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gravity is the force that pulls people
and objects toward the earth's surface
without gravity sitting in a chair or
walking down stairs would be difficult
for example
when you drop a ball at any point on
earth it will always fall straight down
that is gravity at work pulling the ball
towards the earth's surface
but there is a difference between
dropping and throwing a ball
when a ball is thrown it still falls to
earth but lands at a point further away
from where it was thrown
if a ball could be thrown with enough
forward velocity
it would fall around the earth creating
a low earth orbit
like the ball the space shuttle is
actually in a continuous fall around the
earth
astronauts and objects inside the
shuttle are falling at exactly the same
rate as the shuttle
thus creating the effects of
weightlessness
imagine an astronaut in an elevator on
earth
the elevator is going to the top of a
very tall building
suddenly when he reaches the top the
cable breaks
the elevator begins to fall
inside the car the astronaut begins to
float he is weightless
if he had an apple it would float too
that is because the car the astronaut
and the apple are falling at the same
rate of speed
you may have experienced moments on
earth when the effects of gravity seem
to disappear
such as when you bounce on a trampoline
or crest the hill on a roller coaster
scientists can take advantage of a
reduced gravity environment to isolate
the effects gravity has on physical
chemical and biological processes
a better understanding of these
processes can be achieved by studying
phenomena usually obscured by the
effects of gravity
on earth scientists utilize specialized
facilities such as drop towers and
aircraft in parabolic dive sequences to
test experiments for a few seconds at a
time in an environment which is
approximately 1 100th of the earth's
normal gravity level
however many experiments require even
smaller gravity levels and longer
durations of free fall that cannot be
achieved in these earth-based facilities
in the constant microgravity environment
of low earth orbit
researchers have found that experiments
in biotechnology
fluid dynamics and material science have
produced dramatically different results
than ground-based research
one example of this can be seen by
examining crystals grown in a
microgravity environment
these crystals contain fewer flaws and
imperfections than crystals grown on
earth
the result
higher quality crystals for potential
applications on earth
however even in the microgravity
environment aboard the shuttle there are
other forces that may affect the results
of experiments
disturbances and vibrations caused by
thruster firings
crew movements and equipment operation
can mimic the effects of gravity on
experiment results
disturbances that are significant for
sensitive experiments
that may negatively affect the results
of those experiments
a simple demonstration illustrates how
an outside force can affect the results
of an experiment
the slightest disturbance to just one
domino will cause the others to fall
or try this experiment in your kitchen
the surface tension of a glass of water
will support common paper clips
when the glass is bumped the paper clips
sink to the bottom of the glass
in order to understand the final data
from an experiment conducted in
microgravity
these disturbances and other parameters
such as temperature and pressure need to
be measured
researchers may then use the data to
determine if unexpected results were
caused naturally or by these measured
outside factors
at nasa's lewis research center in
cleveland ohio scientists and engineers
have developed the space acceleration
measurement system or sams to measure
and record vibrations and disturbances
that may alter experiment results
sams is designed to measure characterize
and record low gravity disturbances on
board the space shuttle
a single sams unit can monitor three
experiments directly as well as other
experiments in close proximity
the sams hardware consists of a main
signal processing unit
and three remote tri-axial sensor heads
the three sensors on each of these heads
detect the different disturbances and
their levels
the data is sent through cables and
stored on disks similar to the compact
discs that are found in homes today the
sensor heads are mounted on or near an
experiment
permitting disturbances affecting that
experiment to be sampled
sams has the ability to collect data up
to 20 feet away from the main unit
this enhances its versatility and allows
it to serve a wide variety of
microgravity science and technology
experiments
sams is scheduled to fly as part of the
second united states microgravity
payload mission
usmp2 aboard the space shuttle columbia
in march of 1994.
during this mission scientists in the
payload operations control center or
park will be able to monitor some of the
data that the sams unit is collecting in
real time as the disturbances are
occurring
scientists can use this information to
determine if adjustments need to be made
to their experiments to avoid any
unacceptable conditions
sams will support four materials science
experiments on the usmp2 mission
three of these experiments were
developed or are managed by the nassau
lewis research center
the data that sams will collect for
these experiments could lead to many
advancements in processed materials such
as improved industrial casting methods
the development of superconductors and
the ability to produce higher quality
crystals for use in commercial military
and consumer electronic equipment
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