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microgravity - I stand corrected



 
 
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Old October 30th 06, 08:45 PM posted to sci.space.policy,sci.space.history
Eric Chomko
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Default microgravity - I stand corrected

Why reading the following two pages:

http://www.nasa.gov/centers/glenn/re.../microgex.html
http://en.wikipedia.org/wiki/Weightlessness

I realized that I misunderstood the notion of microgravity in space and
the fact that it is created in LEO as opposed to naturally existing.

In the first link on microgravity it became clear after reading this
paragragh:

Many people mistakenly think that there is no gravity above the Earth's
atmosphere, i.e., in "space," and this is why there appears to be no
gravity aboard orbiting spacecraft. Typical orbital altitudes for human
spaceflight vary between 120 - 360 miles (192 to 576 km) above the
surface of the Earth. The gravitational field is still quite strong in
these regions, since this is only about 1.8% the distance to the Moon.
The Earth's gravitational field at about 250 miles (400 km) above the
surface maintains 88.8% of its strength at the surface. Therefore,
orbiting spacecraft, like the Space Shuttle or Space Station, are kept
in orbit around the Earth by gravity.

The part about being motionless at 250 mi. above the earth's surface
and still having 88.8% gravity did it.

Also, in the second link, this part:

As a thought experiment, imagine a spacecraft that had the ability to
rise up to orbital altitude by going straight up like a helicopter and
hovered over one spot on the Earth. The astronauts inside would not
experience weightlessness. Their ride inside this hovering spacecraft
would be similar to riding an elevator up an incredibly tall building
and stopping at the top floor. While hovering above Earth's atmosphere,
their weight would be very close to what they weigh on the surface of
the Earth, even as a space shuttle goes zinging by them. So astronauts
in a hovering spacecraft are being pulled by strong gravity just as
space shuttle astronauts are pulled by strong gravity. The difference
between them is that the orbiting shuttle is freely being pulled toward
the center of the Earth. The lack of relative acceleration between the
orbiting shuttle and its astronauts inside (who are also being freely
pulled toward the center of the Earth) result in them being weightless.
But the hovering spacecraft (as with an elevator at the top of an
incredibly tall building) is not freely falling. The pull of gravity it
is experiencing is being opposed by the hovering force. This force gets
transfered to the astronauts within (along with everything else within
the spacecraft) resulting in weight. This example illustrates the fact
that there is plenty of gravity out in space. If you were to take any
object that is orbiting the Earth and stop it dead in its track and
then release it, the Earth's gravity would pull it straight down back
toward the Earth's surface.

Yep, very clear there.

Eric

 




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