Talk:Space-based solar power/Archive 2

Wolfkepper's hasty reversion
Way to toally not understand the edits and blow away everything because of two minor issues. Quoth WK:

"no, not sunsynchronous- geosynchronous orbits are the primary location typically proposed, ssp >> sbsp on google"

I agree, there has been less discussion of sunsynchonous than geosynchronous, but sunsynchronous = solar synchronous has several important advantages: 1 The satellite flies about half way to GEO altitude, so the transmitting antenna is smaller and/or the beam can be narrower, making slightly smaller scale practical, thus lower initial cost. 2 Two sun synchronous satellites can supply most of the countries of Earth, every peak demand period, when the wholesale price of electricity is highest. This because the satellites orbit approximately over the sunshine terminator 3 The antenna aiming is slightly less critical. 4 station keeping for the satellite is much less critical. 5 The rectennas can be smaller, and/or less energy falls outside the rectennas. 6 Rectennas optimised for sunsynchronous can serve other types of SSP reasonably well. 7 I think the brief shading of the solar panels near the equinox is illiminated, but the moon still causes a solar eclipse rarely and briefly, so the beam is available more than 99% of the time. The 96% in the article should be 99% unless it is allowing for repair shutdowns. 8 We don't have to compete with communications satellites for a geosynchronous slot. The disadvantages: The expensive rectennas are only used a few hours per day, until there are other types of SSP. 2 A very large sunsychronous SSP will briefly increase the path loss of an average of one geosynchronous communications satellite each time it passes the Equator in it's semi-polar orbit. I suggest a separate article for solar synchronous = sunsynchronous, but do not merge Solar Power Satellite and Space Solar Power as both are well written. Ccpoodle (talk) 15:44, 23 November 2007 (UTC)

Please revisit the original edits with a more open mind. ---Belg4mit
 * 1) What are you talking about? My version said "advantageous orbits (for example, sunsynchronous)". What, pray tell, is "inaccurate" about that? It simply provided a clearer more concise introduction, but all of the other flavors remain in the body. Also note that the edited text in no way said anything about which variant was most often discussed.
 * 2) Frequency counts on google are not meaningful evidence here, and that particular point becomes even more meaningless had the synonyms been left in.

Possible Merges
I would favor reconcilliation of all three pages, keep them separate, but move content from one to the other to make each of them more focussed and to remove redundancy and duplication: Charles (talk) 18:32, 16 February 2008 (UTC)


 * Space solar power
 * Solar panels on spacecraft
 * Solar Power Satellite

Proposed heirarchy:

Solar power satellite

 * Note: Articles do not need to be organized into a hierarchical structure. Delphi234 (talk) 18:42, 22 May 2008 (UTC)

Merge "Solar power satellite" with "Space solar power"
This entry is largely redundant of Solar power satellite and the two ought undergo some synchronization or merger. --Belg4mit 17:07, 8 November 2007 (UTC)


 * Agree. Need then more clarity about what the lines of division should be, if two distinct articles are actually warranted.


 * I would propose that one should concentrate on the "classical SSP" concept of photovoltaic power stations in GSO, and its close relatives, and the comparative economics, environmental impacts, and technical feasibility of alternative variations and implementations. (It is my opinion right now that the Pearson lunar space elevator concept, with Si mined and refined, and PV cells fabricated on the Moon (or at L1), completed cells or Si then lifted to Earth-Moon L1, and moved to GSO with ion drives, may be the leading candidate, but this needs to be documented and connected to external references, of which there there are currently few so far as I know.  The advantage of course is that there seem dubious prospects for finding useful rocket propellant on the Moon, and obtaining it from Earth would be extremely expensive, so it avoids that major problem of lunar resource usage.)  I think concentrating on the classical concept and its nearest relatives and descendants should be enough to fill a good article of reasonable length, maybe too much.


