eli@bbn.com (Steve Elias) (03/28/88)
In article <4091@bloom-beacon.MIT.EDU> jfc@athena.mit.edu (John F Carr) writes: !In article <22670@bbn.COM! eli@BBN.COM (Steve Elias) writes: !!In article <2963@sfsup.UUCP! glg@/guest4/glgUUCP (xt1112-G.Gleason) writes: !: !: (regarding solar power satellites) ! !:!In any case something seems bogus here, because in order to be significant !:!we would have to be considering SPS's with a total area that is *very* !:!large (significant relative to the earths total collection are). total receiver area is not the only factor which will upset thermal equilibrium. !: indeed something is bogus: the very idea of Solar Power Satellites !: being a useful energy source. they would be enormously expensive !: and enormously dangerous (thermally), if enough were built to !: actually provide a decent amount of energy. ! !If we ever get a lot of energy out of them, we will need a cheaper launch !system. We will also use very large thin films to minimize weight and !cost. The SPS's will not be built if they are too expensive. regardless of cost or efficiency, the SPS idea is inherently dangerous. let me reiterate why this is so... (below)... !Assuming international cooperation in space (else !the SPS is too vulnerable to attack) the SPS is more reliable than other !systems, and has a greater thermal efficiency on earth. regardless of the efficiency of any of the ground receiver systems, solar power satellites would add incredible amounts of energy to the earth/atmosphere system, whether in the form of electricity, or in the form of waste heat. this is their function. the form the energy takes is not relevant to the global thermal considerations. !If the only criterion for choosing a generator were, !"what is the danger to man, both short- and long-term", then solar power !satellites would be a good choice. no way. they are as dangerous a choice as we could make. regardless of efficiency, they would add on the order of the same amount of energy flux we receive from the sun now. (i recall the order of magnitude -- haven't dug up numbers yet). !: energy put into building earthside collectors is not leaving the !: earth/atmosphere system, so it doesn't negate the energy sent down !: by the power satellites. reflectivity changes due to the collectors !: would have to be considered, as well. but, regardless of reflectivity !: changes, thermal equilibrium would be quite goofed up -- by waste heat !: from the microwave receivers... !You have assumed <= 50% efficiency, others have claimed higher. Either !way, this is better efficiency than for a heat engine. So, it is better !(if trying to minimize waste heat) to use solar power. i wasn't specific enough. waste heat alone would be dangerous, but that isn't the only source of extra thermal energy -- the electricity itself is as dangerous as the waste heat. my point isn't that we have to minimize waste heat -- it is that we have to minimize the amount of energy that enters the earth ecosystem that would not otherwise be there. !: the greenhouse effect can theoretically be kicked off by both CO2 !: buildup and by large thermal changes -- both factors are 'cause' and !: both factors are 'effect'. that's Frank Drake's point... !The effect is far more sensitive to CO2 concentration; present power !sources produce more CO2 as a fraction of the total present than they !do heat. once again: the greenhouse effect is a theory. we don't know exactly where the 'points of no return' are, on either the CO2 or the thermal side. !By the time we are generating a few % of the solar flux on the earth as !waste heat, we will have to worry. By then, I hope we will have moved !power intensive industry into space (if not, we can produce more power, !and use the excess to drive a heat pump [perhaps, a large laser] and !refridgerate the earth.) and: waste heat is not the problem. energy that would not otherwise enter the earth/atmosphere system is the problem. moving power intensive industry into space would solve the problem quite nicely... (i'm not holding my breath).
