A Space & astronomy forum. SpaceBanter.com

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » SpaceBanter.com forum » Space Science » Space Station
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Dynamics of an Earth Ring



 
 
Thread Tools Display Modes
  #91  
Old October 10th 04, 09:17 AM
AA Institute
external usenet poster
 
Posts: n/a
Default

"Grimble Gromble" wrote in message news:pWV9d.425
Are you familiar with this equation (quoted by Henry Spencer on
sci.space.tech a while back):-
An Earth circling satellite orbit will precess along the equator over
time according to the equation:-
-3/2 * J2 * (R^2 / p^2) * n * cos (i)
[Where J2 is a constant related to Earth's flattening, R is the
Earth's eq. Radius, p = a*(1-e^2) (in which a is the orbit's
semi-major axis and e is its eccentricity), n is the mean motion and i
is the orbit's inclination.]

Being familiar with an equation is not the same as understanding it. That
the earth's flattening is involved suggests that this precession is caused
by tidal influences experienced by the satellite as it orbits above and
below the earth's equatorial plane. That there is no term relating to the
lunar and stellar masses, suggests that this is a very simplified analysis
in which all other influences have been ignored. Is there any reason you
introduce this (idealised particulate) satellite into a discussion on earth
rings? Perhaps you are comparing the effect on an orbiting satellite of the
earth's equatorial bulge to that of an independently orbiting ring? You do
realise that there are significant electromagnetic forces operating between
the 'equatorial' bulge and the 'spherical' earth?


Since each discrete particle in a ring system, such as the one I
envision here, is effectively a *satellite* in its own right, and the
individual particles are orbiting the Earth at appreciably different
distances (the ring has some *width*), the above equation - along with
another similar equation - can be used to show that under certain
favourable orientations of a ring system the particles are unlikely to
scatter significantly.

Probably doesn't make too much sense here... I am working on a short
paper to better illustrate this, which I hope to make available when I
get some spare time.

Abdul
Ads
  #93  
Old October 10th 04, 01:52 PM
Grimble Gromble
external usenet poster
 
Posts: n/a
Default

"AA Institute" wrote in message
om...
"Grimble Gromble" wrote in message
news:pWV9d.425
Are you familiar with this equation (quoted by Henry Spencer on
sci.space.tech a while back):-
An Earth circling satellite orbit will precess along the equator over
time according to the equation:-
-3/2 * J2 * (R^2 / p^2) * n * cos (i)
[Where J2 is a constant related to Earth's flattening, R is the
Earth's eq. Radius, p = a*(1-e^2) (in which a is the orbit's
semi-major axis and e is its eccentricity), n is the mean motion and i
is the orbit's inclination.]

Being familiar with an equation is not the same as understanding it. That
the earth's flattening is involved suggests that this precession is
caused
by tidal influences experienced by the satellite as it orbits above and
below the earth's equatorial plane. That there is no term relating to the
lunar and stellar masses, suggests that this is a very simplified
analysis
in which all other influences have been ignored. Is there any reason you
introduce this (idealised particulate) satellite into a discussion on
earth
rings? Perhaps you are comparing the effect on an orbiting satellite of
the
earth's equatorial bulge to that of an independently orbiting ring? You
do
realise that there are significant electromagnetic forces operating
between
the 'equatorial' bulge and the 'spherical' earth?


Since each discrete particle in a ring system, such as the one I
envision here, is effectively a *satellite* in its own right, and the
individual particles are orbiting the Earth at appreciably different
distances (the ring has some *width*), the above equation - along with
another similar equation - can be used to show that under certain
favourable orientations of a ring system the particles are unlikely to
scatter significantly.

Probably doesn't make too much sense here... I am working on a short
paper to better illustrate this, which I hope to make available when I
get some spare time.


