Extraterrestrial Civilizations (31 page)

If the key to the paradox of the existence of many civilizations in a Universe in which to all appearances we are alone, rests with the presumed difficulty of space exploration, let us examine that problem more closely.

After all, human beings managed to place the first object in orbit, thus initiating the “Space Age,” only on October 4, 1957. Before the Spage Age was a dozen years old, human beings stood on the Moon. That is a rather promising beginning. Surely we can go farther now.

In a way, we already have. Instruments have been soft-landed on the surface of Venus and Mars, and photographs and other data have been sent back to Earth. Probes have, without landing, skimmed by the surfaces of Mercury and Jupiter and have, again, returned photographs and other data. As I write, probes are on the way to Saturn and beyond.

This far penetration of human instruments without the involvement of human beings themselves does not, however, have the
glorious ring of accomplishment that we associate with the mystique of exploration. Can human beings
themselves
, as distinct from their inanimate instruments, move to worlds beyond the Moon?

Unfortunately, the Moon is not a particularly hopeful precedent. It is so close to Earth that it can’t help but give us a false confidence; it lures us on to underestimate the distances involved in space exploration.

The Moon, after all, is so close to Earth that it takes only 3 days to reach it, as compared with the 7 weeks it took Columbus to cross the Atlantic Ocean.

In reaching the Moon, we have made only the most microscopic dent in the true vastness of space. Indeed, we have not really left Earth, since the Moon is as much a slave to Earth’s gravitational influence as an apple on a tree—something Isaac Newton perceived three centuries ago.

To be sure, there are small bodies that occasionally come to within a few million kilometers of the Earth, 10 to 50 times the distance of the Moon—an occasional asteroid or comet. The nearest sizable body other than the Moon, however, is the planet Venus.

Even when Venus is at its closest to Earth, it is 40 million kilometers (25 million miles) away in a straight line, and is 105 times the distance of the Moon.

We cannot expect a space vessel to move straight across the gap between the planetary orbits. The most economical route for a space vessel to follow is an elliptical orbit of its own that begins at Earth and intersects the orbit of Venus just as that planet approaches the intersection point.

The probes that we have sent out to Venus take 7 months to cover the distance. Those probes, however, are given one burst of acceleration at the start of their journey and are then allowed to coast the rest of the way. Time is of little importance to an inanimate object.

In the case of a manned vessel, time
is
of importance. The journey must be carried through quickly, and the easiest way of doing that is to build up greater speeds.

Human beings have more than once cancelled distance by increasing speed. I have already said that the astronauts take three days to reach the Moon, while Columbus took seven weeks to cross the Atlantic, despite the fact that the distance to the Moon is nearly
80 times the width of the Atlantic.

It’s just that the astronauts travel at an average speed 1,300 times that of Columbus. Well, increase that speed by another factor of 70 and it will take only three days to reach Venus.

One way to gain the necessary speed is to place a spaceship under seventy times the acceleration of a Moon rocket, using rocket engines with seventy times the capacity for thrust. Even if we build such large engines and are willing to expend so much fuel, it remains true that the human body can only endure so much (and not very much) acceleration. The acceleration required to send the vessel on its way to Venus at a speed that would make the voyage short work would kill the astronauts at once.

The alternative is to use an acceleration no higher than that required to launch a vessel to the Moon, but then to use further acceleration at a bearable level for a prolonged period. In this way, the vessel would go faster and faster till the halfway point was reached. After that the rocket exhaust could be aimed in the other direction and a prolonged and gradual deceleration could reduce the vessel’s speed for the tryst with Venus.

It would take time to accelerate and decelerate, so the voyage would take considerably more than three days. Worse yet, acceleration and deceleration requires the expenditure of energy, and we can make the general rule that to decrease the time required for any voyage means an increase in energy expenditure. (For that matter, if the astronauts move at an average speed 1,300 times that of Columbus, their total energy expenditure is far more than 1,300 times that of Columbus.)

We don’t know of any way of uncoupling time lapse and energy expenditure, and if our understanding of the laws of nature is correct there is no conceivable way. Between the demands of the human body where acceleration is concerned and the demands of the human economy where energy expenditure is concerned, our first manned flights to Venus (if any) are going to take at best four months.

Already men have remained in space for almost that long, but that has been in space stations such as Skylab, in Earth’s immediate neighborhood, with rescue at short notice possible. To spend 120 days in space in cramped quarters, with every moment taking you farther from home, is a psychological hazard indeed.

Worse yet, having arrived in the neighborhood of Venus, there
would be no chance of a landing in view of the planet’s almost redhot surface temperature. Any exploration of the surface would have to be carried out by unmanned probes launched by the space vessel, which would itself remain in orbit about Venus and would then launch itself on another four-month journey back to Earth.

Since exploration of Venus’s surface would have to be carried out by an unmanned probe, that probe might as well travel all the way from Earth—as several probes have indeed already done. The benefits achieved by having the probe launched from, and the signals received by, a manned mother ship would scarcely justify the traumatic experience of over eight continuous months in space.

Mercury, the planet nearest the Sun, is farther from us than Venus, being never closer to us than 80 million kilometers (50 million miles) or twice Venus’s closest approach.

Mercury would at least offer a landfall to the long-distance astronauts, for one can visualize them as landing on the night side of Mercury and being able to explore the surface for several weeks before the approach of sunrise makes it absolutely necessary to leave.

The flight to Mercury, however, would carry the astronauts to a distance no farther from the Sun than 65 million kilometers (40 million miles). Solar radiation would be over 4 times as concentrated at that distance as it is in the neighborhood of the Earth. For what might be gained in a manned voyage to Mercury, over an unmanned probe, the price paid in risking the effects of the greater radiation may prove too high.

