ajw@hou2h.UUCP (A.WIENERS) (08/08/84)
<<>> > Microwaves have been proposed for power transmissions, but whenever I think > of microwaves carrying enough energy to actually be useful, I keep on seeing > all these birds, airliners, etc. flying through the beam and getting cooked. > > David Smith The proposed SunSat (SPS, whatever) uWave beams carry less energy (even in the center of the beam!) than full sunlight; their advantage is that they irradiate the rectenna (RECtifying anTENNA, as I recall) 24 hrs/day and are unblocked by clouds (I assume the xmission freq is tuned for a window in the H2O etc. absorption spectra). The real problem the originators had was whether the uWaves would effect the ionosphere (sp?). Subsequent testing (reported around 18 months ago?) showed no significant problems, although the details escape me. Anyone out there at Princeton/SSI (Space Studies Institute, i.e. G. K. O'Neill) to clarify this? (note: I'm not sure what the relationship between Princeton & the SSI is, and do NOT wish to imply any). art ihnp4!hou2h!ajw HO1B612 201/834-1142 (Earth)
wls@astrovax.UUCP (William L. Sebok) (08/09/84)
> The real problem the originators had was whether the uWaves would effect the > ionosphere (sp?). Subsequent testing (reported around 18 months ago?) showed > no significant problems, although the details escape me. Anyone out there at > Princeton/SSI (Space Studies Institute, i.e. G. K. O'Neill) to clarify this? > (note: I'm not sure what the relationship between Princeton & the SSI is, and > do NOT wish to imply any). > > art ihnp4!hou2h!ajw HO1B612 201/834-1142 (Earth) None, that I know of between the Astrophysics Dept. here and the SSI. -- Bill Sebok Princeton University, Astrophysics {allegra,akgua,burl,cbosgd,decvax,ihnp4,noao,princeton,vax135}!astrovax!wls
henry@utzoo.UUCP (Henry Spencer) (08/10/84)
>> Microwaves have been proposed for power transmissions, but whenever I think >> of microwaves carrying enough energy to actually be useful, I keep on seeing >> all these birds, airliners, etc. flying through the beam and getting cooked. Airliners are no problem; they have metal skins, which reflect microwaves quite well. The beam intensities are too low to have any gross effects on birds, although there is some concern about long-term low-level effects on them. This is actually the most (!) serious known problem. > The proposed SunSat (SPS, whatever) uWave beams carry less energy (even in > the center of the beam!) than full sunlight; their advantage is that they > irradiate the rectenna (RECtifying anTENNA, as I recall) 24 hrs/day and are > unblocked by clouds... They have another big advantage: microwave-to-electricity conversion can be quite efficient (70-80%), whereas converting sunlight to electricity is dismally inefficient (15% is good for solar cells). Of course, the power satellite itself probably uses solar cells, but it is out in space, where (a) the sun shines 24 hours/day, and (b) the waste heat does not go into Earth's biosphere. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
nather@utastro.UUCP (Ed Nather) (08/12/84)
[] >They have another big advantage: microwave-to-electricity conversion can >be quite efficient (70-80%), whereas converting sunlight to electricity is >dismally inefficient (15% is good for solar cells). Of course, the power >satellite itself probably uses solar cells, but it is out in space, >where (a) the sun shines 24 hours/day, and (b) the waste heat does not >go into Earth's biosphere. >-- > Henry Spencer @ U of Toronto Zoology a) The sun shines 24 hours/day everywhere, not just out in space, but it may be difficult to get a satellite far enough away from the earth so it never passes through its shadow, particularly if it is in synchronous orbit, which means it goes around once in 24 hours, and must therefore be at 25,000 miles altitute. b) If the solar cells aren't there to convert the heat into electricity (i.e. make some use of 15% of it) then it will *all* go into the earth's bioshphere if it isn't reflected back into space. The "saved" 15% will presumably get converted into work somewhere, which degrades into heat, which enters the earth's biosphere. So where is the "waste?" c) If the Sunsat is put up it will be bright enough to rival the full moon, just from reflected light alone (the moon reflects ~8%, is bigger but is *much* farther away, and the inverse-square law does a bit of good) ... which means ground-based astronomy goes out of business, since most of the interesting observations of quasars, distant galaxies, black hole candidates and vibrating stellar corpses are confined to "dark time," when the moon is nearly aligned with the sun and the night sky is dark. d) If all astronomers become shoe salesmen or zoologists then who will be watching when the Klingons come? -- Ed Nather {allegra,ihnp4}!{ut-sally,noao}!utastro!nather Astronomy Dept., U. of Texas, Austin
henry@utzoo.UUCP (Henry Spencer) (08/15/84)
