Life on the Moon has been thoroughly described in science fiction stories, and there's no point in my doing it again. For an excellent book on the uses of the Moon, see Neil Rusczic's WHERE THE WINDS SLEEP. The lunar colony is, after all, a complex cave with lower gravity than Earth's.
Zero gravity is another story. Any long trip through space will have to be made by Hohmann transfer orbits, which use the lowest amounts of fuel, but which also take a lot of time: about a year and a half to get from Earth to Ceres, for example. Even a trip to Mars takes something over eight months.
It's possible to design ships so that they have artificial spin gravity, of course. There are some problems with that, and since many of my readers like to do their own preliminary design work, I'll give the equations here. Readers uninterested in the details can skip the next paragraphs.
Newton's First Law says that an object in inertial space wants to continue at the same velocity (that's both direction and speed) forever. It takes a
force
to
make any change in velocity. Gravity serves as the force to get moving objects into an orbit, exactly as the string serves to provide a force when you whirl a weight around on the end of a rope. In both cases the object wants always to go in a straight line, which is to say it wants always to go off in a direction tangent to its circle of motion. It does
not
"fly out from the center," although the result, as seen by an observer
moving with the system,
looks that way.
Thus if you stand on a moving carousel it feels as if you're trying to fly out radially from the center, and in free space the "floor" of a centrifuge will be "down." If you let go of an object it will experience an acceleration relative to the carousel, and for those inside the system that looks very much like gravity.
The acceleration is:
(equation one)
a
R
= w
2
R
The acceleration is: (equation one) where we have used w in place of the Greek letter "omega" as a kindness to typesetters. R is the radius of the rotation, and w is the rate of rotation in
radians
per second. There are 2 pi radians in a circle, so if you multiply radians per second by 360 and divide by 2 pi, you get degrees per second. Multiply the result by 60 and you have degrees per minute; divide the end result by 360 and you have revolution per minute, (equation two)
Going the other way,
rpm x 2π / 60 = radians/second.
Since force equals mass times acceleration (the most basic equation in Newtonian physics), it's easy to see that the force exerted by (and the tension on) the cord when you whirl a weight on a rope is, (equation three)
F = ma = m w
2
R
where m is the mass of the whirled object. This is the centripetal force, and it's real. If the cord were suddenly cut, the object would fly away in a straight line tangential to the radius of rotation. The velocity it would have is (equation four)
v
T
= R w
and we're finished with the math.
Now we're ready to design a ship, and immediately we see the problem. The shorter the radius, the faster you have to spin the ship to get a given artificial gravity. Now it happens that the faster the spin, the worse the Coriolis effect. If the radius of rotation is long compared to, say, the height of a man, there's no big problem, but as it gets short there can be devastating physiological effects.
It seems silly enough now that we've put men into orbit, but at one time planners seriously thought space stations and ships needed something like a full Earth gravity to keep humans alive, and we did plans for such things. If you try for a full g in a ship of small radius, the Coriolis effect is so severe that a water-hammer is set up in the circulatory system. A man could kill himself of stroke simply by turning his head rapidly in the wrong direction.
We now know that humans don't need a full gravity, and we suspect that a tenth might be enough forever. That can be arranged for a long trip if we send ships in multiples: join the ships with long cables and rotate them around each other. That's also very inefficient, of course: we have to duplicate life support systems, etc. There's less dead weight in one large ship than in many small ones.
Also, the tension in the cable can get quite high, as you can find from equation three.
Maybe we don't need any gravity at all? True, the first Apollo astronauts came out much the worse for wear, and so did the first Skylab crew; but the interesting part is that the longer men stay in space, the better they adapt to it. The Skylab Four (third manned Skylab, in NASA's screwy counting system) crew came out in much better shape than did the second crew. Okay, in retrospect maybe it's not so surprising that the longer you stay in zero-g the better you adapt, but it did in fact surprise a number of space physiologists who had thought that a month of zero-g might be beyond human endurance.
