Broca's Brain (35 page)

We have caught our first glimpses of the ammonia clouds and great storm systems of Jupiter; the cold, salt-covered surface of its moon, Io; the desolate, crater-pocked, ancient and broiling Mercurian wasteland; and the wild and eerie landscape of our nearest planetary neighbor, Venus, where the clouds are composed of an acid rain that falls continuously but never patters the surface because that hilly landscape, illuminated by sunlight diffusing through the perpetual cloud layer, is
everywhere at 900°F. And Mars: What a puzzle, what a joy, enigma and delight is Mars, with ancient river bottoms; immense, sculpted polar terraces; a volcano almost 80,000 feet high; raging windstorms; balmy afternoons; and an apparent initial defeat of our first pioneering effort to answer the question of questions—whether the planet harbors, now or ever, a home-grown form of life.

There are on Earth only two spacefaring nations, only two powers so far able to send machines much beyond the Earth’s atmosphere—the United States and the Soviet Union. The United States has accomplished the only manned missions to another body, the only successful Mars landers and the only expeditions to Mercury, Jupiter and Saturn. The Soviet Union has pioneered the automated exploration of the Moon, including the only unmanned rovers and return sample missions on any celestial objects, and the first entry probes and landers on Venus. Since the end of the Apollo program, Venus and the Moon have become, to a certain degree, Russian turf, and the rest of the solar system visited only by American space vehicles. While there is a certain degree of scientific cooperation between the two spacefaring nations, this planetary territoriality has come about by default rather than by agreement. There have in recent years been a set of very ambitious but unsuccessful Soviet missions to Mars, and the United States launched a modest but successful set of Venus orbiters and entry probes in 1978. The solar system is very large and there is much to explore. Even tiny Mars has a surface area comparable to the land area of the Earth. For practical reasons it is much easier to organize separate but coordinated missions launched by two or more nations than cooperative multinational ventures. In the sixteenth and seventeenth centuries, England, France, Spain, Portugal and Holland each organized on a grand scale missions of global exploration and discovery in vigorous competition. But the economic and religious motives of exploratory competition then do not seem to have their counterparts today. And there is every reason to think that national competition
in the exploration of the planets will, at least for the foreseeable future, be peaceful.

THE LEAD TIMES
for planetary missions are very long. The design, fabrication, testing, integration and launch of a typical planetary mission takes many years. A systematic program of planetary exploration requires a continuing commitment. The most celebrated American achievements on the Moon and planets—Apollo, Pioneer, Mariner and Viking—were initiated in the 1960s. At least until recently, the United States has made only one major commitment to planetary exploration in the whole of the decade of the 1970s—the Voyager missions, launched in the summer of 1977, to make the first systematic fly-by examination of Jupiter, Saturn, their twenty-five or so moons and the spectacular rings of the latter.

This absence of new starts has produced a real crisis in the community of American scientists and engineers responsible for the succession of engineering successes and high scientific discovery that began in 1962 with the Mariner 2 fly-by of Venus. There has been an interruption in the pace of exploration. Workers have been laid off and drifted to quite different jobs, and there is a real problem in providing continuity to the next generation of planetary exploration. For example, the earliest likely response to the spectacularly successful and historic Viking exploration of Mars will be a mission that does not even arrive at the Red Planet before 1985—a gap in Martian exploration of almost a decade. And there is not the slightest guarantee that there will be a mission even then. This trend—a little like dismissing most of the shipwrights, sail weavers and navigators of Spain in the early sixteenth century—shows some slight signs of reversal. Recently approved was Project Galileo, a middle-1980s mission to perform the first orbital reconnaissance of Jupiter and to drop the first probe into its atmosphere—which may contain organic molecules synthesized in a manner analogous to the chemical events which on Earth led to the origin of life. But the following year Congress so reduced the funds available
for Galileo that it is, at the present writing, teetering on the brink of disaster.