Sadly, this won't work for a solid ring because the 'individual' particles
are being acted on by the significant electromagnetic forces I referred to
earlier. You might want to consider what will happen to your 'solid' ring
when one of the 'individual' particles on the inner edge has travelled one
more revolution in its orbit than one of the 'individual' particles on the
outer surface. Since the particles won't actually have moved relative to
each other, there must exist stresses with the structure. These tidal
stresses actually exist in any solid body moving through a non-uniform
gravitational field. For small bodies, these stresses are quite small, but
there is a limit at which the gravitational forces acting within the body to
hold it together are overcome by the tidal forces pulling it apart.
Electromagnetic forces are very much stronger than gravitational forces so
we could build a very large space station with little concern, but a planet
circling ring?

Hopefully you can see that not only would you have to constantly monitor and
adjust the position of a ring to maintain its distance from a planet, as
discussed previously, you'd also have to cope with massive tidal stresses
attempting to distort the ring - and I'm not even considering the tidal
effects of the moon here.

Is there any particular reason that you'd want to build a planetary ring
other than inspiration from science fiction stories?

I trust this hand-waving response will not irritate those who deem numerical
simulation to be the be-all and end-all of discussions (though I expect this
comment will).
Grim



  #94  
Old October 10th 04, 09:05 PM
AA Institute
external usenet poster
 
Posts: n/a
Default

"Grimble Gromble" wrote in message news:bgaad.1897

Is there any particular reason that you'd want to build a planetary ring
other than inspiration from science fiction stories?


Time to own up... Yes that was *exactly* the inspiration! Although
creating a ring was never a sought after goal in my propsal, rather a
*desirable* side-effect from carving out my asteroid to build a
habitat within its interior.

I trust this hand-waving response will not irritate those who deem numerical
simulation to be the be-all and end-all of discussions (though I expect this
comment will).


Your hand waving in this instance makes sense. I have done my highly
intricate dynamical analysis and I hereby report that a ring system
that is not oriented along the Earth's equator, which is emanating
from a non-circular orbit of an asteroid, will scatter its particles
at the fastest rate, and no Earth orbiting ring system could ever be
formed in those circumstances. This is mainly due to the differential
rates of precession of each ring particle's orbital nodes owing to the
un-even (oblate) mass distribution of the Earth.

On the other end of the scale, a perfectly circular, concentric system
of ring particles orbiting exactly co-planer with the Earth's
equatorial plane has a very short term (a couple of years at most)
chance of staying together in a ring formation. That's assuming an
orbital altitude of 40,000 km above the equator. However, such a
particulate ring system is then subject to two kinds of external
perturbing influences: that coming from the Sun and that from the
Moon, acting along the ecliptic plane and the plane of the Moon's
orbit, respectively. The combined effects of both these forces will
cause the ring material to scatter into a 'band' of +/- 15 degrees
geocentric latitude (30 degree spread around the equatorial plane)
over several years...

The final conclusion is therefore no stable ring system would be
possible around the Earth in the long term, hence any excavation
debris carved out of an Earth orbiting asteroid will require serious
containment/safe disposal. Thus, such an orbital engineering project
is not going to be viable around the Earth.

That said, there is always a possibility of deploying a number of
robotic digging vehicles on the surface of an asteroid and performing
the excavation in-situ, in *its* orbit prior to summoning it to Earth
orbit. An advanced series of nuclear powered rovers, much larger and
with more 'clout' than the Mars rovers of today, could be despatched
onto the surface of a candidate asteroid where they progressively dig
their way into its interior. The mass reduction from such excavation
would make the task of subsequent transportation of the asteroid to
Earth that much 'lighter' and leave no scattering debris near Earth.

AAI
  #96  
Old October 20th 04, 08:55 PM
Hop David
external usenet poster
 
Posts: n/a
Default



Steve Maudsley wrote:

... the Star Trek transporters was invented because the TV
production company didn't have enough budget to do a "space ship landing"
special effect.



Could have sworn I saw Star Trek like transporters in Forbidden Planet
(or is my memory playing tricks on me?)




