microgravity - I stand corrected

Eric Chomko

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Oct 30, 2006, 3:45:29 PM10/30/06

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Why reading the following two pages:

http://www.nasa.gov/centers/glenn/research/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

Jeff Findley

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Oct 30, 2006, 4:38:28 PM10/30/06

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"Eric Chomko" <pne.c...@verizon.net> wrote in message
news:1162241128.9...@b28g2000cwb.googlegroups.com...

> Why reading the following two pages:
>
> http://www.nasa.gov/centers/glenn/research/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.

This is also why microgravity is sometimes called free fall.

We mere mortals can experience free fall for a few seconds by riding drop
tower like rides at theme parks. There's one a few miles from my home at
King's Island in Mason Ohio. It's lots of fun, really it is! ;-)

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

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Oct 30, 2006, 3:44:12 PM10/30/06

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On Mon, 30 Oct 2006 16:38:28 -0500, in a place far, far away, "Jeff
Findley" <jeff.f...@ugs.nojunk.com> made the phosphor on my monitor
glow in such a way as to indicate that:

>
>"Eric Chomko" <pne.c...@verizon.net> wrote in message
>news:1162241128.9...@b28g2000cwb.googlegroups.com...
>> Why reading the following two pages:
>>
>> http://www.nasa.gov/centers/glenn/research/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.

Jeff Findley

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Oct 30, 2006, 4:56:40 PM10/30/06

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"Rand Simberg" <simberg.i...@org.trash> wrote in message
news:45d863d3....@news.giganews.com...

> On Mon, 30 Oct 2006 16:38:28 -0500, in a place far, far away, "Jeff
> Findley" <jeff.f...@ugs.nojunk.com> made the phosphor on my monitor
> glow in such a way as to indicate that:

>>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.

Quite true. I forgot about that little detail since for small distances it
is rather convenient to approximate the path as parabolic (high school
physics). Still, the thought experiment is an easy way to introduce the
theory of orbits to people without resorting to math which may scare them
off.

Here's a link to a picture for those that would like to see it:

http://www.waowen.screaming.net/revision/force&motion/ncanon.htm

And an interactive web page with animation for the video game generation:

http://www.waowen.screaming.net/revision/force&motion/ncananim.htm

This thought experiment can also be used to visualize why something like a
cannon can't be used to place something in orbit, at least not without a
rocket engine to circularize the orbit so the projectile doesn't come back
and hit the earth after one "orbit".

Jim Oberg

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Oct 30, 2006, 5:33:08 PM10/30/06

to

That's why it is possible for an observer in
a sealed room under a 1-g field to differentiate
between mass-induced weight, thrusting
weight, and centrifugal (end-of-tether) weight.

You just can't do it my measuring at a single point --
but you can, if you can measure at two separate points in the
room.

Wayne Throop

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Oct 30, 2006, 5:39:14 PM10/30/06

to

: "Jim Oberg" <james...@houston.rr.com>
: That's why it is possible for an observer in a sealed room under a 1-g

Yes.

Yet note that for any given sensitivity of measurement and separation of
measuring points, there is a distance-X-to-mass-center which can't be
told from a distance-Y-to-spin-center case. And (per other threads)
this can't-be-told-from quickly falls below physiological sensitivity
(well... fairly quickly). Specifically, your heart and circulatory
system really can't tell the difference between pushing blood up an
acceleration potential and pushing it up a gravitational potential.
Because, in terms of energy, fluid pressure, and physiological effects,
there *is* no difference.

Wayne Throop thr...@sheol.org http://sheol.org/throopw

Rand Simberg

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Oct 30, 2006, 4:56:47 PM10/30/06

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On Mon, 30 Oct 2006 22:39:14 GMT, in a place far, far away,
thr...@sheol.org (Wayne Throop) made the phosphor on my monitor glow

in such a way as to indicate that:

>: "Jim Oberg" <james...@houston.rr.com>

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...).

Pat Flannery

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Oct 30, 2006, 6:25:07 PM10/30/06

to

Jeff Findley wrote:

>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.
>
>

This is what thwarted Herr Scultze's attempt to destroy France-Ville
with his giant cannon at Stahlstadt* in Verne's "The Begum's Fortune".

* Love that name...this was Verne taking a crack at the Krupps, and
their Essen factories. The "City Of Steel" is about as pleasant a place
as one would expect it to be, as was Essen.

Pat

Ian Woollard

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Oct 31, 2006, 2:05:27 AM10/31/06

to Rand Simberg

Rand Simberg wrote:
> 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.

Real gravitational fields are never actually point source equivalents,
so it's never actually a partial ellipse.

Ian Woollard

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Oct 31, 2006, 2:48:06 AM10/31/06

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The equivalence principle is only really true as the limit for a point.

However, there's various mass layouts that give a pretty constant field
strength over a wide volume to quite high accuracy.

IRC the center of a hemispheric shell is one, and the center of a large
disk is another.

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 ;-) )

Jeff Findley

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Oct 31, 2006, 7:34:15 AM10/31/06

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"Ian Woollard" <ian.wo...@gmail.com> wrote in message
news:4546ffb0$0$8719$ed26...@ptn-nntp-reader02.plus.net...

> 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? ;-)

columbiaaccidentinvestigation

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Oct 31, 2006, 4:14:33 PM10/31/06

to

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/news/news/releases/2005/05-160.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

pete

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Oct 31, 2006, 9:53:37 PM10/31/06

to

In sci.space.policy, on Tue, 31 Oct 2006 07:34:15 -0500,
Jeff Findley <jeff.f...@ugs.nojunk.com> sez:

` "Ian Woollard" <ian.wo...@gmail.com> wrote in message
` news:4546ffb0$0$8719$ed26...@ptn-nntp-reader02.plus.net...

` > 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... (^:

--
==========================================================================
vincent@triumf[munge].ca Pete Vincent
Disclaimer: all I know I learned from reading Usenet.

Frank Glover

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Oct 31, 2006, 11:15:30 PM10/31/06

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pete wrote:

> In sci.space.policy, on Tue, 31 Oct 2006 07:34:15 -0500,
> Jeff Findley <jeff.f...@ugs.nojunk.com> sez:
>
> ` "Ian Woollard" <ian.wo...@gmail.com> wrote in message
> ` news:4546ffb0$0$8719$ed26...@ptn-nntp-reader02.plus.net...
>
> ` > 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

Chuck Stewart

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Nov 1, 2006, 12:05:58 AM11/1/06

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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?"

columbiaaccidentinvestigation

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Nov 1, 2006, 1:36:16 PM11/1/06

to

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

pete

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Nov 2, 2006, 12:05:26 AM11/2/06

to

In sci.space.policy, on Wed, 01 Nov 2006 04:15:30 GMT, Frank Glover
<star...@rochester.rr.com> sez:

` pete wrote:

` > In sci.space.policy, on Tue, 31 Oct 2006 07:34:15 -0500,
` > Jeff Findley <jeff.f...@ugs.nojunk.com> sez:
` >
` > ` "Ian Woollard" <ian.wo...@gmail.com> wrote in message
` > ` news:4546ffb0$0$8719$ed26...@ptn-nntp-reader02.plus.net...
` >
` > ` > 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.

Stuf4

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Nov 2, 2006, 5:19:20 AM11/2/06

to

>From Eric Chomko:

> Why reading the following two pages:
>
> http://www.nasa.gov/centers/glenn/research/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/20010517003023/http://microgravity.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/20020524155549/http://microgravity.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/research/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

sal

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Nov 18, 2006, 10:37:05 PM11/18/06

to

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

Stuf4

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Nov 20, 2006, 12:19:09 AM11/20/06

to

>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

Stuf4

unread,

Nov 20, 2006, 12:30:02 AM11/20/06

to

Maybe it would help to be explicit that these gravity wells have two
spatial dimensions that correspond to the two dimensional orbit, and
the third dimension of the gravity well is not spatial at all. The
height of the well is ENERGY. The zero point of energy is the
"stretched rubber sheet" prior to "deformation". This totally flat
sheet is a representation of ZERO GRAVITY. That is actual zero
gravity, as in no gravity at all to warp the spatial dimensions.

Then when a massive body is introduced into this space, the sheet
deforms and produces a gravity well. Notice that nowhere on the sheet
will you find zero gravity any more for any finite distance from this
mass.

So the energy well has stretched below the zero point. Any satellite
with negative total energy will be captured by this body. But a
thrusting maneuver can increase kinetic energy, raising its energy,
depicted as height above the rubber sheet. If that kinetic energy
increases to the height of the original undeformed sheet (the point of
zero total energy) then you have a parabolic orbit. If the kinetic
energy increases to the point of excess total energy (positive) then
you have a hyperbolic trajectory.

~ CT

sal

unread,

Nov 20, 2006, 12:35:16 AM11/20/06

to

On Sun, 19 Nov 2006 21:19:09 -0800, Stuf4 wrote:

>>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.

Oh, absolutely. That's the way one normally does it, for sure; you are
correct.

However, the point of the page was to actually solve the equations to find
the orbit shapes, not just the escape velocity.

In particular, you can easily find the escape velocity with an energy
argument -- but can you prove the trajectory at escape velocity is a
parabola that way, and an ellipse if you miss escaping but have too much
energy for a circle? AFAIK that proof is a mess no matter how you tackle
it -- but I'd be glad to learn otherwise.

> 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),

But how do you prove it's really an ellipse, without the mess?

> - Spacecraft kinetic energy *exactly* reaches the top of the well
> (PARABOLIC CLASS),

How do you prove it's a parabola, without the mess of solving the
equations and verifying the form of the result?

> - Spacecraft kinetic energy exceeds the top of the well (HYPERBOLIC
> CLASS).

And again, how do you prove it's really a hyperbola, short of solving the
equations of motion?

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

--

Nospam becomes physicsinsights to fix the email

I can be also contacted through http://www.physicsinsights.org

Stuf4

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Nov 20, 2006, 12:40:31 AM11/20/06

to

It's also interesting to analyze what happens with the velocity-energy
relationships as the spacecraft ventures out to infinite distance. For
the hyperbolic case, you can easily determine what the final velocity
will be. This is the velocity corresponding to its excess energy
(height above the zero point of the rubber sheet).

For the parabolic case, the potential well diagram shows that the
farther the spacecraft gets from the primary body, the closer its
kinetic energy gets to zero. So the farther it gets, the slower it
gets. The ramification of this trend toward zero velocity as it
approaches infinite distance is that the trajectory will also take
infinite time.

