3.3 Accelerated Motion and Life
41
As indicated earlier, it is possible to create real weightless conditions in so-called
‘vomit comets’, aircraft which move on a parabolic curve matching the speed of a
free-falling rock which might be on the same curve. People inside experience ‘zerog’ conditions for up to about 25 s. 22 Entering and exiting the parabolic path produces
about 2.5 g on test subjects.
One can imitate zero-g conditions by opposing gravity at the molecular level
with a magnetic force acting on each molecule. This is possible with materials that
have a negative magnetic susceptibility if they are placed in a magnetic field having
a gradient pointing in the direction of the gravitational force. The force per unit
volume is given by f = (χ /(2μ 0 ))∇(B 2 ), where χ is the magnetic susceptibility, μ 0
is the magnetic permeability of free space, and B is the external magnetic field. For
biological tissue, we can take advantage of the fact that cells contain a large fraction
of water. Water is diamagnetic, i.e. χ < 0, although the effect of this diamagnetism
is quite small compared to ferromagnetic effects (χ water = −9×10 −6 while χ iron =
2 × 10 5 ). Live frogs and mice have been suspended in this way unharmed (see
Sect. 6.5.8) in very strong magnetic field gradients. However, such fields are very
dangerous if the tissue contains any ferromagnetic materials, such as a surgery pin!
Here are some observed effects of microgravity on humans and other organisms
over a period of time:
• Disorientation: The brain must reprogram signals from the otoliths in the inner
ear; The eyes become the main source of orientation information; On return to
Earth, a new disorientation results which may take weeks to overcome.
• Euphoria is experienced by some after the initial disorientation;
• Bone density loss of 3% per month; calcium loss, kidney stones may develop
from excess calcium expulsion;
• Muscle atrophy because of reduced demand;
• Reduced red blood cell production occurs, causing ‘space anemia’;
• Blood shifted to upper torso, brain senses excess fluid, kidney filtration rate
increases, making dehydration;
• Heart reduced in strength because of lesser load;
• Immune system compromised by lack of exposure to pathogens;
• Bacteria acquire increased virulence when grown in zero-g, probably through
reduced stress on cell structures.
Half of all astronauts are affected, with resulting nausea, headache, lethargy, and
sweating. On return to Earth’s gravity, the body recovers from this sickness in a few
days, but balance, muscle tone and bone density restoration requires more time.
Zero gravity is experienced by astronauts in spacecraft orbiting the Earth, as
long as air friction is negligible, and no propulsion is being used. In fact, occupants
of any free non-rotating craft moving through space will have no weight. Because
we have adapted to the Earth’s gravity, physiology, pathology, and psychology are
22 More than about 25 s and the airplane has trouble pulling out of the dive part of the parabola
before hitting the ground!
41
As indicated earlier, it is possible to create real weightless conditions in so-called
‘vomit comets’, aircraft which move on a parabolic curve matching the speed of a
free-falling rock which might be on the same curve. People inside experience ‘zerog’ conditions for up to about 25 s. 22 Entering and exiting the parabolic path produces
about 2.5 g on test subjects.
One can imitate zero-g conditions by opposing gravity at the molecular level
with a magnetic force acting on each molecule. This is possible with materials that
have a negative magnetic susceptibility if they are placed in a magnetic field having
a gradient pointing in the direction of the gravitational force. The force per unit
volume is given by f = (χ /(2μ 0 ))∇(B 2 ), where χ is the magnetic susceptibility, μ 0
is the magnetic permeability of free space, and B is the external magnetic field. For
biological tissue, we can take advantage of the fact that cells contain a large fraction
of water. Water is diamagnetic, i.e. χ < 0, although the effect of this diamagnetism
is quite small compared to ferromagnetic effects (χ water = −9×10 −6 while χ iron =
2 × 10 5 ). Live frogs and mice have been suspended in this way unharmed (see
Sect. 6.5.8) in very strong magnetic field gradients. However, such fields are very
dangerous if the tissue contains any ferromagnetic materials, such as a surgery pin!
Here are some observed effects of microgravity on humans and other organisms
over a period of time:
• Disorientation: The brain must reprogram signals from the otoliths in the inner
ear; The eyes become the main source of orientation information; On return to
Earth, a new disorientation results which may take weeks to overcome.
• Euphoria is experienced by some after the initial disorientation;
• Bone density loss of 3% per month; calcium loss, kidney stones may develop
from excess calcium expulsion;
• Muscle atrophy because of reduced demand;
• Reduced red blood cell production occurs, causing ‘space anemia’;
• Blood shifted to upper torso, brain senses excess fluid, kidney filtration rate
increases, making dehydration;
• Heart reduced in strength because of lesser load;
• Immune system compromised by lack of exposure to pathogens;
• Bacteria acquire increased virulence when grown in zero-g, probably through
reduced stress on cell structures.
Half of all astronauts are affected, with resulting nausea, headache, lethargy, and
sweating. On return to Earth’s gravity, the body recovers from this sickness in a few
days, but balance, muscle tone and bone density restoration requires more time.
Zero gravity is experienced by astronauts in spacecraft orbiting the Earth, as
long as air friction is negligible, and no propulsion is being used. In fact, occupants
of any free non-rotating craft moving through space will have no weight. Because
we have adapted to the Earth’s gravity, physiology, pathology, and psychology are
22 More than about 25 s and the airplane has trouble pulling out of the dive part of the parabola
before hitting the ground!