eli@spdcc.COM (Steve Elias) (03/31/88)
In article <4195@bloom-beacon.MIT.EDU> jfc@athena.mit.edu (John F Carr) writes: !In article <761@spdcc.COM> eli@spdcc.COM (Steve Elias) writes: !: efficiency has nothing to do with the problem of thermal pollution. !Efficiency has everything to do with thermal pollution. For a fixed power !consumption, efficiency determines the amount of heat generated relative to !useful power. A system with a 50% efficient converter would produce twice !as much heat as a 90% converter (including the rest of the system, and the !consumer). you are wrong, here. both the 'useful power' and the 'waste heat' end up in the environment as heat. !argued for zero growth in consumption, I must assume that you think certain !power sources are worse than others producing the same useful power. The !only factor determining the waste heat produced by a system is its !efficiency. SPS are among the most efficient power generation systems again: efficiency doesn't matter. SPS is the only power source which uses energy which would not otherwise enter the earth's atmosphere. it is worse than most other power sources in this respect. why do you insist that efficiency is a factor? all useful energy will turn up as heat in the environment. ! !If you are arguing that SPS are worse than earth-based systems capable of !generating the same power you are wrong. If you are arguing against !increasing our generating capacity you should say so. i am arguing against increasing our generating capacity by collecting massive amounts of energy from exo-atmospheric sources. ! !My conclusions from these: the earth reacts to thermal pollution on a very !short timescale (days to weeks). The timescale of the feedback by which !an increase in temperature produces a runaway greenhouse effect is millions !of years. On the other hand, the timescale for CO2 pollution to produce a !greenhouse effect is very short. Adding heat will not raise the temperature !noticeably until the rate of addition approaches the solar flux on the earth. !Adding CO2 has already warmed the earth (the articles have numbers). yes! my point is that hundreds of solar power satellites WILL add energy on the order of the present solar flux!
eli@spdcc.COM (Steve Elias) (04/01/88)
i'll try to find Frank Drake's notes on the subject. does anyone out there respect his findings? we know Jef doesn't -- he likes Jerry Pournelles attitude instead... their boneheaded personal attacks belong in the bitbucket. to those who continue to be civil -- thanks. Jef apparently likes to attribute random quotes to me as well as telling me what my beliefs are. not the acts of a responsible usenetter... i won't be holding my breath for civil replies from him -- but i will provide a few numbers and i'll concede that i overstated things, if that is the result.
owen@xyzzy.UUCP (Karl Owen) (04/02/88)
>, >!: eli@spdcc.COM (Steve Elias) >! jfc@athena.mit.edu (John F Carr) >!: efficiency has nothing to do with the problem of thermal pollution. >!Efficiency has everything to do with thermal pollution. For a fixed power >!consumption, efficiency determines the amount of heat generated relative to >!useful power. > you are wrong, here. both the 'useful power' and the 'waste heat' > end up in the environment as heat. Steve is apparently not reading what he is responding to, or is unbeleivably slow to pick up the central idea here. Note the phrase "for a fixed power consumption". Under that assumption, the less efficent the power production, the more total energy must be liberated to support the "fixed power consumption". Thus, while it is correct to say that both the "useful power" and the "waste heat" wind up in the environment as heat, this is irrelevant to the point being made, which is that for the more efficent process, the sum of these is smaller. >!Adding heat will not raise the temperature >!noticeably until the rate of addition approaches the solar flux on the earth. >!Adding CO2 has already warmed the earth (the articles have numbers). > yes! my point is that hundreds of solar power satellites > WILL add energy on the order of the present solar flux! Simple arithmetic makes this claim incredible. The present solar flux reaches earth through an effective window perhaps 1X10^8 square kilometers. For "hundrds of solar power satellites" to produce energy "on the order of the present solar flux", each one would have to be 100 kilometers across. As far as I know, proposals for SPS have satellites with 1/100th of that surface area, and only a few tens of them, not "hundreds". And all this without even accounting for the fact that much of the waste heat in this process would be released outside the biosphere. Certainly, the claim that SPS would necessarily create more thermal pollution than competing ground-based systems involving solar, biomass, petrochemical, or nuclear processes is nowhere nearly established by anything Steve has put forward so far. -- Nothing is so useless as a general maxim. --- Thomas Babington -- Karl M. Owen owen@dg-rtp.dg.com Data General, RTP, NC ...!mcnc!rti!xyzzy!owen