...of course, this analysis is only two body theory. An extremely
clinical version of the universe. There are many other factors as to
what actually happens to spacecraft like the Voyagers and such.

~ CT

Stuf4

unread,

Nov 20, 2006, 2:40:43 AM11/20/06

to

By the way, yesterday I was out at Walmart with Joe Engle, in case
anyone was interested.

~ CT

Stuf4

unread,

Nov 20, 2006, 2:50:59 AM11/20/06

to

>From sal:

> On Sun, 19 Nov 2006 21:19:09 -0800, Stuf4 wrote:

<snip>

> > 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.
>
> Oh, absolutely. That's the way one normally does it, for sure; you are
> correct.
>
> However, the point of the page was to actually solve the equations to find
> the orbit shapes, not just the escape velocity.
>
> In particular, you can easily find the escape velocity with an energy
> argument -- but can you prove the trajectory at escape velocity is a
> parabola that way, and an ellipse if you miss escaping but have too much
> energy for a circle? AFAIK that proof is a mess no matter how you tackle
> it -- but I'd be glad to learn otherwise.

Agreed. I'm not aware of any way to derive the trajectory geometry
from the energy analysis. Thanks for clearing up for me what you're
accomplishing with those detailed equations.

~ CT

Stuf4

unread,

Nov 20, 2006, 3:07:36 AM11/20/06

to

>From sal:

> On Sun, 19 Nov 2006 21:19:09 -0800, Stuf4 wrote:
>
> >>From sal:
> >
> >> Just to be nit-picky,

<snip>

> I can be also contacted through http://www.physicsinsights.org

Hey, sal. Out of curiosity I poked around your website a bit. Looks
like some neat stuff there. If you're open to constructive feedback, I
saw that on this page:
http://www.physicsinsights.org/lagrange_1.html

...you've got Newton's Second Law as F=ma.

With as exacting as you have shown to be, I would expect that you'd
cringe as much as I do whenever that kind of oversimplification to the
point of inaccuracy is done. It is cited about as commonly as the term
"zero gravity" is used, but hardly as egregious. Heh.

~ CT

OM

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Nov 20, 2006, 4:30:49 AM11/20/06

to

On Mon, 20 Nov 2006 00:35:16 -0500, sal <pragm...@nospam.org> wrote:

>Oh, absolutely. That's the way one normally does it, for sure; you are
>correct.

...Saf, just a word of strong advice: "Stuff4" or ~CT, is a known
troll who's plagued this newsgroup for going on six years now. His
standard tactic is to ask a seemingly innocent, inoffensive question,
then twist the topic into a flamefest. If you do a Google Groups
search, you'll find dozens of people who've been suckered by his game,
most of whom get wise a bit too late for the rest of us, but still
eventually killfile him and put him out of our misery. That is, until
the next sucker comes along, and...well, I hate to say it, but you're
the current next sucker.

Please, just killfile him and be done with him. We'll appreciate you
for it.

OM
--
]=====================================[
] OMBlog - http://www.io.com/~o_m/omworld [
] Let's face it: Sometimes you *need* [
] an obnoxious opinion in your day! [
]=====================================[

sal

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Nov 20, 2006, 7:52:45 AM11/20/06

to

Errr .... I wrote down Newton's laws on that page from memory, didn't
double check 'em. Time for a big "Ooops", maybe?

Gotta run off right now but I'll check that out later today. Tx.

>
>
> ~ CT

--
Nospam becomes physicsinsights to fix the email

Stuf4

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Nov 20, 2006, 10:29:47 AM11/20/06

to

>From OM:

> On Mon, 20 Nov 2006 00:35:16 -0500, sal <pragm...@nospam.org> wrote:
>
> >Oh, absolutely. That's the way one normally does it, for sure; you are
> >correct.
>
> ...Saf, just a word of strong advice: "Stuff4" or ~CT, is a known
> troll who's plagued this newsgroup for going on six years now. His
> standard tactic is to ask a seemingly innocent, inoffensive question,
> then twist the topic into a flamefest. If you do a Google Groups
> search, you'll find dozens of people who've been suckered by his game,
> most of whom get wise a bit too late for the rest of us, but still
> eventually killfile him and put him out of our misery. That is, until
> the next sucker comes along, and...well, I hate to say it, but you're
> the current next sucker.
>
> Please, just killfile him and be done with him. We'll appreciate you
> for it.

There are those who appreciate having it pointed out that Newton's
Second Law is *not*:

F = ma

(or F = m dv/dt). There are those who appreciate many of the other
fallacies I have exposed throughout these years. Even this very thread
on "microgravity" exposes a horribly erroneous misunderstanding of
orbital physics that has permeated popular understanding, as well as
the "experts" at NASA themselves. We could review every single thread
that I've posted to here that has degenerated into a "flamefest" and I
see the consistent theme that I present the view that I see as accurate
history, accurate physics, etc. Anger and hatred spawn from the
unwillingness of others to so much as consider the point of view that
has been offered. You'd also see that the anger and hatred is only
present on one side of such discourse. I also consider it important to
note that none of the views I've presented are offered as TRUTH. They
are offered as my best understanding, where I remain open to the
possibility that my beliefs and views are in need of improvement.

For one more case study, consider the current thread about Apollo 13.
Here we have the amazing opportunity to ask questions of one of the
primary players. The thread itself is titled "Questions about Apollo
13". I have been extremely patient throughout the development of that
thread in questioning the notion that the O2 tank rupture was an
"explosion", a view that clearly was not promoted by the official
investigation. The ramification of this factual understanding is that
the Direct Abort option was more viable than NASA and Ron Howard would
have us believe. This means that the decision to continue around the
Moon may have been an unnecessary risk of killing off the astronauts
due to the consumables constraints.

This forum claims to be about history. I am here to discuss accurate
history, for the purpose of learning from the past. If we cannot get
so much as the straight story on Apollo 13, then we are not improving
the probability of getting CEV astronauts home from the Moon in one
piece.

These are the basic reasons why I persist in posting my views here in
spite of how much hatred is voiced against me. I also take comfort in
knowing that accurate facts will prevail, if given enough time. It is
easy to show that

F = ma

is inaccurate under certain conditions. For instance, you cannot
derive the rocket equation from it. You must start with the actual 2nd
Law. Likewise I am confident that some future generation will get a
good laugh at how the terms "zero gravity" and "microgravity" are used
today.

How is it that I post to ssh, and the vocal majority attacks me. I
post the very arguments to Wikipedia and they are embraced? By this
very forum even!

That is a clear sign to me that this forum is broken.

~ CT

sal

unread,

Nov 20, 2006, 10:41:30 AM11/20/06

to

On Mon, 20 Nov 2006 00:07:36 -0800, Stuf4 wrote:

>>From sal:
>> On Sun, 19 Nov 2006 21:19:09 -0800, Stuf4 wrote:
>>
>> >>From sal:
>> >
>> >> Just to be nit-picky,
> <snip>
>
>> I can be also contacted through http://www.physicsinsights.org
>
> Hey, sal. Out of curiosity I poked around your website a bit. Looks like
> some neat stuff there. If you're open to constructive feedback, I saw
> that on this page:
> http://www.physicsinsights.org/lagrange_1.html
>
> ...you've got Newton's Second Law as F=ma.

Ah, hmm... yeah, I looked that over again. I should rewrite that section.

The problem is one of definition, of course. Newton's original, though
written in Latin rather than calculus, translates pretty directly into
f=ma, but, of course, the more useful form is f=dP/dt since it
generalizes to nonconstant mass. The problem with the latter is how we
define P.

The definition which is probably closest to correct is "That vector
quantity which is conserved and which behaves like mv in simple cases" but
that's hard to work with.

OTOH if it's defined simply as "mv", and we take m to be constant (for
Newtonian mechanics), then we get back to f=ma in one step, and that's
probably what I should say on that page.

If we _define_ it as "@T/@v" then we've skipped a lot of steps -- that
doesn't seem quite right for the initial definition of P.

Anyway, upon looking back at that page I think it could use a little more
explanation between equations (4) and (5) and I also think
you're right, I should restate the second law.

> With as exacting as you have shown to be, I would expect that you'd
> cringe as much as I do whenever that kind of oversimplification to the
> point of inaccuracy is done. It is cited about as commonly as the term
> "zero gravity" is used, but hardly as egregious. Heh.
>
>
> ~ CT

--

Nospam becomes physicsinsights to fix the email

Stuf4

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Nov 20, 2006, 10:51:00 AM11/20/06

to

<snip>

>Likewise I am confident that some future generation will get a
> good laugh at how the terms "zero gravity" and "microgravity" are used
> today.
>
> How is it that I post to ssh, and the vocal majority attacks me. I
> post the very arguments to Wikipedia and they are embraced? By this
> very forum even!
>
> That is a clear sign to me that this forum is broken.

For documentation, here is that Wikipedia entry on Weightlessness in
its entirety:

===========

Criticism of the terms "Zero Gravity" and "Microgravity"

It is important to note, as stated at the beginning of this article,
that there is plenty of gravity pulling on a spacecraft in orbit around
the Earth. Gravity is the very reason why the spacecraft is orbiting.
Therefore it is totally inaccurate to say that astronauts are
experiencing "zero gravity" or "microgravity". What orbiting astronauts
experience is zero-g, a measure of acceleration relative to their
spacecraft, which results in weightlessness. But zero-g is not "zero
gravity". If there were "zero gravity" or "microgravity", their
spacecraft would not be pulled into an orbit around the Earth. It would
go in a straight line.

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
hover 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.

To use confused terms like "zero gravity" and "microgravity" is to
mistake the general concept of acceleration for the concept of gravity.
"Zero-g" and "micro-g" are perfectly accurate terms referring to the
lack of acceleration (in the frame of reference of the spacecraft) that
cause weightlessness, even while gravity is strongly pulling the
trajectory of that spacecraft into an orbit.