Since voyages in the direction of the Sun offer no suitable target, what about voyages away from the Sun?

The nearest planet to Earth in the direction away from the Sun is, of course, Mars. It is, at its closest, some 58 million kilometers (36 million miles) away, closer than any other planet but Venus. Traveling Mars-ward means steady progress in the direction of decreasing intensities of Solar radiation. Furthermore, Mars is a cold world that can be explored for indefinite periods even with the Sun in the sky (provided there is some protection against the Solar ultraviolet other than Mars’s thin and ineffective atmosphere).

Nevertheless, the round trip to Mars would certainly take more than a year of travel time. Even though that will be broken, for a shorter or longer time, by a landing on a planet that next to Earth itself is the most comfortable in the Solar system, the task would
surely stretch human endurance to the limit.

And beyond Mars? To reach the larger asteroids, or the satellites of the giant planets, would mean crossing the much greater spatial gaps of the outer Solar system, and the voyages would take years and even decades one way. Manned voyages of such lengths do not seem practical at the moment.

Beyond the Moon, then, we are left with only Mars as a sizable target and that only as a borderline possibility.

In a practical sense, then, our initial triumphs in space do not seem to count for much. It looks as though we will be confined to the Earth-Moon system for the foreseeable future.

That may be true, however, only because I have been assuming so far that Earth itself is the base to be used for space exploration. Is there an alternative?

If we are to be confined to the Earth-Moon system, it would seem that the Moon is the only possible alternative. Suppose we establish an elaborate base on the Moon, one where it is possible to build space vessels and gather fuel. The Moon has a much smaller escape velocity than Earth, so it would take considerably less energy for a launching from the Moon than from the Earth. There would be more energy left for acceleration and deceleration, so the time lapse for a given trip would be smaller. It would not be sufficiently smaller, however, to make the trips practical.

But wait. Because we, and all the life forms we know, live on the surface of a world, we have a natural tendency to find anything else unnatural. In 1974, the American physicist Gerard Kitchen O’Neill (1927–) suggested the alternative of artificial settlements for human beings in space. It was not an altogether new concept and had been used in science fiction on occasion, but it had never before been put forward in such careful detail.

O’Neill even suggested two places as bases for humanity; places that were not on the Moon, but were just as far as the Moon is from Earth.

Imagine the Moon at zenith, exactly overhead. Trace a line against the sky due eastward from the Moon down to the horizon.
Two-thirds of the way along that line, one-third of the way up from the horizon, at a distance equal to that of the Moon, is one of those places. Trace another line westward from the Moon down to the horizon. Two-thirds of the way along that line, one-third of the way up from the horizon, at a distance equal to that of the Moon, is another of those places.

Put an object in either place, and it will form an equilateral triangle with the Moon and Earth. It is 384,400 kilometers (238,900 miles) from the Moon to the Earth. It is that same distance from either point to the Moon, or from either point to the Earth.

What is so special about those places? Back in 1772, the Italian-French astronomer Joseph-Louis Lagrange (1736–1813) showed that in those places any small object would remain essentially stationary with respect to the Moon. As the Moon moved about the Earth, any small object in either of those places would also move about the Earth in such a way as to keep step with the Moon. The competing gravities of Earth and Moon would keep it where it was.

If the small object were not exactly in the place, it would wobble back and forth (“librating”) about the point. The two points in space are called Lagrangian points or libration points.

Lagrange discovered five such points altogether, but three of them are of no practical importance because they represent an unstable condition. An object would have to remain exactly at those points to remain at rest with respect to the Moon. Once pushed out of place, however slightly, the object would continue to drift away and would never return. The two points in which an object remains stably in place (except for libration) are those points that form equilateral triangles with the Moon and the Earth. The one that lies toward the eastern horizon is L4 and the one toward the western is L5.

O’Neill suggested that advantage be taken of that gravitational lock and that space settlements be built in the regions around the two libration points, settlements that would become permanent parts of the Earth-Moon system. The settlements themselves could consist of spheres, cylinders, or doughnut-shaped objects that would be large enough to hold 10,000 to 10 million people.

Human beings could live on the inner surface of such objects, which would be set to spinning at a rate that would produce a centrifugal effect that would hold everything and everyone to that inner surface with a force equivalent to Earth’s surface gravity. The
inner surface could then be designed and contoured into a familiar world. It could be spread with soil, which could be used for agriculture and, eventually, animal husbandry. All the artificial works of man—his buildings and machines—would be there, too.

The material forming the hull of the settlement would be composed of alternations of metal and glass. Sunshine, reflected by large mirrors that would accompany the settlement into orbit, would enter and illuminate the settlement, turning what would otherwise be a cave into a sunlit world. The entry of light could be controlled by louvers over the windows to allow for alternating day and night and to keep the temperature of the settlement equable.

It is from the Sun that the colony would obtain its energy—a copious, easily handled, nonpolluting form of energy.

The larger settlements would have a content of air thick enough to allow a blue sky and to support clouds. Parts of the inner surface of large settlements could be modeled into mountainous territory—full-sized mountains and not just bas-reliefs.

It would be expensive to build such settlements, but the expense would be far less than the world now spends on its various military machines. Since Earth, if it is to survive, will have to practice increasing international cooperation, those military machines will have to wither, and the effort to build settlements in space may well offer us a constructive way to make use of the money and people that are now engaged in war and its preparations.

Besides, the expense of building settlements will decrease as the techniques for the purpose are improved and as the space settlers themselves, in the natural urge to expand their range, take over the building of further settlements.