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Global Cooling
Hi,
Does anyone know if a ballistic trajectory exists directly from the Moon’s surface to the Earth-Sun L1 Lagrange point? I’m interested to know if it’s possible to eject material from the surface of the Moon so that it reaches L1 at near zero velocity before dispersing. I would also like to know for how long each month these trajectories exist, from where on the Moon’s surface (the far-side I assume) and for how long the material would lie between the Sun and Earth. I’m interested to see if Moon dust could be used to reduce sunlight reaching Earth in the event that global warming is not controlled. The low gravity, absence of atmosphere and plentiful supply of dust on the Moon may make this possible, providing trajectories exist and the technology can be developed. If trajectories do exist then the problems with implementing a project will be formidable: establishing a base and infrastructure might be the easy part. Accelerating massive quantities of dust to the required velocity (2.5km/sec) will pose huge technical problems. I’m also interested to know what impact the solar wind might have on small particles and if the dust might require grading or processing beforehand. I suspect many members of this group will be appalled at what I’m suggesting, given the implications it has for space pollution. I trust it should be obvious that no one would attempt such a crazy and costly project except in the most dire circumstances when all reasonable alternatives had failed. Because most of the dust will disperse over time the process is arguably reversible, however some dust could remain in stable orbits around the Earth and Moon leading to a long term problem. In the worst case converting global warming into an ice age! Regards John Hampson |
#2
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Global Cooling
On Apr 18, 10:14 am, John Hampson wrote:
Hi, Does anyone know if a ballistic trajectory exists directly from the Moon’s surface to the Earth-Sun L1 Lagrange point? I stumbled at this point. The Moon is so low-mass (relatively) and close, and the distance to the Earth-Sun L1 point is so large, that a trajectory from the Moon's surface to L1 would be essentially the same as a trajectory from the Earth to L1. Nobody has proposed the latter, AFAIK. As for a stable orbit at Earth-Sun L1, all the debris in the Solar System has had 4.5 billion years to drift there and stay, if that were true. Nothing's visible. Comments? |
#3
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Global Cooling
In sci.space.tech message 08c31a93-7cf1-46bb-9a5e-6f46511ca9e2@l9g2000v
ba.googlegroups.com, Sat, 18 Apr 2009 22:18:44, Oneandonly1 posted: On Apr 18, 10:14 am, John Hampson wrote: Does anyone know if a ballistic trajectory exists directly from the Moon’s surface to the Earth-Sun L1 Lagrange point? I stumbled at this point. The Moon is so low-mass (relatively) and close, and the distance to the Earth-Sun L1 point is so large, that a trajectory from the Moon's surface to L1 would be essentially the same as a trajectory from the Earth to L1. Nobody has proposed the latter, AFAIK. The trajectory is similar. But, from the Moon, one is starting from a place with a quarter of the radius, a sixth of the surface gravity, no atmosphere, no residents, and a sufficient supply of non-volatile material there for the picking. Anything arriving at or near any Lagrange point with a non-negligible speed has a strong tendency to depart with a similar speed. Anything arriving with a negligible speed either has propulsion or takes too long to get there. Approximately. -- (c) John Stockton, nr London, 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. |
#4
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Global Cooling
On Apr 18, 7:14 am, John Hampson wrote:
Hi, Does anyone know if a ballistic trajectory exists directly from the Moon’s surface to the Earth-Sun L1 Lagrange point? I’m interested to know if it’s possible to eject material from the surface of the Moon so that it reaches L1 at near zero velocity before dispersing. I would also like to know for how long each month these trajectories exist, from where on the Moon’s surface (the far-side I assume) and for how long the material would lie between the Sun and Earth. I’m interested to see if Moon dust could be used to reduce sunlight reaching Earth in the event that global warming is not controlled. The low gravity, absence of atmosphere and plentiful supply of dust on the Moon may make this possible, providing trajectories exist and the technology can be developed. If trajectories do exist then the problems with implementing a project will be formidable: establishing a base and infrastructure might be the easy part. Accelerating massive quantities of dust to the required velocity (2.5km/sec) will pose huge technical problems. I’m also interested to know what impact the solar wind might have on small particles and if the dust might require grading or processing beforehand. I suspect many members of this group will be appalled at what I’m suggesting, given the implications it has for space pollution. I trust it should be obvious that no one would attempt such a crazy and costly project except in the most dire circumstances when all reasonable alternatives had failed. Because most of the dust will disperse over time the process is arguably reversible, however some dust could remain in stable orbits around the Earth and Moon leading to a long term problem. In the worst case converting global warming into an ice age! Regards John Hampson Nature has recently provided a sort of yard stick as to dust quantity effects on climate, http://expo.edu.ph/pinatubo/index.html That seriously affects the DVI, (Dust Veil Index), http://www.geo.mtu.edu/volcanoes/vc_...o_climate.html Personal experience: In 1991 we were wintering in central Ontario, and normally used ~6 cords of wood / year, with 1 cord back-up and 250 gallons of heating oil emergency reserve if the woodstove malfunctioned. We ended up burning 9 cords that winter. Daily high's stayed below -20F to 0F for weeks. By putting a fist at arm's length in front of the day-time Sun, the dust was quite apparent in the sky region around it. Regards Ken |