> a) The sun shines 24 hours/day everywhere, not just out in space, but it may > be difficult to get a satellite far enough away from the earth so it never > passes through its shadow, particularly if it is in synchronous orbit, which > means it goes around once in 24 hours, and must therefore be at 25,000 miles > altitute. The sun sure doesn't shine 24 hours a day in Toronto! That statement is true only if you qualify "everywhere" to mean "all places in empty space, or without a solid body between themselves and the sun". The problem of powersats passing through the Earth's shadow is less major than you might think. Remember that the Earth's axis, and hence the axis of the Clarke orbit, is inclined to the ecliptic. For most of the year, the Earth's shadow passes "under" or "over" the "back half" of the Clarke orbit, so powersats are never in shadow. For short periods during spring and fall, powersats are in shadow briefly at midnight [assuming rectennas at about the same longitudes as the satellites themselves]. Midnight is not a time of high power demand, and this problem could be handled by backup power sources or by load-sharing among several well-spaced powersats. > b) If the solar cells aren't there to convert the heat into electricity (i.e. > make some use of 15% of it) then it will *all* go into the earth's bioshphere > if it isn't reflected back into space. The "saved" 15% will presumably get > converted into work somewhere, which degrades into heat, which enters the > earth's biosphere. So where is the "waste?" Nope. For the same reasons why the powersats are seldom in the Earth's shadow, they are seldom between the Earth and the Sun. Most of the time, the sunlight they are intercepting would have gone out into interstellar space. The only reason this whole thing comes up is that people fuss over powersats adding heat to the biosphere. They do, but not as much as (say) ground-based solar, since the 85% that powersats don't convert successfully into electricity is radiated into space, not the biosphere. Ground-based solar power plants are generally in desert areas, where most solar energy goes straight back out into space -- until you put a power plant there. > c) If the Sunsat is put up it will be bright enough to rival the full moon, > just from reflected light alone (the moon reflects ~8%, is bigger but is > *much* farther away, and the inverse-square law does a bit of good) ... > which means ground-based astronomy goes out of business, since most of the > interesting observations of quasars, distant galaxies, black hole candidates > and vibrating stellar corpses are confined to "dark time," when the moon is > nearly aligned with the sun and the night sky is dark. This is a serious problem. In the long run, ground-based astronomy is doomed anyway, both because of increasing volumes of stuff in orbit and because space is a much better place to do astronomy. But a ring of powersats in equatorial orbit may well hasten its demise considerably. It helps that powersats are designed to *absorb*, not reflect, light. But it probably doesn't help enough. The one consolation is that major powersat construction will involve enough space activity that the costs of other space activities, e.g. space astronomy, may drop as a side effect. I agree, this is a painful and undesirable side effect. I don't see any way around it, though, and if powersats work as well as people hope, it may well be worth it. Perhaps the sale/lease price of a finished powersat should include a modest "tax" to support space-based astronomy. > d) If all astronomers become shoe salesmen or zoologists then who will be > watching when the Klingons come? Given that "utzoo" is a Zoology-department machine, the prospect of such job shifts doesn't horrify me as much as you might think. The Klingons are unlikely to advertise their presence by occulting quasars anyway. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
fair@dual.UUCP (Erik E. Fair) (08/15/84)
>> From: nather@utastro.UUCP (Ed Nather) >> Subject: Re: Alternate Energy & Microwaves >> Date: Sun, 12-Aug-84 13:09:31 PDT >> >> c) If the Sunsat is put up it will be bright enough to rival the full moon, >> just from reflected light alone (the moon reflects ~8%, is bigger but is >> *much* farther away, and the inverse-square law does a bit of good) ... >> which means ground-based astronomy goes out of business, since most of the >> interesting observations of quasars, distant galaxies, black hole candidates >> and vibrating stellar corpses are confined to "dark time," when the moon is >> nearly aligned with the sun and the night sky is dark. Clearly the thing to do is put the astronomers up there in Reagan's Space Station, where the pesky atmosphere won't get in their way. After all, if we can put a few tons of Sunsat up, why not a few pounds of Astronomer? >> >> d) If all astronomers become shoe salesmen or zoologists then who will be >> watching when the Klingons come? >> That's easy: the astrologers! >> -- >> Ed Nather >> {allegra,ihnp4}!{ut-sally,noao}!utastro!nather >> Astronomy Dept., U. of Texas, Austin As a concession to netiquette: :-) Erik E. Fair ucbvax!fair fair@ucb-arpa.ARPA dual!fair@BERKELEY.ARPA {ihnp4,ucbvax,hplabs,decwrl,cbosgd,sun,nsc,apple,pyramid}!dual!fair Dual Systems Corporation, Berkeley, California
jsq@ut-sally.UUCP (John Quarterman) (08/15/84)
On putting astronomers in the space station:
Actually, the planned space station will be in low earth orbit,
quite a ways below geosynchronous orbit, which is the most likely
place for power satellites. The astronomers would at least not
have to contend with Earth's atmosphere, but they'd still have
the power satellites in plain view. The space station is mostly
for industrial research, anyway.