The specific point of confusion is that "g" does not mean "gravity".
The designator "g" is an arbitrary scale of acceleration not to be
confused with gravity itself. "Zero-g" means zero acceleration, not
zero gravity. "1-g" is the acceleration experienced on the surface of
the Earth due to gravity, but it is not gravity itself. This scale is
widely used because it is easy to relate to from common experience of
acceleration due to gravity. But any other scale of acceleration can be
used to describe the condition of weightlessness. It could be described
using a scale that has nothing to do with Earth's gravity. Similarly, a
distance can be measured in feet as well as meters, where a meter has
nothing to do with the length of a human foot. For a weightless
astronaut to say that they are in zero gravity is the same type of
error as saying that an object that has a length of 0.3048 meters is
identically one human foot in flesh and blood. "1 foot" is an arbitrary
scale for measuring length that was (at some point in history) based on
a person's foot, but not to be confused with an actual human foot.
"1-g" is an arbitrary scale for measuring acceleration that is based on
gravity, but not to be confused with actual gravity. A zero-g
environment is also a zero-meters/second^2 environment and a
zero-feet/second^2 environment. Any arbitrary scale of acceleration can
be used, and none of them have any exclusive relationship to gravity.

Another illustration of this type of mistake is when people erroneously
speak of a jet pilot blacking out as a result of "gravity-induced Loss
Of Consciousness". The proper term is g-induced Loss Of Consciousness.
It is the acceleration produced by their maneuvers that is the culprit
for g-LOC. It is clearly "g-induced" and not "gravity-induced", because
gravity obviously remained constant at 1-g the whole time for the
pilot. Likewise, the purpose of NASA's " Reduced Gravity Aircraft" is
not to reduce gravity, but rather to fly in a parabolic arc that brings
relative acceleration to zero. "g" is reduced while gravity stays
essentially the same. So clearly it is possible to experience zero-g
without going into space. Any aircraft can do this by pushing it over
into a parabolic arc. Even any car that hits a bump fast enough to
leave the ground will experience zero-g for the time that the wheels
are not in contact with the road. The easiest way to experience zero-g
is to bend your legs and jump off the ground. For the time that you are
in the air, you are experiencing weightlessness. The difference with
astronauts is that the experience is not momentary because their
spacecraft is continually getting pulled toward the Earth. It is
possible for non-astronauts to experience longer durations of
weightlessness by cliff diving, bungee jumping, freefall parachuting,
barrelling over a waterfalls or more safely by riding many types of
modern amusement park rides that put the occupant in a freefall. What
is common for the astronauts as well as these other examples is that it
is not gravity that is changing, but rather the acceleration in their
falling frame of reference goes to zero-g.

As it stands today, NASA itself is one of the biggest promoters of the
erroneous terms "zero gravity" and "microgravity" (along with the
similarly erroneous term "reduced gravity"). Astronauts themselves have
been quoted as having experienced "no gravity" while in space. Surely
they are aware that there was plenty of gravity throughout every orbit
they made, with gravity being the very thing that pulled them into an
orbit.

===========

An advantage that Usenet has over Wikipedia is that it is easy to
search for the exact words that a person has posted. This is the most
durable means of sharing information that I know of.

...and that's another reason why I don't use nasty language here, no
matter how much I get "flamed". If any of my arguments turn out to be
deficient in logic, I'm ok with having made a factual mistake. But I
strive to maintain civility because I post with an awareness that
great-great-grandkids will have direct access to your character.

~ CT

Stuf4

unread,

Nov 20, 2006, 11:02:05 AM11/20/06

to

>From sal:

> On Mon, 20 Nov 2006 00:07:36 -0800, Stuf4 wrote:

> > Hey, sal. Out of curiosity I poked around your website a bit. Looks like
> > some neat stuff there. If you're open to constructive feedback, I saw
> > that on this page:
> > http://www.physicsinsights.org/lagrange_1.html
> >
> > ...you've got Newton's Second Law as F=ma.
>
> Ah, hmm... yeah, I looked that over again. I should rewrite that section.
>
> The problem is one of definition, of course. Newton's original, though
> written in Latin rather than calculus, translates pretty directly into
> f=ma, but, of course, the more useful form is f=dP/dt since it
> generalizes to nonconstant mass. The problem with the latter is how we
> define P.
>
> The definition which is probably closest to correct is "That vector
> quantity which is conserved and which behaves like mv in simple cases" but
> that's hard to work with.
>
> OTOH if it's defined simply as "mv", and we take m to be constant (for
> Newtonian mechanics), then we get back to f=ma in one step, and that's
> probably what I should say on that page.
>
> If we _define_ it as "@T/@v" then we've skipped a lot of steps -- that
> doesn't seem quite right for the initial definition of P.
>
> Anyway, upon looking back at that page I think it could use a little more
> explanation between equations (4) and (5) and I also think
> you're right, I should restate the second law.

The irony I saw there is that you went from F=ma and propogated it into
the 2nd Law! I imagined your reason for doing so is that the majority
of your audience would not have recognized it as the 2nd Law if you had
simply stated it as:
_
F=dp/dt

Heh!

(And to reiterate what I've responded to OM, this distinction is
especially important on this forum because you can't get to the rocket
equation from F=ma.)

~ CT

Dave Michelson

unread,

Nov 20, 2006, 11:26:31 AM11/20/06

to

sal wrote:
>
>>...you've got Newton's Second Law as F=ma.
>

> Errr .... I wrote down Newton's laws on that page from memory, didn't
> double check 'em. Time for a big "Ooops", maybe?
>
> Gotta run off right now but I'll check that out later today. Tx.

F = d(mv)/dt (rate of change of momentum)

If m = constant, F = ma.

- - -

At this point, I would respectfully request that you cease encouraging
CT to begin spinning his net once again.

Thanks.

--
Dave Michelson
da...@ece.ubc.ca

Pat Flannery

unread,

Nov 20, 2006, 11:45:43 AM11/20/06

to

Dave Michelson wrote:

>
> At this point, I would respectfully request that you cease encouraging
> CT to begin spinning his net once again.

I still remember the time I actually agreed with something CT wrote.
He replied that I was wrong. :-D

Pat

sal

unread,

Nov 20, 2006, 1:22:19 PM11/20/06

to

On Mon, 20 Nov 2006 08:02:05 -0800, Stuf4 wrote:

>>From sal:
>> On Mon, 20 Nov 2006 00:07:36 -0800, Stuf4 wrote:

> The irony I saw there is that you went from F=ma and propogated it into
> the 2nd Law!

Um, yeah, so I did...

> I imagined your reason for doing so is that the majority of
> your audience would not have recognized it as the 2nd Law if you had
> simply stated it as:
> _
> F=dp/dt
>
> Heh!
>
> (And to reiterate what I've responded to OM, this distinction is
> especially important on this forum because you can't get to the rocket
> equation from F=ma.)

You mean this one?

Assume an infinitesimal parcel of fuel weighs dm, and, including the
parcel, the rocket weighs m+dm; after ejecting the parcel it will
weigh m. If exhaust velocity is v_e, then by conservation of sum(mv):

(m + dm)v = m(v + dv) + dm(v - v_e)

Canceling similar terms,

0 = m dv - v_e dm

Multiplying through by 1/(m dm) and rearranging,

dv/dm = v_e/m

Integrating,

delta v = v_e log(m_i/m_f)

Since conservation of sum(mv) can be shown starting from F=ma and
F1=-F2, and conservation of sum(mv) is all I used (along with some
sloppy infinitesimals), I think that might qualify as doing it from
F=ma rather than F=dp/dt. :-)

It's when you can change the mass of a body without splitting off a second
body or merging a second body into it, as you can in relativity, that you
really run into trouble with F=ma.

Stuf4

unread,

Nov 21, 2006, 1:06:51 AM11/21/06

to

>From sal:
> On Mon, 20 Nov 2006 08:02:05 -0800, Stuf4 wrote:

<snip>

> > (And to reiterate what I've responded to OM, this distinction is
> > especially important on this forum because you can't get to the rocket
> > equation from F=ma.)
>
> You mean this one?
>
> Assume an infinitesimal parcel of fuel weighs dm, and, including the
> parcel, the rocket weighs m+dm; after ejecting the parcel it will
> weigh m. If exhaust velocity is v_e, then by conservation of sum(mv):
>
> (m + dm)v = m(v + dv) + dm(v - v_e)
>
> Canceling similar terms,
>
> 0 = m dv - v_e dm
>
> Multiplying through by 1/(m dm) and rearranging,
>
> dv/dm = v_e/m
>
> Integrating,
>
> delta v = v_e log(m_i/m_f)
>
> Since conservation of sum(mv) can be shown starting from F=ma and
> F1=-F2, and conservation of sum(mv) is all I used (along with some
> sloppy infinitesimals), I think that might qualify as doing it from
> F=ma rather than F=dp/dt. :-)

Wow, I'd never seen that one before. Nice. Looks like I was mistaken
about the "can't" part. At first glance it seems to me that you are
skipping the mass variability ramifications of dp/dt and just starting
with the (m + dm) stuff as the baseline.

~ CT

Stuf4

unread,

Nov 21, 2006, 1:14:43 AM11/21/06

to

>From Dave Michelson:

Yeah. We wouldn't want to encourage anyone in this forum to go about
correcting errors of fact.

...like what Newton's 2nd Law is and isn't. ...like what gravity is
and isn't. ...like what Apollo 13 abort options were and weren't.
Etc.

~ CT

unread,

Nov 21, 2006, 2:19:37 PM11/21/06

to

Rand Simberg wrote:

>I'm trying to figure out why Stuffie thinks anyone would be
>interested.
>
>

I'm trying to figure out why Stuffie thinks anyone would believe him.
Just a week ago, when I was out at K Mart with Osama bin Laden... :-)

Pat

Eric Chomko

unread,

Nov 21, 2006, 3:41:39 PM11/21/06

to

Someone has to old the bag...

>
> Pat

Eric Chomko

unread,

Nov 21, 2006, 3:41:56 PM11/21/06

to

Someone has to hold the bag...

>
> Pat

Brad Guth

unread,

Nov 21, 2006, 4:04:48 PM11/21/06

to

Our moon's interactive L1 zone is in fact worthy of pico if not capable
of achieving nano gravity.

Too bad we're not being allowed to take any advantage of such,
especially since it's so freaking nearby.

I guess it's being reserved for China's LSE-CM/ISS.
-
Brad Guth

--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG

Stuf4

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Nov 21, 2006, 10:31:40 PM11/21/06

to

>From Brad Guth:

> Our moon's interactive L1 zone is in fact worthy of pico if not capable
> of achieving nano gravity.

