Reviewed 3/29/2003

THE CASE FOR MARS: The Plan to Settle the Red Planet and Why We Must
Robert Zubrin
with Richard Wagner
New York: The Free Press, 1996




ISBN 0-684-82757-3 328pp. HC/BWI $25.00

The plan is called Mars Direct. It begins with the launch of an automated craft to Mars atop a multi-stage rocket having the lift capacity of the Saturn V, but of new design. The craft, known as the ERV (Earth Return Vehicle) first aerobrakes into Mars orbit. Then, when the proper landing site and time are chosen, it is directed into the atmosphere again. This time it aerobrakes to subsonic speed, and a parachute system slows it the rest of the way. After it settles down on the surface, a compact chemical plant goes to work reacting compressed Martian atmosphere (mostly carbon dioxide) with hydrogen stored on board to produce methane and water. The methane is stored for later use as fuel for the return journey1. The water is electrolyzed to release oxygen, which is stored in another tank as the oxidizer for the methane. The other product of the electrolysis, hydrogen2, is recycled to produce more methane. These chemical processes, known since the nineteenth century, are powered by a small nuclear reactor.

The elegance of this plan is that it greatly reduces the weight of fuel that must be carried for the Mars mission. Not only is there no need to carry fuel for the trip home, but fuel for slowing into Mars orbit can also be dispensed with. Carrying significantly less fuel means significantly smaller spacecraft, hence significantly lower mission cost. Mars Direct is estimated to cost $20 billion, versus $450 billion for NASA's 90-Day-Study version. Now, that's what I call significantly lower. Mars Direct would also take much less time to accomplish.

You might expect that a cost and time advantage like that would have everyone falling all over themselves to support Mars Direct. That has been found not to be the case. There are organizations with a vested interest in multi-decade programs, and companies eager to build large, expensive systems. Quite often, the efficient and cost-effective solution will be resisted; Mars Direct is a prime example, and Zubrin must continually re-sell it.

This book is a part of that sales pitch. Its preface is the executive summary. Chapter 1 explains the scenario for the mission in detail. Chapter 2 provides background material: the proud but persecuted history of astronomy, and the more recent investigations of the possibilty of life on Mars that culminated in the Viking missions. Chapter 3 describes the genesis and development of the plan, and introduces us to some of the individuals and groups that worked with Zubrin on it.

The real heart of the book comes in Chapter 4. Here Zubrin sets forth the technical tradeoffs and alternatives. Most noteworthy is the choice of trajectory: Opposition-class versus conjunction-class. It might seem at first glance that the best option is to launch the mission when Mars is closest to Earth — that is, in opposition. That does give a third less total travel time, and it is in fact what the 90-Day Study specified. However, Mars Direct would launch when Mars is in conjunction, behind the Sun3. While this trip takes longer — 910 versus 640 days — it is better in every other way (See Table 4.1.) By keeping the explorers on the Martian surface for 550 days instead of only 30, it minimizes their exposure to radiation and microgravity while allowing much more scientific work. Chapter 4 provides the amounts of consumables needed. It even gives a detailed mass breakdown of the vehicle.

Chapter 5 is devoted to debunking six misconceptions4 that Zubrin says threaten the Mars mission. These are, using my terms:

Zubrin cites various research papers to demolish these, pointing out, for example, that the radiation exposure on a Mars Direct mission adds less that 1 percent to anyone's risk of cancer. The various problems of microgravity can be avoided quite simply — by avoiding the microgravity. I have some concerns about Zubrin's specific method of spinning the ship; but the basic idea is sound. So are his arguments on the other points.

Tools and strategies for exploring Mars are examined in Chapter 6. Zubrin first discusses motivation, pointing out that once, for about a billion years, Mars was a warm, wet place where life could have arisen, and that hardy forms of life, such as the earthly forms called "extremophiles", might persist in favored locations underground. He lists a number of interesting sites at varying distances from his proposed base, and then describes a "Mars car" that could get the explorers there and back again. This vehicle would be powered by the same locally produced methane and oxygen that fuel the rockets, but carbon dioxide would be mixed with the methane to keep the car engines from overheating. Zubrin describes this fuel production in great detail, and goes on to set forth means of providing the other necessities of exploration: life support, communication, navigation, tele-operated robotic assistants. He even designs a Martian timekeeping system and a calendar based on the Zodiac.

The exploration base itself is discussed in Chapter 7. The first step beyond the "hab" modules that brought the explorers to Mars is to bake soil into bricks and build simple shelters out of them. Next come inflatable domes 50 meters in diameter. If made of Kevlar or similar modern material, their mass would permit shipment from Earth. Once anchored by a few meters of soil and protected by outer geodesic domes of locally-produced plastic, these would be pressurized to 5 psi to create roomy quarters. In Zubrin's conception, these living and working quarters grow progressively larger and more comfortable, paced by the concurrent development of materials processing: ceramics and glass; metals like iron, copper, silicon and aluminum, alternative fuels. He describes the chemical reactions involved for each product in detail, and also considers the production of power. Although imported nuclear reactors will bootstrap the operations, indigenous sources will be tapped to drive the expansion of capabilities. Zubrin mentions wind, solar and geothermal power. I think his proposal for the latter source of power rests on a very shaky assumption. I also question his proposal to fuel automated rockets with silane and diborane. These are rather nasty substances to handle; and silane burns to produce silicon dioxide. It's hard to imagine how the rocket nozzles fail to clog up with deposits of this quartz. And his advocacy of winged rocketplanes able to "punch through any weather" seems rash to me. However, in the main this chapter's ideas are feasible and presented in a logical progression.