A useful place for astronomers would be the L2 Terra-Luna libration
point, which is a (more or less) stable point above the far side of the
moon: no atmosphere, no interference from most light sources on earth
or in most likely earth orbits. This is preferable to an observatory
on the lunar far side itself because of ease of access. Or at least
I'd think so. Doubtless some opinions from astronomers will follow up....
--
John Quarterman, CS Dept., University of Texas, Austin, Texas 78712 USA
jsq@ut-sally.ARPA, jsq@ut-sally.UUCP, {ihnp4,seismo,ctvax}!ut-sally!jsqkissell@flairvax.UUCP (Baba ROM DOS) (08/15/84)
(ahem) First off, Ed Nather's fears about the effect on ground-based astronomy of an SPS (sunsat) system are shared by a lot of people. Erik Fair's comment: > Clearly the thing to do is put the astronomers up there in Reagan's Space > Station, where the pesky atmosphere won't get in their way. > After all, if we can put a few tons of Sunsat up, why not a few pounds of > Astronomer? misses a couple of points (though I suspect it was made lightheartedly). The problem is not to get a few pounds of astronomer into space, it is to get a few tons of telescope and other instruments up there. The astronomers, few of whom do much naked-eye work any more, can work down here. This is precisely the goal of the space telescope program. Lots of neat work has been done by unknown people in small observatories, the kind of people who would not get any say in which way an orbital instrument will be pointed, and it would be a shame to see them put out of business by SPS. One question I've never heard answered has to do with the siting of receiving antennas for the microwaved power. The power satelites must presumably be in a geostationary, and therefore equatorial, orbit. Receiving stations on the equator are a long way from the industrialized northern regions. Overland power transmission losses from, say, Equador to the U.S. would be huge, perhaps prohibitive. If the recieving sites are to be in the U.S., the beams would have to be angled through more atmosphere, and would strike an enlongated "footprint". Can anyone tell me the amount of distortion that would be incurred angling from a geostationary orbit to central Nevada, for instance? Kevin D. Kissell Fairchild Research Center Advanced Processor Development uucp: {ihnp4 decvax}!decwrl!\ >flairvax!kissell {ucbvax sdcrdcf}!hplabs!/ "Any closing epigram, regardless of truth or wit, grows galling after a number of repetitions"
nather@utastro.UUCP (Ed Nather) (08/15/84)
[] >On putting astronomers in the space station: > >Actually, the planned space station will be in low earth orbit, >quite a ways below geosynchronous orbit, which is the most likely >place for power satellites. The astronomers would at least not >have to contend with Earth's atmosphere, but they'd still have >the power satellites in plain view. The space station is mostly >for industrial research, anyway. You are so right. Note that SPACE TELESCOPE is to be in the *same* dumb orbit. Why? Because it has to be carried aloft by the shuttle. But ... couldn't we use another booster, and get it into synchronous orbit where it would be *much* more useful, Sir? Go away, kid. You bother me. >A useful place for astronomers would be the L2 Terra-Luna libration >point, which is a (more or less) stable point above the far side of the >moon: no atmosphere, no interference from most light sources on earth >or in most likely earth orbits. This is preferable to an observatory >on the lunar far side itself because of ease of access. Or at least >I'd think so. Another nifty location is at the lunar poles -- down in a crater, where the sun *never* shines! That way, it's dark 24 hours a day (at L2 it's *light* all the time, unless you provide your own shadowing) and you can see half the Universe all the time. It goes around once every 28 days or so. What about the other half? Well, another telescope at the other pole will do the job. Hey! Is NASA interested in this? ...I said, go *away*, kid! > Doubtless some opinions from astronomers will follow up.... >-- >John Quarterman, CS Dept., University of Texas, Austin, Texas 78712 USA *sigh* -- you know us too well, John. -- Ed Nather {allegra,ihnp4}!{ut-sally,noao}!utastro!nather Astronomy Dept., U. of Texas, Austin
cem@intelca.UUCP (Chuck McManis) (08/16/84)
Why does a powersat have to reflect light back to earth at all?
