Space Travel Troubles
by Neil deGrasse Tyson
From Natural History Magazine, September 1998
Published under the title
Space, You Can’t Get There From Here.
From listening to space enthusiasts talk about space travel, or from watching blockbuster science fiction movies, you might think that sending people to the stars is inevitable and will happen soon. Reality check: It's not and it won't —the fantasy far outstrips the facts.
A line of reasoning among those who are unwittingly wishful might be,
We invented flight when nobody thought it was possible. A mere sixty-five years later, we went to the Moon. It's high time we journeyed among the stars. The people who say it isn't possible are ignoring history.
My rebuttal is borrowed from a legal disclaimer of the investment industry:
Past performance is not an indicator of future returns. Analysis of the problem leads to a crucial question: What does it take to pry money and labor from a population to pay for major initiatives? A study of the world's famously funded projects across time and place reveals three common drivers: praise of person or deity, economics, and war. Some expensive investments in praise include the Great Pyramids, the Taj Mahal, and plush cathedrals. Some expensive projects launched in the hope of economic return include Columbus's voyage to the new world, Magellan's round-the-world voyage, and Marco Polo's voyage to the Far East. Expensive projects with military or defense incentives include the Great Wall of China, which helped to keep the Mongols out of China, the Manhattan Project, which designed and built the first atomic bomb, and the Apollo Project, which vaulted the United States past our Soviet enemies in the race for superiority in space.
During the 1960s, the prevailing rationale for space travel presented to children was that we were going to the Moon because humans are innate explorers—and that space was America's next frontier. When President Kennedy's addressed a joint session of Congress on 25 May 1961, in what many consider to be his
second inaugural address, he waxed eloquently about the need for Americans to explore the Moon, including the famous lines:
I believe that this nation should commit itself to achieving the goal, before the decade is out, of landing a man on the moon and returning him safely to the earth. No single space project in this period will be more impressive to mankind, or more important for the long-range exploration of space; and none will be so difficult or expensive to accomplish.
This statement alone confused me (when I grew old enough to care about politics and be confused by it) because I knew that nearly every astronaut in the space program was drawn from the military, yet our voyage to the Moon was hardly ever mentioned in the same breath as the Soviet Union or the Cold War. Only later in Kennedy's speech do you hear him take a military posture, triggered by the successful launch of Cosmonaut Yuri Gagarin into Earth orbit, but this portion is hardly ever replayed:
If we are to win the battle that is now going on around the world between freedom and tyranny, the dramatic achievements in space which occurred in recent weeks should have made clear to us all, as did Sputnik in 1957, the impact of this adventure on the minds of men everywhere who are attempting to make a determination of which road they should take.
Had the political landscape been different, Americans (Congress in particular) would have been loath to part with the two-hundred billion dollars that accomplished the task. In spite of such rhetoric, the debates that followed on the floor of Congress certainly demonstrated that funding for Apollo was not a foregone conclusion.
Still, once liquid fuel rockets had been invented by Robert Goddard in 1926, enabling flight without the lift provided by air moving over a wing, a trip through the vacuum of space to the Moon was in sight even if the idea was technologically distant—it was just a matter of time. Goddard, himself, realized that a trip to the Moon was finally possible but that it might be prohibitively expensive;
It might cost a million dollars he mused naively.
Calculations that were possible the day after Isaac Newton introduced his universal law of gravitation show that the most efficient trip to the Moon would be in a craft escaping Earth's atmosphere at a speed of seven miles per second and coasting all the way. Such a trip takes about a day and a half. Such a trip has been taken only nine times—between 1968 and 1972. Otherwise, when NASA sends astronauts into
space they launch a crew into orbit a few hundred miles above our 8,000-mile-diameter Earth. Space travel this isn't. If you had told John Glenn after his historic three orbits and successful splashdown in 1962, that in 37 years NASA was going to send him into space once again, you can bet the last place he would have imagined going is back into Earth orbit.
What seems to be the trouble with space travel?
Let's start with money. If we can send somebody to Mars for less than a hundred billion dollars then I say let's go for it. But I have a friendly bet with Louis Friedman, a fellow Board member and the Executive Director of The Planetary Society (a membership funded-organization founded by the late Carl Sagan and others to promote the peaceful exploration of space) that we are not going to Mars any time soon. More specifically, I bet him that there will be no funded plan in place by any government to send one or more people to Mars before the year 2005. I hope I am wrong. But I will only be wrong if the cost of modern missions is brought down considerably compared with those of the past. Below is a note on NASA's legendary spending habits forwarded to me from a Russian colleague.
