microgravity - I stand corrected

"Ian Woollard" wrote in message
...
Bob forward pointed out that you can in principle make a zero-gravity room
on the Earth if you could mount a disk of neutronium above it. (The minor
implementation details for doing that are left to the reader ;-) )

Hold it up with scrith? ;-)

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)

Rand Simberg wrote:

Right. We're not talking about practical differences. We're talking
about "Einsteinian equivalence" differences (note: the elevator
thought experiment is always careful to state that it's impossible to
tell the difference between an acceleration and a "uniform
gravitational field"--it if gets it right, that is...).

Here you guys might want to check out the sites from the Gravity Probe
B launched april 20 2004 at Nasa, and the site at Stanford where the
scientists will be publishing their results soon.
Tom

http://www.nasa.gov/centers/marshall...05/05-160.html

"Launched on April 20, 2004, from Vandenberg Air Force Base, Calif.,
Gravity Probe B has been using four spherical gyroscopes to precisely
measure two extraordinary effects predicted by Einstein's theory. One
is the geodetic effect, the amount by which the Earth warps the local
space time in which it resides. The other, called frame-dragging, is
the amount by which the rotating Earth drags local space time around
with it."

http://einstein.stanford.edu/
"We are now proceeding with Phase III, the final phase-of the data
analysis, which will last until January-February, 2007. Whereas in
Phases I and II the focus was on individual gyro performance, during
Phase III, the data from all four gyros is being integrated over the
entire experiment. The results of this phase will be both individual
and correlated changes in gyro spin axis orientation covering the
entire 50-week experimental period for all four gyros."



Open sharing of information is crucial to improving everybody's
understanding of the universe around us.
tom

In sci.space.policy, on Tue, 31 Oct 2006 07:34:15 -0500,
Jeff Findley sez:

` "Ian Woollard" wrote in message
` ...

` Bob forward pointed out that you can in principle make a
` zero-gravity room on the Earth if you could mount a disk of
` neutronium above it. (The minor implementation details for
` doing that are left to the reader ;-) )

` Hold it up with scrith? ;-)

I think an engineering study would be likely to conclude that a
cheaper alternative would be to dig down and construct the
room at the centre of the earth... (^:

--
================================================== ========================
Pete Vincent
Disclaimer: all I know I learned from reading Usenet.

pete wrote:

In sci.space.policy, on Tue, 31 Oct 2006 07:34:15 -0500,
Jeff Findley sez:

` "Ian Woollard" wrote in message
` ...

` Bob forward pointed out that you can in principle make a
` zero-gravity room on the Earth if you could mount a disk of
` neutronium above it. (The minor implementation details for
` doing that are left to the reader ;-) )

` Hold it up with scrith? ;-)

I think an engineering study would be likely to conclude that a
cheaper alternative would be to dig down and construct the
room at the centre of the earth... (^:

Dig down?

A signifigant mass of neutronium (disregarding how it would be kept
at that density, once removed from a neutron star [and however that
removal process would be accomplished]) would likely find its way to
Earth's core in short order...just, um, follow it.



--

Frank

You know what to remove to reply...

Check out my web page: http://www.geocities.com/stardolphin1/link2.htm

"To confine our attention to terrestrial matters would be to limit the
human spirit."
- Stephen Hawking

On Tue, 31 Oct 2006 07:48:06 +0000, Ian Woollard wrote:

Bob forward pointed out that you can in principle make a zero-gravity room
on the Earth if you could mount a disk of neutronium above it. (The minor
implementation details for doing that are left to the reader ;-) )

Actually, Heinlein mooted this concept, and a few problems with
the idea, in the short story "—We Also Walk Dogs" ...

.... in 1941

--
Chuck Stewart
"Anime-style catgirls: Threat? Menace? Or just studying algebra?"

Rand Simberg wrote:"Right. We're not talking about practical
differences. We're talking
about "Einsteinian equivalence" differences (note: the elevator thought
experiment is always careful to state that it's impossible to tell the
difference between an acceleration and a "uniform gravitational
field"--it if gets it right, that is...)."

