c60a-2jm@tart23.BERKELEY.EDU (Adam J. Richter;260E;;) (11/01/86)
In article <531179395.amon@h.cs.cmu.edu> Dale.Amon@H.CS.CMU.EDU writes: In re: powersats... >I might add that laser transmission has also been considered as an >alternative means of transmitting power to the surface. The laser >technique is not as well known a quantity. Microwave energy >transmission has been done experimentally over reasonably long distances >with high efficiencies. Actually better than power transmission lines, >and the cost effectiveness gap widens with distance. Does anyone remember the Scientific American ("Scientific Democrat") articles on "Phase Conjugate Mirrors," or something like that. These little buggers are supposed to reflect back light, by reversing the direction of every beam that hits it. They also can amplify light, to the point where some researchers were able to make lasers just by waving a metal cooking spatula near them. Anyhow, one of their neat applications, is that if you aim a beam through a scattering medium and it hits a phase conjugate mirror, the "mirror" will exactly reverse the scattered light so it goes back through the scattering medium and becomes perfrectly "unscattered." So here's the idea: Small guide beam --> LEO powersat. LEO powersat --> LOTS OF ENERGY focused almost perfectly back down the "guide beam." Comments? + + + Adam + + + Adam J. Richter ...ucbvax!miro!richter 2504 College Avenue \ richter@miro.berkeley.edu Berkeley, CA 94704 >= May change soon (415)459-9672 /
chiaraviglio@husc2.UUCP (lucius) (11/02/86)
In article <1575@jade.BERKELEY.EDU>, c60a-2jm@tart23.BERKELEY.EDU (Adam J. Richter;260E;;) writes: [Reference to _S_c_i_e_n_t_i_f_i_c _A_m_e_r_i_c_a_n article, and explanation of how phase-conjugate mirrors work, deleted.] > Small guide beam --> LEO powersat. > LEO powersat --> LOTS OF ENERGY focused almost > perfectly back down the "guide beam." [ . . .from an amplifying phase-conjugate mirror.] Problem is, a powersat in geostationary orbit will be so far away that in the time it takes for your guide beam to get to the satellite, and the power beam to get back, the atmospheric distortions recorded by your guide beam will have changed enough to botch it up. This is not a problem over short distances -- turbulence can't do much in a few nanoseconds or microseconds -- but the round-trip time (at lightspeed) to a satellite in geostationary orbit is something like 0.3(?) second, enough time to mess things up. -- -- Lucius Chiaraviglio lucius@tardis.harvard.edu {insert your favorite brave system here}!seismo!tardis!lucius Please do not mail replies to me on husc2 (disk quota problems, and broken mail system won't let me send mail out). Please send only to the address given above.
c60a-2jm@tart15.BERKELEY.EDU (Adam J. Richter;260E;;) (11/02/86)
In article <1007@husc2.UUCP> chiaraviglio@husc2.UUCP (lucius) writes: >In article <1575@jade.BERKELEY.EDU>, c60a-2jm@tart23.BERKELEY.EDU (Adam J. Richter;260E;;) writes: >[Reference to Scientific American article, and explanation of how >phase-conjugate mirrors work, deleted.] >> Small guide beam --> LEO powersat. ^^^ >> LEO powersat --> LOTS OF ENERGY focused almost ^^^ >> perfectly back down the "guide beam." >[ . . .from an amplifying phase-conjugate mirror.] > > Problem is, a powersat in geostationary orbit will be so far away that ^^^^^^^^^^^^^ >in the time it takes for your guide beam to get to the satellite, and the >power beam to get back, the atmospheric distortions recorded by your guide >beam will have changed enough to botch it up. This is not a problem over >short distances -- turbulence can't do much in a few nanoseconds or >microseconds -- but the round-trip time (at lightspeed) to a satellite in >geostationary orbit is something like 0.3(?) second, enough time to mess >things up. Yes, that had occurred to me, which is why I was specific to say an LEO station. Such a station would have a number of receiving points on the ground. Sorry for not being clearer about that point. Alternatively, one could have one GEO powersat and one fixed receiving point on the ground, where the powersat excites an amplifying phase-conjugate mirror that is flying by at LEO. This model has a number of LEO "mirrors" being energized from above, or allows for service during part of the day. It also becomes more practicle as more powersats along different points of the "mirror" orbits come on line. + + + Adam + + + Adam J. Richter ...ucbvax!miro!richter 2504 College Avenue \ richter@miro.berkeley.edu Berkeley, CA 94704 >= May change soon (415)459-9672 /
OCONNORDM@GE-CRD.ARPA (OCONNOR DENNIS MICHAEL) (11/03/86)
Date: 3-NOV-1986 14:25
From: Dennis O'Connor
Sender: OCONNORDM
Subject: Powersats
To: space@angband@smtp
--------
Does anyone know the proposed power densities
of powersat receivers? Also, how flexible do the
focusing mechanism have to be to compensate for
thermal warpage of the transmission antenna, atmospheric
changes, et cetera.