--
Hop David
http://clowder.net/hop/index.html

  #97  
Old October 20th 04, 10:34 PM
Chuck Stewart
external usenet poster
 
Posts: n/a
Default

On Wed, 20 Oct 2004 12:55:47 -0700, Hop David wrote:

Steve Maudsley wrote:


... the Star Trek transporters was invented because the TV
production company didn't have enough budget to do a "space ship landing"
special effect.


Could have sworn I saw Star Trek like transporters in Forbidden Planet
(or is my memory playing tricks on me?)


Er... no, but you saw something that looked like the transporter...kinda.

When the C-57D prepared to exit hyperspace and go sublight the crew hopped
onto small transporter-like platforms scattered around the ship and
for the duration of the transition from FTL were turned into green-glowing
masses of energy (or something)... Afterwards the crew went about the
business of getting the ship into orbit and landing it. Just a neat setup
implying that FTL travel was no simple thing. Presumambly the faux
transporter thingies somehow protected the crew during the transition.

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

  #98  
Old October 21st 04, 04:46 PM
AA Institute
external usenet poster
 
Posts: n/a
Default

Jose Pina Coelho wrote in message

Time to own up... Yes that was *exactly* the inspiration! Although
creating a ring was never a sought after goal in my propsal, rather a
*desirable* side-effect from carving out my asteroid to build a
habitat within its interior.


Desirable ? Poluting an already congested space with megatons of rock
shards ?

So, why don't you carve your habitat in the place where you find the
asteroid, then leave the rubble there and bring the thing here, not it's
probably 1/3 of the mass, hence easier/cheaper to move ?


You're right. That's exactly what I did in the end:-

http://uk.geocities.com/aa_spaceagen...arth-ring.html

I mean... that's exactly how things will be done in the end by a
future generation. The future hasn't happened yet... I must remember
that!

Although having said that, in an *alternate reality*, in a parallel
universe... somewhere, the AA Institute is leading a consortium of
national governments, world space agencies and corporate conglomerates
to advance a planet-wide effort toward building the Celestial Titanic
- even as I write!!!

Dreams...

AAI
  #99  
Old October 21st 04, 06:12 PM
Allen Thomson
external usenet poster
 
Posts: n/a
Default

Chuck Stewart wrote

[snip other attributions 'n stuff]

... the Star Trek transporters was invented because the TV
production company didn't have enough budget to do a "space ship landing"
special effect.


Could have sworn I saw Star Trek like transporters in Forbidden Planet
(or is my memory playing tricks on me?)


Er... no, but you saw something that looked like the transporter...kinda.



Note that the subsequent scene showing the landing was a really neat
"space ship landing." A most amazing film.
  #100  
Old October 22nd 04, 11:53 PM
James
external usenet poster
 
Posts: n/a
Default

"Allen Thomson" wrote in message
om...
Chuck Stewart wrote

[snip other attributions 'n stuff]

... the Star Trek transporters was invented because the TV
production company didn't have enough budget to do a "space ship
landing"
special effect.


Could have sworn I saw Star Trek like transporters in Forbidden Planet
(or is my memory playing tricks on me?)


Er... no, but you saw something that looked like the transporter...kinda.



Note that the subsequent scene showing the landing was a really neat
"space ship landing." A most amazing film.


Supposedly Gene Roddenberry got some of the ideas for the interplay between
Kirk/Spock/McCoy from the way the captain/first officer/doctor "got on with
each other" in Forbidden Planet ... at least, according to an interview I
saw with Walter Koenig.

James


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Space Calendar - August 27, 2004 Ron Misc 14 August 30th 04 11:09 PM
Space Calendar - November 26, 2003 Ron Baalke History 2 November 28th 03 10:21 AM
Space Calendar - August 28, 2003 Ron Baalke Misc 0 August 28th 03 05:32 PM
Space Calendar - July 24, 2003 Ron Baalke Misc 0 July 24th 03 11:26 PM


All times are GMT +1. The time now is 06:03 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright 2004-2019 SpaceBanter.com.
The comments are property of their posters.