eli@spdcc.COM (Steve Elias) (04/02/88)
hi there friends of Pournelle and normal folks. Jef's second set of numbers are indeed on the mark. my statement about large power needs and incident solar flux on the earth was 99% off. i'd appreciate a bit of restraint from the more excited readers out there. there's no need for replies filled with curses and slurs written in capital letters. the theory i am espousing is not random, nor is it my own. i have access to Drake's notes on the subject and will provide them if a single person out there really cares. if not, never mind & hit 'n'. my own back of the envelope silly numbers agree with Jef's second set. his first set dealt with earthside efficiency of the power receiving stations, which is irrelevant. incident energy from the power satellites is the only factor. Jef's calculations show that incident power from solar power satellites would have to be many times present power needs in order to equal solar flux. this is true -- i came up with 5e16 watts absorbed by the earth. it would take a thousand terawatt satellites in order to equal that flux. if we estimate that power needs will grow -- we would need only a few tens of satellites to be on the order of a few percent of the solar flux. one of the more atmospheric types out there (jwm?) mentioned that the earth system responds on the order of days or months to small additions of energy. a question for you, jwm or jfc: how does the earth's atmosphere respond to long term flux increases of a few percent? i think that the reaction would not be simple reradiation of the energy into space. i don't think i'm far from Drake's thinking on this issue. would anybody like to see his calculations and thoughts when i get his notes? or would you prefer to see slurs written in either lower or capital case? i don't recall making any such slurs until Jef and Jerry Pournelle got into the action. both Jef and Pournelle ought to turn down their Tera-Egos. one of the only things that pisses this asshole off is snobbish behavior. i may have bullshitted my flux claim, but it was in response to a super-snob article filled with slurs in capital letters -- the one from "Jef Pournelle". later, SETI fans. steve
throopw@xyzzy.UUCP (Wayne A. Throop) (04/02/88)
Due to a glitch in our local inews software, which is now under investigation, an article that I, Wayne Throop, throopw@xyzzy.UUCP posted was attributed to Karl Owen instead. Please, please: if you wish to follow up, remember that you are following up to me, and not to him. Deity willing, this article itself will not fall prey to the same bug... -- Wayne Throop <the-known-world>!mcnc!rti!xyzzy!throopw
glg@sfsup.UUCP (G.Gleason) (04/02/88)
In article <763@spdcc.COM> eli@spdcc.COM (Steve Elias) writes: >In article <4195@bloom-beacon.MIT.EDU> jfc@athena.mit.edu (John F Carr) writes: >!In article <761@spdcc.COM> eli@spdcc.COM (Steve Elias) writes: >!: efficiency has nothing to do with the problem of thermal pollution. >!Efficiency has everything to do with thermal pollution. For a fixed power > you are wrong, here. both the 'useful power' and the 'waste heat' > end up in the environment as heat. He is not wrong. He stated this explicitly in his first article. Useful power = Total energy input * Efficiency and Waste heat = Total energy input - Useful power The second equation isn't really relevant because it is the total energy input that ends up in the environment. The first equation says that for a given power need (i.e. hold useful power constant), the energy added to the environment is inversly proportional to efficiency. It matters. >!efficiency. SPS are among the most efficient power generation systems > again: efficiency doesn't matter. SPS is the only power source > which uses energy which would not otherwise enter the earth's > atmosphere. it is worse than most other power sources in this > respect. why do you insist that efficiency is a factor? all > useful energy will turn up as heat in the environment. I see you totally missed his analysis. Passive solar also brings in energy that would not otherwise remain the system (it shines in, but normally it would be reflected off). You must include this factor in your analysis. John's arguments are the most informative I have seen in this debate. I would advise you to study them until you understand the points he is making, you may learn something. There is no point in your continuing this debate until you have a better understanding of the issues. Gerry Gleason
lazarus@athena.mit.edu (Michael Friedman) (04/02/88)
