Case for Mars

Robert Zubrin, Richard Wagner

• Publisher: Free Press
• Year: 2011
• ISBN:
  9781451665765
• Topic: Sciences physiques
• Subtopic: Science de l'espace

Since the beginning of human history Mars has been an alluring dream—the stuff of legends, gods, and mystery. The planet most like ours, it has still been thought impossible to reach, let alone explore and inhabit.Now with the advent of a revolutionary new plan, all this has changed. Leading space exploration authority Robert Zubrin has crafted a daring new blueprint, Mars Direct, presented here with illustrations, photographs, and engaging anecdotes. The Case for Mars is not a vision for the far future or one that will cost us impossible billions. It explains step-by-step how we can use present-day technology to send humans to Mars within ten years; actually produce fuel and oxygen on the planet's surface with Martian natural resources; how we can build bases and settlements; and how we can one day "terraform" Mars—a process that can alter the atmosphere of planets and pave the way for sustainable life.

1: MARS DIRECT

The planet Mars is a world of breathtaking scenery, with spectacular mountains three times as tall as Mount Everest, canyons three times as deep and five times as long as the Grand Canyon, vast ice fields, and thousands of kilometers of mysterious dry riverbeds. Its unexplored surface may hold unimagined riches and resources for future humanity, as well as answers to some of the deepest philosophical questions that thinking men and women have pondered for millennia. Moreover, Mars may someday provide a home for a dynamic new branch of human civilization, a new frontier, whose settlement and growth will provide an engine of progress for all of humanity for generations to come. But all that Mars holds will forever remain beyond our grasp unless and until men and women walk its rugged landscapes.

Some have said that a human mission to Mars is a venture for the far future, a task for the “next generation.” On the contrary, we have in hand all the technologies required for undertaking within a decade an aggressive, continuing program of human Mars exploration. We can reach the Red Planet with relatively small spacecraft launched directly to Mars by boosters embodying the same technology that carried astronauts to the Moon more than forty years ago.

How can this be? Looking at almost any plan for a human mission to Mars, be it from the 1950s or the 1990s, we see enormous spaceships hauling to Mars all the supplies and propellant required for a mission. The size of the spacecraft demands that they be assembled in Earth orbit—they’re simply too large to launch from the Earth’s surface in one piece. This requires that a virtual parallel universe of gigantic orbiting “dry docks,” hangars, cryogenic fuel depots, power stations, checkout points, and construction crew habitation shacks be placed in orbit to enable assembly of the spaceships and storage of the vast quantities of propellant. Based upon such concepts, it has been endlessly repeated that a mission to Mars would have to cost hundreds of billions of dollars and incorporate technologies that won’t be available for another thirty years.

Yet landing humans on Mars requires neither miraculous new technologies nor the expenditure of vast sums of money. We don’t need to build Battlestar Galactica–like futuristic spaceships to go to Mars. Rather, we simply need to use some common sense and employ technologies we have at hand now to travel light and live off the land, just as was done by nearly every successful program of terrestrial exploration undertaken in the past. Living off the land—intelligent use of local resources—is not just the way the West was won; it’s the way the Earth was won, and it’s also the way Mars can be won. The conventional Mars mission plans are impossibly huge and expensive because they attempt to take all the materials needed for a two- to three-year round-trip Mars mission with them from Earth. But if these consumables can be produced on Mars instead, the story changes, radically.

Starting in the spring of 1990, I led a team of engineers and researchers at Martin Marietta Astronautics in Denver in developing a plan to pioneer Mars in this way. The name of the plan is “Mars Direct,” and it represents the quickest, safest, most practical, and least expensive way to undertake the exploration and settlement of Mars.

Mars Direct says what it means. The plan discards unnecessary, expensive, and time-consuming detours: no need for assembly of spaceships in low Earth orbit; no need to refuel in space; no need for spaceship hangars at an enlarged Space Station, and no requirement for drawn-out development of lunar bases as a prelude to Mars exploration. Avoiding these detours brings the first landing on Mars perhaps twenty years earlier than would otherwise happen, and avoids the ballooning administrative costs that tend to afflict extended government programs.

