The Case for Mars (24 page)

THE LUNAR SIREN: WHY WE DON’T NEED LUNAR BASES TO GO TO MARS

We now come to a totally different kind of mythical creature blocking the path to Mars, one appearing not in the guise of a threatening monster or fearsome dragon, but in the alluring dress of a lovely goddess. This is Diana, the Lunar Siren, whose seduceemong has probably done as much to wreck would-be Mars ventures to date as all five dragons combined.

According to Diana’s followers, it is a point of religious belief that we cannot venture human expeditions to Mars until after the goddess has been appeased by the construction of a substantial array of temples—that is, bases—on the lunar surface. This is a commendably original basis for a pagan religion, and it really shows how far we’ve come since the days of the Roman Empire, but the fact of the matter is that it has no basis in reason.

Yes, it is quite true that due to its low gravity and negligible atmosphere, it would be much easier to send a rocket from the surface of the Moon to Mars than to launch it from the surface of the Earth. Furthermore, it is also true that Moon rocks are almost 50 percent oxygen by weight, so that once technologies are developed that can break down the iron and silicon oxides that make up most of the Moon’s materials, a copious supply of liquid oxygen could be made available for spacecraft refueling on the lunar surface. Unfortunately, fuel to burn in this oxygen, such as hydrogen or methane, is essentially unavailable on the Moon. Nevertheless, since the oxygen content of various rocket propellant mixtures varies from 72 percent to 86 percent by weight, the Moon can in principle be made into a base that could support a substantial fraction of required space transportation logistics.

But this analysis neglects some basic facts about solar system transportation. You see, before the spacecraft can refuel at the Moon, it has to get to the Moon. Now the ΔV required to go from low Earth orbit (LEO) to the lunar surface is 6 km/s (3.2 km/s
for trans-lunar injection, 0.9 km/s to capture into low Lunar orbit, and 1.9 km/s to land on the airless Moon.). On the other hand, the ΔV required to go from LEO to the Martian surface is only about 4.5 km/s (4 km/s for trans-Mars injection, 0.1 km/s for post-aerocapture orbit adjustment, and 0.4 km/s to land after using the aeroshield—but no parachute—for aerodynamic deceleration). Put briefly, from a propulsion point of view,
it is much easier to go from LEO directly to Mars than it is to go from LEO to the surface of the Moon.
So, even if infinite quantities of free rocket fuel and oxygen were sitting right now in tanks on the lunar surface (and they aren’t), it would make absolutely no sense to send a rocket there to refuel itself for a voyage to Mars. Basically, refueling at the Moon on your way to Mars is about as smart as having an airplane flying from Houston to San Francisco stop over for refueling in Saskatoon. Putting the lunar refueling node in lunar orbit doesn’t change things very much. You still have to perform almost as much ΔV to move the spacecraft from LEO to lunar orbit as you do to send it to Mars. Add in the supplies required to support the making of oxygen on the Moon along with the hardware and fuel to haul large quantities of it to lunar orbit (you have to ship hydrogen or methane to the lunar surface to use to lift oxygen to orbit) and it quickly becomes apparent that the whole scheme is nothing but a logistics nightmare that would enormously increase the cost, complexity, and risk required to mount a piloted Mars mission.

So, the Moon is not useful as a Mars transportation base. Well then, say Diana’s followers, you still need to use the Moon as a test bed and training site to prepare for a Mars mission.

But lunar conditions are so dissimilar from those on Mars that Antarctica (or Wyoming for that matter) would do just as well for crew training, and at far lower expense. Mars has an atmosphere and a twenty-four-hour day, with daytime temperatures varying between -50°C and +10°C. The Moon has no atmosphere, a 672-hour day, and typical daytime temperatures of about +100°C. While the Earth’s gravity is 2.6 times that of Mars, Mars’ gravity is 2.4 times that of the Moon. Furthermore, the types of resource utilization that one would undertake on Mars (exploitation of the atmosphere in gas-based chemical reactors and extraction of permafrost from soi
l) are completely different from the high-temperature rock-melting techniques that will be employed on the Moon. In addition, the types of geologic investigations needed on Mars, given its complex hydrologic and volcanic history, will much more closely resemble those that can be done on Earth than those that can be done on Luna. We won’t learn how to live on Mars by practicing on the Moon.

The Moon does have some uses, most notably as a platform for astronomy using a coordinated array of optical telescopes to obtain super-high-resolution views of the universe at large (an “optical interferometer”). It makes sense, therefore, to gain maximum benefit by ensuring that the same set of hardware used to accomplish Mars missions is designed in such a way that it can also be used to support transportation of humans and equipment to the Moon. As discussed in
Chapter 3
, this is the case with the Mars Direct mission design. Therefore, in much the same way as Apollo lunar hardware could be used as an afterthought to create the Skylab space station, so an ancillary benefit of the Mars Direct mission is that it will give us the capability of setting up lunar observatories whenever we want them.

However, what needs to be clearly understood is that a lunar base is neither necessary nor desirable as an asset to support piloted missions to Mars. With respect to the path to Mars, it is a fatal Siren, a diversion into a dead end. The late NASA administrator Thomas O. Paine knew all about this trap. In one of the last speeches of his life he put it this way: “As Napoleon Bonaparte once said explaining his winning strategy for war with Austria: ‘If you want to take Vienna, take Vienna!’ Well, if you want to go to Mars, go to Mars!”

Well said, Tom. On to Mars.

Simplified topographic map of Mars showing the elevated continents of Tharsis and Syrtis Major and the depressed Vasitas Borealis region which once may have contained a large polar ocean
.