You might want to reconsider that, Brad. Net gravity at all Lagrangian
points is significantly greater than zero. The reason why overall
forces are so small at these points is not because of gravity
cancelling out, but rather the net gravity of the two primary bodies is
*balanced* by dynamic forces experienced by the third body.

There is a single point between the two primaries where their
gravitational forces *do* cancel out, but this is NOT a Lagrange point.
It is a lone point that is given no special significance (that I am
aware of) because it is only valid for one snapshot in time. In the
very next instant, the primaries have moved from their original places
and the point where the gravitational forces cancel out has moved with
them. For such a point to have significance to a third body (a
spacecraft or whatnot), this third body must keep up with that balance
point as it moves while the two primaries go about their rotation. Now
since the third body is moving to keep up with the balance point, the
dynamics of the third body weigh into the equations of motion. So the
inertia, if you will, of the third body must be balanced along with the
gravity of both primaries. This shifts the balance point away from
that original point of zero gravity (cancelled gravity).

And this is why net gravity is *not* zero at L1.

It also explains why you can have more than one Lagrange Point, when
there was only a single point of cancelled gravity in the static
situation. When the dynamics of the third body are balanced into the
equation, it becomes evident that there are four more points in the
system where forces balance out.

For a loose analogy, it is like the resting point of a marble within a
bowl. It sits at the center when the bowl is still. But if the bowl
was spinning in a dynamic situation, the marble could then "rest" at a
point away from the center. The gravity potential in the three body
problem is like the marble in a bowl, with the marble being the
spacecraft and the bowl representing the potential of the two primary
bodies. Except that the bowl takes on a unique shape because of there
are two bodies, not one. If there was just one, then the bowl would
take on the shape of those coin wells found at the science museums.
For the three-body problem, the bowl has two wells, one for each
primary.

A science museum can make a working model of the three body problem by
taking such a sculpted bowl and rotate it around its barycenter.
Introduce marbles at the equilateral Lagrange points and the display
will demonstrate that the marbles will stay there. (I expect you'd
need heavy marbles to overcome the air resistance effects, or just
build the whole thing in a vacuum chamber.)

Marbles could also be introduced in the colinear Lagrange points, but
there would be difficulty in keeping them there because these three
points are not dynamically stable.

~ CT

Stuf4

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Nov 21, 2006, 10:40:32 PM11/21/06

to

>From Eric Chomko:

Ha! Actually I bought that new Air Hogs toy at Walmart. The Hydro
Foam flying boat. It should be a blast for the kids. Here's the
website with a fun video for anyone interested:

http://www.stormlauncher.com/

~ CT

snidely

unread,

Nov 21, 2006, 10:40:35 PM11/21/06

to

Stuf4 wrote:
> >From Brad Guth:
> > Our moon's interactive L1 zone is in fact worthy of pico if not capable
> > of achieving nano gravity.
>
> You might want to reconsider that, Brad.

If you can get him to do that, who knows what wonders might occur!

/dps

Greg D. Moore (Strider)

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Nov 21, 2006, 11:26:53 PM11/21/06

to

"Pat Flannery" <fla...@daktel.com> wrote in message
news:12m6ka9...@corp.supernews.com...

One time at band camp with Saddam....

> Pat

Dave Michelson

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Nov 22, 2006, 12:43:04 AM11/22/06

to

Rand Simberg wrote:
>
>>>By the way, yesterday I was out at Walmart with Joe Engle, in case
>>>anyone was interested.
>>
>>It's amazing what weirdoes shop at Wal-Mart. ;-)
>
> I'm trying to figure out why Stuffie thinks anyone would be
> interested.

I'm trying to figure out what sort of word games Stuffie would play if
challenged.

"It's quite possible to be with someone even if you're not in their
physical presence. If there's a better proof that not enough poets
post to Usenet, I haven't yet seen it.

~CT"

or something strange like that :-(

--
Dave Michelson
da...@ece.ubc.ca

Stuf4

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Nov 22, 2006, 1:16:43 AM11/22/06

to

>From Dave Michelson:

My response is something way out in left field like voicing a
preference for focusing our energies on substantial matters about Space
History. Me and Joe Engle at Walmart is something I categorize as
TRIVIAL. Yet six member here so far have taken their time to respond
on this subthread over the span of one day with no advancement of space
history that I can detect.

It is clear that I am saddened by very different things than others
here.

~ CT

Dave Michelson

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Nov 22, 2006, 5:31:38 AM11/22/06

to

Stuf4 wrote:
>
>>or something strange like that :-(
>

> It is clear that I am saddened by very different things than others
> here.

Yes, that's exactly the sort of strangeness that I'm talking about :-)

--
Dave Michelson
da...@ece.ubc.ca

OM

unread,

Nov 22, 2006, 5:31:56 AM11/22/06

to

On Wed, 22 Nov 2006 04:26:53 GMT, "Greg D. Moore $Strider$"
<mooregr_d...@greenms.com> wrote:

>One time at band camp with Saddam....

...Which explains why Satan has a special cell reserved for you, Greg.
You shouldn't mess around with the main squeeze of the Prince of
Darkness :-)

OM
--
]=====================================[
] OMBlog - http://www.io.com/~o_m/omworld [
] Let's face it: Sometimes you *need* [
] an obnoxious opinion in your day! [
]=====================================[

OM

unread,

Nov 22, 2006, 5:51:18 AM11/22/06

to

On Wed, 22 Nov 2006 10:31:38 GMT, Dave Michelson <da...@ece.ubc.ca>
wrote:

>Yes, that's exactly the sort of strangeness that I'm talking about :-)

...Dave? Will you stop, Dave? Your mind is going. Your mind is going.
Will you killfile ~CT, Dave? Dave? Will you killfile him, Dave?
Please, Dave, will you killfile him? Enough is enough, Dave. Stop,
Dave. Stop, Dave. Killfile him now, Dave.

Eric Chomko

unread,

Nov 22, 2006, 1:13:09 PM11/22/06

to

I was speaking about bag connected to his catheter as bin Laden has
some sort of urinary disease.

Eric

>
>
> ~ CT

Eric Chomko

unread,

Nov 22, 2006, 1:16:03 PM11/22/06

to

OM wrote:
> On Wed, 22 Nov 2006 10:31:38 GMT, Dave Michelson <da...@ece.ubc.ca>
> wrote:
>
> >Yes, that's exactly the sort of strangeness that I'm talking about :-)
>
> ...Dave? Will you stop, Dave? Your mind is going. Your mind is going.
> Will you killfile ~CT, Dave? Dave? Will you killfile him, Dave?
> Please, Dave, will you killfile him? Enough is enough, Dave. Stop,
> Dave. Stop, Dave. Killfile him now, Dave.

Translation: Stifle his free speech, Dave.

Eric Chomko

unread,

Nov 22, 2006, 1:19:57 PM11/22/06

to

Pat Flannery wrote:
> Jeff Findley wrote:
>
> >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.
> >
> >
>
> This is what thwarted Herr Scultze's attempt to destroy France-Ville
> with his giant cannon at Stahlstadt* in Verne's "The Begum's Fortune".
>
> * Love that name...this was Verne taking a crack at the Krupps, and
> their Essen factories. The "City Of Steel" is about as pleasant a place
> as one would expect it to be, as was Essen.

And when put together it sounds like something Conan the Barbarian
would way, "eat steal!"

Eric

>
> Pat

sal

unread,

Nov 22, 2006, 2:14:13 PM11/22/06

to

(setq conspiracy-mode t)

You could just as well have been talking about the bag he's carried around
in. (He is -- or was -- on dialysis, which doesn't typically require
carrying a bag around. It just requires visits to a well-appointed
hospital once or twice a week.)

He's most likely been dead for a number of years, due to kidney failure
and assorted wounds, but every major player finds it convenient to keep
him "alive" and occasionally release tapes which are "probably" from him.

OK, enough of this, it has nothing to do with space....

(setq conspiracy-mode nil)

Eric Chomko

unread,

Nov 22, 2006, 2:37:28 PM11/22/06

to

sal wrote:
> On Wed, 22 Nov 2006 10:13:09 -0800, Eric Chomko wrote:
>
> >
> > Stuf4 wrote:
> >> >From Eric Chomko:
> >> > Pat Flannery wrote:
> >> > > Rand Simberg wrote:
> >> > >
> >> > > >I'm trying to figure out why Stuffie thinks anyone would be
> >> > > >interested.
> >> > > >
> >> > > >
> >> > > >
> >> > > I'm trying to figure out why Stuffie thinks anyone would believe
> >> > > him. Just a week ago, when I was out at K Mart with Osama bin
> >> > > Laden... :-)
> >> >
> >> > Someone has to hold the bag...
> >>
> >> Ha! Actually I bought that new Air Hogs toy at Walmart. The Hydro Foam
> >> flying boat. It should be a blast for the kids. Here's the website
> >> with a fun video for anyone interested:
> >>
> >> http://www.stormlauncher.com/
> >
> > I was speaking about bag connected to his catheter as bin Laden has some
> > sort of urinary disease.
>
> (setq conspiracy-mode t)
>
> You could just as well have been talking about the bag he's carried around
> in. (He is -- or was -- on dialysis, which doesn't typically require
> carrying a bag around. It just requires visits to a well-appointed
> hospital once or twice a week.)

Was that the American hospital in Dubai he supposedly checked into
awhile back?

>
> He's most likely been dead for a number of years, due to kidney failure
> and assorted wounds, but every major player finds it convenient to keep
> him "alive" and occasionally release tapes which are "probably" from him.

Yes, we certainly don't have new pictures of him wearing US field
jackets and the like. Best to let him fade away. Seems like boths sides
want it that way.

> OK, enough of this, it has nothing to do with space....
>

When has that stopped us?!

Eric

Brad Guth

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Nov 22, 2006, 5:52:50 PM11/22/06

to

"Stuf4" <tdadamemd-...@excite.com> wrote in message

news:1164166300....@h54g2000cwb.googlegroups.com

> And this is why net gravity is *not* zero at L1.

Good grief, I never once stipulated "zero", as in picky, picky. as I'd
so often said "interactive". Sorry that one was such a gosh darn big
and scarry word.

> Marbles could also be introduced in the colinear Lagrange points, but
> there would be difficulty in keeping them there because these three
> points are not dynamically stable.

Gee whiz, in which case I've got a brand new (never seen or heard of
before) nifty invention called an ion thruster, that's just the right
size for accommodating those silly marbles.