* * *
A long trip in no gravity can be interesting. The accounts of the Skylab experience make for fascinating reading. They also show the need for experience in space. There were some terrible design faults in Skylab.
For instance: Skylab was the first space vehicle in which the astronauts ate at a table using spoons and forks, rather than squeezing everything from tubes and baggies. Their table was a mere pedestal that supported their food trays. There were seats, but those were seldom used: to stay in a sitting position in zero gravity requires that you bend at the waist and hold yourself bent. It puts a constant and severe strain on stomach muscles, and in fact those were the only muscles better developed when the crew landed than when they went up. The real problem, though, was the table itself.
It didn't do a very good job of holding the trays, to begin with. They tray lids were held down with what Lousma called "the most miserable latch that's ever been designed in the history of mankind or maybe before." Pogue said of the table, "I wouldn't want the people that designed that table to do anything else. . ."
Despite their attempt at normal meals, the Skylab astronauts never had much appetite. Part of that is due to less need for food: you're not working very hard in zero gravity. Also, the thinner air (kept at low pressure to avoid strain in the pressure bulkheads and such) doesn't transmit food smells very well. Everyone had head congestion, caused by pooling of body liquids in the torso and head, so nothing tasted very good anyway. However, they did eat.
With food in plastic bags (which were inside cans, which were supposed to be fitted into the trays on the table, but which often drifted loose because the cans didn't fit the trays very well) they could use spoons and forks. Eating in zero-g takes practice. You have to be careful to bring the spoon in a smooth arc from tray to mouth. Any hesitation and the food travels on in a straight line, probably into your eye.
The Skylab astronauts were almost constantly dehydrated, but never felt thirsty. The human organism is designed with a number of mechanisms to get the blood back out of the legs and up into the torso. So long as the legs are below the body those work fine; but when there's no such thing as "below," the blood gets into the torso and stays there. With all that fluid pooled in the abdominal region the thirst mechanisms don't work well, and the Sty-lab crews had to train themselves to take a quick drink every time they passed the water fountain. The fountain wasn't designed very well either, with metal nozzles that would have been easy to use on the ground, but which could chip teeth when not under control The fountain buttons were so stiff that when a crewman pushed one, the button didn't go down, the crewman went up, unless he was holding onto something.
Of course it's hard to blame the designers. Until Skylab nobody had any real experience at designing living quarters for space. Apollo was a ship, and there wasn't much room to move around in it. The crew mission was to get somewhere and come back, not live in space. Gemini was worse, and Mercury was downright primitive: when we stuffed people into the Mercury capsules they were fitted in precisely, without even room to straighten arms and legs. John Glenn once said you don't ride a Mercury capsule, you wear it.
And prior to Mercury we hadn't any real experience at all. We flew transport planes in parabolic courses that might give as much as 30 seconds of almost-zero-g, and that was all we knew. I will not soon forget some of our early low-g experiments. Some genius wanted to know how a cat oriented: visual cues, or a gravity sensor? The obvious way to find out was to take a cat up in an airplane, fly the plane in a parabolic orbit, and observe the cat during the short period of zero-g.
It made sense. Maybe. It didn't make enough that anyone would authorize a large airplane for the experiment, so a camera was mounted in a small fighter (perhaps a T-bird; I forget), and the cat was carried along in the pilot's lap. A movie was made of the whole run.
The film, I fear, doesn't tell us how a cat orients. It shows the pilot frantically trying to tear the cat off his arm, and the cat just as violently resisting. Eventually the cat was broken free and let go in mid-air, where it seemed magically (teleportation? or not really zero gravity in the plane? no one knows) to move, rapidly, straight back to the pilot, claws outstretched. This time there was no tearing it loose at all. The only thing I learned from the film is that cats (or this one, anyway) don't like zero gravity, and think human beings are the obvious point of stability to cling to. . .