The Astronaut Pen
During the heat of the space race in the 1960s, the U.S. National Aeronautics and Space Administration [NASA] decided it needed a ball point pen to write in the zero gravity confines of its space capsules. After considerable research and development, the Astronaut Pen was developed at a cost of approximately $1 million U.S. The pen worked and also enjoyed some modest success as a novelty item back here on earth. The Soviet Union, faced with the same problem, used a pencil.
Unless we have a reprise of the socio-political circumstances that dislodged two hundred billion dollars for space travel from taxpayers' wallets in the 1960s, my reading of history leaves me unconvinced that we will ever send Homo sapiens anywhere outside of Earth orbit. I quote a Princeton colleague J. Richard Gott, from a panel discussion held few years ago at the Hayden Planetarium that touched upon the health of the manned space program:
In 1969, [space flight pioneer] Werner von Braun had a plan to send astronauts to Mars by 1982. It didn't happen. In 1989, President Bush promised that we would send astronauts to Mars by the year 2019. This is not a good sign. It looks like Mars is getting farther away! To this I add that as we approach the millennium, the only correct prediction from the 1968 sci-fi classic 2001: A Space Odyssey is that things can go wrong.
Space is vast and empty beyond all earthly measure. When Hollywood shows a starship cruising through the galaxy, they typically indicate this fact with points of light (stars) drifting past at a rate of one or two per second. The distance between stars in the galaxy is so vast, that for these ships to move as indicated would require speeds up to five-hundred-million times faster than the speed of light.
The Moon is far when compared with where you might go in a jet airplane, but it sits at the tip of our noses compared with anything else in the universe. If the Earth were the size of a basketball, the Moon would be the size of a softball some ten paces away—the farthest we have ever sent people into space. On this scale, Mars (at its closest) is a mile away. Pluto is 100 miles away. And the nearest star to the Sun is a half million miles away.
Let's assume money is no object. In this pretend-future, our noble quest to discover new places and uncover scientific truths has become as effective as war at drumming up funds. If a spaceship managed to sustain Earth's escape speed of seven miles per second, a trip to the nearest star would last a long-and-boring 100,000 years. Too long, you say? Energy increases as the square of your speed, if you want to double your speed you must invest four times as much energy. A tripling of your speed requires nine times as much energy. No problem. Let's just assemble some clever engineers who will build us a space ship that can summon as much energy as we want.
How about a spaceship that travels as fast as Helios B, the U.S.-German solar probe that was the fastest-ever unmanned space probe. Launched in 1976, it was clocked at nearly 42 miles per second (150,000 miles per hour) as it accelerated toward the Sun. (Note that this is only one-fiftieth of one percent of the speed of light.) This craft would cut the travel time to the nearest star down to a mere 15,000 years—three times the length of human recorded history.
What we really want is a spaceship that can travel near the speed of light. How, about ninety-nine percent the speed of light? All you would need is seven hundred million times the energy that thrust the Apollo astronauts on their way to the Moon. Actually, that's what you would need if the universe were not described by Einstein's special theory of relativity. As predicted by Einstein, however, while your speed increases, so too does your mass, which forces you to spend even more energy than previously figured to accelerate your space ship near the speed of light. A back-of-the-envelope calculation shows that you would need at least ten billion times as much energy used for our Moon voyages.
No problem. These are very clever engineers. But now we learn that the nearest star that is known to have planets is not Proxima Centauri, the nearest star, but one that is about fifteen light-years away. While traveling ninety-nine percent of the speed of light, Einstein's special relativity shows that you will age at only ten percent the pace of everybody back on Earth, so the round trip for you will last not thirty years, but about three. On Earth, however, thirty years actually does pass by and everybody has forgotten about you.
