Section 3.7*Biological Effects of Weightlessness
3.7*Biological Effects of Weightlessness
The usefulness of outer space was brought home to North Americans in
1998 by the unexpected failure of the communications satellite that had
been handling almost all of the continent’s cellular phone traffic. Compared
to the massive economic and scientific payoffs of satellites and space probes,
human space travel has little to boast about after four decades. Sending
people into orbit has just been too expensive to be an effective scientific or
commercial activity. The downsized and over-budget International Space
Station has produced virtually no scientific results, and the space shuttle
program now has a record of two catastrophic failures out of 113 missions.
Within our lifetimes, we are probably only likely to see one economi-
cally viable reason for sending humans into space: tourism! No fewer than
three private companies are now willing to take your money for a reserva-
tion on a two-to-four minute trip into space, although none of them has a
firm date on which to begin service. Within a decade, a space cruise may be
the new status symbol among those sufficiently rich and brave.
Well, rich, brave, and possessed of an iron stomach. Travel agents will
probably not emphasize the certainty of constant space-sickness. For us
animals evolved to function in g=9.8 m/s
, living in g=0 is extremely
unpleasant. The early space program focused obsessively on keeping the
astronaut-trainees in perfect physical shape, but it soon became clear that a
body like a Greek demigod’s was no defense against that horrible feeling
that your stomach was falling out from under you and you were never going
to catch up. Our inner ear, which normally tells us which way is down,
tortures us when down is nowhere to be found. There is contradictory
information about whether anyone ever gets over it; the “right stuff” culture
creates a strong incentive for astronauts to deny that they are sick.
Effects of long space missions
Worse than nausea are the health-threatening effects of prolonged
weightlessness. The Russians are the specialists in long-term missions, in
which cosmonauts suffer harm to their blood, muscles, and, most impor-
tantly, their bones.
The effects on the muscles and skeleton appear to be similar to those
experienced by old people and people confined to bed for a long time.
Everyone knows that our muscles get stronger or weaker depending on the
amount of exercise we get, but the bones are likewise adaptable. Normally
old bone mass is continually being broken down and replaced with new
material, but the balance between its loss and replacement is upset when
people do not get enough weight-bearing exercise. The main effect is on the
bones of the lower body. More research is required to find out whether
astronauts’ loss of bone mass is due to faster breaking down of bone, slower
replacement, or both. It is also not known whether the effect can be sup-
pressed via diet or drugs.
The other set of harmful physiological effects appears to derive from the
redistribution of fluids. Normally, the veins and arteries of the legs are
tightly constricted to keep gravity from making blood collect there. It is
uncomfortable for adults to stand on their heads for very long, because the
U.S. and Russian astronauts
aboard the International Space
Station, October 2000.
The International Space Station,
September 2000. The space station
does not rotate to provide simulated
gravity. The completed station will
be much bigger.
More on Apparent Weightlessness
Astronauts in orbit are not really
weightless; they are only a few
hundred miles up, so they are still
affected strongly by the Earth’s
gravity. Section 10.3 of this book
discusses why they experience
More on Simulated Gravity
For more information on simulating
gravity by spinning a spacecraft, see
section 9.2 of this book.