“He’s pretty inventive all right,” Barbary said.
“I do not wish to ask a rude question,” one of the beings said, “But why is the small person permitted to operate the vehicle? The controls have not been adapted to him.”
“Um, that’s a long story,” Barbary said.
“We love long stories. They help pass the time of travel between the stars.”
Heather drew herself back from her troubled reverie. “How long have you been traveling?” she asked.
“About a billion of your years.”
“Your people have had space travel for a billion years?”
“Oh, no, we have had space travel for a time an order of magnitude longer: for ten billion of your years. I thought you meant to ask how long we here had been exploring the stars.
“Ten billion years of star travel,” Heather said. “You must be the oldest intelligent species in the universe.”
“We have not found any older, but we search, and hope.”
Heather stared at the beings in awe. “No wonder you like long stories.” She tried to smile. “Barbary, you can show them magic tricks.”
“Magic? You have begun to use technology… yet you believe in magic?”
“Not real magic, that’s just what it’s called.” Barbary tried to think of a quick way to explain, but gave up. “Um, it’s another long story.”
“How excellent,” the being said. “We will look forward to hearing it.”
“I’m Barbary,” Barbary said, remembering her manners, “and this is Heather, my sister. And the — the small person is Mickey.”
“We do not have names, as you know them,” one of the beings said. “Each of us forms impressions of all others, and refers to the individual by the position in the image.”
“That sounds complicated,” Barbary said
“Not as complicated as recalling so many individual designations,” the crystal being said. “Without a pattern, how do you tell each other apart?”
Barbary, who had been trying to fix in her mind the variations between the beings so she could remember each one’s name — if they had had names to tell her — looked over at Heather. They both burst out laughing.
The delicate filaments on each being quivered and twined, and multitudes of wind-chime voices rang. At first Barbary wondered if she had hurt their feelings by laughing, and then she believed the beings were laughing along with her.
“Another ship is approaching,” the musical voice said. “The beings within appear to be… quite perturbed.”
“They don’t know what’s happened to us,” Heather said. “They probably think we’ve been swallowed up.”
“As indeed you have.”
“To be eaten, I mean.”
“No. We do not ingest organic molecules. Will you speak with them?”
“Can we? Please?” Heather said. “My father will be worried.”
“Should we?” Barbary said.
“Of course we should!” Heather said. “What do you mean?”
“Maybe if they worry about us a little more, they won’t be so mad at us when we go back.”
“If they’re going to be mad, they’re going to be mad,” Heather said. “I don’t want Yoshi to be worried anymore and I don’t want anybody out there to do anything that the other beings might think they need to be shown is futile.”
“Okay,” Barbary said.
“Would you like to speak to them now?”
“Yes, please,” Heather said.
“They will hear you.”
Barbary saw no radio equipment, no change in the chamber to indicate a transmitter.
“Hi, this is Heather,” Heather said to the air.
“Heather!” Yoshi said. “Are you all right? What about Barbary?”
“I’m okay.”
“So am I,” Barbary said. “And so is Mick.”
“What’s happening in there?” Jeanne asked.
Barbary looked at Heather, who gazed back at her and smiled.
“We’re with the — the beings in the starship,” Barbary said. “They’re bringing us home.”
Artificial Gravity: Which Way Is Up?
John G. Cramer
The space station doughnut of 2001 and the O’Neill space-habitat cylinder have become part of the furniture of science fiction, so much so that we take spin-generated artificial gravity to be interchangeable with the Earth-normal variety in which we live. But there are differences that would be quite apparent to anyone living in the spin-generated variety. The subject of this AV column is an exploration of the differences between the “natural” gravity of Earth and the “artificial” gravity of a rotating space station.
My interest in the physics of space station gravity developed because last year Vonda McIntyre was writing a book with a space station setting, and she asked my advice. The book, Barbary, is about a teenager who leaves Earth to live in a space station with spin-generated gravity. I helped Vonda in a very minor way by identifying the physical effects that the heroine would experience in that environment. What’s it like to ride an elevator in a space station? How would a ball game look if it were played there? If you woke up in a strange location, what simple tests would tell if you were in a rotating space station rather than at rest on the ground? And so on... I found that there are some interesting side-effects of artificial gravity, perhaps well known to NASA experts but obscure to the rest of us. And I was surprised to find that some recent SF hasn’t been too accurate in describing the space habitat environment.
Looking at the world from a rotating vantage point (be it a merry-go-round or a space station) is odd and confusing. So let’s start with a simple concrete example. Suppose that we are on a doughnut space station, about half the size of the big one in 2001, providing living and working space at earth-normal gravity (1 g) for about 150 people. Such a station might take the form of a “wheel” 15 m wide and 160 m in diameter, rotating on its axis so that it makes a full rotation every 18 seconds. Because the floor of the space station rotates through its full circumference in this time, it has a speed (called the tangential velocity because the velocity lies along the tangent of the circle of travel) of 27.9 m/s. A note here on scaling to other sizes: If the station had 4 times this diameter, the rotation period to give 1 g of artificial gravity would be twice as long and the speed of the floor would be twice as large.
Let’s do a simple “Mr. Science” experiment in this space station. Place a phonograph turntable on floor and use it to spin a cake pan filled with water. Let’s use a cake pan 40 cm in diameter and spin it at the 78 RPM setting of the turntable. The outer edges of the spinning cake pan will be moving at a speed of 1.6 m/s with respect to the floor. Therefore, the edge of the cake pan towards one outside wall of the station is traveling at an absolute speed of (27.9+1.6)=29.5 m/s, while the opposite edge of the pan has a speed of (27.9-1.6)=26.3 m/s. The pull of artificial gravity depends on the square of this tangential speed, so the “fast” edge experiences an increased pull of 1.12 g, while the pull on the “slow” edge decreases to 0.89 g. The water in the pan will tend to tilt, climbing higher on the slow edge and dropping lower on the fast edge. A spinning gyroscope would tumble in the same way, making the toy top a poor gift for a space child. And so we see different physical effects in the artificial gravity of a space station than would be found if the same experiments were performed in the “natural” gravity of Earth.
This simple experiment has an interesting implication for the psycho-physiology of human balance. Our equilibrium and our perception of vertical orientation come from the interaction of the fluid in the semicircular canals of our inner ears with the nerve fibers there. The vertigo experienced during and after spinning in an amusement park ride demonstrates what happens when this mechanism is disturbed. Seasickness is another example. Now suppose that you stand looking spinward down the long upward-curving hall along the rim of the space station, and then rapidly turn your head clockwise so that you are looking at the side wall to your right. Your head has made a rotation similar to that of the pan on the turntable. The fluid in your semicircular canals will therefore rise on one side and drop on the other as the water did. The subjective consequence is that you will “see” the floor tilt to the left, with the right side wall “rising” and the left side wall “dropping” momentarily. The amount of perceived floor tilt depends on the ratio of ear-velocity to floor velocity, but for any but the very largest of space stations the tilt sensation will be a quite unmistakable. This effect is likely to be fairly disorienting and may be a source of nausea and vertigo for the “greenhorn” who has just arrived from “natural” gravity. For the experienced space station inhabitant, however, the “floor-tilt effect” will become a useful aid to orientation because it will allows the user to tell whether he is looking “spinward” (in the direction that the floor is moving due to the spin) or “anti-spinward” (against the floor velocity) down the hall.