In article <763@spdcc.COM> eli@spdcc.COM (Steve Elias) writes: >In article <4195@bloom-beacon.MIT.EDU> jfc@athena.mit.edu (John F Carr) writes: >!In article <761@spdcc.COM> eli@spdcc.COM (Steve Elias) writes: >!: efficiency has nothing to do with the problem of thermal pollution. >!Efficiency has everything to do with thermal pollution. For a fixed power >!consumption, efficiency determines the amount of heat generated relative to >!useful power. A system with a 50% efficient converter would produce twice >!as much heat as a 90% converter (including the rest of the system, and the >!consumer). > you are wrong, here. both the 'useful power' and the 'waste heat' > end up in the environment as heat. Let's use an example to make this clear. Say I need a megawatt of electricity. Assume I have two choices - a 50% efficient method (A) and a 10% efficient method (B). To get a megawatt of electricity from A I must produce 2 megawatts of energy. 1 megawatt will be wasted, and released as heat. The second will be used, and later released as heat. Total energy released into environment: 2 megawatts. To get a megawatt of electricity from B I must produce 10 megawatts of energy. 9 megawatts will be wasted, and released as heat. The tenth will be used, and later released as heat. Total energy released into environment: 10 megawatts. See the difference? > SPS is the only power source > which uses energy which would not otherwise enter the earth's > atmosphere. it is worse than most other power sources in this > respect. This is not important for reasonable power use. If we increase the total energy flux reaching the earth's surface by .001 % we are unlikely to do damage. Even an increase that insignificat is probably well beyond the reach of technology either today or for the foreseeable future. On the other hand, we are quite capable of significantly increasing the CO2 content of the atmosphere. That can prevent energy from escaping and increase the net energy flux reaching the Earth by a significant amount. > yes! my point is that hundreds of solar power satellites > WILL add energy on the order of the present solar flux! Unless you plan to have millions of square kilometers of collecting surface beaming more power down to Earth than we can possibly use you are off by many orders of magnitude. These are the official opinions Mike Friedman of my organization. So, TOUGH!!
tdh@frog.UUCP (T. Dave Hudson) (04/02/88)
>> A system with a 50% efficient converter would produce twice >> as much heat as a 90% converter (including the rest of the system, and the >> consumer). > you are wrong, here. both the 'useful power' and the 'waste heat' > end up in the environment as heat. Yes, he was wrong. A 50% efficient plant producing X electricity ends up producing 2X heat, and a 90% produces 1.1X heat. It is only a 1.8 ratio, not 2. :-) David Hudson
edk@gryphon.CTS.COM (Ed Kaulakis) (04/03/88)
In article <763@spdcc.COM>, eli@spdcc.COM (Steve Elias) writes: >In article <4195@bloom-beacon.MIT.EDU> jfc@athena.mit.edu (John F Carr) writes: > !In article <761@spdcc.COM> eli@spdcc.COM (Steve Elias) writes: > > !: efficiency has nothing to do with the problem of thermal pollution. > > !Efficiency has everything to do with thermal pollution. For a fixed power > !consumption, efficiency determines the amount of heat generated relative to > !useful power. A system with a 50% efficient converter would produce twice > !as much heat as a 90% converter (including the rest of the system, and the > !consumer). > > you are wrong, here. both the 'useful power' and the 'waste heat' > end up in the environment as heat. Aaah... God forbid I should ruin anyones' day, but let's do a little arithmetic, shall we? Suppose I need 1 Mw of power. Then I could get it from an SPS by beaming 1.1Mw to a 90% rectenna. Or, I could pave some desert that used to re-radiate 5 or so Mw in solar cells. In the first case, the Earth's energy balance is loaded with 1.1Mw thermal. In the second case, the Earth's energy balance is loaded with ~4Mw thermal. READ MY LIPS, OR MOVE TO TALK.BIZARRE!
leonard@bucket.UUCP (Leonard Erickson) (04/04/88)
In article <763@spdcc.COM> eli@spdcc.COM (Steve Elias) writes:
<!Efficiency has everything to do with thermal pollution. For a fixed power
<!consumption, efficiency determines the amount of heat generated relative to
<!useful power. A system with a 50% efficient converter would produce twice
<!as much heat as a 90% converter (including the rest of the system, and the
<!consumer).
<
< you are wrong, here. both the 'useful power' and the 'waste heat'
< end up in the environment as heat.
No he is *correct*! Assume 100 MW of useful power is needed.
At 50% efficiency, we get 100 MW of power & 100 MW of heat, after use of
the power we have a *total* of 200 MW of heat.
At 90% efficiency we get 100 MW of power & 11.1... MW of heat, after use
we have a total of 111.1... MW of heat.
If we use an SPS we get 100 MW *period*!