The reason I'm asking this is to get a feel for
how good a weapon a powersat would be. Personally, I
think I'm most likely to stay at the bottom of the
gravity well, and I don't particularly want anyone
sitting in the relative security of geo-sync orbit
( it takes hours to get there ) deciding to write
his name on a glacier with a laser, or boil Lake Placid
with a microwave. Just call me paranoid, but where
people are concerned, these types of things happen.
This whole infrastructure-in-space discussion
ignores the tactical superiority of a position
at the top of a gravity well, relative to us poor
taxpayers at the bottom. Remember that anything that
deliver energy to a target is a weapon. And it is one
of the major tenants of the infrastructure supporters
that delivering anything to the top of a well starting
at the bottom is very very difficult.
--------chiaraviglio@husc2.UUCP (lucius) (11/04/86)
In article <1577@jade.BERKELEY.EDU>, c60a-2jm@tart15.BERKELEY.EDU (Adam J. Richter;260E;;) writes: > In article <1007@husc2.UUCP> chiaraviglio@husc2.UUCP (lucius) writes: > >In article <1575@jade.BERKELEY.EDU>, c60a-2jm@tart23.BERKELEY.EDU (Adam J. Richter;260E;;) writes: > >[Reference to Scientific American article, and explanation of how > >phase-conjugate mirrors work, deleted.] > >> Small guide beam --> LEO powersat. > ^^^ > >> LEO powersat --> LOTS OF ENERGY focused almost > ^^^ > >> perfectly back down the "guide beam." > >[ . . .from an amplifying phase-conjugate mirror.] > > > > Problem is, a powersat in geostationary orbit will be so far away that > ^^^^^^^^^^^^^ [Rest of my garbage deleted.] > Yes, that had occurred to me, which is why I was specific to say > an LEO station. Such a station would have a number of receiving > points on the ground. Sorry for not being clearer about that point. Wow -- that was really stupid of me. How could I mess up 1 abbreviation, especially after reading neuroscience articles with so many abbreviations that you have to keep track of that it rivals the government? Hmmm. . .hope that doesn't say something about how well I am going to do in that course. . . . > Alternatively, one could have one GEO powersat and one fixed > receiving point on the ground, where the powersat excites an > amplifying phase-conjugate mirror that is flying by at LEO. I wonder how big a beam would you need so that it wouldn't be so concentrated as to fry something flying through (we're not talking about misses here, since presumably you could use conjugatable guide beams for the long leg as well, as long as it didn't have to go through atmosphere), but about the beams during normal use. People assigning satellite orbits would have to worry not only about objects (essentially small spheres of safety distance), but now about laser beams (long cylinders of safety distance to keep out of). This is not a problem unique to what you propose, although having the powersats track moving retransmitter satellites could complicate this problem, although how big a powersat you can build in low earth orbit might be an overriding consideration. The same problem holds true for microwave transmission, except that a laser beam can be considerably more concentrated (sizzle. . .). -- -- Lucius Chiaraviglio lucius@tardis.harvard.edu {insert your favorite brave system here}!seismo!tardis!lucius Please do not mail replies to me on husc2 (disk quota problems, and broken mail system won't let me send mail out). Please send only to the address given above.
henry@utzoo.UUCP (Henry Spencer) (11/05/86)
> Does anyone know the proposed power densities > of powersat receivers? ... Roughly comparable to normal sunlight, so the heating load by itself is not enormously significant. (The reasons to use microwaves from powersats rather than just settling for normal sunlight are (a) much higher conversion efficiencies, and (b) the powersat beam is there day and night and largely ignores clouds.) > The reason I'm asking this is to get a feel for > how good a weapon a powersat would be... A pretty poor one. The physical size of the transmitting antenna dictates how tight the focus can be, so one can set limits by restricting antenna size. Powersats per se are intended to be built so that they need a guide signal from the ground for antenna focusing, also. Custom-building one as a weapon might eliminate the need for a guide beam, but the limitations of focus based on antenna size are quite fundamental. The above is for microwave transmission; laser transmission is a different and rather less comforting story. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,decvax,pyramid}!utzoo!henry
henry@utzoo.UUCP (Henry Spencer) (11/11/86)
> >(b) the powersat beam is there day and night and largely ignores clouds.) > > There day and NIGHT? Where does it get its night power (I am presuming > a solar power source)? It would have to be in a pretty durn high orbit > ( :-), and synchronous orbits are kinda low, aren't they? ) for the earth > not to block the sun from the powersat at night! Clarke (geosynchronous) orbit is 40000 km up; for much of the year, the tilt of the Earth's axis means that the Earth's shadow misses Clarke orbit completely. In spring and fall there will be a few weeks when there is a short interruption in the power feed at local midnight, as the satellite passes through the Earth's shadow. This will need to be planned for, but midnight is not a time of high power demand. Otherwise, no problem. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,decvax,pyramid}!utzoo!henry
crowl@rochester.ARPA (Lawrence Crowl) (11/11/86)
