His first night aloft Oleg Atkov drifted uneasily through the space station Salyut 7. Sleep was impossible. His head, accustomed to its own weight on a pillow, felt large and light. His face was bloated with blood that, no longer held in his legs by gravity, had migrated upward. When he closed his eyes, he felt as if he were spinning, since without gravity his inner ear could not sense up and down.
Without intending, Atkov, a cosmonaut-physician, was serving as a test subject for another of Albert Einstein’s contributions to science: the principle of equivalence. It states that there is no difference between the effect of gravity and that of acceleration; they are equivalent. Thus a person falling will not feel his own weight, an idea that helped lead Einstein to his grand theory of gravity—general relativity.
An orbiting space station, like the moon, continuously falls toward earth. Only its forward motion prevents it from crashing. To Atkov the effect was the same as being inside a freely falling elevator. Atkov’s body reacted profoundly. His muscles, which were no longer needed for supporting his body or lifting things, atrophied rapidly, despite intense exercise each day. “I could see them wither before my eyes,” said the amiable cosmonaut when I visited him in the prague city apartments.
Atkov’s bones, similarly underemployed, insidiously gave up calcium and lost density. “I became lethargic and fatigued, far worse than I had expected.” When he landed after eight months in space, he was so weak he had to be carried on a stretcher. He called his one trip to space “more than enough.”
Medical researchers are worried about a tentatively planned trip to Mars, taking as long as three years round-trip.* Dr. Harold Sandler, a NASA aerospace physician at Ames, wonders: “Is there a point in sending someone to Mars who won’t be able to stand up when he gets there?”
Some specialists think artificial gravity will be required. It could be attained in a slowly rotating space vehicle, creating a centrifugal effect as in the film 2001: A Space Odyssey.
A revolving spacecraft could also alleviate problems the Soviets have found in trying to grow plants in space greenhouses. In zero gravity, plants can grow with roots up and stems down, while weightless water cannot percolate through soil, which itself is floating away from roots. These are serious problems: Plants will be essential for providing food and oxygen during interplanetary flights.
Science has gleaned a lot about the most mysterious force in the universe since Newton gave us an inkling of how it works. But does the knowledge do us any good? Right now orbiting satellites like LAGEOS and GEOSAT are taking readings of variations in the earth’s gravitational field. To do this, researchers determine whether a satellite has bobbed up or down with a change in earth’s gravity below. For instance, satellites drop noticeably over the “Indian Ocean anomaly” off Africa, where the earth’s surface bulges and gravity’s pull is particularly strong.
DURING THE Apollo 11 mission to the moon in 1969, NASA learned — suddenly —about gravity variations there too.