by Carl Sagan
and he’s treading on my tail.”
LEWIS CARROLL,
Alice in Wonderland
FOR MUCH OF human history we could travel only as fast as our legs would take us-for any sustained journey, only a few miles an hour. Great journeys were undertaken, but very slowly. For example, 20,000 or 30,000 years ago, human beings crossed the Bering Strait and for the first time entered the Americas, gradually working their way down to the southernmost tip of South America, in Tierra del Fuego, where Charles Darwin encountered them on the memorable voyage of H.M.S. Beagle. A concerted and single-minded effort of a dedicated band to walk from the straits between Asia and Alaska to Tierra del Fuego might have succeeded in a matter of years; in fact, it probably took thousands of years for diffusion of the human population to carry it so far south.
The original motivation for traveling fast must have been, as the whiting’s plaint reminds us, to escape from enemies and predators, or else to seek enemies and prey. A few thousand years ago a remarkable discovery was made: the horse can be domesticated and ridden. The idea is a very peculiar one, the horse not having been evolved for humans to ride. If looked at objectively, it is only a little less silly than, say, an octopus riding a grouper. But it worked and-especially after the invention of the wheel and the chariot-horseback or horse-drawn vehicles represented for millennia the most advanced transportation technology available to the human species. One can travel as much as 10 or perhaps even 20 miles an hour with horse technology.
We have emerged from horse technology only very recently-as, for example, our use of the term “horsepower” to rate automobile engines clearly shows. An engine rated at 375 horsepower has very roughly the pulling capacity of 375 horses. A team of 375 horses would make a very interesting sight. Arrayed in ranks of five horses each, the team would extend for about two-tenths of a mile in length and would be astonishingly unwieldy. On many roads the front rank of horse would be out of sight of the driver. And, of course, 375 horses do not travel 375 times as fast as one horse. Even with enormous teams of horses the speed of transportation was only ten or so times faster than when we could depend upon only our legs.
Thus the changes of the last century in transportation technology are striking. We humans have relied on legs for millions of years; horses for thousands; the internal-combustion engine for less than a hundred; and rockets for transportation for a few decades. But these products of human inventive genius have enabled us to travel on the land and on the surface of the waters a hundred times faster than we can walk, in the air a thousand times faster, and in space more than ten thousand times faster.
It used to be that the speed of communication was the same as the speed of transportation. There were a few fast communication methods earlier in our history-for example, signal flags or smoke signals or even one or two attempts at arrays of signal towers with mirrors employed to reflect sunlight or moonlight from one to another. News of the recapture of the Fortress of Györ by Hungarian commandos from the Turks was apparently conveyed to the Hapsburg Emperor Rudolf II through such a device: the “moonbeam telegraph,” invented by the English astrologer John Dee, which apparently consisted of ten relay stations placed at intervals of forty kilometers between Györ and Prague. But with only a few exceptions, these methods proved impractical, and communications proceeded no faster than a man or a horse. This is no longer true. Communication by telephone and radio is now at the velocity of light-186,000 miles per second, or about two-thirds of a billion miles per hour. This is not simply the latest advance: it is the last advance. So far as we know, from Einstein’s Special Theory of Relativity, the universe is constructed in such a way (at least around here) that no material object and no information can be transmitted faster than the velocity of light. This is not an engineering barrier like the so-called sound barrier, but a fundamental cosmic speed limit built deeply into the fabric of nature. Still, two-thirds of a billion miles per hour is fast enough for most practical purposes.
What is remarkable is that in communications technology we have already reached this ultimate limit and have adapted to it so well. There are few people who emerge breathless and palpitating from a routine longdistance telephone call, astounded at the speed of transmission. We take this almost instantaneous means of communication for granted. Yet in transportation technology, while we have not achieved speeds at all approaching the velocity of light, we find ourselves colliding with other limits, physiological and technological:
Our planet turns. When it is midday at one spot on the Earth, it is the dead of night on the other side. The Earth has therefore been conveniently arranged into twenty-four time zones of more or less equal width, making strips of longitude around the planet. If we fly very fast, we create situations our minds can accommodate but our bodies can abide only with great difficulty. It is a commonplace today to fly in relatively short trips westward and arrive before we leave-for example, when we take less than an hour to fly between two points separated by one time zone. When I take a 9 P.M. flight to London, it is already tomorrow at my destination. When I arrive, after a five- or six-hour flight, it is late at night for me but the beginning of the business day at my destination. My body senses something wrong, my circadian rhythms go awry, and it takes a few days to get adjusted to English time. A flight from New York to New Delhi is, in this respect, even more vexing.
I find it very interesting that two of the most gifted and inventive science-fiction writers of the twentieth century-Isaac Asimov and Ray Bradbury-both refuse to fly. Their minds have come to grips with interplanetary and interstellar spaceflight, but their bodies rebel at a DC-3. The rate of change in transportation technology has simply been too great for many of us to accommodate conveniently.