Colonization logically follows large-scale exploration, and this is the topic of Chapter 8. Ably drawing on historical precedents like the Louisiana Purchase and "Seward's Folly" (Alaska), Zubrin argues that new territorial acquisitions have a way of repaying their purchase price many times over — and usually in ways not foreseen. He points out that Mars is second only to Earth in its assortment of raw materials necessary to support an industrial population, and projects that a thriving "triangle trade" between Mars, Earth and the Asteroid Belt could be established fairly quickly, and at reasonable expense. Many numbers buttress this thesis, and it holds together well in my estimation. I especially like his analysis of the motivational factors that will drive Martian civilization to excellence. However, I dispute his contention on page 222 that "Mars and Earth are the only two locations in the solar system where humans will be able to grow crops for export." This seems far too broad a statement, and I also think his denigration of the Moon as a base for settlement is overstated.

Chapter 9 presents Zubrin's take on a radical final step: terraforming Mars. Terraforming is the general term for the transformation of a planet to a more nearly Earthlike state. When I call it "radical", I mean that in every sense. It is radical scientifically, for it must rest on a host of assumptions which are poorly tested, and because it involves so many interacting processes. It is radical technologically in its requirements (in most forms) for devices of near-planetary scale, for vast quantities of material, and for torrents of power. And it is radical politically and culturally because of its enormous expense, its unproven outcome, and its aura of hubris. Add to this the moral quandary of whether it is right to terraform another world.

Zubrin presents his terraforming plan as if it were a fairly routine matter. In my opinion, he displays hubris in doing so, as well as glossing over a host of technical details. (One example: the effect of changing albedo.) In fairness, though, it is more a sketch than a plan. A planet is an immensely complicated system. Undertaking to modify it without at least a century or two of study goes beyond hubris to intentional invitation of catastrophe. So I'll give him this: what he has described is plausible, even if incomplete.

In the final chapter, Zubrin returns to the political realm. He discusses three models for a Mars mission: the Kennedy model (flags and footprints to promote national pride); the Sagan model (international partnerships to promote cooperation) and the Gingrich model (monetary prizes to promote competition). The first two have of course been tried. Apollo was built on the Kennedy model; ISS follows the Sagan model. It remains to be seen how effective the Gingrich model will be, but again historical precedent gives us hope. Lindbergh flew the first solo crossing of the Atlantic to win a prize. The Kremer prizes motivated Paul MacReady and his team to design and fly several different man-powered airplanes. Here, Zubrin presents an incremental series of twelve prizes intended to spur travel to Mars. If it were enacted, I believe it would work. Alas, I feel the chances of our current political establishment enacting such a measure are slim. However, the aviation prizes were privately funded, as is the current X Prize for a repeated suborbital flight. I hold this more likely as a source of funds.

An epilogue quotes Frederick Jackson Turner, famous exponent of the value of the Western Frontier to America. That frontier had been declared closed in 1890, three years before Turner gave his seminal address at the University of Wisconsin. Since then, Zubrin maintains, we have seen the cultural deterioration brought about by the lack of a frontier. He thus closes his sales pitch by pushing yet one more emotional button.

A glossary, a list of notes on sources, a brief bibliography, and a thorough index round out the book. The bibliography lists twelve books. Five of those are Proceedings from one or another Case for Mars Conference (two not yet published when this book went to press); one, edited by Zubrin, is a collection of papers about Mars exploration from the Journal of the British Interplanetary Society; and one, edited by fellow "Mars Undergrounder" Carol Stoker, is entitled Strategies for Mars: A Guide to Human Exploration.

A great many man-hours of research underly the Mars Direct plan presented in this book. The main elements of that plan are feasible. The technical details are well worked out and clearly described. Zubrin is also a student of history, and makes effective use of historical occurrences to bolster his pitch. His analysis is thorough and mostly accurate, and he argues his case persuasively. The book is therefore a valuable contribution to our common effort to summon a true space age. However, in the final analysis, I think he underestimates the technical and political difficulties of implementing the bold plan he pitches. I still feel that the wisest course is to gain more experience with space flight hardware, and more practice with space exploration, on the less remote frontier of Luna.

1 Zubrin's nominal design would collect 108 metric tons of methane. This includes an extra amount for operating a surface rover vehicle.
2 Pure hydrogen would be more effective as a fuel. But liquid hydrogen must be stored at very near absolute zero temperature, an engineering challenge even on Earth. Methane is much easier to liquify and store for long periods.
3 These terms are carry-overs from when astrology and astronomy were the same. Back then, the Earth was thought to be the center of the universe, so when Mars (or any of the other planets) was on one side of the Earth and the Sun on the other, they were said to be in opposition; when on the same side, they were in conjunction. Now that we understand the true layout of the solar system, the terms are counterintuitive. Yet they persist.
4 Zubrin calls the first five dragons, the sixth a seductive siren: Diana, representing what in his view is a needless diversion to the Moon. It reminds me strongly of Lyndon LaRouche's reference to "the Moon-worshiping L5 cult".
List of errata for The Case for Mars
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