There were five more moon landings after Apollo 11. Each one landed at a spot geologists thought looked interesting, where the rock formations might contain new information about the structure of the moon. The last three flights carried a dune buggy, the Lunar Rover, a lightweight battery-powered car that enabled the astronauts to travel several miles from their point of landing.
Most of the rocks brought back from the moon were basalt, a dark, smooth stone formed by the cooling of molten lava. These rocks have helped scientists understand how the moon was formed, but doubts still persist. The most popular theory is that, about four billion years ago, a huge object collided with the earth, and the moon was formed from the resulting debris.
After Apollo 17, the last flight to the moon, some of the Apollo hardware was used in earth orbit. The upper stage of the Saturn V moon rocket was converted into living quarters for three astronauts. About the size of a three-bedroom house, this space station, called Skylab, orbited the earth for six years on a journey that covered nearly one billion miles. Three crews lived aboard Skylab, the longest for eighty-four days. The nine men spent their time doing experiments that increased our knowledge of the sun, the surface of the earth, and the human body.
The final flight of the Apollo series took place in 1975, when a command module made a rendezvous with a Soviet Soyuz spacecraft. Hooked together in earth orbit, the group of three astronauts and two cosmonauts got along fine. Since the Soviet Union and the United States were not friendly at that time, this flight showed that people with something in common, in this case flying, can quickly become friends, even if their governments have different points of view.
For nearly six years, between 1975 and 1981, no American astronauts flew in space. Then my old friend John Young, along with Bob Crippen, made the first flight of a strange new machine, the Space Shuttle. It was so named because it was designed to shuttle back and forth between Cape Canaveral and earth orbit. Previously, all spacecraft had been designed to fly only once and then be retired to a museum. But the Shuttle, half spacecraft and half airplane, can be used over and over again. It is launched vertically, attached to rockets, but it has wings and can glide back to a runway and land like an airplane.
To date, the Shuttle has flown about sixty times, all but one of the flights successful. In 1986, the Shuttle Challenger was destroyed about a minute after liftoff, when a hole burned through the side of a solid rocket booster, causing a gigantic explosion. All seven crew members died, including Christa McAuliffe, a high-school teacher from Concord, New Hampshire. Christa was to have been the first teacher in space and was going to conduct televised classes from the Challenger. The seven deaths were the first since Grissom, White, and Chaffee perished in a launchpad fire nearly twenty years previously. In both cases, the losses came as a shock to NASA and the American people. The Shuttle was grounded for nearly three years while NASA made changes to improve its safety.
Besides killing seven people, the Shuttle has been a disappointment in that it has been more expensive to operate than its fans had hoped. On the other hand, it has been very useful, not only in putting satellites into orbit, but also in bringing them back to earth for repair or replacement.
It seems to me that the idea behind the Shuttle is a good one: a space machine that can be used over and over again. Even better than the Shuttle, which must be launched with rockets, would be an aerospace plane that could take off from a runway, like a jetliner, and fly up into orbit by itself. Such a machine would need two kinds of engines. For takeoff and climb, it would need advanced jet engines that sucked in air, mixed it with fuel, and burned the mixture. As it climbed above the atmosphere and the air ran out, the aerospace plane would have to switch to rocket engines. These motors would burn fuel mixed with oxygen carried in separate tanks.
The problem so far with such an aerospace plane is that, in order to get into orbit, the plane must fly very fast through the upper atmosphere. So fast, in fact, that the friction of the air entering the engines would produce enough heat to melt the engines. Melting your engines is not a good way to travel! But people in laboratories are working on new materials, such as ceramic or carbon compounds, that could withstand such high temperatures without melting.
The next use of the Shuttle, NASA hopes, will be to carry pieces of a space station to earth orbit, where astronauts will assemble them. Named Freedom, this small space station will be an international effort, with help from the Europeans, Japanese, Canadians, and Russians. It is being designed so that four people will be able to stay aboard for long periods of time, working in a laboratory, exploring ideas that involve gravity or the lack of it. For example, on earth, mixing two or more molten metals is difficult because the light ones float to the top while the heavy ones sink to the bottom. Aboard Freedom, not only could there be perfect mixing, but gas bubbles could be distributed evenly throughout, making a kind of Swiss cheese, or foam-metal alloy. Such a foam metal would be light but very strong. But would it be practical to manufacture anything in orbit? How much extra would it cost to haul it back and forth? Would there be a market for such expensive products? Freedom will permit exploration of such ideas.
