Chapter 5-1

Our New Domain

Scarcely twenty years have passed since Russian cosmonaut Yuri Gagarin became the first person to orbit the Earth. In less than a single generation, human beings have extended their domain from the upper fringes of the Earth's atmosphere to the mountains of the Moon. If this human progress continues, we can expect that some of those already born since Gagarin's 1961 flight will walk on Mars and that some of their grandchildren will be born, live, and die in colonies beyond the Earth.

There has always been a human drive to expand and explore. The last twenty years have shown that space travel is feasible. Now a more profound question faces us: Will our own biology permit us to become full-time residents of outer space? Spaceflight produces many severe atomic stresses on the body and mind. The astronaut is subject to high accelerations (G-forces) on launch and reentry; in between these are long periods of weightlessness. In space, there is radiation more intense, dangerous, and sometimes quite unlike anything encountered on Earth. Inside a spacecraft, high noise levels are produced by the powerful rocket motors and by the continuous operation of life support machinery. Spaceflight involves long periods of isolation, nagging vibrations, and disturbances in normal day-night cycles.

Sun scorches anything that it strikes, and the temperature of shaded objects approaches absolute zero. In the almost perfect vacuum of space, an unprotected human would survive less than a minute before his blood would boil.

We are already quite familiar with many effects involved in space flight. Exposure to highly accelerative forces has become commonplace to the pilots of experimental jet and rocket aircraft. The same forces are pro duced on rocket-propelled sleds and in centrifuges, where their biological effects can be studied in great detail. The dawning of the Atomic Age, combining the threat of nuclear devastation with the promise of unlimited useful energy, has given great empha sis to studies of the effects of ionizing radiation on living things. Incessant noise, vibration, and jet lag are common accompaniments to modern civilization, and despite all the teeming billions of humanity we need only to recall that people live and work in isolation on the polar ice caps, under the oceans, and on the windswept slopes of the Himalayas to be reassured of our capacity to adapt to the most lonely environments.

The unique aspects of spaceflight, so far as the human body is concerned, are weightlessness and the heavy, energetic atomic particles (known as HZE radiation) that are sprayed out of Beyond these specific problems is the the ever present element of physical danger. Only the thin wall of the spacecraft separates the occupants from an environment more hostile than any on Earth. Above the atmosphere, the unfettered energy of the Sun and other stars and that fill the space around us. The key to under standing the effects of spaceflight on humans comes from the reactions of astronauts to weightlessness and HZE radiation, and the evaluation of how much of each they can tolerate.

astronaut in space with 'blue planet' Earth behind
Extravehicular affair.
Astronaut Ed White outside his Gemini 4 spacecraft in 1965, in America's first "space walk".

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