< again: efficiency doesn't matter. SPS is the only power source
< which uses energy which would not otherwise enter the earth's
< atmosphere. it is worse than most other power sources in this
< respect. why do you insist that efficiency is a factor? all
< useful energy will turn up as heat in the environment.
See the above for an explanation of why efficiency matters.
<!If you are arguing that SPS are worse than earth-based systems capable of
<!generating the same power you are wrong. If you are arguing against
<!increasing our generating capacity you should say so.
<
< i am arguing against increasing our generating capacity by
< collecting massive amounts of energy from exo-atmospheric sources.
<!
<!My conclusions from these: the earth reacts to thermal pollution on a very
<!short timescale (days to weeks). The timescale of the feedback by which
<!an increase in temperature produces a runaway greenhouse effect is millions
<!of years. On the other hand, the timescale for CO2 pollution to produce a
<!greenhouse effect is very short. Adding heat will not raise the temperature
<!noticeably until the rate of addition approaches the solar flux on the earth.
<!Adding CO2 has already warmed the earth (the articles have numbers).
<
< yes! my point is that hundreds of solar power satellites
< WILL add energy on the order of the present solar flux!
Good grief. Try doing the math... To get an increase equivalent to the
present *total* solar flux, you will need an area of SPS's *greater*
than the cross-sectional area of the earth!!! Assume an SPS is 50%
efficient (number picked solely to simplify the math). To get a 1%
increase in the Earth's heat budget, you'd need an energy input equal
to 1% of the total flux. At 50% efficiency, this means we'd need an
area equal to 2% of the Earth's. That is 4000**2*2*pi*.02 miles.
Or approximately 2 *million* square miles of collector.
And that is a power generating capacity of around four and a half
MILLION GIGAWATTS!!!!! That sounds like a lot more than a couple of
hundred SPS units.
Also you are forgetting that every watt we send down means that all
the waste heat associated with generating a watt of power on the ground
is dropped. Remember up above where I showed that generating a watt
of *power* means adding *more* than a watt of heat? So if an SPS
replaces a 100 MW 50% eff. plant on the ground, we have 100 MW *less*
heat! (11.1... MW less for the 90% efficienct plant).
Add in the lack of CO2 if it was a fossil fuel burning plant and you have
an even better gain. Note that fossil fuels are stored energy form the solar
flux millions of years ago.
--
Leonard Erickson ...!tektronix!reed!percival!bucket!leonard
CIS: [70465,203]
"I used to be a hacker. Now I'm a 'microcomputer specialist'.
You know... I'd rather be a hacker."jwm@stdc.jhuapl.edu (James W. Meritt) (04/05/88)
In article <767@spdcc.COM> eli@spdcc.COM (Steve Elias) writes:
:one of the more atmospheric types out there (jwm?) mentioned that the
:earth system responds on the order of days or months to small additions
:of energy. a question for you, jwm or jfc:
:how does the earth's atmosphere respond to long term flux increases of a
:few percent? i think that the reaction would not be simple reradiation
:of the energy into space. i don't think i'm far from Drake's thinking
:on this issue. would anybody like to see his calculations and thoughts
:when i get his notes?
I had planned to get out of this: Those capable of reason had, and those
incapable do not rate the trouble, but since I was asked.....
I don't know any of the time constants or phase delays for the current system.
What I do remember (and think may be relevant) is something I vaguely remember
called the "Gia hypotheses" (ok, my spelling stinks.....) This advanced the
concept that the easth/seas/atmosphere system was a self-correcting "living"
organism. As a support for this, it is estimated that the solar flux has
varied, and in fact was 120% of current, while there has been life on earth.
This amount of heat should have boiled a lot of water, but obviously didn't:
Life (as we know it, on earth, our chemistries,.......) NEEDS liquid water!
That, and the isotope balances in the shells, indicates that while the flux
varied greatly, the temperature didn't. Anybody got better data?
Now as to "small additional amounts of energy": beats me, but I know it gets
cold at night and warms up in the morning!
Disclaimer: Individuals have opinions, organizations have policy.
Therefore, these opinions are mine and not any organizations!