Much stranger possibilities are now practical. The Earth turns on its axis once every twenty-four hours. The circumference of the Earth is 25,000 miles. Thus, if we were able to travel at 25,000/24 = 1,040 miles per hour, we could just compensate for the Earth’s rotation, and traveling westward at sunset, could maintain ourselves at sunset for the entire journey even if we circumnavigated the planet. (In fact, such a journey would also maintain us at the same local time as we journey westward from time zone to time zone, until we cross the international dateline and plunge precipitously into tomorrow.) But 1,040 miles per hour is less than twice the speed of sound and there are, worldwide, dozens of kinds of aircraft, chiefly military, that are capable of such speeds. [12]
Some commercial aircraft, such as the Anglo-French Concorde, have comparable capabilities. The question, I think, is not: Can we go faster? but Do we have to? There has been concern expressed, some of it in my view quite appropriately, about whether the conveniences supersonic transports provide can possibly compensate for their overall cost and their ecological impact.
Most of the demand for high-speed long-distance travel comes from businessmen and government officials who need to have conferences with their opposite numbers in other states or countries. But what is really involved here is not the transportation of material but the transportation of information. I think much of the necessity for high-speed transport could be avoided if the existing communications technology were better used. I have many times participated in government or private meetings in which there were, say, twenty participants, each of whom was paid $500 for transportation and living expenses merely to attend the meeting-the cost of which was therefore $10,000 just to get the participants together. But all the participants ever exchange is information. Video phones, leased telephone lines, and facsimile reproducers to transmit paper copies of notes and diagrams would, I believe, serve as well or even better. There is no significant function of such a meeting-including private discussions among the participants “in the corridor”-that cannot be performed less expensively and at least equally conveniently with communications rather than transportation technology.
There are certainly advances in transportation that seem to me promising and desirable: vertical takeoff and landing (VT
OL) aircraft are a remarkable boon for isolated and remote communities in case of medical or other emergencies. But the recent advances in transportation technology that I find most appealing are rubber fins for snorkel and scuba diving and hang gliders. These are technological advances much in the spirit of those sought by Leonardo da Vinci in mankind’s first serious technological pursuit of flight in the fifteenth century; they permit an individual human being with little more than his own resources to enter-at a speed that is adequately exhilarating-another medium entirely.
WITH THE DEPLETION of fossil fuels I think it very likely that automobiles powered by internal-combustion engines will be with us for at most a few decades longer. The transportation of the future will simply have to be different. We can imagine quite comfortable and adequately speedy steam, solar, fuel-cell or electric ground vehicles, generating very little pollution and employing a technology comfortably accessible to the user.
Many responsible medical experts are concerned that we in the West-and increasingly even in developing countries-are becoming too sedentary. Driving an automobile exercises very few muscles. The demise of the automobile surely has many positive aspects when viewed in the long run, one of which is a return to the oldest transportation mechanism, walking, and to bicycling, which is in many ways the most remarkable.
I can easily imagine a healthy and stable future society in which walking and bicycling are the primary means of transportation; with pollution-free low-speed ground cars and railed public transportation systems widely available, and the most sophisticated transportation devices used relatively rarely by the average person. The one application of transportation technology that requires the most sophisticated technology is spaceflight. The returns in immediate practical benefits, scientific knowledge and appealing exploration provided by unmanned spaceflight are very impressive, and I would expect an increasing rate of space-vehicle launches by many nations in the next few decades, using more subtle forms of transportation, as described in the previous chapter. Nuclear electric, solar sailing and ion propulsion schemes have been proposed and are to some degree under development. As nuclear-fusion power plants are developed for Earth-bound applications in a few decades, there should be a development of fusion space engines as well.
The gravitational forces of planets have already been used to give velocities otherwise unobtainable. Mariner 10 reached Mercury only because it flew so close to Venus that Venus’ gravity provided a significant boost in speed. And Pioneer 10 was boosted into an orbit that will carry it out of the solar system entirely, only because of a close passage by the giant planet Jupiter. In a way Pioneer 10 and 11 and Voyager 1 and 2 are our most advanced transportation systems. They are leaving the solar system at a speed of roughly 43,000 miles per hour, carrying messages to anyone who may intercept them out there in the dark of the night sky from the people of the Earth-who, only a little while ago, could travel no faster than a few miles per hour.
CHAPTER 18
VIA CHERRY TREE, TO MARS
O for a Muse of fire, that would ascend
The brightest heaven of invention…
WILLIAM SHAKESPEARE,
Henry V, Prologue
IT IS A LAZY afternoon in an exquisite New England autumn. In about ten weeks it will be January 1, 1900, and your diary, into which are committed the events and ideas of your young life, will never again bear an entry with a date in the 1800s. You have just turned seventeen. You are looking forward to being a sophomore in high school, but you are now at home, in part because your mother is seriously ill with tuberculosis and in part because of your own chronic stomach pains. You are bright, with a certain flair for the sciences, but no one has ever indicated that you might have an extraordinary talent. You are complacently viewing the New England countryside from the limb of a tall old cherry tree which you have climbed, when suddenly you are struck by an idea, an overpowering and compelling vision that it might be possible, in fact rather than in fancy, to voyage to the planet Mars.