In article <1310@ttrdc.UUCP> levy@ttrdc.UUCP (Daniel R. Levy) writes: >In article <7278@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes: >>(The reasons to use microwaves from powersats rather than just settling >>for normal sunlight are (a) much higher conversion efficiencies, and >>(b) the powersat beam is there day and night and largely ignores clouds.) > >There day and NIGHT? Where does it get its night power (I am presuming >a solar power source)? It would have to be in a pretty durn high orbit >( :-), and synchronous orbits are kinda low, aren't they? ) for the earth >not to block the sun from the powersat at night! The earth is inclined 23 degrees off the earth's orbital plane. So, any powersat in (geosynchronous) orbit around earth will be out of the earth's orbital plane almost all the time, so could not possibly be blocked from the sun. Even if the powersat were in the earth's orbital plane, it will probably be sufficiently far from the earth so that for most (95%?) of its orbit it will not be blocked from the sun. To see this, place a cup on your desk and draw a large circle around it. From how many points on the circle can you see your doorknob? Remember, how many lunar eclipses happen? Certainly no where near one a month, let alone one a month for half the month. -- Lawrence Crowl 716-275-5766 University of Rochester crowl@rochester.arpa Computer Science Department ...!{allegra,decvax,seismo}!rochester!crowl Rochester, New York, 14627
andrew@alberta.UUCP (11/12/86)
In article <1310@ttrdc.UUCP> levy@ttrdc.UUCP (Daniel R. Levy) writes: >In article <7278@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes: >>(The reasons to use microwaves from powersats rather than just settling >>for normal sunlight are (a) much higher conversion efficiencies, and >>(b) the powersat beam is there day and night and largely ignores clouds.) > >There day and NIGHT? Where does it get its night power (I am presuming >a solar power source)? It would have to be in a pretty durn high orbit >( :-), and synchronous orbits are kinda low, aren't they? ) for the earth >not to block the sun from the powersat at night! 22,300 miles is not *that* low. The important fact is that the plane of the powersat's orbit (equatorial) is inclined to that of the Earth's orbit by 23.5 degrees. The powersat only passes through the Earth's shadow when the line of intersection of the two planes is collinear with the Earth and the Sun, which only happens twice a year. The net result is that objects in Clarke orbits are only in darkness for about 90 minutes each year. -- Andrew Folkins ...ihnp4!alberta!andrew The University of Alberta, Edmonton, Alberta, Canada Arthur C. Clarke's Law : It has yet to be proven that intelligence has any survival value.
levy@ttrdc.UUCP (Daniel R. Levy) (11/12/86)
In article <1310@ttrdc.UUCP>, levy@ttrdc.UUCP (thats'a me) writes: >In article <7278@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes: >>(The reasons to use microwaves from powersats rather than just settling >>for normal sunlight are (a) much higher conversion efficiencies, and >>(b) the powersat beam is there day and night and largely ignores clouds.) > >There day and NIGHT? Where does it get its night power (I am presuming >a solar power source)? It would have to be in a pretty durn high orbit >( :-), and synchronous orbits are kinda low, aren't they? ) for the earth >not to block the sun from the powersat at night! Oh, boy. Matt Crawford pointed out the fallacy of that one to me right quick. I'm chowing down on the ol' crow here, people. Synchronous-orbit satellites ARE high enough to get the sun most of the time. -- ------------------------------- Disclaimer: The views contained herein are | dan levy | yvel nad | my own and are not at all those of my em- | an engihacker @ | ployer or the administrator of any computer | at&t computer systems division | upon which I may hack. | skokie, illinois | -------------------------------- Path: ..!{akgua,homxb,ihnp4,ltuxa,mvuxa, go for it! allegra,ulysses,vax135}!ttrdc!levy
timothym@tekigm2.UUCP (11/12/86)
In article <1310@ttrdc.UUCP> levy@ttrdc.UUCP (Daniel R. Levy) writes: >There day and NIGHT? Where does it get its night power (I am presuming >a solar power source)? It would have to be in a pretty durn high orbit >( :-), and synchronous orbits are kinda low, aren't they? ) for the earth >not to block the sun from the powersat at night! Geosync orbits are at 22,000 +/- miles. They can be placed where Earth shadow isn't a problem (at least for the most part a minimum of 3 hours of cooling down and 22 hours of warming up). -- Tim Margeson (206)253-5240 PO Box 3500 d/s C1-937 @@ 'Who said that?' Vancouver, WA. 98668 {allegra..inhp4..decvax..ucbvax}!tektronix!tekigm2!timothym
Dale.Amon@H.CS.CMU.EDU (11/13/86)
OCONNORDM@ge-crd.arpa: Out of fear you would apply draconian controls. You are applying the same paranoia that pollutes the world we already live on. Paranoia and fear breed deeper paranoia and fear. And once they reach a certain point, the reality of hatreds and weapons no longer allows other paths to be taken. Can't we ever consider stopping the cycle? Let others alone and they will leave you alone too. Prior to this discussion, I had thought that arming a space colony was a foolish idea, and I had told friends so. If the mentality of jealousy and fear already exists a hundred years before the fact, I may have to eat my words. You may be right: we should indeed consider moving colonies far from nuthouse Earth, as soon as it is feasible to do so. I do wonder if such an escape will require a bloody revolt, since you suggest that the earliest colonists will be held under oppressive control by fearful ground based authorities.