|
|
Thread Tools | Display Modes |
#91
|
|||
|
|||
"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 |
#92
|
|||
|
|||
"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 |
#93
|
|||
|
|||
|
#94
|
|||
|
|||
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 |
#95
|
|||
|
|||
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?" |
#96
|
|||
|
|||
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 |
#97
|
|||
|
|||
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. |
#98
|
|||
|
|||
"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 | |
|
|
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 09:21 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 |