In recent years the entire NASA budget has been well below one percent of the federal budget. The funds spent on planetary exploration have been less than 15 percent of that. Requests by the planetary science community for new missions have been repeatedly rejected—as one senator explained to me, the public has not, despite
Star Wars
and
Star Trek
, written to Congress in support of planetary missions, and scientists do not constitute a powerful lobby. And yet, there are a set of missions on the horizon that combine extraordinary scientific opportunity with remarkable popular appeal:

Solar Sailing and Comet Rendezvous.
In ordinary interplanetary missions, spacecraft are obliged to follow trajectories that require a minimum expenditure of energy. The rockets burn for short periods of time in the vicinity of Earth, and the spacecraft mainly coast for the rest of the journey. We have done as well as we have not because of enormous booster capability, but because of great skill with severely constrained systems. As a result, we must accept small payloads, long mission times and little choice of departure or arrival dates. But just as on Earth we are considering moving from fossil fuels to solar power, so it is in space. Sunlight exerts a small but palpable force called radiation pressure. A sail-like structure with a very large area for its mass can use radiation pressure for propulsion. By positioning the sail properly, we can be carried by sunlight both inwards toward and outwards away from the Sun. With a square sail about half a mile on each side, but thinner than the thinnest Mylar, interplanetary missions can be accomplished more efficiently than with conventional rocket propulsion. The sail would be launched into Earth orbit by the manned Shuttle craft, unfurled and strutted. It would be an extraordinary sight, easily visible to the naked eye as a bright point of light. With a pair of binoculars, detail on such a sail could be made out—perhaps even what on seventeenth-century sailing ships was called the “device,” some appropriate graphic symbol, perhaps a representation of
the planet Earth. Attached to the sail would be a scientific spacecraft designed for a particular application.

One of the first and most exciting applications being discussed is a comet-rendezvous mission, perhaps a rendezvous with Halley’s comet in 1986. Comets spend most of their time in interstellar space and should provide major clues on the early history of the solar system and the nature of the matter between the stars. Solar sailing to Halley’s comet might not only provide close-up pictures of the interior of a comet—about which we now know close to nothing—but also, astonishingly, return a piece of a comet to the planet Earth. The practical advantages and the romance of solar sailing are both evident in this example, and it is clear that it represents not just a new mission but a new interplanetary technology. Because the development of solar-sailing technology is behind that of ion propulsion, it is the latter that may propel us on our first missions to the comets. Both propulsion mechanisms have their place in future interplanetary travel. But in the long term I believe solar sailing will make the greater impact. Perhaps by the early twenty-first century there will be interplanetary regattas competing for the fastest time from Earth to Mars.

Mars Rovers.
Before the Viking mission, no terrestrial spacecraft had successfully landed on Mars. There had been several Soviet failures, including at least one which was quite mysterious and possibly attributable to the hazardous nature of the Martian landscape. Thus, both Viking 1 and Viking 2 were, after painstaking efforts, successfully landed in two of the dullest places we could find on the Martian surface. The lander stereo cameras showed distant valleys and other inaccessible vistas. The orbital cameras showed an extraordinarily varied and geologically exuberant landscape which we could not examine close up with the stationary Viking lander. Further Martian exploration, both geological and biological, cries out for roving vehicles capable of landing in the safe but dull places and wandering hundreds or thousands of kilometers to the exciting places. Such a rover would be able to wander to its own horizon
every day and produce a continuous stream of photographs of new landscapes, new phenomena and very likely major surprises on Mars. Its importance would be improved still further if it operated in tandem with a Mars polar orbiter which would geochemically map the planet, or with an unmanned Martian aircraft which would photograph the surface from very low altitudes.

Titan Lander.
Titan is the largest moon of Saturn and the largest satellite in the solar system (see
Chapter 13
). It is remarkable for having an atmosphere denser than that of Mars and is probably covered with a layer of brownish clouds composed of organic molecules. Unlike Jupiter and Saturn, it has a surface on which we can land, and its deep atmosphere is not so hot as to destroy the organic molecules. A Titan entry-probe and lander mission would probably be part of a Saturn orbital mission, which might also include a Saturn entry probe.

Venus Orbital Imaging Radar.
The Soviet Venera 9 and 10 missions have returned the first close-up photographs of the surface of Venus. Because of the permanent cloud pall, the surface features of Venus are not visible through Earth-bound optical telescopes. However, Earth-based radar and the radar system aboard the small Pioneer Venus orbiter have now begun to map Venus surface features, and have revealed mountains and craters and volcanoes as well as stranger morphology. A proposed Venus orbital imaging radar would provide pole-to-pole radar pictures of Venus with much higher detail than can be achieved from the surface of the Earth, and would permit a preliminary reconnaissance of the Venus surface comparable to that achieved for Mars in 1971-72 by Mariner 9.