 * I am not sure what the other article should contain, or if it just has odd fragments that really should be attached to other articles on space exploration and utilization. An exhaustive discussion of unlikely or niche possibilities for the sake of completeness seems unattractive to me as part of the first focussed, "classical SSP" one, so that might be a place for the second article.  Yet the decision about what goes where is implicitly POV, so we would have to reach consensus on that.


 * I have made a few changes in the main text today, but guess I will refrain from more until the above issues are discussed (or not) at more length and sorted out. Wwheaton (talk) 19:40, 13 February 2008 (UTC)

You are right about the proposed merger. We can create one article as they both refer to the same thing.

A better header for the article would be "Space Power". We can discuss both these topics under that heading.--ZainAliK 19:25, 14 February 2008 (UTC)


 * Space Power and Space Solar Power are not the same thing. They need different pages.   Space Solar Power is a subset of Space Power.   Space Power can cover other non-solar power sources, e.g. nuclear, chemical fuel cells etc. Charles (talk) 18:07, 16 February 2008 (UTC)

Disagree. Solar Power Satellites are a SUBSET of Space Solar Power. They should not be merged,  but they should be linked. The "Space Solar Power" page covers both the use of solar power in space as well as beaming to Earth. The solar power satellite is purely for beaming to Earth and does not cover use in space. The SPS page is already very large, and merging them would make it even larger, which would be very cumbersome. But somebody should reconcile the two pages to makes sure there is not too much redundancy or duplication. Would be better to remove the description of SPS from the parent Space Solar Power page and move it to the Solar Power Satellite page Charles (talk) 18:02, 16 February 2008 (UTC)

Oppose merging. SPS is actually about beaming power to earth and not using it in space at all. So that article is not a space solar power article at all, it is an earth solar power article. Delphi234 (talk) 18:24, 22 May 2008 (UTC)

This article, SSP, on the other hand needs to have most of its material moved to SPS, as that is what most of the article is about. Delphi234 (talk) 18:32, 22 May 2008 (UTC)

Merge "Solar panels on spacecraft" with "Space solar power"
Doubtful -- My first thought is that this might be a mistake, as spacecraft power is a large and important discipline, and probably it deserves a place of its own, including both solar and non-solar (eg, batteries, Brayton cycle, nuclear, & solar) sources. Similarly I think "SSPs for on-Earth power application" has so many complex issues that are unique to it, that it does not really fit too well as a branch of space technology or spacecraft power, even though space is importantly involved and obviously there would be many cross-links. Some of these at first seem to make a logical hierarchy, set & subset,..., but there maybe other logical axes that will make it awkward to force everything into a logically clean system. Maybe we ought to think of what the big self-contained chunks are, and then try more to make the logic as tidy as possible with that in mind, but no tidier? Sounds hard, like a lot of concentrated work for a few dedicated heroes (& heroines). Wwheaton (talk) 01:06, 20 February 2008 (UTC)

 unwarranted  average reader will search for their general intended topic of interest - and it is doubtful that person interested in spacecraft will think about looking up topic related to theoretical approaches to solving terrestrial power generation problems - and vice versa people looking for SERT or Laser power beaming have more interest in global warming than in spacecraft. It would be better is one topic simply referred to the other (specialized) one. Awatral (talk) 08:59, 10 February 2009 (UTC)

Another comment
Such a merger might initially make sense, but it is also conseivable that power will eventually be generated from the moon, asteroids, or other planets... would this be refered to as space solar power, or put name of respective body here solar power? —Preceding unsigned comment added by 132.210.90.81 (talk) 14:14, 27 May 2008 (UTC)

Very likely I think. We do not call Earth solar power "space solar power", though logically of course it is, since the Earth is in space.
 * I think solar power for use on a particular planet or moon, say "X", derived from on the surface of X, should be called "X solar power".
 * Power for use on spacecraft is a whole separate subject, a branch of astronautical engineering, and "spacecraft solar power" is a subfield of that.
 * Finally, solar power generated in space, but for use on a planet or moon, is yet a third broad category, with some considerable overlap with the preceding, but several essential differences (eg, need to beam or otherwise move power from space to the surface; big difference in scale, kilowatts vs gigawatts; likely some human presence in space for construction and maintenance, etc). I would call only this "satellite solar power".