When you descend from the cherry tree you know that you are a very different boy from the one who climbed it. Your life’s work is clearly set out for you, and for the next forty-five years your dedication never wavers. You have been smitten by the vision of flight to the planets. You are deeply moved and quietly awed by the vision in the cherry tree. The next year, on the anniversary of that vision, you climb the tree again to savor the joy and meaning of the experience; and forever after you make a point in your diary of calling the anniversary of that experience “Anniversary Day”-every October 19 until your death in the middle 1940s, by which time your theoretical insights and practical innovations have solved essentially all technological impediments to interplanetary flight.
Four years after your death a WAC Corporal mounted on the nose of a V-2 is successfully fired to an altitude of 250 miles, for all practical purposes to the threshold of space. All essential design elements of the WAC Corporal and the V-2, and the very concept of the multiple staging of rockets, have been worked out by you. A quarter of a century later, unmanned space vehicles will have been launched to all the planets known to ancient man; a dozen men will have set foot on the Moon; and two exquisitely miniaturized spacecraft named Viking will be on their way to Mars to attempt the first search for life on that planet.
ROBERT H. GODDARD never questioned or equivocated on the resolve he made in the cherry tree on the farm of his great-aunt Czarina in Worcester, Massachusetts. While there were others who had comparable visions-notably Konstantin Eduardovich Tsiolkovsky in Russia-Goddard represented a unique combination of visionary dedication and technological brilliance. He studied physics because he needed physics to get to Mars. He was for many years professor of physics and chairman of the physics department at Clark University in his hometown of Worcester.
In reading the notebooks of Robert Goddard, I am struck by how powerful his exploratory and scientific motivations were, and how influential speculative ideas-even erroneous ones-can be on the shaping of the future. In the few years surrounding the turn of the century, Goddard’s interests were profoundly influenced by the idea of life on other worlds. He was intrigued by the claims of W. H. Pickering, of the Harvard College Observatory, that the Moon has a perceptible atmosphere, active volcanism, variable frost patches, and even changing dark markings, which Pickering interpreted variously as the growth of vegetation or even as the migration of enormous insects across the floor of the crater Eratosthenes. Goddard was captivated by the science fiction of H. G. Wells and Garrett P. Serviss, particularly the latter’s Edison’s Conquest of Mars, which, Goddard reported, “gripped my imagination tremendously.” He attended and enjoyed lectures by Percival Lowell, who was an eloquent advocate of the proposition that intelligent beings inhabit the planet Mars. And yet, through all of this, while his imagination was intensely stimulated, Goddard managed to retain a sense of skepticism very rare in young people given to interplanetary epiphanies high up in cherry trees: “The actual conditions may be entirely different… from those which Professor Pickering suggests… The only antidote for fallacies is-in a word-to take nothing for granted.”
On January 2, 1902, we know from Goddard’s notebook, he wrote an essay on “The Habitability of Other Worlds.” The paper had not been found among Goddard’s writings, which seemed to me a great pity, since it might have given us a better understanding of the extent to which the search for extraterrestrial life was a prime motive in Goddard’s lifework. [13]
In his early postdoctoral years Goddard successfully pursued an experimental verification of his ideas on solid- and liquid-fueled rocket flight. In this endeavor he was supported principally by two men: Charles Greeley Abbott and George Ellery Hale. Abbott was then a young scientist at the Smithsonian Institution, of which he later became secretary, the quaint designation by which the executive officer of that organization is still known. Hale was the driving force behind American observational astronomy at the time; before he died he had founded the Yerkes, Mount Wils
on and Mount Palomar observatories, each housing, in its time, the largest telescope in the world.
Both Abbott and Hale were solar physicists, and it seems clear that both had been captured by the young Goddard’s vision of a rocket sailing free above the obscuring blanket of the Earth’s atmosphere, able to view the Sun and stars unimpeded. But Goddard soared far beyond this daring vision. He talked and wrote of experiments on the composition and circulation of the upper atmosphere of the Earth, of performing gammaray and ultraviolet observations of the Sun and stars from above the Earth’s atmosphere. He conceived of a space vehicle passing 1,000 miles above the surface of Mars-by a curious historical accident just the low point in the orbits of the Mariner 9 and Viking spacecraft. Goddard calculated that a reasonably sized telescope at such a vantage point would be able to photograph features tens of meters across on the surface of the Red Planet, which is the resolution of the Viking orbiter cameras. He conceived of slow interstellar flight at velocities and time scales just equivalent to that of the Pioneer 10 and 11 spacecraft, our first interstellar emissaries.
Goddard’s spirit soared higher still. He conceived, not casually but quite seriously, of solar-powered spacecraft, and in a time when any practical application of nuclear energy was publicly ridiculed, nuclear propulsion for spacecraft over vast interstellar distances. Goddard imagined a time in the far distant future when the Sun has grown cold and the solar system become uninhabitable, when manned interstellar spacecraft would be outfitted by our remote descendants, to visit the stars-not merely the nearby stars, but also remote star clusters in the Milky Way Galaxy. He could not imagine relativistic spaceflight and so hypothesized a method of suspended animation of the human crew or-even more imaginative-a means of sending the genetic material of human beings which would automatically, at some very distant time, be allowed to recombine and produce a new generation of people.