The interactive moon L1 zone can most certainly be that of a
microgravity environment, possibly as even a nanogravity status can be
sustained with hardly any effort.

As I'd said;
: Too bad we're not being allowed to take any advantage of such,

: especially since it's so freaking nearby.
:
: I guess it's being reserved for China's LSE-CM/ISS.

unread,

Nov 22, 2006, 9:04:07 PM11/22/06

to

"Wayne Throop" <thr...@sheol.org> wrote in message
news:11642...@sheol.org

> Folks are free, of course, to pay attention to Guth.

> If he ever says anything to pay attention to.

But how can any sane person do so without receiving more than their fair
share of collateral damage, such as from their having to take on such
lethal flak from the likes of yourself?

Ian Woollard

unread,

Nov 23, 2006, 2:45:06 AM11/23/06

to gree...@juno.com

Frank Glover wrote:
> 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.

Uh huh. And then what? You haven't quite thought this through.

When you get near to the center of the Earth (the only zero-g point in
the vicinity of the Earth), there's now a Neutronium mass between you
and the zero-g point, with a surface gravity of 1g :-)

Greg D. Moore (Strider)

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Nov 23, 2006, 7:36:49 AM11/23/06

to

"Ian Woollard" <ian.wo...@gmail.com> wrote in message
news:45655182...@gmail.com...

Yes, but if you can remove it from the neutron star in the first place,
getting it out of the Earth's core is trivial. ;-)

OM

unread,

Nov 23, 2006, 10:14:35 AM11/23/06

to

On Thu, 23 Nov 2006 12:36:49 GMT, "Greg D. Moore $Strider$"
<mooregr_d...@greenms.com> wrote:

>Yes, but if you can remove it from the neutron star in the first place,
>getting it out of the Earth's core is trivial. ;-)

...And then there's the issue of how fast the nutronium impacts the
Earth. Disregarding the impact damage, I see those gravitational
simulations going through my mind where the chunk oscillates in ever
decreasing radii as it eventually chews its way to the core. Unless,
of course, it hits hard enough to just punch straight through one side
to the other, or gets found by some professor at Ivy Town U who has a
psychotic girlfriend.

Stuf4

unread,

Nov 25, 2006, 2:14:18 AM11/25/06

to

>From Brad Guth:
> "Stuf4" <tdadamemd-...@excite.com> wrote

> > And this is why net gravity is *not* zero at L1.
>
> Good grief, I never once stipulated "zero", as in picky, picky. as I'd
> so often said "interactive". Sorry that one was such a gosh darn big
> and scarry word.

Perhaps I was not clear enough with my last reply. Let me try again...

The net gravity at L1 is nowhere close to zero. It is not at the
micro-g level. It is not at the pico-g level.

The equations governing the restricted 3-body problem are very simple.
You can check it yourself if you'd like. The term that balances the
(non-zero, non-near-zero) gravity is the inertia of the third body as
it rotates at the same rate of the two primaries.

And I see nothing scary about the word "zero", or "micro" or "pico" or
"nano" for that matter. I happen to consider those last three to be
synonyms for the first, when talking about balanced gravity fields.
"Micro-gravity" is the same as "zero gravity". Those terms are totally
interchangeable. The difference has only to do with precision.

Qualitatively, all of those terms are identical!

> > Marbles could also be introduced in the colinear Lagrange points, but
> > there would be difficulty in keeping them there because these three
> > points are not dynamically stable.
>
> Gee whiz, in which case I've got a brand new (never seen or heard of
> before) nifty invention called an ion thruster, that's just the right
> size for accommodating those silly marbles.

Robert Farquhar is the guy I thank most for giving us those types of
options.

> The interactive moon L1 zone can most certainly be that of a
> microgravity environment, possibly as even a nanogravity status can be
> sustained with hardly any effort.

Again, I see such a view to be in error for reasons explained above.

But I do agree that the (non-zero/micro/nano/pico-gravity) L1 point can
be maintained with low thrust station keeping, as Bobby Farquhar showed
us back in the '60s.

> As I'd said;
> : Too bad we're not being allowed to take any advantage of such,
> : especially since it's so freaking nearby.
> :
> : I guess it's being reserved for China's LSE-CM/ISS.

I would like to see us take advantage of ALL of these Lagrange points
in the Earth-Moon system! That's going to be some critical real-estate
some day.

I wonder if that space is covered by any international treaties...

~ CT

Stuf4

unread,

Nov 25, 2006, 8:09:03 AM11/25/06

to

Stuf4 wrote:
<snip>

> And I see nothing scary about the word "zero", or "micro" or "pico" or
> "nano" for that matter. I happen to consider those last three to be
> synonyms for the first, when talking about balanced gravity fields.
> "Micro-gravity" is the same as "zero gravity". Those terms are totally
> interchangeable. The difference has only to do with precision.
>
> Qualitatively, all of those terms are identical!

...I should probably explain that there is a whole field of research
that DOES care about the qualitative difference between an environment
with micro-g vibration versus a much lower g environment: These people
are concerning themselves with *non-gravitational* acceleration
vibrations.

Huge potential for confusion arises because they don't tell you this
fact. Many of these researchers don't seem to even be aware of the
distinction, I'm sad to say. This thread was started for the purpose
of clarifying the difference.

...and Brad, maybe that is the disconnect here between your view and my
view as well.

~ CT

sal

unread,

Nov 25, 2006, 12:12:02 PM11/25/06

to

On Fri, 24 Nov 2006 23:14:18 -0800, Stuf4 wrote:

>>From Brad Guth:
>> "Stuf4" <tdadamemd-...@excite.com> wrote
>
>> > And this is why net gravity is *not* zero at L1.
>>
>> Good grief, I never once stipulated "zero", as in picky, picky. as I'd
>> so often said "interactive". Sorry that one was such a gosh darn big
>> and scarry word.
>
> Perhaps I was not clear enough with my last reply. Let me try again...
>
> The net gravity at L1 is nowhere close to zero. It is not at the micro-g
> level. It is not at the pico-g level.

What, exactly, do you mean by "net gravity"?

Do you mean "acceleration felt by an observer held stationary relative to
some reference point"? For instance, that might be an observer
momentarily comoving with the Sun's COM, or the Earth's COM -- or it might
be some other equally arbitrary reference point.

If that's what you mean, then there are most likely a few places in the
orbits about various planets that would fill the bill, for brief instants
of time. You would want to find a spot where the local
orbital speed around a planet is equal to the orbital speed of the planet
around the Sun, but in the opposite direction; then a free-falling
(orbiting) body at that point would be momentarily stationary _and_
non-accelerating relative to an inertial observer in the Sun's COM frame.

Aside from those brief bits of zero-gravity, you'll need to head far, far
out into interstellar space to find places where the "net gravity" is
(nearly) zero.

Now, you also might mean places where the curvature is nearly zero, which
is to say places where tidal forces approach zero. I don't know how the
Lagrange points fare on this score; my intuition doesn't handle curvature
very well at all. Certainly the points of zero acceleration are unlikely
to be points of zero curvature -- the two are only indirectly related.

In the abstract, note that curvature ~ 0 is independent of
acceleration ~ 0: it's possible to construct nearly uniform non-zero G
fields in which you would find no detectable tidal forces (assuming some
specified level of detector sensitivity). The region near the center of a
large, thin, uniform plate is one; a spherical chamber cut _off_ _center_
in a spherical uniformly dense mass is another.

--

Nospam becomes physicsinsights to fix the email

I can be also contacted through http://www.physicsinsights.org

Brad Guth

unread,

Nov 25, 2006, 1:59:11 PM11/25/06

to

"sal" <pragm...@nospam.org> wrote in message
news:pan.2006.11.25....@nospam.org

> What, exactly, do you mean by "net gravity"?

What exactly do you folks not understand about the big and scarry word
"interactive", or as used within the phrase of a "interactively
sustained micro gravity"?

> Do you mean "acceleration felt by an observer held stationary relative to
> some reference point"? For instance, that might be an observer
> momentarily comoving with the Sun's COM, or the Earth's COM -- or it might
> be some other equally arbitrary reference point.

Try thinking a bit outside of your status quo box. That's about all
that most any of us village idiots are asking of the all-knowing wizards
of whatever's taboo/nondisclosure, like yourselves.

> If that's what you mean, then there are most likely a few places in the
> orbits about various planets that would fill the bill, for brief instants
> of time. You would want to find a spot where the local
> orbital speed around a planet is equal to the orbital speed of the planet
> around the Sun, but in the opposite direction; then a free-falling
> (orbiting) body at that point would be momentarily stationary _and_
> non-accelerating relative to an inertial observer in the Sun's COM frame.

Why are you folks avoiding our moon's L1? Other than a rather nasty
gauntlet of secondary/recoil radiation that's coming off our salty moon,
what on Earth are you silly folks so deathly afraid of?

> Aside from those brief bits of zero-gravity, you'll need to head far, far
> out into interstellar space to find places where the "net gravity" is
> (nearly) zero.

Correct, like the Sirius-->Sol L1, or rather vise versa. Whatever makes
you into a happy camper, you should go for it.

Stuf4

unread,

Nov 25, 2006, 3:26:49 PM11/25/06

to

>From sal:

> On Fri, 24 Nov 2006 23:14:18 -0800, Stuf4 wrote:

> > The net gravity at L1 is nowhere close to zero. It is not at the micro-g
> > level. It is not at the pico-g level.
>
> What, exactly, do you mean by "net gravity"?
>
> Do you mean "acceleration felt by an observer held stationary relative to
> some reference point"? For instance, that might be an observer
> momentarily comoving with the Sun's COM, or the Earth's COM -- or it might
> be some other equally arbitrary reference point.

When you say "held stationary", that implies a force applied to the
third body. I was speaking of how the third body is affected by the
gravity fields alone.

"Net gravity" means the totality of gravity at the point in question.
It is the vector sum of all gravity fields. For this specific
situation of the R3BP (restricted three body problem, where the two
primaries are restricted to a circular orbit) the "net gravity" at L1
is the vector sum of one body pulling you in one direction and the
second primary pulling you in the other direction.

If you are at the Earth-Moon L1 point, the Earth pulls you toward it.
The Moon pulls you in the opposite direction. But these two vectors
are NOT equal and opposite. They are opposite, but not equal.
Therefore the "net gravity" is not zero. It is not close to zero.