Solar Probe.
The Sun is the nearest star, the only one we are likely to be able to examine close up, at least for many decades. A near approach to the Sun would be of great interest, would help in understanding its influence on Earth, and would also provide vital additional tests of such theories of gravitation as Einstein’s General Theory of Relativity. A solar probe mission is difficult for two reasons: the energy required to undo
the Earth’s (and the probe’s) motion around the Sun so it can fall into the Sun, and the intolerable heating as the probe approaches the Sun. The first problem can be solved by launching the spacecraft out to Jupiter and then using Jupiter’s gravitation to fling it into the Sun. Since there are many asteroids interior to Jupiter’s orbit, this might possibly be a useful mission for studying asteroids as well. An approach to the second problem, at first sight remarkable for its naïveté, is to fly into the Sun
at night.
On Earth, nighttime is of course merely the interposition of the solid body of the Earth between us and the Sun. Likewise for a solar probe. There are some asteroids that come rather close to the Sun. A solar probe would approach the Sun in the shadow of a Sun-grazing asteroid (meanwhile making observations of the asteroid as well). Near the point of closest approach of the asteroid to the Sun, the probe would emerge from the asteroidal shadow and plunge, filled with a fluid that resists heating, as deeply into the atmosphere of the Sun as it could until it melted and vaporized—atoms from the Earth added to the nearest star.

Manned Missions.
As a rule of thumb, a manned mission costs from fifty to a hundred times more than a comparable unmanned mission. Thus, for scientific exploration alone, unmanned missions, employing machine intelligence, are preferred. However, there may well be reasons other than scientific for exploring space—social, economic, political, cultural or historical. The manned missions most frequently talked about are space stations orbiting the Earth (and perhaps devoted to harvesting sunlight and transmitting it in microwave beams down to an energy-starved Earth), and a permanent lunar base. Also being discussed are rather grand schemes for the construction of permanent space cities in Earth orbit, constructed from lunar or asteroidal materials. The cost of transporting materials from such low-gravity worlds as the Moon or an asteroid to Earth orbit is much less than transporting the same materials from our high-gravity planet. Such space cities might ultimately be self-propagating—new ones constructed
by older ones. The costs of these large manned stations have not yet been estimated reliably, but it seems likely that all of them—as well as a manned mission to Mars—would cost in the $100 billion to $200 billion range. Perhaps such schemes will one day be implemented; there is much that is far-reaching and historically significant in them. But those of us who have fought for years to organize space ventures costing less than one percent as much may be forgiven for wondering whether the required funds will be allocated, and whether such expenditures are socially responsible.

However, for substantially less money, an important expedition that is preparatory for each of these manned ventures could be mustered—an expedition to an Earth-crossing carbonaceous asteroid. The asteroids occur mostly between the orbits of Mars and Jupiter. A small fraction of them have trajectories that carry them across Earth’s orbit and occasionally within a few million miles of the Earth. Many asteroids are mainly carbonaceous—with large quantities of organic materials and chemically bound water. The organic matter is thought to have condensed in the very earliest stages of the formation of the solar system from interstellar gas and dust, some 4.6 billion years ago, and their study and comparison with cometary samples would be of extraordinary scientific interest. I do not think that materials from a carbonaceous asteroid are likely to be criticized in the same way that the Apollo returned lunar samples were—as being “only” rocks. Moreover, a manned landing on such an object would be an excellent preparation for the eventual exploitation of resources in space. And finally, landing on such an object would be fun: because the gravity field is so low, it would be possible for an astronaut to do a standing high jump of about ten kilometers. These Earth-crossing objects, which are being discovered at a rapidly increasing pace, are called—by a name selected long before manned spaceflight—the Apollo objects. They may or may not be the dead husks of comets. But whatever their origin, they are of great interest. Some of them are the easiest objects in space for humans to get to, using only the
Shuttle technology, which will be available in another few years.