Beyond Freedom, the twenty-first century may see much larger objects in earth orbit. Perhaps even a small town could be assembled piece by piece. It could include facilities for food production, health care, manufacturing, leisure activities—just as a town on earth can do. The main difference, of course, is that this tiny town would be circling the earth every two hours or so. For over half this time, it would be in direct sunlight, and the energy coming from the sun could be put to use on a regular schedule, without having to worry about whether it was a cloudy day or not. All clouds would be far below. The sun’s energy could be used to generate electricity, and to heat the town, and to grow crops. Solar energy is not only abundant (and free) but it is also clean, unlike other popular sources, such as coal. One big problem for this orbital town would be water. At first, water would have to be brought from earth, and then it would have to be recycled so that it could be used over and over again. The town would be sealed against the vacuum of space, and very little air or water would be allowed to escape. They would be purified and used over again. The animals and people in the town, as they breathed, would use up oxygen and produce carbon dioxide. The plants grown for food would do just the opposite (using carbon dioxide and producing oxygen), keeping the entire system in balance. Using the same water and air over and over again sounds terribly complicated, and a little bit messy, but it’s really not such an outlandish idea. After all, that is what happens here on earth. For example, when dirty dishwater goes down the drain and into the sewer system, it enters a complicated purification process which finds the water ending up in the ocean, where the sun’s heat causes it to evaporate and,enter the atmosphere, where it cools and falls back down onto the land as rain. Then the water works its way into a stream and then a reservoir and finally is pumped back into the sink to be used as dishwater once again.
Another problem, but also a pleasure, for our orbital town would be weightlessness. Weightlessness can be a lot of fun, but in many ways it would be a dreadful nuisance if everything in our town had to be tied down to prevent its floating off somewhere. Especially a big thing, like a cow. Maybe it would be better not to include cows but instead rely on other food sources, such as shrimp floating in large plastic bags full of water. Another solution would be to do away with weightlessness. How? It’s not possible to restore gravity in space, but it is possible to replace it with something that feels similar—centrifugal force. If we designed our orbital town to spin, there would be weightlessness only at the center. On the edges the inhabitants would be plastered up against the walls with a force that would change as the rotation rate changed. By picking the right rotation rate, we could be as light or as heavy as we chose. But wouldn’t we get dizzy? Tests have shown that if you are turning in a large enough circle (in this case, if the town were big enough), you wouldn’t get dizzy. T
he center of the town could be saved for a weightless recreation center, where all sorts of new games could be invented. How about weightless basketball, where you score two points for a ball that went up through the hoop as well as down through it? But how would you make your shots curve through the air, with no gravity to pull at the ball?
Another use for the center of a rotating town would be a manufacturing facility. Gravity hinders the manufacture of some items, like crystals used in electronics, and much bigger and better crystals can be formed in weightlessness. Another solution might be to build a space station, or town, in two parts: one rotating and the other stationary. The inhabitants could pass back and forth from one to the other, depending on which activities were involved. Personally, I think about an hour a day of weightlessness would be great fun, very restful, and probably good for your body.
If the idea of a small town in earth orbit worked out, the next step might be something much, much larger—more like a new country in space. Again, such a country would have to be put together piece by piece, and its location would have to be chosen with care. One convenient spot would be at a point where the pull of the earth, moon, and sun balance each other, so that the new country would stay there indefinitely. There are a couple of such locations in our solar system. They are called libration points, from the Latin word for balance, so we could properly name our new country Libra. Libra would be created by hauling material from the earth and the moon. Moon material would be used wherever possible, because the moon’s lower gravity would make the trip less costly. Analysis of the Apollo lunar rocks shows that they contain plenty of metals and silica, from which glass is made, so that Libra would be built mostly of metal (such as aluminum and titanium) and glass. There is no water on the moon, but plenty of oxygen is contained in moon rocks, so only hydrogen need be brought from earth to form water (H2O). Fortunately, hydrogen is a lot lighter than oxygen, so that almost 90 percent of the weight of the water would have come from the moon.
Two very important elements in our lives on earth are carbon and nitrogen, and we would also need them on Libra. They are found in all living plants and animals. Carbon joins with oxygen to form carbon dioxide, which plants need to live, and nitrogen is in the air we breathe and the fertilizer we need to grow crops. Unfortunately, neither nitrogen nor carbon is plentiful on the moon, so Libra’s supply would have to come from the earth or some other place. Perhaps a trip from Libra to one of the asteroids would bring back materials rich in carbon and nitrogen.
Life on Libra could be as interesting and varied as life on earth. Rotating slowly in eternal sunshine, Libra would have abundant solar energy, so much, in fact, that some could be converted into microwaves and beamed back to earth. Libra not only could help earth by providing clean solar energy, but could also relieve overcrowding on earth by giving people someplace else to live. At first, Librans would consider themselves earth people, but after a while they would probably begin to think of themselves as slightly different. In time, they would truly become different, as their bodies adapted to their new environment. In the reduced gravity of Libra, they would not need the heavy muscles of earth people, so children growing up on Libra would tend to be slimmer, (especially in the legs) than if they had been living on earth. Their bodies would also become less tolerant of heat and cold, for Libra would not experience the extremes of temperature that we find in Alaskan winters or Arizona summers. If they visited earth, Librans would also find windstorms most startling and unpleasant, compared to the gentle air currents they knew. As a matter of fact, they would probably find the raw uncontrolled conditions on earth too primitive for their taste. (“A nice place to visit, but I certainly wouldn’t want to live there!”) Since harmful organisms (poison-ivy plants, jellyfish, measles, certain germs, etc.) would have been prevented from entering Libra, a trip to earth for Librans could be dangerous indeed, because their bodies would be more susceptible to earth diseases. Librans would have to worry about dying from earth diseases, or carrying them back to Libra and infecting others. It might be necessary for visiting Librans to wear germ-tight space suits, just as we Apollo astronauts did.