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Global Cooling
Oneandonly1 wrote: I stumbled at this point. The Moon is so low-mass (relatively) and close, and the distance to the Earth-Sun L1 point is so large, that a trajectory from the Moon's surface to L1 would be essentially the same as a trajectory from the Earth to L1. Nobody has proposed the latter, AFAIK. As for a stable orbit at Earth-Sun L1, all the debris in the Solar System has had 4.5 billion years to drift there and stay, if that were true. Nothing's visible. Comments? Must stop hand... must stop hand from getting near the keyboard... "No precious, we _wants_ to post to the moderated newsgroup, _don'ts we_?" L1, L2, and L3 are unstable; L4 and L5 are theoretically stable, so things sent there will remain in the same spot, rotating in a small orbit around the center of the L point as the Sun-Earth-Moon geometry changes during any given month. Pat |
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Global Cooling
Thanks for your various posts. I appear to have confused everyone,
sorry. I understand L1 is unstable, in fact I’m depending on it, since I intend the process to be reversible and this requires that the dust disperse over time. Ejecting dust for global cooling would require an ongoing process until warming was fixed by other means. Ideally the dust would then disperse and avoid the risk of creating an ice-age. Dispersal would involve dust falling to the Sun, Earth and Moon (and perhaps the inner planets). A small quantity might find stable orbits around the Earth and Moon (though not L1) but I suspect even this would disperse under the action of the solar wind. In addition to having low gravity the Moon also has an orbital velocity sufficient to resist the Earth’s gravity, so avoiding the dust falling directly to Earth should simply be a question of pointing the ejection nozzle in the right direction. The key issue concerns how long dust can be kept between the Sun and Earth in a free trajectory originating from the Moon’s surface. If the period is too short then the amount that needs to be ejected will be impossibly large. If the period is too long then we risk losing control and over-cooling the planet. The chances of a trajectory existing that is just right is perhaps slim and of course I don’t know what “just right” is at this stage. But I still think the question is worth asking, does anyone know the answer? John Hampson |
#7
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Global Cooling
In article ,
John Hampson writes: Dispersal would involve dust falling to the Sun, Earth and Moon (and perhaps the inner planets). A small quantity might find stable orbits around the Earth and Moon (though not L1) but I suspect even this would disperse under the action of the solar wind. It's actually solar radiation pressure that's relevant for dust. Note the difference between comet dust tails and ion tails. How big an effect radiation pressure is, relative to gravity, depends on particle size. It occurs to me that by making the particles the right size, one might be able to launch the material in a cannister on a fast trajectory, disperse it at L1, and allow radiation pressure to slow the dispersed dust down so it remains in place for a useful duration. I have no quantitative idea what this would involve, and maybe it's silly. Depending on the quantity of dust needed -- and I haven't calculated that -- it isn't obvious why launching from the Moon would be better than launching from Earth. To get the benefit of the lower gravity well, you have to create a massive infrastructure on the lunar surface. -- Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) |
#8
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Global Cooling
In sci.space.tech message , Wed, 22
Apr 2009 18:31:31, Steve Willner posted: It occurs to me that by making the particles the right size, one might be able to launch the material in a cannister on a fast trajectory, disperse it at L1, and allow radiation pressure to slow the dispersed dust down so it remains in place for a useful duration. I have no quantitative idea what this would involve, and maybe it's silly. You're right : it is. If radiation pressure is enough to retard particles to a stop, it is also sufficient to accelerate them back out. Unless your particles are more-or-less disc shaped, travel in the axial direction, and turn sideways on arrival - which more or less defeats the object of the exercise - or are clever enough to be reflective when slowing, and merely slightly dispersive when stopped. Note : there's no need to absorb the light which would have hit the Earth; it just needs to be deflected a little. A thin converging Fresnel lens with a focal length a fraction of the Earth-lens distance will do that, and the refraction will tend to keep the lens stretched out. For radiation pressure to match solar gravity, the mass of a perfectly- reflecting disc-shaped particle would have to be about 1.6 grams per square metre, i.e. rather thin. Neglecting perturbations, a reflecting body of that thickness would be able to hover over the Sun, remaining on a line of fixed absolute direction from the Sun, at any altitude. See below. If radiation pressure is significant, the point of unstable equilibrium is no longer at L1. Since both radiation and gravity are inverse- square, the radiation in effect reduces big G for the sun-particle interaction; the particle has to be correspondingly nearer to the sun in order to be in a 365.242...-day orbit and remain between Sun and Earth. -- (c) John Stockton, nr London, 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. |