A rough cost estimate for Mars Direct would be about $30 billion to develop all the required hardware, with each individual Mars mission costing about $3 billion once the ships and equipment were in production. While certainly a great sum, spent over a period of ten years it would only represent about 7 percent of the existing combined military and civilian space budgets. Furthermore, this money could drive our economy forward in just the same way as the spending of $100 billion (in today’s terms) on science and technology in the Apollo program contributed to the high rates of economic growth of America during the 1960s.

Conventional wisdom might deem Mars Direct attractive because of its simplicity, but it would also deem it infeasible—the mass of the propellant and supplies needed for a human mission to Mars is much too large to be launched directly from Earth to Mars. Conventional wisdom would be right except for one thing: The required propellant and supplies needed for a Mars mission do not have to come from Earth. They can be found on Mars.

From a vantage point of the present, here’s how the Mars Direct plan would work:

FEBRUARY 2029

A new, multistage rocket fashioned from currently existing parts rests on the launch pad at Cape Canaveral, its thin metal skin steaming in the morning sunlight. The booster reminds some of the old Saturn V’s, the rockets that carried men to the shores of the Sea of Tranquility. The new Ares booster has about the same heavy lift capacity as the Apollo-era Saturn V’s, but at its heart are the workhorses of the past several decades, four Space Shuttle main engines and two shuttle solid rocket boosters. The engines ignite. Flame and smoke describe the signature of a new space age as the Ares hurtles skyward. High above Earth’s atmosphere, the Ares upper stage separates from the spent booster, fires its single hydrogen-and-oxygen-burning engine, and hurls an unmanned 45-tonne (45-metric-ton) payload to Mars: the Earth return vehicle. (NB: 1 tonne=2204.6 lb.)

The ERV’s name says it all. The vehicle is designed to carry a crew of astronauts back from the surface of Mars direct to a splashdown in Earth’s waters. On its journey to Mars the ERV carries a small nuclear reactor mounted atop a light truck, an automated chemical processing unit along with a set of compressors, and a few scientific rovers. The ERV’s crew cabin stores a life-support system, food, and other necessities to sustain a four-member crew on an eight-month journey back to Earth. Though its two propulsion stages will consume some 96 tonnes of methane/oxygen bipropellant on the return flight, the ERV arrives at Mars with its fuel tanks essentially empty, carrying just 6 tonnes of liquid hydrogen propellant production feedstock.

AUGUST 2029

Traveling across space at an average speed of about 27 kilometers per second, the ERV reaches Mars after a six-month trip. Upon arrival the ERV uses its aeroshell—a blunt, mushroom-shaped shield—to plow through the upper reaches of Mars’ thin atmosphere. The craft’s speed drops, allowing it to brake into orbit. A few days are spent in orbit to allow the flight controllers to perform a final system checkout. Then upon arrival of a clear dawn with low winds and well-defined shadows at the chosen landing site, the craft is targeted back into the atmosphere for final entry. Using its aeroshell again, the ERV decelerates to subsonic speeds until a parachute can pop open and start the spacecraft on a gentle descent toward the surface of Mars. A few hundred meters above the surface, the parachute drops away and small rockets fire up to take the ERV carefully through the last moments before touchdown.

