Barbary
Page 16
The memorable jogging scene of 2001 when astronaut Frank Poole runs in what we see as a vertical circle brings to mind another effect. The jogger running spinward down a hall along the rim of the station increases his tangential velocity, thereby creating a slight increase in the centrifugal pull he experiences and giving the impression of running uphill. Running anti-spinward will decrease the pull slightly and create the impression of running downhill. The change in pull will depend on the ratio of running speed to floor speed, and the effect would be less in a big station than a small one.
The mysterious “force” that makes the water tilt in the pan, moves the fluid in the semicircular canals, and changes the pull on the runner is called the Coriolis force. Like the “centrifugal force” which makes spin-generated artificial gravity, the Coriolis force is not a real force of nature, but rather a sort of illusion or pseudo-force which appears to observers in rotating systems. But if the Coriolis force is an illusion, its effects are nevertheless quite real. Its actions on air flow on the Earth’s surface are responsible for the circular weather patterns visible in satellite weather pictures: the ragged spiral of the hurricane and the gentle swirl and counter-swirl of high and low pressure areas.
Another Coriolis effect appears when we ride the space station’s elevator. There are good astronautical engineering reasons for arranging the station so that arriving shuttles dock at the station hub, matching velocity and spin with the station before establishing tight mechanical contact. Arriving passengers exit the shuttle in the zero-gravity zone of the hub and then ride an elevator to the 1 g zone at the rim where the living and working areas are located. But what is the elevator ride like? The elevator must travel 80 m from hub to rim, the rough equivalent of the elevator in a 25 story building. Let’s assume that the elevator is set to accelerate to a speed of 5 m/s in a period of 2 seconds, then travel toward the rim at that speed for 14 seconds, and finally decelerate to zero velocity in the final 2 seconds of the trip.
With this arrangement, the elevator riders will be pushed against the ceiling of the car for two second with a force of 0.25 g. During that 2 second period a pull toward the anti-spinward wall of the car will build up to a force of 0.22 g. During the 14 second ride this sideways force will remain constant, but added to it will be a downward force which builds up to 1 g as the centrifugal force of the station’s spin builds. Finally in the last 2 seconds of the ride the downward force will rise to 1.25 g and the pull toward the anti-spinward wall will diminish to zero. As the car stops and the passengers step out the constant 1 g downward pull of the station is all that remains. And so the passengers have had a very peculiar ride. Their perception of “down-ness” has migrated from the ceiling to the anti-spinward wall and finally to the floor, as if the car had rotated 180o during the trip.
The source of the sideways pull in the elevator is the Coriolis force. An equivalent view is that the riders in the elevator must travel from the hub, where they have zero tangential velocity, to the rim, where they must match the 27.9 m/s tangential velocity of the floor. Clearly during the elevator ride they must not only be taken “down” along a radius from the hub to the rim, but they must also be accelerated up to the speed of their new environment. The sideways push of the elevator wall accomplishes this. A similar ride in the upward direction from rim to hub would reverse these forces, and now the sideways pull toward the spinward wall removes the rim’s tangential speed to match the hub environment.
Finally, let’s consider space station sports. How would a baseball pitch or a basketball pass be changed in the environment of the space station? The answer depends on the direction of travel of the ball. Movement parallel to the station’s axis of rotation, across the long hallway for example, shows no Coriolis effects. But a ball thrown spinward will seem to drop, and an anti-spinward pitch will rise due to Coriolis effects. Similarly a falling object will curve antispinward, a rising object will curve spinward due to the Coriolis effects, as we saw in the case of the descending elevator. Athletes after sufficient practice will begin to view these distortions of trajectory as natural and will automatically include compensations for them as a part of optimum performance. However, the size of the compensations needed depends on the tangential velocity of the space station floor, with higher velocities leading to smaller Coriolis effects. In an Inter-Orbital Olympics where participants from a variety of stations of different sizes are assembled for athletic competition there will be a definite “home-court” advantage. Participants from smaller-diameter space stations will tend to overcorrect for the Coriolis effects and participants from larger diameter stations will undercorrect. I wonder how the Inter-Orbital Olympic Committee will handle that one?
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Reference:
Spin Generated Gravity: “An Overview of Artificial Gravity”, R. W. Stone, Jr., NASA Report SP-314 (1973).
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Alternate View Column AV-18
Keywords: centrifugal, Coriolis, force, artificial gravity, rotation, space station
Published in the February 1987 issue of Analog Science Fiction & Fact Magazine; This column was written and submitted 8/1/86 and is copyrighted © 1986 John G. Cramer. All rights reserved.
No part may be reproduced in any form without the explicit permission of the author.
Reprinted in Barbary with the kind permission of the author.
Author’s Note
I’m grateful to Dr. John G. Cramer of the University of Washington in Seattle and “The Alternate View” columnist for Analog Science Fiction and Fact. He offered expert advice that helped immeasurably in the creation of the research station Einstein and, particularly, in the descriptions of what it would feel like to live and work in an environment in which gravity is provided by radial acceleration.
I’m also indebted to the late Gerard K. O’Neill and the Space Studies Institute. The society to which Barbary emigrates grew out of Dr. O’Neill’s proposals for permanent inhabited orbiting colonies, the mass driver, and other practical ideas for allowing human beings to live in space.
— VNM
Author’s Note, 2011
I wrote Barbary in 1986, when security at airports was less stringent than it is today. Will security at spaceports be equally stringent? I hope that won’t be necessary.
I considered revising the text, but once a writer begins revising a published book, there’s probably no stopping.
The book does include one correction from the first edition, replacing a change I originally made under protest. My editor was under the impression that nobody under 21 knows or ever uses any profanity. This isn’t true now and it wasn’t true then, so I changed it back.
— VNM
Author’s Note, 2012
Dr. John G. Cramer kindly gave me permission to reprint his Alternate View column, “Artificial Gravity: Which Way Is Up?” in the ebook edition of Barbary.
— VNM
Copyright & Credits
Barbary
Vonda N. McIntyre
Book View Café
September 2011
Copyright © 1986 Vonda N. McIntyre
ISBN: 978-1-61138-082-8
First Published by Houghton Mifflin Company, 1986
Cover Design by Amy Sterling Casil
“Artificial Gravity: Which Way Is Up?” by John G. Cramer. Copyright © 1986 by John G. Cramer. Reprinted with the kind permission of the author.
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Table of Contents
Chapter One
Chapter Two
Chapter Three
Chapter Four
Chapter Five
Chapter Six
Chapter Seven
Chapter Eight
Chapter Nine
Chapter Ten
Chapter Eleven
Chapter Twelve
Chapter Thirteen
Artificial Gravity: Which Way Is Up?
Author’s Note
Author’s Note, 2011
Author’s Note, 2012
Copyright & Credits
About Book View Café