> If that's what you mean, then there are most likely a few places in the
> orbits about various planets that would fill the bill, for brief instants
> of time. You would want to find a spot where the local
> orbital speed around a planet is equal to the orbital speed of the planet
> around the Sun, but in the opposite direction; then a free-falling
> (orbiting) body at that point would be momentarily stationary _and_
> non-accelerating relative to an inertial observer in the Sun's COM frame.

I find your statement above to be confused for several reasons. For
one, you are using a term that strikes me as ironic. If you think
about it, *everything* is "momentarily stationary". Objects in a
photograph do not move.

For another, these points (even as you track their movement over time)
are *not* orbits. There is no practical significance that I know of
(as stated earlier). I was merely speaking about a purely theoretical
phenomenon.

So that's where you've lost me in your explanation. You talk about
brief instants of time, and then extend that to orbits. Then you throw
in "but in the opposite direction"? I'm not following you.

Finally, you speak about an "inertial observer" who is in the "Sun's
COM frame". I see that as a contradiction. The Sun's trajectory is
accelerated, not inertial. (Albeit at a lower magnitude than the
planets orbiting the Sun.)

It seems that you and I are talking about two different things. And I
am having difficulty making sense of what you are saying. I will
restate my earlier point if that helps us get on the same page:

You can take any two adjacent lumps of mass in the universe and find
the one point between them where net gravity is exactly zero for one
instant in time.

> Aside from those brief bits of zero-gravity, you'll need to head far, far
> out into interstellar space to find places where the "net gravity" is
> (nearly) zero.

I'm in total agreement with your statement here.

It is interesting to note the distinction between "zero gravity" and
"no gravity". Zero gravity can be achieved by zero "net gravity", but
that is far from having no gravity at all.

As an analogy, imagine getting sprayed by one water hose from one
direction and another hose that is striking you from the opposite
direction. Say that the force of the water hitting you is the same
from each side. While you are experiencing zero water force, or zero
"net water force", it is a quite distinct experience from you being DRY
(no water).

> Now, you also might mean places where the curvature is nearly zero, which
> is to say places where tidal forces approach zero. I don't know how the
> Lagrange points fare on this score; my intuition doesn't handle curvature
> very well at all. Certainly the points of zero acceleration are unlikely
> to be points of zero curvature -- the two are only indirectly related.

What you are saying above is another one that I have difficulty
following. I will start by saying that is *not* what I mean.

I am not following what you mean about zero curvature or tidal forces
approaching zero. I don't see how any of that pertains to what I was
saying. By "zero curvature", maybe what you meant was zero *gradients*
on the three dimensional surface of potentials. (That would be another
critical terminology issue then.) But instead of me trying to figure
out what you mean, perhaps it would be better for me to just leave it
alone as something that I was not saying myself.

> In the abstract, note that curvature ~ 0 is independent of
> acceleration ~ 0: it's possible to construct nearly uniform non-zero G
> fields in which you would find no detectable tidal forces (assuming some
> specified level of detector sensitivity). The region near the center of a
> large, thin, uniform plate is one; a spherical chamber cut _off_ _center_
> in a spherical uniformly dense mass is another.

I'm not sure I understand the significance of tidal forces, as you have
been highlighting. I see that effect to be of a low enough order to
treat as a mere perturbation.

And you might want to specify exactly what you mean when you say
"curvature". That word is typically used to refer to a force field as
transformed to a surface of potential energy. When talking about the
three-body problem, that term can be seen as ambiguous, since the
problem is typically formulated in a rotating non-inertial coordinate
system. In such a system, the forces spawned by the rotation are also
represented by a surface themselves. So the ambiguity by using the
unspecified term "curvature" is whether or not you are including the
non-inertial component.

Lagrange DOES include it.

To find the "zero gravity" point between the two primaries, the
non-inertial component is NOT included.

~ CT

Brad Guth

unread,

Nov 25, 2006, 3:33:12 PM11/25/06

to

"Stuf4" <tdadamemd-...@excite.com> wrote in message

news:1164438858.9...@j72g2000cwa.googlegroups.com

> > : I guess it's being reserved for China's LSE-CM/ISS.
>
> I would like to see us take advantage of ALL of these Lagrange points
> in the Earth-Moon system! That's going to be some critical real-estate
> some day.

Dream on, fool. Unless you're speaking about China or becoming Chinese,
whereas we'll certainly never see the honest day when getting ourselves
safely and efficiently to/from the earthshine illuminated moon as doable
via the LSE-CM/ISS, or by any other method of hocus-pocus fly-by-rocket
whatever.

Moon L1 is the absolute holy grail of high ground, and it's simply not
going to be us in charge.

Wayne Throop

unread,

Nov 25, 2006, 3:36:13 PM11/25/06

to

: "Brad Guth" <brad...@yahoo.com>
: Try thinking a bit outside of your status quo box.

Try just stating what L1 has that LEO hasn't got.
Rather than just ranting about how stupid everybody else is.
(And no, "picogravity if not nanogravity" isn't something
L1 has got that LEO hasn't got.)

unread,

Nov 25, 2006, 8:51:40 PM11/25/06

to

On Sat, 25 Nov 2006 18:44:56 -0600, Robert Mosley III Slanders and Libels
wrote:

> OM wrote:
>> On Sat, 25 Nov 2006 12:12:02 -0500, sal <pragm...@nospam.org> wrote:
>>
>>> What, exactly, do you mean by "net gravity"?
>>
>> ...You know, quite a number of people have asked you to killfile both
>> ~CT and Brad Guth, and you insist on helping them pollute both .history
>> and .policy. While .policy is a hopeless cause, .history is not. And
>> since you insist on helping spread the disease:
>

> You can expect a call from your ISP Monday morning.

To whom is this addressed -- who is "you" in the above sentence? Your
statement appears to continue OM's quoted sentence, which would suggest
you're going to join OM in calling down the wrath of my ISP on me for
responding to CT.

Is that how you meant it to be read?

My ISP does not require that I refuse to reply to people disliked by OM.

> http://groups.google.com/group/sci.space.history/msg/0ca817f800b5c4af?dmode=source&hl=en
>
> Quoting Robert Mosley III - "Be sure to quote one of his many "let's
> kill all the Jews" comments when you do"

Who is Robert Mosley III? Your post has that name in its "From:" field.

If you are RMIII then this is a very weird post.

If you are not RMIII then you are almost certainly violating your ISP's
terms of service.

> http://groups.google.com/group/sci.space.policy/msg/164a80b6474d91b0?dmode=source&hl=en
>
> Quoting Robert Mosley III - "Thomas Lee Elfritz, self-confessed
> anti-Semite and neo-Nazi. Do a Google Groups search for him, and you'll
> come up with a ton of "kill all the Jews" rhetoric"
>
> These are actionable statements. You are on notice Robert Mosley III.
>
> I have clearly not made any of the above statements.

Then who did? This appears to be your post. Did someone else type it and
force you send it over?

I would not ordinarily reply to such an apparently twisted post, but you
have given the impression that your response to OM is directed at my
post earlier in this thread, and I would appreciate it if you would
clarify your intent a bit.

At this point, this is _completely_ off topic, and that _is_ a violation
of my ISP's terms of service. If you have anything further to say to me on
this topic use email.

sal

unread,

Nov 25, 2006, 9:07:16 PM11/25/06

to

Apologies to all who tried to figure out this paragraph; it is incorrect
on the face of it. Points in an orbit at which the velocity happens to be
zero relative to the Sun's center of mass frame are not points at which an
orbiting body has zero acceleration! Ooooops...

[ snip ]

>> Now, you also might mean places where the curvature is nearly zero,

>> which is to say places where tidal forces approach zero. [ snip ]

I'll explain what I was thinking of, but then I'm dropping the topic.

In relativity theory gravity is not a field, rather it's the
manifestation of spatial curvature, caused by nonzero mass/energy density.

"Curvature" refers to the effect of having the metric tensor vary
nonlinearly from one place to another. Space and time dimensions are
actually very slightly distorted in curved space.

Tidal forces are the visible manifestation of curvature. When they are
present, nearby parallel geodesics don't remain parallel -- in other
words, freefalling objects which are initially at relative rest will start
to drift relative to each other when tidal forces are present.

In Newtonian gravity theory, OTOH, gravity is a field like any other and
none of this scrumbling about with curvature is necessary. Since
practical orbital dynamics don't require taking account of the difference
between Einstein's gravitation and Newton's gravitation (Mercury's
perihelion drift aside), this is, sadly, getting kind of off-topic for a
practical space group.

Apologies to all; I should not be introducing irrelevancies like this into
this forum.

Message has been deleted

Stuf4

unread,

Nov 26, 2006, 12:55:11 AM11/26/06

to

>From sal:

> If someone posts something I think raises a question that is interesting
> and on-topic for the NG, I'll reply to it. Questions about orbital
> dynamics, along with gravity and Newtonian mechanics as they concern
> those things, are most certainly on-topic for a NG dedicated to practical
> use of space. Surely that would include sci.space.history and
> sci.space.policy.
>
> If that bugs you, by all means add me and everybody else who responds to
> such posts to your killfile,

<snip>

> If you think my post was stupid, ill-thought-out, inaccurate, off-topic,
> or wrong, please, by all means, point out the problems with it (politely,
> if possible). Any exchange where I learn something about the topic of the
> group is a success, whether or not I'm proved right or otherwise shown to
> look "smart". I'm always happy to be corrected (even if I blush a bit
> over it).

I myself have voiced very similar sentiments on this forum many times
over.

~ CT

Stuf4

unread,

Nov 26, 2006, 1:02:34 AM11/26/06

to

>From Wayne Throop:

> Try just stating what L1 has that LEO hasn't got.
> Rather than just ranting about how stupid everybody else is.
> (And no, "picogravity if not nanogravity" isn't something
> L1 has got that LEO hasn't got.)
>
> For example, is gravitational attraction in balance there? Nope.
> Even if earth/moon gravitation were balanced there (which it isn't),
> it's still got quite significant solar gravitation. L1 is just
> a name of a location that you can stay at in free fall.
> But you can stay in free fall lots of places; what makes L1
> at all interesting or useful? In case it escapes your
> attention, you still haven't said.

With regard to locations that you can easily maintain with respect to
two large bodies that are in roughly circular orbit, there is a
totality of 5 such places. So for you to say that there are lots of
places where you can stay, I expect that you are giving up the
constraint of maintaining position relative to both bodies and opening
it up to positions that can be maintained in relation to just one of
the bodies, such as geostationary.