Once settled on the rust-colored soils of Mars, the ERV gets down to the business at hand, making fuel for the return flight home out of thin air—in this case, Martian air. A door pops open on the side of the squat ERV landing stage and a light truck carrying a small nuclear reactor trundles out. Using a small TV camera on board as their eyes, mission controllers in Houston slowly drive the truck a few hundred meters away from the landing site. As the truck wheels along, a power cable snakes off its windlass, keeping the ERV’s chemical plant connected to the small reactor. Once the controllers maneuver the truck to an appropriate spot, a winch lifts the reactor from the truck’s bed and lowers it into a small crater or other natural depression in the landscape. The reactor kicks in and begins to energize the chemical processing unit with 100 kilowatts of electricity (kWe). Now the chemical plant goes to work, producing rocket propellant by sucking in the Martian air with a set of pumps and reacting it with the hydrogen hauled from Earth aboard the ERV. Martian air is 95 percent carbon dioxide gas (CO₂). The chemical plant combines the carbon dioxide with the hydrogen (H₂), producing methane (CH₄), which the ship will store for later use as rocket fuel, and water (H₂O). This methanation reaction is a simple, straightforward chemical process that has been practiced in industry since the 1890s. As the methanation reaction proceeds, it rids us of a potential problem, that of storing super-cold liquid hydrogen on the Martian surface. The chemical plant continues its work, splitting the water produced by the methanation process into its constituents, hydrogen and oxygen. The oxygen is stored as rocket propellant, while the hydrogen is recycled back into the chemical plant to make more methane and water. Additional oxygen is produced by a third unit which takes Martian carbon dioxide and splits it into oxygen, which is stored, and carbon monoxide, which it vents as waste. At the end of six months of operation, the chemical plant has turned the initial supply of 6 tonnes of liquid hydrogen brought from Earth into 108 tonnes of methane and oxygen—enough for the ERV plus 12 tonnes extra to support the use of combustion powered ground vehicles on the Martian surface. Using Mars’ most freely available resource, its air, we have leveraged the portion of our return propellant hauled from Earth eighteen times over.

This chemical synthesis sequence may appear to some to be rather involved, but it’s actually all Gaslight Era technology, utterly trivial by comparison with practically every other significant operation required for a successful interplanetary mission of any kind. Moreover, it is this concept of living off the land that makes Mars Direct possible. If we attempted to haul up to Mars all the propellant required, we indeed would need massive spacecraft requiring multiple launches and on-orbit assembly. The cost of the mission would shoot out of sight. It should come as no surprise that local resources make such a difference in developing a mission to Mars, or anywhere else for that matter. Consider what would have happened if Lewis and Clark had decided to bring all the food, water, and fodder needed for their transcontinental journey. Hundreds of wagons would have been required to carry the supplies. Those supply wagons would have needed hundreds of horses and drivers, who in turn would have required further supplies. A logistics nightmare would have been created that would have sent the costs of the expedition beyond the resources of the America of Jefferson’s time. Is it any wonder that Mars mission plans that don’t make use of local resources manage to ring up $450 billion price tags?

MARCH 2030

Thirteen months following launch, a fully fueled spacecraft—the ERV—sits on the surface of Mars, awaiting the arrival of a human crew. Engineers at NASA’s Johnson Space Center have monitored every step of the chemical production process, and, certifying its successful completion, give the go-ahead for the next step in the Mars Direct mission to proceed. The ERV deploys small robots to examine and photograph the terrain in its immediate vicinity. The crew of the first human expedition, skilled and vitally interested in landing site selection, takes an active role in exploring the ERV’s neighborhood via these distant explorers. After several months of robotic exploration, an ideal landing spot is identified. One of the ERV robots ambles across the rough Martian terrain and places a radar transponder at the landing site to help guide the crew to a safe touchdown.

APRIL 2031

The Ares 3 launch vehicle, carrying a spacecraft called the “Beagle” after the ship of exploration that carried Charles Darwin on his historic voyage, towers majestically over the flatlands of the Cape, moments away from opening a new era of human history. Just a few weeks ago a similar booster, Ares 2, climbed into the skies over Florida. Identical to the first Ares booster and carrying a similar ERV payload, Ares 2 hurtles toward Mars even as crowds gather to watch the launch of the Beagle, the ship that will carry the first four humans to Mars.