If you designed them to concentrate solar energy, as I assume one
would, since metalized mylar is cheaper than solar cells, why
wouldn't you design them to focus light in a "hidden" area of the
sattelite(sp?) ie
light ---> \/ <-+ light continues on --->
\/ <-|
<-- uWaves \ |
/ +-- Two solar panels
^
|
MicroWave Antenna
Light is reflected to the solar cells (shown on the right)
that are not reflecting back to earth. The incoming
microwaves would be invisible to us (not radio telescopes of course)
but certainly optical telescopes. Am I missing something here?
--
-- Chuck - - - D I S C L A I M E R - - -
{ihnp4,fortune}!Dual\ All opinions expressed herein are my
{proper,idi}-> !intelca!cem own and not those of my employer, my
{ucbvax,hao}!hplabs/ friends, or my avocado plant. :-}
ARPAnet : "hplabs!intelca!cem"@Berkeleyhoward@metheus.UUCP (08/17/84)
>>They have another big advantage: microwave-to-electricity conversion can >>be quite efficient (70-80%), whereas converting sunlight to electricity is >>dismally inefficient (15% is good for solar cells). Of course, the power >>satellite itself probably uses solar cells, but it is out in space, >>where (a) the sun shines 24 hours/day, and (b) the waste heat does not >>go into Earth's biosphere. >>-- >> Henry Spencer @ U of Toronto Zoology >a) The sun shines 24 hours/day everywhere, not just out in space ... I know Texas is in the Sun Belt, Ed, but REALLY! There is something called NIGHT! Just ask Wendy if you don't believe me! >b) If the solar cells aren't there to convert the heat into electricity (i.e. >make some use of 15% of it) then it will *all* go into the earth's bioshphere >if it isn't reflected back into space. The "saved" 15% will presumably get >converted into work somewhere, which degrades into heat, which enters the >earth's biosphere. So where is the "waste?" Henry was clearly referring to solar cells IN SPACE, ON THE SOLAR POWER SATELLITE. The efficiency advantage he refers to could be relative to a scheme in which you used a huge space mirror to reflect sunlight to a solar power station on earth. Or, if the albedo of a solar cell is significantly lower than that of sand, then more light will be absorbed by the solar cell than by the desert it replaces, leading to real excess heat in the biosphere. All the solar cells I've seen look pretty much black. If we assume that sand = albedo 0.6 and solar cells = albedo 0.1 then the excess heat will be (.6 - .1) - .15, or 35% of the total energy of the sunlight falling on them. So the total biosphere heat for ground-based solar would be 3.33 watts per watt of electricity, whereas for microwave beaming it would be 1.33 watts of heat per watt of electricity. That's where. [P.S. Anybody got REAL albedo numbers for this computation?] >c) If the Sunsat is put up it will be bright enough to rival the full >moon, just from reflected light alone (the moon reflects ~8%, is bigger >but is *much* farther away, and the inverse-square law does a bit of >good) ... which means ground-based astronomy goes out of business, >since most of the interesting observations of quasars, distant >galaxies, black hole candidates and vibrating stellar corpses are >confined to "dark time," when the moon is nearly aligned with the sun >and the night sky is dark. Ground-based astronomical OBSERVATION is slowly going out of business anyway, because it can't compete with observations made from satellites, except in lower cost. But ground-based astronomy will do just fine; witness all the analysis of Jovian moons by ground-based astronomers. >d) If all astronomers become shoe salesmen or zoologists then who will be >watching when the Klingons come? A goodly share of the TV audience at the time, no doubt. Howard A. Landman "Searchlight casting for faults in the clouds of delusion"
bradley@godot.UUCP (Bradley C. Kuszmaul) (08/17/84)
>> At L2 it is *LIGHT* all the time.
What does it matter? There's no atmosphere to reflect the light, and
I thought you guys liked looking straight into the sun...