In the Gravity Probe B Stanford website, on the page for technical
papers and under the topic "The Origins of Drag-Free Satellites & the
GP-B Experiment" , there is a great list of sources in support of the
experiment.

http://einstein.stanford.edu/

Proposal for a Satellite Test of the Coriolis Prediction of General
Relativity
G. E. Pugh. Reprinted in Nonlinear Gravitodynamics, The Lense Thirring
Effect, a documentary introduction to current research. Editors: Remo
J. Ruffini, Costantino Sigismondi, 2002, pp. 414-425. Orininally
Published as U.S. Department of Defense Weapons Systems Evaluation
Group Research Memorandum No. 11, 1959.

Possible New Experimental Test of General Relativity Theory
L. I. Schiff. Physical Review Letters, Vol 4, Number 5, March 1960, pp.
215-217.

Motion of a Gyroscope According to Einstein's Theory of Gravitation
L. I. Schiff. Proceedings of the National Academy of Sciences, Vol. 46,
June 1960, pp. 871-882.

Proceedings of the July 1961 Conference on Experimental Tests of
Theories of Relativity
Held at Stanford University, July 20-21, 1961 and sponsored by the
National Aeronautics and Space Administration, Office of Space
Sciences, headed by Dr. Nancy G. Roman, Chief of Astronomy, Solar
Physics, Geophsics, and Relativity programs. The conference was chaired
by H. P. Robertson, Professor of Physics at the California Institute of
Technology, and participants included over 30 well-known authorities in
physics and aerospace engineering.

Requirements and Design for a Special Gyro for Measuring General
Relativity Effects from an Astronomical Satellite
Robert H. Cannon, Jr., Chairman of the Department of Aeronautics &
Astronautics, Stanford University, 1962. Published in the Proceedings
of the International Union of Theoretical and Applied Mechanics,
Kreiselproleme Gyrodynamics, Symposium Celerina, August 20-23, 1962, pp
145-157. Copyright © 1963, Springer-Verlag, Berlin.

The Control and Use of Drag-Free Satellites
Benjamin Lange, Doctoral Dissertation, Stanford University Department
of Aeronautics & Astronautics, Paper #194, June, 1964.

The Drag-Free Satellite (Drag free satellite design and use, analyzing
control and guidance system with respect to system performance and gas
usage)
Benjamin Lange. American Institute of Aeronautics & Astronautics
Journal (AIAA), Volume 2, Number 9, Septermber 1964, pp. 1590-1606.

A Satellite Freed of all but Gravitational Forces: "TRIAD I"
Staff of the Space Department, The Johns Hopkins University Applied
Physics Laboratory, Silver Spring, MD AND Staff of the Guidance and
Control Laboratory, Stanford University, Stanford, CA. American
Institute of Aeronautics & Astronautics Journal (AIAA), Volume 11,
Number 9, September 1974, pp. 637-644.

The Stanford Relativity Gyroscope Experiment: History and Overview
C. W. F. Everitt, Excerpt from the book, Near Zero: New Frontiers of
Physics
.. Chapter VI, Section 3A. Edited by J.D. Fairbank, B.S Deaver, Jr.,
C.W.F. Everitt, & P.F. Michelson, Copyright © 1988, W. H. Freeman &
Company, New York.

The Stanford Relativity Gyroscope Experiment: Translation and
Orientation Control
Daniel B. De Bra, Excerpt from the book, Near Zero: New Frontiers of
Physics
.. Chapter VI, Section 3G. Edited by J.D. Fairbank, B.S Deaver, Jr.,
C.W.F. Everitt, & P.F. Michelson, Copyright © 1988, W. H. Freeman &
Company, New York.


Open sharing of information is crucial to improving everybody's
understanding of the universe around us.
Tom



columbiaaccidentinvestigation wrote:
Rand Simberg wrote:

Right. We're not talking about practical differences. We're talking
about "Einsteinian equivalence" differences (note: the elevator
thought experiment is always careful to state that it's impossible to
tell the difference between an acceleration and a "uniform
gravitational field"--it if gets it right, that is...).

Here you guys might want to check out the sites from the Gravity Probe
B launched april 20 2004 at Nasa, and the site at Stanford where the
scientists will be publishing their results soon.
Tom

http://www.nasa.gov/centers/marshall...05/05-160.html

"Launched on April 20, 2004, from Vandenberg Air Force Base, Calif.,
Gravity Probe B has been using four spherical gyroscopes to precisely
measure two extraordinary effects predicted by Einstein's theory. One
is the geodetic effect, the amount by which the Earth warps the local
space time in which it resides. The other, called frame-dragging, is
the amount by which the rotating Earth drags local space time around
with it."

http://einstein.stanford.edu/
"We are now proceeding with Phase III, the final phase-of the data
analysis, which will last until January-February, 2007. Whereas in
Phases I and II the focus was on individual gyro performance, during
Phase III, the data from all four gyros is being integrated over the
entire experiment. The results of this phase will be both individual
and correlated changes in gyro spin axis orientation covering the
entire 50-week experimental period for all four gyros."



