilometers during their stay, giving them the kind of mobility necessary to conduct a serious search for evidence of past or present life--an investigation that is key to revealing whether life is a phenomenon unique to Earth or commonplace throughout the universe.

MASS ALLOCATIONS FOR MARS DIRECT MISSION

Because no one will be left in orbit, the crew will benefit from the natural gravity and protection against radiation offered by the Martian environment. As a result, there is no need for a quick return to Earth, a complication that has plagued conventional mission plans that consist of an orbiting mother ship and small landing parties sent to the surface. At the conclusion of their stay, the Mars astronauts will return by direct flight in the ERV. As the series of missions progresses, a string of small bases will be left behind on the planet, opening broad stretches of Mars to continued human exploration and, eventually, habitation.

In 1990, when my colleague David A. Baker and I (we were then both at Martin-Marietta, which is now part of Lockheed Martin) first put forward the basic Mars Direct plan, the National Aeronautics and Space Administration viewed it as too radical for serious consideration. But since then, with encouragement from Michael Griffin, NASA's former associate administrator for exploration, as well as from the current head of NASA, Daniel S. Goldin, the group in charge of designing human missions to Mars at the NASA Johnson Space Center decided to take another look at our idea.

The Mars Society

In 1994 researchers there produced a cost estimate for a program based on an expanded version of the Mars Direct plan that had been scaled up by about a factor of two. Their result: $50 billion. Notably, in 1989 this same group had assigned a $400-billion price tag to the traditional, cumbersome approach to a manned mission based on orbital assembly of megaspacecraft. I believe that with further discipline in the design of the mission, the cost could be brought down to the $20- to $30-billion range. Spent over 10 years, this amount would constitute an annual expenditure of about 20 percent of NASA's budget, or around 1 percent of the U.S. military's budget. It is a small price to pay for a new world.

To mobilize public support for an expanded Mars effort--including robotic as well as human exploration--and to initiate privately funded missions, the Mars Society was formed in 1998. As its first private project, the society is building a Mars simulation base at the Haughton meteorite impact crater on Devon Island in the Canadian Arctic. Because of its geologic and climatic similarities to the Red Planet, this area has been of interest to NASA scientists for some time. The society's Mars Arctic Research Station, or MARS, will support a greatly expanded study of this environment and will provide a location for field-testing human exploration tactics and prototype equipment, including habitation modules, ground-mobility systems, photovoltaic systems and specialized drilling rigs. The current plan is to have the Devon Island MARS base operational by the summer of 2000. This should be possible on a budget of about $1 million.

We hope that the credibility earned through this project will enable the society to expand its financial resources. It could then help fund robotic missions to Mars and, eventually, human expeditions, perhaps on a cost-sharing basis with NASA or other government agencies. But it is clear that the fastest way to send humans to Mars is to show the government why it should invest in this endeavor. The society has therefore launched an educational campaign directed toward politicians and other power brokers.

Someday millions of people will live on Mars. What language will they speak? What values and traditions will they cherish as they move from there to the solar system and beyond? When they look back on our time, will any of our other actions compare in importance with what we do now to bring their society into being? Today we have the opportunity to be the parents, the founders, the shapers of a new branch of the human family. By so doing, we will put our stamp on the future. It is a privilege beyond reckoning.

This article updates a version that appeared in the Spring 1999 issue of Scientific American Presents.

The Author

ROBERT ZUBRIN is president of the Mars Society and founder of Pioneer Astronautics, which does research and development on space exploration. He is the author of The Case for Mars: The Plan to Settle the Red Planet and Why We Must (Simon & Schuster, 1996) and Entering Space: Creating a Space-Faring Civilization (Tarcher-Putnam, 1999).