Apollo set a precedent for the future in another interesting way. It was probably the only major human expedition in which no weapons were carried. In similar fashion, no weapons would be permitted on Libra, and Librans simply would not be able to understand why earth people continued to shoot one another. On Libra, if people felt hostile, they would be urged to put their energies into athletic contests or other competitive events, or simply to let off steam by going flying. Libran sports flying machines would be powered by muscles. On earth, a few people have been able to build muscle-powered airplanes which can overcome our heavy gravity for a short time, but on Libra it would be possible for a muscle-powered machine to stay aloft indefinitely. The machines would be a cross between a bicycle and a glider, a winged bicycle with a propeller. The flier’s legs would provide the power to keep the propeller turning, while his hands would control elevators, ailerons, and rudders. With a little practice, a Libran could learn to soar and to wheel to his heart’s content, both for recreation and as a practical method of traveling across his miniature country. Life on Libra would be pleasant.
Life could also be pleasant on the moon. With one sixth earth’s gravity, the moon would be a comfortable place to live. Just as with Libra, a colony on the moon would have to be sealed to keep its atmosphere from escaping into the vacuum of space. But a colony could easily be built underneath a dome. Probably most of it would be underground, to protect people from radiation. The back side of the moon—the side away from earth—would be a great spot for an observatory. On earth, astronomers are hindered by electric lights and radio signals that pollute the night sky, but on the back side of the moon astronomers could view the universe without interference.
Venturing beyond the moon, we can travel toward the sun or away from it. Two planets are nearer to the sun than earth, but neither Mercury nor Venus is fit for humans. Both are way too hot. Mercury has almost no atmosphere and a daytime surface temperature that would melt lead. Venus has a very dense but unbreathable atmosphere, and a human on its surface would be crushed by the pressure.
As we move out away from the sun, our nearest neighbor is Mars. It, not the moon, is the place I wanted to go as a child, and I have never lost my interest in it.
Mars is in an almost circular orbit around the sun, at a distance of about 142 million miles. The earth’s orbit is closer to the sun, at approximately 93 million miles.
Since the earth and Mars orbit the sun independent of each other, there are times when the two are as close together as 49 million miles (142 minus 93) or as far away as 235 million miles (142 plus 93).
Because the orbits of both the earth and Mars are slightly lopsided, these numbers aren’t exact (once in a dozen years or so, earth and Mars actually get within 35 million miles of each other). To travel from earth to Mars, you must aim not at Mars but at the point in the sky where Mars will be on your arrival. We did the same thing with the moon on Apollo, but in that case we had to lead the moon only by three days’ worth. In the case of Mars, the trip can take as long as nine months, following a curving arc approximately 460 million miles long. The situation might look like this:
The dotted line represents the 460-million-mile journey. To travel a shorter are requires less time but more fuel. Upon our arrival at Mars, the earth would be approximately 200 million miles away, which means that radio signals (traveling at the speed of light) would take nearly twenty minutes to make the trip, one way. Therefore, it would take our Mars astronauts forty minutes to ask for, and receive, any advice from earth. That means they had better be able to solve most problems themselves, especially problems involving the Mars landing itself, where the situation might change drastically, minute by minute. On the other hand, just as in the Apollo program, the big earth-based computers would be helpful in keeping our Mars spacecraft on course, and avoiding obstacles along the way, such
as Mars’ two moons, Phobos and Deimos.
Once safely on the surface of Mars, what would our astronauts find? No one can say for sure, and that is part of the reason for going. Mars has fascinated people for centuries, and they have made countless wild guesses about it. Called the Red Planet by early astronomers, Mars is actually sandy orange in color. Its diameter is about half the earth’s, its surface desert-like, marked by huge mountains and deep canyons. One mountain, a volcano called Olympus Mons, is fifteen miles high and three hundred miles across. A canyon named Valles Marineris is 20,000 feet deep—three times as deep as Arizona’s Grand Canyon. Mars has days and nights of about the same length as ours, and seasons which last twice as long. At night the temperature is bitter cold, as much as two hundred degrees below zero, but at noontime near the equator it can reach a comfortable sixty-five degrees. Mars has an atmosphere, but a very thin one, and it is composed mostly of carbon dioxide, so astronauts would have to bring their own oxygen to breathe. Very high winds have been recorded on the surface of Mars, and sometimes nearly the entire surface of the planet is obscured by blowing dust. However, the atmosphere is so thin that an astronaut would not have to worry about being blown over: a fierce hurricane on Mars would push against him with about the same force as a gentle breeze on earth. Because Mars is smaller than earth, Mars’ gravity is not as strong. In fact, it is only one third that of earth, so that a typical male astronaut would weigh around sixty pounds and a female astronaut forty pounds. That might be a good argument for an all-female crew. It wouldn’t take as much fuel to lift the lighter person from the surface, and besides, during the voyage a small woman probably wouldn’t eat as much food, drink as much water, or breathe as much oxygen as a large man.
Flying to the Moon Page 13