The differences among these are so significant that I think they need separate articles, no doubt with some cross-referencing to avoid needless redundancy. Wwheaton (talk) 15:40, 27 May 2008 (UTC)
 * Concur w/ Wwheaton for the reaons given. ww (talk) 00:08, 15 June 2008 (UTC)

Misleading diagram?
The second image in this article suggests that something like 1/4 or less of sunlight reaches the Earth's surface through a very thick atmosphere. In fact, the atmosphere is extremely thin (2% of radius) and lets the vast majority of solar energy through to the surface. Including about 30% albedo, including clouds, I believe the overall amount of energy reaching the surface is on the order of 50% or more. The Insolation article states that space insolation is 1366 watts per square meter, falling to 1000 on the surface on a clear day. I think this image needs to go. Maury (talk) 20:42, 14 August 2008 (UTC)

Despite that, it must be understood in any case that, in regards to solar power being over 99% effective in open, empty space must necessarily be better than any lower percentage on land. Still, land-set sources of solar energy are yet unreachable to developing countries, the most needy, which may also be understood as unstable economies, impotent prosperities, politically swerving governments that set a very poor grade on the security report card looking down the road to possible terrorism. These are still incapable of producing their own technology or even their own solar energy collectors sufficient enough to feel free from fossils, in an unexpensive manner. But they could also reach some sort of energetic independence. A look into the future of such an idea will prove quite unacceptable, and also a very good idea to keep that diagram the way it is... It's not a scientific issue.

Looking into the politics involved, it should be said that energy is definetely a highly political issue, not a resources matter. Whoever controls energy, controls what everyone else can possibly do and how far he can go in any direction or intention and can also limit the operativity of anyone hooked to the source. Now, looking at it from a scenario of temporarily and intelligently "giving away free energy from space sources", it is extremely improbable that loosing control over the politically unstable regions of the world by allowing them to produce their own "freedomizing" energy sources (not "liberating" because their is no way their enslavement can be demonstrated although it certainly is a true matter) will ever be possible at all. The core of present history would have to change overnight, maybe if Europe were drowned under tons of water and America knelt before a foreign enemy powerful enough to bring her to a total halt. Completely improbable... Therefore, luring the unstable into free solar energy sources and later levered into obedience seems much more feasible. Fossil fuels will certainly be over any minute now and whatever is left will be used for very specific and probably completely different matters, never to recover its current values nor importance. Gasoline and other fuels will be used only for whatever energy sources need explosion systems only. New, unthought of applications of severely expensive types will last only for a a liitle less than a century and then remembered only in history books. For the price of solar power, all new sources of oil will surprise the world dramatically, but by then, those who control oil will show up again controlling the energy panorama. The solar power distributors will be quite the same players but with a different type of energy. I may be ready to assume that fossil fuels will be exclusively laid aside for war purposes, not more.

So, the diagram, notwithstanding the fact that it may be wrong, even unintentionally, is politically correct to keep as it is if the power players are to scientifically exercise control over unstable left- or right-tending democracies and non democratic impositions. The sole idea of bringing down amounts of energy from the skies, or readjusting or reducing energy supplies at will and even blacking out energy from certain points in the planet can give us an idea of how useful the diagram is from a non-scientifical point of view, shunning the use of expensive solar sources in a non-fossil-fuel world in comparison to hardly-any-value sources from above. Let us welcome science divided by politics fairly equal to power, as the true source of the democratic distribution of energy in a pain-ridden planet that can easily be controlled by the brightest, hired by the powerful. Something the brightest have been doing since Einstein's days. —Preceding unsigned comment added by 200.87.244.173 (talk) 01:10, 1 September 2008 (UTC)