Open sharing of information is crucial to improving everybody's
understanding of the universe around us.
tom

In sci.space.policy, on Wed, 01 Nov 2006 04:15:30 GMT, Frank Glover
sez:

` pete wrote:

` In sci.space.policy, on Tue, 31 Oct 2006 07:34:15 -0500,
` Jeff Findley sez:
`
` ` "Ian Woollard" wrote in message
` ` ...
`
` ` Bob forward pointed out that you can in principle make a
` ` zero-gravity room on the Earth if you could mount a disk of
` ` neutronium above it. (The minor implementation details for
` ` doing that are left to the reader ;-) )
`
` ` Hold it up with scrith? ;-)
`
` I think an engineering study would be likely to conclude that a
` cheaper alternative would be to dig down and construct the
` room at the centre of the earth... (^:

` Dig down?

` A signifigant mass of neutronium (disregarding how it would be kept
` at that density, once removed from a neutron star [and however that
` removal process would be accomplished]) would likely find its way to
` Earth's core in short order...just, um, follow it.

As the original object was just a room with 0 net gravitational force
on the earth, being at the earth's centre would remove the need
for any neutronium.

--
================================================== ========================
Pete Vincent
Disclaimer: all I know I learned from reading Usenet.

From Eric Chomko:
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.
snip

Yep, very clear there.

That is a huge improvement on what the folks at Glenn(/Lewis) used to
say about "microgravity". Here is one webpage that was scrutinized on
this forum a long time ago:

http://microgravity.grc.nasa.gov/

At the time of that discussion (mid-2001) their webpage said this:

"Microgravity literally means a state of very weak gravity
(one-millionth of what is felt on Earth)."

....revealing a complete disconnect with fundamental physics when that
term is applied to the orbital environment.

(Ref -
http://web.archive.org/web/200105170....grc.nasa.gov/)

Not long after this forum highlighted the error, the webpage was
changed to offer this involved explanation:

========
Microgravity is a condition where the effects of gravity appear to be
small or even negligible compared to the normal effects of gravity on
Earth. Where the effects appear to be very small, as on an orbiting
spacecraft, microgravity is generally meant to be synonymous with zero
gravity, zero g, and weightlessness.

The term microgravity can be used to describe a condition where gravity
is actually small, for example on the Moon where gravity is about one
sixth of that on Earth. But we generally use the term microgravity to
describe a condition where gravity is not small, but appears to be
small. This is the condition experienced on orbiting spacecraft, such
as the International Space Station, and all objects in free fall.

The force of gravity diminishes with distance, so gravity is weaker on
the International Space Station (ISS) than on Earth. But ISS is only
about 300 km above the Earth, hardly off the surface on a planetary
scale. At that altitude, the gravitational acceleration is about 90% of
that at the Earth's surface. So gravity on ISS is almost the same as it
is on Earth. And weight is defined as the force of gravity on an
object, so weight on ISS is nearly the same as that on Earth. But given
the images of floating astronauts, it appears that gravity and weight
are reduced by much more than 10%. What's happening?

Gravity causes objects to fall, unless their motion is restricted by
some other force, such as that of the floor. If gravity is the only
force acting on an object's motion, then it is in free fall. Neglecting
the fall itself, free-falling objects behave like there is no gravity.
This happens because free-falling objects experience the same
gravitational acceleration regardless of their mass (in contrast to the
common preconception). Imagine you have an apple on a scale, which
displays the apple's weight. If you drop the scale, the apple and scale
will fall together, but the scale will no longer be compressed by the
apple, so the scale will show zero weight. In the same way, both the
astronauts and ISS are falling towards the Earth. Since they have the
same acceleration, the astronauts seem to have no weight and float
within the ISS. Fortunately, the astronauts and the ISS are moving so
quickly (about 28,000 kph) that they fall around the Earth in a
circular orbit. Similarly, Space Shuttle astronauts experience free
fall while they coast around the Earth (with engines off at 8 minutes
after launch). In both cases, microgravity is achieved because the
spacecraft are in a continuous state of free fall.