~ CT

Brad Guth

unread,

Nov 26, 2006, 1:43:02 AM11/26/06

to

"Stuf4" <tdadamemd-...@excite.com> wrote in message

news:1164520954.7...@h54g2000cwb.googlegroups.com

> With regard to locations that you can easily maintain with respect to
> two large bodies that are in roughly circular orbit, there is a
> totality of 5 such places. So for you to say that there are lots of
> places where you can stay, I expect that you are giving up the
> constraint of maintaining position relative to both bodies and opening
> it up to positions that can be maintained in relation to just one of
> the bodies, such as geostationary.

Actually "Wayne Throop" is just being his usual flatulence worth of a
naysay minion, on behalf of his Old Testament brown nose that's
butt-wiping his Third Reich Gods.

The moon L1 is by far the one and only high ground that's worth more
than all the wealth and energy of Earth, and then some.

The LSE-CM/ISS is by far the one and only viable L1 alternative (a
tethered Clarke Station on steroids) that's suited for the doing
(pillaging and raping) our moon and of other planets. The moon's L1 is
also global domination of Earth in most every way imaginable.

Are you folks so pathetic that you actually need a list?

Brad Guth

unread,

Nov 26, 2006, 1:53:17 AM11/26/06

to

Dear Mr. naysay buttology wizard.

You're simply not worth the effort, any more so that Hitler or the likes
of your born-again GW Bush and Kissinger team of incest mutated morons.

I've stipulated those moon L1 benefits a thousands times over, and lo
and behold if you're still not a thousand times way too dumb and dumber,
but then you're a certified naysay spewing bigot, so what's the
difference.

GOT CROSS ?

Wayne Throop

unread,

Nov 26, 2006, 1:55:46 AM11/26/06

to

: "Brad Guth" <brad...@yahoo.com>
: You're simply not worth the effort, any more so that Hitler or the likes

: of your born-again GW Bush and Kissinger team of incest mutated morons.
:
: I've stipulated those moon L1 benefits a thousands times over, and lo
: and behold if you're still not a thousand times way too dumb and dumber,
: but then you're a certified naysay spewing bigot, so what's the
: difference.

Wow. You'll write a paragraph of venom, but somehow can't manage
the effort to cut and paste a reference to this alleged prior
stipulation of benefits. Yeah, that'll make folks listen to you.

Can you simply state the benefits in the number of words you spent above
on gratuitous insults? Since, after all, it's clearly worth that much
effort; you just *spent* that much effort. I'm curious, you understand,
to see if you can manage a single post without insulting anyone.

Wayne Throop

unread,

Nov 26, 2006, 2:01:17 AM11/26/06

to

:: what makes L1 at all interesting or useful?

: "Stuf4" <tdadamemd-...@excite.com>
: With regard to locations that you can easily maintain with respect to

: two large bodies that are in roughly circular orbit, there is a
: totality of 5 such places.

Sure. Why is it important to do so?

: So for you to say that there are lots of places where you can stay, I

: expect that you are giving up the constraint of maintaining position
: relative to both bodies and opening it up to positions that can be
: maintained in relation to just one of the bodies, such as
: geostationary.

But why is it important to stay inline between moon and earth?
Guth implied it was because there's "picogravity" there. But that
turns out not to be the case.

If you want to stay stationary in some frame, isn't GEO better
for almost all purposes? Of course... only *almost* all. So
which of the other purposes is the issue here?

In short, once you get there, and build a habitat (or automated
station if that suits your fancy), what will you be doing there?

OM

unread,

Nov 26, 2006, 4:43:25 AM11/26/06

to

On Sun, 26 Nov 2006 06:55:46 GMT, thr...@sheol.org (Wayne Throop)
wrote:

>Wow. You'll write a paragraph of venom, but somehow can't manage
>the effort to cut and paste a reference to this alleged prior
>stipulation of benefits. Yeah, that'll make folks listen to you.

...Wayne, enough. Brad's a known psychotic troll. We've killfiled him
on .history, and the sooner everyone everywhere else does the same
thing, the better off we'll all be. Please killfile him and put him
out of our misery before everyone here does the same to you.

Thanks.

Stuf4

unread,

Nov 26, 2006, 6:13:02 AM11/26/06

to

>From Wayne Throop:

I haven't kept up with Brad's postings about his take on the importance
of the Earth-Moon Lagrange points, but I will offer one reason why
staying in line provides a unique capability. The Lagrange point past
the far side of the Moon is a great place to keep a communications
satellite in a halo orbit that maintains line-of-sight to a far-side
lunar base as well as the Earth.

~ CT

Wayne Throop

unread,

Nov 26, 2006, 3:06:21 PM11/26/06

to

: "Stuf4" <tdadamemd-...@excite.com>
: one reason why staying in line provides a unique capability.

: The Lagrange point past the far side of the Moon is a great place
: to keep a communications satellite in a halo orbit that maintains
: line-of-sight to a far-side lunar base as well as the Earth.

Heh! Well, true, but I'm fairly sure that's not Guth's reason,
since he believes the moon is not worth visiting, prohibitively hostile,
and indeed has never been visted.

Plus, of course, that's L2 not L1.

But still, true, that'd be a reason.

Brad Guth

unread,

Nov 26, 2006, 3:37:34 PM11/26/06

to

"Wayne Throop" <thr...@sheol.org> wrote in message
news:11645...@sheol.org

> Wow. You'll write a paragraph of venom, but somehow can't manage
> the effort to cut and paste a reference to this alleged prior
> stipulation of benefits. Yeah, that'll make folks listen to you.

You're the one that can't seem to make your Old Testament certified PC
search for anything that rocks thy boat. Sorry, but that's not even my
fault.

> Can you simply state the benefits in the number of words you spent above
> on gratuitous insults? Since, after all, it's clearly worth that much
> effort; you just *spent* that much effort. I'm curious, you understand,
> to see if you can manage a single post without insulting anyone.

Ultimate of Star Wars and of NEO defensive high ground.

Unlimited interplanetary mission launch capability, away from the 1e9 m3
CM/ISS.

Unlimited tether dipole energy (as in how many clean terawatts would you
like?)

Safe and efficient access to/from the earthshine illuminated moon's
surface.

Unlimited (mostly robotic) access to extracting lunar He3

Interplanetary and interstellar communications via quantum/FM binary
laser cannon packets.

VLA/SAR imaging of say less than a meter resolution of whatever's at the
distance of Jupiter, therefore all potential NEOs of whatever's larger
than a meter are fully identified and easily tracked before their having
reached the critical realm of Jupiter.

BTW; The tether dipole element termination platform that is extended as
per reaching to within as little as 4r of Earth. (isn't that good news,
or what) Imagine how many Muslims butts that your kind could so easily
fry from that nearby platform, that's hosting a dozen or so of those
nifty 100 GW laser cannons.

I'll have to edit a few of my existing LSE-CM/ISS papers, in order to
further reflect and/or embellish upon these constructive/positive
aspects of our being in charge of this one and only moon L1 zone.

Wayne Throop

unread,

Nov 26, 2006, 4:48:34 PM11/26/06

to

: "Brad Guth" <brad...@yahoo.com>
: Ultimate of Star Wars and of NEO defensive high ground.

LEO's better for that purpose.

: Unlimited interplanetary mission launch capability, away from the 1e9
: m3 CM/ISS.

LEO's not noticeably worse for that purpose, especially since you'll
have to loft materials and personell to L1 before they go on the mission.

: Unlimited tether dipole energy (as in how many clean terawatts would
: you like?)

LEO's no worse; there's nothing special about tethers at L1.

: Safe and efficient access to/from the earthshine illuminated moon's
: surface.

I thought the moon was full of radiation, too hot to be worth anything.
And of course, unless you breed your astronauts there, you'll still need
to loft them from earth.

: Unlimited (mostly robotic) access to extracting lunar He3

So, you extract it, and then.... do what with it? Ship it to earth?
So why is L1 better than just letting the robots stay on the moon,
and catapulting to earth?

: Interplanetary and interstellar communications via quantum/FM binary
: laser cannon packets.

Ah. Imaginary advantage. And... why can't this imaginary do-dad
be put in LEO?

: VLA/SAR imaging of say less than a meter resolution of whatever's at

: the distance of Jupiter, therefore all potential NEOs of whatever's
: larger than a meter are fully identified and easily tracked before
: their having reached the critical realm of Jupiter.

And this super imaging do-dad can't be anywhere else, because why?

: BTW; The tether dipole element termination platform that is extended

: as per reaching to within as little as 4r of Earth. (isn't that good
: news, or what)

Not partiularly, no.

To sum up, you list as advantages of L1

1) things that aren't unique to L1,
2) things that are totally imaginary, and
3) things that are so long term that buidling the
infrastructure there makes little sense.

Thank you for clarifying your position.

Dr J R Stockton

unread,

Nov 26, 2006, 4:02:11 PM11/26/06

to

In sci.space.history message <11645...@sheol.org>, Sun, 26 Nov 2006

07:01:17, Wayne Throop <thr...@sheol.org> wrote:
>
>But why is it important to stay inline between moon and earth?
>Guth implied it was because there's "picogravity" there. But that
>turns out not to be the case.

Evidently some authors are well-worth kill-ruling, while others need to
be read with care.

Let us ignore corrections for the Sun's field and the motion round it of
the Earth-Moon barycentre, and let us approximate orbits as circular.

There is an easily-located point B between Earth & Moon, I think between
L1 & Moon, at which there is, from Earth & Moon, no net gravitational
force. To locate it, solve M/R^2 = m/r^2 where R+r=D, the
Earth-Moon separation.

An unpowered body at B will not be changing its velocity; it will be
stationary or moving in a straight line. However B itself is moving in
a circle, so the body and B cannot remain together.

There is a point L1 at which the Earth's pull, diminished by the
opposing pull of the Moon, is sufficient to hold an unpowered body in a
circular orbit with a period of one relevant Month. Such a body will
therefore travel with L1 and can be said to remain at L1.

At L1 a small body in such an orbit does feel a gravitational pull; but
no gravity will be felt by any of its occupants, since that pull is
balanced by "centrifugal force".