6: EXPLORING MARS

We are not sending a cre
w to Mar
s to set a new altitude record for the Aviation Almanac. We are going to Mars to explore a planet; to determine if it ever harbored life in the past and to survey its potential as a future home for a new branch of human civilization. Sending a few robotic probes, no matter how sophisticated, will never get the job done. Nor will even a few piloted excursions to the Red Planet’s surface, especially if the crews are limited to lingering near their short-term base. No, to learn about Mars, we’ll have to get about Mars, and in a major way.

With a surface area of 144 million square kilometers, the Red Planet has as much terrain to explore as all the continents and islands of Earth put together. Moreover, the Martian terrain is incredibly varied. It includes canyons, chasms, mountains, dried river and lake beds, flood runoff plains, craters, volcanoes, ice fields, dry-ice fields, and “chaotic terrain,” to name just a few surface features. The U.S. Geological Survey currently records no lfe in tan thirty-one types of Martian terrain on its “Simplified Geologic Map,” and all these before real high-resolution imaging of Mars has even begun. Some of the Martian terrain features, such as the 3,000-kilometer-long Valles Marineris, are of continental extent, and the thorough exploration of even a single such feature will require contine
ntal scale mobility.

The dry riverbeds discovered on Mars by
Mariner 9
are proof that Mars once had a warm, wet climate, suitable for the origin of life. This was possible in Mars’ early years, because in its youth the planet’s carbon dioxide atmosphere was much thicker, endowing it with a very strong “greenhouse effect.” Venus has a thick carbon dioxide atmosphere today, but it has turned that planet into a baking hell. At Mars’ greater distance from the Sun, though, a thick carbon dioxide greenhouse is just what is needed to create the temperate conditions required for the development of life. Most Mars scientists currently believe that such conditions persisted on Mars for a period of time considerably longer than it took life to evolve on Earth. Current theories on the origin of life regard the emergence of life as a natural development of progressive self-organization by matter that should inevitably occur wherever the appropriate physical and chemical conditions exist. If that is indeed the case, life should have appeared on Mars, because during the period of life’s origin on Earth, Earth and Mars were similar environments. Over geologic time, Mars lost its greenhouse and became the frigid, arid world it is today, and this climatic deterioration almost certainly has driven life from its surface and possibly into extinction. Nevertheless, microscopic organisms can leave macroscopic fossils. We have found some on Earth, called bacterial stromatelites, that date back 3.7 billion years, making them contemporary with Mars’ tropical era. Even if Martian life died out entirely, its fossil remains could still be there. Today, all we know about the chances for the evolution of life is that it occurred on one planet, our own. We have no way of knowing whether that development was a one-in-a-trillion freak chance or whether it was a dead sure bet. Freak chances can occur in a single sample experiment, but never twice in row. If we were to find either living organisms or simply fossils on Mars, we would know that the universe belongs to life.

Thus the search for life, either extant or fossilized, will be the highest priority for early Mars explorers, as around its result turns the question of whether life is a universal or unique phenomenon. But the results of the
Viking
missions showed that if extant life does exist on Mars, it is rare, and its finding will take more than a bit of searching. Likewise, the experience of professional paleontologists on Earth has shown that the hunt for fossils will require much footwork, because the creation of a detectable fossil is a very low-probability event. Imagine the sequence of events necessary to create a fossil. First, when the organism dies it must be immediately isolated from the environment. If not, it will soon decay, or perhaps be scavenged by its former pals who want for themselves whatever it was made of. Then it must sit hidden in isolation from the environment for millions or billions of years, only to be revealed just before you happen to come along looking for it. (If it is exposed any significant time before your arrival, the environment will destroy it before you get to see it.) Recall that triceratops, and, more recently, bison once roamed the plains of North America in herds of tens of millions, yet American hikers today don’t run much risk of accidentally tripping over their fossilized skeletons. No, if you want to find yourself a fossilized dinosaur, or Martian stromatelite, you better be prepared to do quite a bit of travel>
LiAnd if you want prove that they’re
not
there, you’ll have to travel even more, because the ability to demonstrate a convincing negative result will depend upon a search of virtually the planet’s entire surface. In the end, the mobility requirements of Martian exploration are profoundly simple: to explore a planet you need mobility on a planetary scale. It’s a simple but often overlooked point.

So how will the crew of our first piloted Mars mission get around? The battery-powered Lunar rover used during the Apollo program had a one-way range of about 20 kilometers, giving it a sortie range of 10 kilometers from the landing site. A manned Mars expedition equipped with equivalent transportation would be able to explore only about 300 square kilometers, regardless of the length of its surface stay, and nearly
half a million
such missions would be required to examine the entire surface of Mars
just once.
Even if it were considered sufficient simply to examine a variety of points of interest, the limited mobility afforded by such a vehicle would be a severe impediment and vastly increase the cost of mounting a serious manned Mars exploration program. For example,
Table 6.1
shows a list of points of interest in the Coprates triangle area, surrounding a landing site at 0° latitude and 65° west longitude. Because it is near the equator (and thus comparatively warm and sunny year-round) and has such a large variety of interesting targets for investigation nearby, this site is one of the leading candidates as the landing zone for the fi
rst human expedition to Mars.

We can see that if surface mobility were limited to a 100-kilometer range (ten times the Apollo lunar rover’s), at least twelve landings would be needed to visit all the sites listed. If the mission had a surface mobility of 500 kilometers, then only four missions would be required to visit all fourteen sites, and these four missions could access eight times the surface area as that available to the twelve missions conducted by crews with a 100-kilometer range.

TABLE 6.1
Surface Features of Interest in the Exploration of Mars