The distance to the Moon is ten-million times farther than the distance flown by the original Wright Flyer of the Wright brothers. But the Wright Brothers were two guys with a garage. Apollo 11, the first moon landing, was two guys with two hundred billion dollars and ten thousand scientists and engineers and the mandate of a beloved, assassinated president. These are not comparable achievements. The cost and effort of space travel is a consequence of the fact that space is supremely hostile to life. You might think that the early explorers had it bad too. Consider the Gonzalo Pizarro's 1540 expedition from Quito east across Peru in search of the fabled land of Oriental Spices. In the William H. Prescott account of this ill-fated adventure in the classic History of the Conquest of Peru, the oppressive terrain and the hostile natives ultimately led to the death of half his expedition party of more than 4,000. Prescott describes the state of the expedition party a year into the journey:
At every step of their way, they were obliged to hew open a passage with their axes, while their garments, rotting from the effects of the drenching rains to which they had been exposed, caught in every bush and bramble, and hung about them in shreds. Their provisions spoiled by the weather, had long since failed, and the live stock which they had taken with them had either been consumed or made their escape in the woods and mountain passes. They had set out with nearly a thousand dogs, many of them of the ferocious breed used in hunting down the unfortunate natives. These they now gladly killed, but their miserable carcasses burnished a lean banquet for the famished travelers.
What happens next has no meaningful counterpart in space travel. On the brink of abandoning all hope, Pizarro and his men build from scratch a boat large enough to take half the remaining men, the weakest half, along the Napo river in search of food and supplies. Prescott describes the construction:
The forests furnished him with timber; the shoes of the horses which had died on the road or had been slaughtered for food, were converted into nails; gum distilled from the trees took the place of pitch; and the tattered garments of the soldiers supplied a substitute for oakum...At the end of two months, a brigantine was completed, rudely put together, but strong and of sufficient burden to carry half the company.
Pizarro transferred command of the makeshift boat to Francisco de Orellana, a cavalier from Truxillo while he stayed behind to wait. After weeks of no return, Pizarro gives up on Orellana and returns to the town of Quito, taking yet another year for the journey. Pizarro later learns that Orellana successfully navigated his boat down the Napo River to the Amazon, and with no intent on returning for Pizarro, continued along the Amazon until he emerged in the Atlantic. Orellana and his men then sail their way to Cuba, where they subsequently find safe transport back to Spain.
There is a profound lesson in this story, first called to my attention by Steve Napear, Deputy Director of the San Diego Supercomputing Center. When nearly all hope was lost, the members of the expedition built a boat, exited the continent along the Amazon, and traveled back to Spain via Cuba. Suppose one of our spacecraft with a ship-load of astronauts crash-lands on a distant hostile planet—the astronauts survive, but the spacecraft is totaled. Hostile planets tend to be considerably more oppressive than hostile natives. The planet might not have air. And if it does have air, the air may be poisonous. And if the air is not poisonous, then the atmospheric pressure may be one hundred times higher than on Earth. If the air is fine, then the planet may be at 200 degrees below zero. Or 500 degrees above zero. None of these conditions bode well for our astronaut explorers, but perhaps they can survive for a while on their reserve life-support system. In the spirit of our sixteenth-century Spanish explorers, all they would need to do is mine the planet for raw materials and build another spacecraft from scratch, along with its controlling computers (using whatever spare parts are musterable from the crash site.) They would also need to build a factory that manufactures rocket fuel. When finished, they would simply launch themselves back into space and fly back home.
I needn't dwell on the absurdity of this scenario.
Perhaps what we really need is a genetically engineered life form that can survive the stress of space and still conduct scientific experiments. Actually, such
life forms have already been engineered. They are called robots. You don't have to feed them . They don't need life support. And most important, they won't get upset if you don't bring them back. People, however, generally want to breathe, eat, and eventually come home.
It's probably true that no city has ever held a ticker-tape parade for a robot. But it's probably also true that no city has ever held a ticker-tape parade for an astronaut who was not the first to do something or go somewhere. Can you name the two Apollo 16 astronauts who walked on the Moon? Probably not. It was the second-to-last moon mission. But I'd bet you have a favorite picture of the cosmos taken by the orbiting robot known as the Hubble Space Telescope. I'd bet you remember the images from the Mars robotic lander Pathfinder and its deployed rover Sojourner, which went
six-wheeling across the Martian terrain. I'd further bet that you remember the Voyager images of the Jovian planets and their zoo of moons from the early 1980s.
In the absence of a few hundred billion dollars in travel money, and in the presence of the hostile cosmic conditions, what we need is not wishful thinking and science-fiction rhetoric inspired by a shallow reading of the history of exploration. What we need, and must wait for, is a breakthrough in our scientific understanding of the structure of the universe so that we might exploit such shortcuts through the space-time continuum as worm holes that connect one part of the cosmos to another. Then, once again, reality will become stranger than fiction.
Neil deGrasse Tyson, an astrophysicist, is the Frederick P. Rose Director of New York City’s Hayden Planetarium and a visiting research scientist at Princeton University.