While gravity and weight seem to vanish in free fall, gravity-driven
motion like sedimentation and buoyant convection are truly absent. This
allows astronauts to conduct unique experiments that may enable further
space exploration or improvements to our quality of life here on Earth.
========
(Ref -
http://web.archive.org/web/200205241....grc.nasa.gov/)

A major improvement on the previous disconnect. But still glaring
errors were present, such as this:

"The term microgravity can be used to describe a condition where
gravity is actually small, for example on the Moon where gravity is
about one sixth of that on Earth."

....a mistake of several order of magnitude ('one-sixth' versus
'micro-'). And then it contains what I'll call dangerous statements,
that support the ill-conceived term 'microgravity':

"While gravity and weight seem to vanish in free fall, ..."
"If gravity is the only force acting on an object's motion, then it is
in free fall. Neglecting the fall itself, free-falling objects behave
like there is no gravity."

Gravity would "seem to vanish in free fall" only if your mind failed to
grasp the concept that the reason you are in freefall is because of
gravity.


Fast forward to today, the biggest problem I have with that Glenn
webpage:
http://www.nasa.gov/centers/glenn/re.../microgex.html
....is their use of the terms "microgravity" and "zero gravity"
themselves. Everything else looks fairly accurate to me.


So kudos to NASA for marching the path toward accurate physics! Those
are huge steps in a relatively short period of time.


~ CT

On Mon, 30 Oct 2006 20:44:12 +0000, Rand Simberg wrote:

On Mon, 30 Oct 2006 16:38:28 -0500, in a place far, far away, "Jeff
Findley" made the phosphor on my monitor
glow in such a way as to indicate that:


"Eric Chomko" wrote in message
groups.com...
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.

This is why you can experience microgravity in an aircraft flying
parabolas. Wasn't it Newton who had the thought experiment about firing a
canon on top of a mountain that extended above the atmosphere? For small
powder loads, you got the expected parabolic shape of the shell falling
to the earth. But as you kept increasing the powder load, eventually you
get to the point where the shell falls all the way around the earth.
That's an orbit.

Also note that it's never a true parabola (as it would be in a uniform
gravitational field, which doesn't actually exist anywhere in the
universe), but for small distances it approximates one. It's always a
partial ellipse.

Just to be nit-picky, I thought I'd point out that, if the Earth looks
like a point mass and gravity is Newtonian, then the path _is_ a true
parabola _if_ you launch the projectile with just enough energy to escape.

So, the issue isn't really that it's only a parabola for _small_ powder
loads. It's that it's only a parabola for one particular whopping _big_
powder load.

The proof's a bit tedious, and is part of the reason Newton got so
famous :-) . FWIW, here's my version, which I just put up, mostly 'cause I
was so pleased at actually getting through all the details:

http://www.physicsinsights.org/orbit_shapes_1.html


--
Nospam becomes physicsinsights to fix the email

From sal:

Just to be nit-picky, I thought I'd point out that, if the Earth looks
like a point mass and gravity is Newtonian, then the path _is_ a true
parabola _if_ you launch the projectile with just enough energy to escape.

So, the issue isn't really that it's only a parabola for _small_ powder
loads. It's that it's only a parabola for one particular whopping _big_
powder load.

The proof's a bit tedious, and is part of the reason Newton got so
famous :-) . FWIW, here's my version, which I just put up, mostly 'cause I
was so pleased at actually getting through all the details:

http://www.physicsinsights.org/orbit_shapes_1.html

Those are some very messy equations you have there on that page. An
extremely clean way to analyze escape vs capture is graphically with an
energy potential well diagram. It's just like those coin wells, except
that it visualizes the energy of the orbiting body in terms of kinetic
energy being the height above the potential well surface. Energy is
conserved so the total (sum of potential + kinetic) stays constant. So
the height of the trajectory doesn't change.

As the spacecraft ventures farther from the primary body, kinetic
energy decreases while potential increases. So the three classes of
orbits become:

- Spacecraft kinetic energy is insufficient to reach the top of the
well (ELLIPTICAL CLASS),
- Spacecraft kinetic energy *exactly* reaches the top of the well
(PARABOLIC CLASS),
- Spacecraft kinetic energy exceeds the top of the well (HYPERBOLIC
CLASS).

The concept can be clearly described with pretty pictures and no messy
equations.


~ CT