The primary component of the Beagle is a habitation module that looks a bit like a huge drum. The module stands about 5 meters high and measures about 8 meters in diameter. With two decks each with 2.5 meters (about 8 feet) of headroom and a floor area of 100 square meters (about 1,000 square feet), it is large enough to comfortably accommodate its crew of four. The “hab,” as everybody calls it, has a closed-loop life-support system capable of recycling oxygen and water, whole food for three years plus a large supply of dehydrated emergency rations, and a pressurized ground car powered by a methane/oxygen internal combustion engine. (See Figure 1.1.)

FIGURE 1.1

The Mars Direct hab and Earth return vehicles (ERV) within their aerobrakes.

The four crew members are true renaissance men and women. Given the nature of their mission—exploration far from home—all are cross-trained in several disciplines. At heart, though, they are a crew of two field scientists and two mechanics. A biogeochemist and a geologist will complement a pilot who is also a competent flight engineer. The last crew member, a jack-of-all-trades, is primarily a flight engineer, but can also provide common forms of medical treatment and understands the broad means and objectives of the scientific investigations. This person backs up all the specialists in their functions, and provides one more—he or she will be the mission commander.

On board the Beagle, four men and women prepare themselves for a journey that will take them to another world and return them home in the span of about two and one half years—about the same amount of time it took explorers centuries before to circumnavigate the globe. Miles distant from their small ship, more than a million people camped around Cape Canaveral gaze in anticipation as the countdown clock approaches zero. The lower-stage engines of the booster erupt, pouring out a sea of flame. A cheer louder than any this country has heard in years sweeps the crowd as the Ares 3 lifts off the pad. The rocket accelerates, propelling the upper stage and its payload through the atmosphere. The upper stage fires its own engines and breaks away, driving the hab to trans-Mars cruise velocity. Four humans are on their way to Mars.

The pilot of the hab directs it to pull away from the burnt-out upper stage of the booster, releasing it on a tether 330 meters long as it goes. A small rocket engine on the hab fires, causing the tethered combination of hab and upper stage to now revolve at 2 revolutions per minute. This generates enough centrifugal force to provide the astronauts in the hab with artificial gravity en route to Mars equal to that found naturally on the Red Planet.

OCTOBER 2031

On the 180th day of flight, the hab arrives at Mars. The vehicle drops the tether and upper stage, and then aerobrakes into orbit. The crew intends to set the Beagle down at the landing site hard by the ERV that flew out to Mars in 2029. A radio beacon in the Ares 1 ERV, detailed photos and maps of the landing site, a landing pad radar transponder, and the crew’s expert handling of the ship virtually guarantee a precision landing. In the unlikely event that the Beagle misses the landing site, the crew has three backup options available. In the first place, they have on board the hab a fueled pressurized rover boasting a one-way range of nearly 1,000 kilometers. So long as they’re within that distance of the landing site, the crew can still get to their ERV by driving overland. If some disaster causes the Beagle to miss the mark by more than a thousand kilometers, the second backup can be brought into play. This is the ERV launched by Ares 2, which, since it was launched on a slower trajectory than the Beagle, is now following the crew to Mars. Even if the crew lands the hab on the wrong side of the planet, this second ERV can be maneuvered to land near them. Finally, as a third-level backup, the crew arrives at Mars with sufficient supplies for three years—if worse came to worst, the four could just tough it out on Mars until additional supplies and another ERV could be sent out in 2033.

The landing, however, is right on target. Though they have studied the landing site in detail, seen it from images captured by rovers and relayed to Earth, nothing can prepare the crew for the sight of the Martian landscape stretching before them. The soils are rust colored, littered with sharp-edged rocks, large and small. In the distance are small hills and dunes. The landscape is akin to the deserts of America’s southwest, save for the skies, which are a ruddy, salmon color. There’s an immense amount to be done just after touchdown, but they take the moment to gaze out at Mars, to savor the fact that no creature with eyes to see has ever gazed out on this vista in the four-billion-year history of Mars and Earth.

With the Beagle safely down at the landing site, the Ares 2 ERV lands some 800 kilometers away, where it begins the process of filling itself with propellant. It will be used as the ERV for the second human expeditio...