#9
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Global Cooling
In article id,
Dr J R Stockton writes: If radiation pressure is enough to retard particles to a stop, it is also sufficient to accelerate them back out. Indeed. Particles will have to be replenished on the deceleration time scale, whatever that is. I won't be surprised if that makes the idea unfeasible, but I haven't done the calculation. For radiation pressure to match solar gravity, the mass of a perfectly- reflecting disc-shaped particle would have to be about 1.6 grams per square metre, If you want particles to remain at L1 for a long time, you want radiation force to be negligible compared with gravitational force. As you wrote, that may conflict with using radiation pressure for deceleration. -- Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) |
#10
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Global Cooling
"Ken S. Tucker" wrote in
: On Apr 18, 7:14 am, John Hampson wrote: Hi, Does anyone know if a ballistic trajectory exists directly from the Moon’s surface to the Earth-Sun L1 Lagrange point? I’m interested to know if it’s possible to eject material from the surface of the Moon so that it reaches L1 at near zero velocity before dispersing. I would also like to know for how long each month these trajectories exist, from where on the Moon’s surface (the far-side I assume) and for how long the material would lie between the Sun and Earth. I’m interested to see if Moon dust could be used to reduce sunlight reaching Earth in the event that global warming is not controlled. The low gravity, absence of atmosphere and plentiful supply of dust on the Moon may make this possible, providing trajectories exist and the technology can be developed. If trajectories do exist then the problems with implementing a project will be formidable: establishing a base and infrastructure might be the easy part. Accelerating massive quantities of dust to the required velocity (2.5km/sec) will pose huge technical problems. I’m also interested to know what impact the solar wind might have on small particles and if the dust might require grading or processing beforehand. I suspect many members of this group will be appalled at what I’m suggesting, given the implications it has for space pollution. I trust it should be obvious that no one would attempt such a crazy and costly project except in the most dire circumstances when all reasonable alternatives had failed. Because most of the dust will disperse over time the process is arguably reversible, however some dust could remain in stable orbits around the Earth and Moon leading to a long term problem. In the worst case converting global warming into an ice age! Regards John Hampson Nature has recently provided a sort of yard stick as to dust quantity effects on climate, http://expo.edu.ph/pinatubo/index.html That seriously affects the DVI, (Dust Veil Index), http://www.geo.mtu.edu/volcanoes/vc_...cano_climate.h tml Personal experience: In 1991 we were wintering in central Ontario, and normally used ~6 cords of wood / year, with 1 cord back-up and 250 gallons of heating oil emergency reserve if the woodstove malfunctioned. We ended up burning 9 cords that winter. Daily high's stayed below -20F to 0F for weeks. By putting a fist at arm's length in front of the day-time Sun, the dust was quite apparent in the sky region around it. Regards Ken Lets throw some numbers at this problem: * How to get from lunar surface to earth-sun L1.. trivial A linear boost of some 2.6 km/s will do the job, taking about a month to get there, at very low resultant velocity. * How much dust will you need? To block just ONE PERCENT of sunlight, you need to block some 1.35 million square kilometers. Assuming you grind down your regolith to about cement-dust scale (10 nm grain size), you will need some 53 million metric tons. In addition, at this dust size, solar radiation pressure is quite significant, imparting some 250 m/s of acceleration per day. If you plan your trajectory well, you could have your dust linger in a usefull region for up to a week, so you only need to be able to sling 200 million tons of material delivered per month. Not too practical. Increasing the dust particle size fixes your solar pressure problem, but increases the initial mass required as the cube of the particle size.. 1mm grains would be stabile, but mass required is some 4.6e12kg For comparison: the cooling effect caused by mount Pinatubo's eruption ejected some 500 million tons of dust and, more significant to the cooling issue, some 20 million tons of SO2. The earth's gravity+atmosphere neatly contains this material from scattering, until normal weather effects wash them from the air, which takes some months. Conclusion: If you want to block the sunlight from reaching earth surface, you need to keep your solution close to earth. On or just above the surface, like volcanoes do, or at most in LEO where you have control over its location. And given the sheer mass required for any meaningfull shading, space is just not an option. |
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