Q.E.D.
jwm@aplvax.jhuapl.edu 128.244.65.5eder@ssc-vax.UUCP (Dani Eder) (04/05/88)
In article <22678@bbn.COM>, eli@bbn.com (Steve Elias) writes: > > regardless of the efficiency of any of the ground receiver systems, > solar power satellites would add incredible amounts of energy to > the earth/atmosphere system, whether in the form of electricity, > or in the form of waste heat. this is their function. > the form the energy takes is not relevant to the global thermal > considerations. > > my point isn't that we have to minimize waste heat -- it is that > we have to minimize the amount of energy that enters the earth > ecosystem that would not otherwise be there. > If you are concerned about heat balance, have you considered tar-paper roofs and asphalt roads? Let us do some ROM calculations. Your typical suburban home has about 160 square meters of roof. Most roofing materials are darn good black body absorbers. Your average temperate latitude home receives 125 Watts of insolation/sqaure meter, over 24 hours. Let us say the roof absorbs 40 watts more than the original cround cover. Thus, the suburban home adds someting on the order of 6.4 kilowatts to the earth's heat balance. This equals the installed electrical generating capacity per household in the US. There is something like 300 square meters of road for every household in the US. In addition, there is a parking spot for every car at a location other than the owner's drivewaay (only that counts, since the car always covers some part of the ground when outdoors) That adds at least another 30 square meters per household. Assume that the same change in absorbtion occurs as for roofs. We are talking several times the effect of the roofsa. In fact, when one looks at Landsat photographs of city areas, the cities stand out as dark splotches. And many city dwellers are familiar with the temperature differential from city to suburb. What most are nmot familiar with is the trend continues into the rural areas. It is partly waste heat and partly darker ground cover. Dani Eder/Boeing/Space Station Program
eder@ssc-vax.UUCP (Dani Eder) (04/07/88)
In all the discussion about SPS's adding to the flux entering the Earth's atmosphere, I have yet to see anyone mention that the SPS also blocks some sunlight. This occurs when the SPS is between the Sun and the Earth. In the canonical SPS designs this blockage was small, but there is no fundamental reason you could not addd a large region of very thin reflective foil around the active sps photovoltaics, so as to enhance the blockage effect. If you worry about net energy entering the Earth, then this might help. In fact, if there is not enough time to run all our power plants backwards to get the CO2 out of the atmosphere before we fry, intentionally placing mirrors in orbit to deflect inco iming sunlight might give us more time to solve the problem. Dani Eder/Boeing/Space Station Program
eli@spdcc.COM (Steve Elias) (04/09/88)
In article <1840@ssc-vax.UUCP> eder@ssc-vax.UUCP (Dani Eder) writes:
!In all the discussion about SPS's adding to the flux entering the
!Earth's atmosphere, I have yet to see anyone mention that the
!SPS also blocks some sunlight.
!you could add a large region of very thin reflective foil
!around the active sps photovoltaics, so as to enhance the
!blockage effect. If you worry about net energy entering the
!Earth, then this might help.
this is a great point. the 'foil' idea could hopefully buy
time -- even if we don't make the mistake (my opinion) of
putting solar satellites in orbit.
!In fact, if there is not enough time to run all our power
!plants backwards to get the CO2 out of the atmosphere before we
!fry, intentionally placing mirrors in orbit to deflect incoming
!sunlight might give us more time to solve the problem.
if we avoid CO2 and thermal effects as power needs
grow, hopefully we can avoid the need for a planetary
air conditioner!
