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.
Extravehicular affair.
Astronaut Ed White outside his Gemini 4 spacecraft in 1965,
in America's first "space walk".