-- Brad
--
{decvax!cca,ihnp4!mit-eddie,allegra!ias}!godot!bradley,
"godot!bradley@mit-eddie"@MIT-XX.ARPAhenry@utzoo.UUCP (Henry Spencer) (08/19/84)
> Actually, the planned space station will be in low earth orbit, > quite a ways below geosynchronous orbit, which is the most likely > place for power satellites. The astronomers would at least not > have to contend with Earth's atmosphere, but they'd still have > the power satellites in plain view.... > You are so right. Note that SPACE TELESCOPE is to be in the *same* dumb > orbit. Why? Because it has to be carried aloft by the shuttle.... Right stick, wrong end. The only *reason* why bright things in the sky make trouble for astronomers is the damn atmosphere in between! Any telescope in orbit, no matter what orbit, is also going to be in bright sunlight most of the time; little things like powersats are trivial by comparison. If the stray-light shield can cope with sunlight, it can cope just fine with minor bits of reflected sunlight from big satellites. It doesn't much matter what orbit telescopes are in, so you might as well put them somewhere easy to reach. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
henry@utzoo.UUCP (Henry Spencer) (08/19/84)
> I have a question about SPS microwaves for those more knowledgeable - > granted the u-waves don't fry birds, wouldn't they fry every radio on an > airliner passing through/close to the beam? ... > ...what about > satellites that might pass between a geostationary power satellite and its > ground station? ... > [he also mentions ground-based microwave transmissions] Communications interference from powersats is not a trivial topic, but it looks manageable. The wavelength for powersat transmissions will be in the industrial-microwave band, almost certainly, and this is not at the same frequency as communications. Note that there is no need for more than one frequency for powersats, so the problem comes down to filtering out one offending frequency that is well away from the normal communications bands. (Well, harmonics complicate the issue a bit...) Powersats will definitely create interference, and communications systems will need some work, but last I heard it didn't look impossibly hard. It helps that powersat beams will be put out by emitters perhaps a kilometer on a side; they'll be by far the tightest microwave beams ever generated. The intensity will fall off very quickly indeed outside the area of the rectenna. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
henry@utzoo.UUCP (Henry Spencer) (08/21/84)
> .................................................. Lots of neat work has > been done by unknown people in small observatories, the kind of people who > would not get any say in which way an orbital instrument will be pointed, > and it would be a shame to see them put out of business by SPS. Such astronomers should make it their first order of business to find out about the Amateur Space Telescope, a totally separate effort from the NASA Space Telescope. Doing astronomy in space does not require the colossal level of investment involved in the NASA version. Having only one telescope in space is silly; we need lots of them. If the AST works the way it looks it will, this will immediately be a realistic notion. > One question I've never heard answered has to do with the siting of receiving > antennas for the microwaved power. The power satelites must presumably be > in a geostationary, and therefore equatorial, orbit. Receiving stations > on the equator are a long way from the industrialized northern regions. > Overland power transmission losses from, say, Equador to the U.S. would be > huge, perhaps prohibitive. If the recieving sites are to be in the U.S., > the beams would have to be angled through more atmosphere, and would strike > an enlongated "footprint". Can anyone tell me the amount of distortion > that would be incurred angling from a geostationary orbit to central > Nevada, for instance? It is necessary to put the rectennas quite near the customers; long-haul power transmission of this size is out. (In fact, probably the best way to do really long-range power transmission is via microwave beam relayed by satellite!) The added atmospheric losses are slight, since atmospheric losses are slight to begin with. The "footprint" will indeed be enlongated, which will mean a somewhat larger rectenna area, but it's not unmanageable anywhere short of the Arctic. Nevada is at maybe 40 degrees of latitude -- I don't have a map handy -- which means that the beam comes in at about 40 degrees off vertical. This is enough to stretch the North-South axis of the rectenna by 30-40%. It's manageable. -- "The trouble with a just economy is, who runs the Bureau of Economic Justice?" Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
dwp@inmet.UUCP (08/22/84)
I have a question about SPS microwaves for those more knowledgeable -
granted the u-waves don't fry birds, wouldn't they fry every radio on an
airliner passing through/close to the beam? Admittedly, there would be losses
because the VHF/UHF antennas are not even closely matched, but would this
matter with the signal powers involved? To further the question, what about
satellites that might pass between a geostationary power satellite and its
ground station? Since these u-waves are highly directional, I doubt that
there would be large amounts of power distributed outsided the antenna
location, but wouldn't even a ridiculously directional antenna at those
power levels spray enough u-waves all over the southwest (say), to foul up
all manner of u-wave transmissions? Maybe this is cheap to fix (relatively
speaking,) but there are billions invested in u-wave communications that
might not be able to co-exist.
David Pachura
{harpo,decvax!cca!ima,esquire}!inmet!dwp