!Dani Eder/Boeing/Space Station Program
steve elias / a guy who studied some planetary science
(how else would i have time to write so much about it?)wooding@daisy.UUCP (Mike Wooding) (04/12/88)
In article <1840@ssc-vax.UUCP>, eder@ssc-vax.UUCP (Dani Eder) writes: > In fact, if there is not enough time to run all our power > plants backwards to get the CO2 out of the atmosphere before we > fry, intentionally placing mirrors in orbit to deflect inco iming > sunlight might give us more time to solve the problem. > > Dani Eder/Boeing/Space Station Program Might be easier to make a cloud (of dust?) for a little shade on a hot day. Wouldn't stay around a long time, but then that could be an advantage. Gets noticeably cooler during an eclipse which lasts only minutes. Were talking a LOT of dust though, more than might be reasonable to lift from earth, but there's the moon. And with a mass launcher, and maybe some static charge to disperse, ... well you get the idea? Could it be kept from falling to earth? Would it matter if it did? m wooding
jwm@stdc.jhuapl.edu (James W. Meritt) (04/13/88)
In article <1033@daisy.UUCP> wooding@daisy.UUCP (Mike Wooding) writes: }In article <1840@ssc-vax.UUCP>, eder@ssc-vax.UUCP (Dani Eder) writes: }> In fact, if there is not enough time to run all our power }> plants backwards to get the CO2 out of the atmosphere before we }> fry, intentionally placing mirrors in orbit to deflect inco iming }> sunlight might give us more time to solve the problem. } Might be easier to make a cloud (of dust?) for a little shade } on a hot day. Wouldn't stay around a long time, but then that } could be an advantage. Gets noticeably cooler during an eclipse } which lasts only minutes. Were talking a LOT of dust though, } more than might be reasonable to lift from earth, but there's } the moon. And with a mass launcher, and maybe some static } charge to disperse, ... well you get the idea? Could it be } kept from falling to earth? Would it matter if it did? Not being much of an astrophysicist, could someone comment on putting dust in an orbit between the earth and the sun? The position I have in mind is an orbit closer to the sun at the point where the earth's gravity balances the suns to the extent that it could orbit at the (slower) speed that the earth does. It sounds to me like it would orbit properly, but I have no idea how far from the earth this point is, nor does it seem overly stable. Could a, say, 5% reduction in incoming solar flux be achieved in this way (balancing the "extra" beamed in from those billions and billions of SPSs ;~))? Disclaimer: Individuals have opinions, organizations have policy. Therefore, these opinions are mine and not any organizations! Q.E.D. jwm@aplvax.jhuapl.edu 128.244.65.5
jfc@athena.mit.edu (John F Carr) (04/14/88)
In article <226@aplcomm.UUCP> jwm@stdc.jhuapl.edu.UUCP (James W. Meritt) writes:
: Not being much of an astrophysicist, could someone comment on putting
: dust in an orbit between the earth and the sun? The position I have in
: mind is an orbit closer to the sun at the point where the earth's
: gravity balances the suns to the extent that it could orbit at the
: (slower) speed that the earth does. It sounds to me like it would orbit
: properly, but I have no idea how far from the earth this point is, nor
: does it seem overly stable.
The point of which you are thinking, one of the Lagrange points, is
not stable. An object placed there will drift away.
John Carr "No one wants to make a terrible choice
jfc@athena.mit.edu On the price of being free" -- Neil Peartmarkey@tybalt.caltech.edu (Ron A Markey) (04/14/88)
In article <226@aplcomm.UUCP> jwm@stdc.jhuapl.edu.UUCP (James W. Meritt) writes: >Not being much of an astrophysicist, could someone comment on putting >dust in an orbit between the earth and the sun? The position I have in >mind is an orbit closer to the sun at the point where the earth's >gravity balances the suns to the extent that it could orbit at the >(slower) speed that the earth does. It sounds to me like it would orbit >properly, but I have no idea how far from the earth this point is, nor >does it seem overly stable. Could a, say, 5% reduction in incoming >solar flux be achieved in this way (balancing the "extra" beamed in >from those billions and billions of SPSs ;~))? > > >Disclaimer: Individuals have opinions, organizations have policy. > Therefore, these opinions are mine and not any organizations! >Q.E.D. >jwm@aplvax.jhuapl.edu 128.244.65.5 The distance from the Earth to the center of mass of the cloud works out to be about 1,530,000 km. Given that the moon is out there swinging around 400,000 km, I don't think that it would be to awfully stable. I anyone is interested in the math, send me mail and I'll give it to you. Another problem with this pops to mind. This dust is not just going to block the sunlight, it is going to absorb and re-radiate it. Given that the cloud is going to spread out (it would even if the moon weren't screwing things up) and potentially occupy a lot of sky it seems likely that it will eventually end up contributing to the problem that it is supposed to solve by absorbing a LOT of energy and radiating it at Earth. - Ron (markey@tybalt.caltech.edu)