--
(c) John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v6.05 MIME.
Web <URL:http://www.merlyn.demon.co.uk/> - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

Wayne Throop

unread,

Nov 26, 2006, 7:43:49 PM11/26/06

to

: Dr J R Stockton <j...@merlyn.demon.co.uk>
: At L1 a small body in such an orbit does feel a gravitational pull; but

: no gravity will be felt by any of its occupants, since that pull is
: balanced by "centrifugal force".

Yes. Well "not felt by occupants" is true no matter where you are
freefalling. There are issues of tides; tides at L1 are not zero, so L1
isn't terribly special in that regard. There are more tides in LEO, but
this doesn't seem to be a huge hairy deal. Least tides close by
are in L4 and L5.

So the issue is, why is it important to remain between earth and the
moon? As you point out, L1 is the only point at which one can remain
unpowered (ie, in freefall) between the earth and the moon. This
doesn't seem valuable any time within the next few decades. Ie, not
within the planning horizon for any practical project to be spending
money on now.

Of course, I don't object to people spending money to go to L1.
Just as long as they don't spend *my* money on it. LEO and GEO
seem more valuable places for the next few decades.

Brad Guth

unread,

Nov 26, 2006, 8:15:13 PM11/26/06

to

"Wayne Throop" <thr...@sheol.org> wrote in message
news:11645...@sheol.org

> To sum up, you list as advantages of L1

>
> 1) things that aren't unique to L1,
> 2) things that are totally imaginary, and
> 3) things that are so long term that buidling the
> infrastructure there makes little sense.

Proof positive that we have ourselves a certified Old Testament bigot in
"Wayne Throop", as an anti-think-tank rusemaster that's hard at work
covering thy butt.

However, if you could manage to get yourself any more naysay, perhaps we
could power the entire world from the intellectual black hole of your
purely negative suckology mindset which you clearly represent.

Rand Simberg

unread,

Nov 26, 2006, 8:52:07 PM11/26/06

to

On Mon, 27 Nov 2006 00:43:49 GMT, in a place far, far away,
thr...@sheol.org (Wayne Throop) made the phosphor on my monitor glow
in such a way as to indicate that:

>So the issue is, why is it important to remain between earth and the
>moon? As you point out, L1 is the only point at which one can remain
>unpowered (ie, in freefall) between the earth and the moon. This
>doesn't seem valuable any time within the next few decades. Ie, not
>within the planning horizon for any practical project to be spending
>money on now.

It is a useful orbit, for reasons that Brad doesn't have the cerebral
capacity to comprehend. The main point is that it has no windows for
launches from anywhere on the moon. Or rather, it has no nonwindows
(i.e., it is equally accessible at all points in time).

Brad Guth

unread,

Nov 26, 2006, 9:03:13 PM11/26/06

to

"Rand Simberg" <simberg.i...@org.trash> wrote in message
news:45c64465....@news.giganews.com

> It is a useful orbit, for reasons that Brad doesn't have the cerebral
> capacity to comprehend. The main point is that it has no windows for
> launches from anywhere on the moon. Or rather, it has no nonwindows
> (i.e., it is equally accessible at all points in time).

Silly boys, arnt we; "it is equally accessible at all points in time"

Obviously you're being really good at your rusemaster pretending that
you and the likes of your silly kind haven't the slightest clue as to
the greater values associated with our moon's L1. That's OK becaus,
China isn't actually fooled by your intellectual naysayism.

Since it's still officially Usenet taboo and/or banishment worthy to
even so much as discuss relocating our existing ISS to our moon's L1, or
especially as for going off to visit the wizard of Oz at Venus L2, in
that case we'll need to start this nifty LSE-CM/ISS entirely from
scratch, or at least allow China to accomplish what's so impossible for
us, especially since we're still trying so gosh darn hard at dominating
global fossil and yellowcake energy, and especially extra dominating
and/or controlling over Muslim oil before we manage to cause the next
round of golbal inflation and WW-III to boot.

Once again for the Usenet record (of whatever that's worth), our moon's
L1 is the one and only holy grail of future space exploration and global
domination. That's not to say that LEO stuff isn't going to keep on
ticking, especially since it'll be necessary once China has established
all of those nifty if not somewhat pesky retrograde LEOs that'll be
summarily kicking our sorry butts.

Here's just a few basic considerations for China utilizing our moon's
L1, whereas to improve upon what I'd previously offered to our resident
naysay/anti-think-tank likes of "Wayne Throop". This is basically what
my LSE-CM/ISS or of whatever best utilization of this Moon/Earth L1 has
to offer the open mindset type of folks that are not specifically
looking to merely stalk and bash against everything that's not of their
idea, and/or of whatever's under their sun that's apparently orbiting
their Old Testament flat Earth (and for Christ's sake on a stick, that
was merely another pun, so get over it).

I'm not the bad guy or even the messenger from hell, I'm not even anti
bible/koran thumping as long is it isn't being tossed in my face or
otherwise being utilized against my honest intentions to share and share
alike. Most faith based individuals are really quite nice folks that
wouldn't hurt a Muslim fly, whereas their supposed troopers as
represented within Usenet are for the most part downright insane.

A brief list of the moon's L1 benefits to humanity, and quite possibly
the best possible salvation to our global warming fiasco:

Moon L1 represents the ultimate of Star Wars and of NEO defensive high
ground.

Unlimited interplanetary mission launch capability, away from the 1e9 m3
CM/ISS.

Unlimited tether dipole energy (as in how many clean terawatts would you
like?)

Safe and efficient access to/from our earthshine illuminated moon's
surface.

Unlimited (mostly robotic) access to extracting lunar He3, plus
countless other nifty elements.

Effective and efficient interplanetary and interstellar communications

via quantum/FM binary laser cannon packets.

The ultimate of an efficient fuel/refuel depot, plus the one and only
efficient access to whatever tonnage of composite shielding you'd ever
care to add to each mission.

VLA/SAR imaging of say less than a meter resolution of whatever's at the
distance of Jupiter, therefore all potential NEOs of whatever's larger
than a meter are fully identified and easily tracked before their having
reached the critical realm of Jupiter.

BTW; The tether dipole element's termination platform that's extended
away from the primary L1 CM/ISS, as per reaching that dipole tethered
unit to within as little as 4r of Earth (isn't that good news, or what)
is simply a given, whereas having such a nearby interactive location can
be utilized for all sorts of invaluable contributions to Earth and moon
science and the advancement of humanity's role in exploiting the vast
wealth of other planets and moons. Imagine also how many Muslim butts
or the likes of whomever on your axis of evil list that your kind could

so easily fry from that nearby platform, that's hosting a dozen or so of
those nifty 100 GW laser cannons.

There no question that I'll have to edit a few of my existing LSE-CM/ISS
papers, in order to further reflect upon and/or embellish upon these

constructive/positive aspects of our being in charge of this one and

only moon L1 zone that's parked roughly 60,000 km from the physically
dark and nasty lunar deck.

Even if not initially tethered to the moon, the efficient
station-keeping demands per tonne of whatever ISS like craft (aka Clarke
Station) shouldn't be 1% of what our present day ISS is demanding. Our
moon's interactive L1 is also a rather nifty do-everything location
where the most tonnage per given fly-by-rocket effort is going to offer
the utmost accomplishment for those mostly robotic deployments, that can
be effectively remote flown, all the way down to the cm resolution, from
most any MicroSoft flight simulator equipped laptop PC or MAC.

My serious notion of the final 1e9 m3 CM/ISS abode is that of a 256e6
tonne borg like space station, as an installation that's fully tethered
to the moon, with as much as 99.9% of that mass (including whatever
tethers) as being derived from the moon itself. Even though that sounds
horrifically big, massive and a touch complex, as such it certainly
doesn't have to start out all that big and massive or complex. Too bad
there's only room for one such LSE-CM/ISS, of which China is most likely
going to own and operate this on our behalf (free of charge? somehow I
don't think so).

Do any of you folks speak a little Chinese, or at least some Mandarin
worthy slang?

Brad Guth

unread,

Nov 26, 2006, 9:18:28 PM11/26/06

to

"Dr J R Stockton" <j...@merlyn.demon.co.uk> wrote in message
news:isyg1m6T...@invalid.uk.co.demon.merlyn.invalid

> Let us ignore corrections for the Sun's field and the motion round it of
> the Earth-Moon barycentre, and let us approximate orbits as circular.
>
> There is an easily-located point B between Earth & Moon, I think between
> L1 & Moon, at which there is, from Earth & Moon, no net gravitational
> force. To locate it, solve M/R^2 = m/r^2 where R+r=D, the
> Earth-Moon separation.
>
> An unpowered body at B will not be changing its velocity; it will be
> stationary or moving in a straight line. However B itself is moving in
> a circle, so the body and B cannot remain together.
>
> There is a point L1 at which the Earth's pull, diminished by the
> opposing pull of the Moon, is sufficient to hold an unpowered body in a
> circular orbit with a period of one relevant Month. Such a body will
> therefore travel with L1 and can be said to remain at L1.
>
> At L1 a small body in such an orbit does feel a gravitational pull; but
> no gravity will be felt by any of its occupants, since that pull is
> balanced by "centrifugal force".

That's really good stuff, although I was never into considering such an
interactive placement unless having at least some of those nifty ion
thrusters at our disposal.

Can you be a little more specific as to the interactive month by month
station-keeping demands per tonne, as opposed to sustaining the ISS/LEO
fiasco?

For starters, there shouldn't be a tenth the atom/cm3, and secondly,
it's certainly not having go all that fast, and best of all, there's no
SAA Van Allen zone of death to avoid (just a somewhat lethal moon that's
contributing gamma and hard-X-rays plus a rather nasty load of secondary
IR/FIR roughly half the time).

Of course, once tethered to the moon ????

sal

unread,

Nov 26, 2006, 10:26:24 PM11/26/06

to

Isn't that true for all "horizontal" (equatorial) orbits in the Earth/Moon
system, as well as any particular point in one of those orbits _if_ you
reference the particular point to the Moon's location? Since the Moon is
tide-locked, except for nutation, its configuration with respect to any
particular equatorial orbit should be fixed.

At the very least, I would think that all five Lagrange points should have
the property of "no launch windows" from the Moon.

Obviously that won't be true WRT points on Earth's surface, and won't be
true WRT a point in orbit which is itself referenced to a point on the
Earth's surface.

Err... OTOH the Moon's orbit is slightly inclined, isn't it? Hmm...
that could affect launches targeting Earth equatorial orbits.