Future dwellers in zero gravity won't have so much to worry about The nine Skylab crewmen dictated hours and hours of notes on design improvement, this time not theory, but well founded in experience. The next space station (if we get one) should be a lot more comfortable.
And life in zero gravity, the Skylab crew tells us, is fun. Almost no one simply went from one place to another. It was impossible to resist turning somersaults, flips, ballet twirls, just for the sheer hell of it. Most of us saw the TV demonstrations: waterballs floating in air, tiny planetary systems that could be set in motion by blowing gently on them. There were other lovely experiments, and just plain play, all described beautifully in a book I recommend, Henry S. F. Cooper's A HOUSE IN SPACE (Holt, Rinehart and Winston, 1976).
* * *
Then there are the asteroids, which are different again. They have
some
gravity, but not much, making them different entirely. Things do fall, but not rapidly. On Ceres, for example, you can jump about 125 feet into the air (oops! into space) and it takes over a minute for the round trip. On very small rocks you can jump clean off, never to return. There are dangers on intermediate sizes, too, ones too large to jump from.
For example, some respectable asteroids, several kilometers in diameter, have such low gravity that if you jumped hard you'd not leave it forever, but it would take hours to go up and come back down again. You could easily run out of air.
And so forth. I've tried to describe some aspects of life in the asteroid belt in my stories 'Tinker" and "Bind Your Sons to Exile," and other SF writers have written hundreds of such. It will be interesting to see how well we've done: despite all the SF stories about zero-gravity (and a number of SF fans among the engineers who designed Skylab), there have been a lot of surprises when we actually got up there.
But—no one questions that we can go. Man can live in space, and by doing so can save the Earth. We have only to want to go.
In the past ten years we have learned more about our Earth and our solar system than did all of mankind through all our history. In the next twenty years we will again double our knowledge. This is a unique generation, a generation of wonder; for no other will ever have such an experience.
It is not that we are more intelligent than our ancestors, for we are not; in some ways we act less intelligently than they. But we have finally arrived at the equipment that lets us learn about our universe. Without deep submersibles we could never have learned about the ocean floors. Without spacecraft we could never have got a close look at other planets—and thus had data for comparison to increase our understanding of Earth itself.
The information curve has never been steeper; in ten years we have learned as much as mankind did in the previous three million. Even that time span changes like dreams. Richard Leakey, Director of the Kenya National Museum, believes he has a skull, #1407, that dates
genus homo
to three million years—and now states that he has a new find, #1805. "If 1407 bothers you, 1805 will horrify you," he told an audience at the 1974 AAAS meeting.
The computer revolution proceeds so rapidly that I own a computer more powerful than the world's best of only 10 years ago; any citizen can now have access to more computing power than was available to the most heavily funded project of the 60's.
Microcircuits let the deaf hear and the blind see, the dumb speak and the lame walk.
The science fiction of the 60's is outdated, gone, destroyed by science; although writers used the best information available at the time, the space probes have sent our old Mare and Venus into the dustbin. But if the science fiction writers have been embarrassed, what of the scientists on whose theories the better writers have relied?
'The spacecraft hang like swords of Damocles over the heads of the astronomers," Carl Sagan has said. "And on their faces you can see a strange amalgam of fear and hope as the probes approach their destinations."
Before 1980 we will have a close look at Saturn. A few years ago we knew nothing of the rings. Now we have bounced radar off them, to find that they're not dust, but chunks several meters in diameter. Within a few years Pioneer will give us an even closer look at them. Meanwhile we find there are rings around Uranus; Saturn is no longer alone in ringed splendor.
We have discovered the Van Allen Belts and the solar wind. Biologists have made giant strides toward cracking the genetic codes. Skylab has shown the way to new materials previously
undreamed
of
.
Soon the Shuttle will take a large telescope to space: a telescope capable of finding terrestrial-sized planets circling the nearer stars.