Transmission
One could transport energy from a land to other one without using wires (i.e. using a beam). --Mac (talk) 06:07, 22 September 2008 (UTC)

GSO/GEO
GSO is not, IMO, the proper TLA here. LEO = Low Earth Orbit. GEO = Geosynchronous Earth Orbit, and is by far the mainstream term in general use. --Grndrush (talk) 06:25, 6 December 2008 (UTC)

Featured article in es:
I have the pleasure to announce that the article Energía solar espacial of the Wikipedia in Spanish has qualified as featured article. Originally based on the article in English, we expanded the contents, added more detail and, most importantly, worked hard to achieve a good balance between the different points of view, so as to ensure neutrality. Special credit should be given to user Poco a poco for his work on this article. --Hispalois (talk) 20:52, 26 October 2008 (UTC)
 * It's today's featured article of the day at the Spanish Wikipedia--and it's definitely a nice article. It would be a good article to translate back into English, if anyone has the ability. 138.78.98.196 (talk) 20:38, 25 January 2009 (UTC)
 * Even easier, some of the illustrations in the Spanish article would be excellent additions to this one. and we really should be adding comments to the end of the current talk page....  ww (talk) 18:49, 20 February 2009 (UTC)

Rewrite
Aside from needing a general rewrite for clarity, this article needs to be converted to focus on the theoretical space-to-Earth solar collection design, rather than also encompassing current uses of solar panels on satellites and rovers, since those are already covered in more than one article (Solar panels on spacecraft). I rewrote the intro already.  Equazcion •✗/C • 08:23, 20 Feb 2009 (UTC)

Merge
As they are essentially two articles describing the same concept, this article and Solar power satellite need to be merged. I've begun cleaning up each article individually, basically to remove extraneous over-specific information, jargon and original research, to get at the essential information each article offers, in preparation to merge the two. So far it seems the Solar power satellite article has more valuable content, however I think "Space-based solar power" would be the better eventual title to put it all under, being that the SPS is just one element in the overall design of space-based solar power.  Equazcion •✗/C • 08:33, 20 Feb 2009 (UTC)
 * I've completed the merge. I did my best to preserve and reorganize the valuable content from both articles. Of course feel free to check it over and adjust, or yell at me. I didn't think to request a history merge of the two pages, and I'm not sure how that would work exactly, but anyone who wants can go ahead and do that, or request an admin do it. Equazcion •✗/C • 10:32, 20 Feb 2009 (UTC)

merge problems
As nearly as I can tell, the merge and revamp noted just above were not discussed before undertaking them. Since I think the revamp has ended up removing material useful to the Average Reader, I regret, on the whole, the work. I suggest that the status quo ante be restored, and the changes proposed be discussed here on the talk page before committing WP to them in the long term. It's an important article in the current planetary context and should be as useful as possible to Readers (even inexpert ones) even at the cost of more discursion and greater length than some editors think appropriate.

I invite comments on this proposal. ww (talk) 18:57, 20 February 2009 (UTC)


 * That's fine. I normally would've waited for discussion but seeing the states of the two articles, the year-old merge proposals on each page, the lack of talk page activity, and the relative inactivity in the recent page histories, I didn't think there would be much interest. If I was wrong then I'm fine with discussing changes to the way I handled the merge, or doing a complete revert if that's what everyone feels is necessary.


 * As for the removed material, yes I did remove substantial chunks of content, but if you take a good look at the specific parts removed you might agree that it needed to go -- it was a lot of overly-specific explanation of things like how the different solar cell technologies work and how other energy-producing technologies work, things that are already available in their separate articles. There was also a lot of original research, not just in terms of facts lacking in-line references, but blatant opinions on the advantages and disadvantages, and what would be the best way to implement the technology.


 * In order to allow editors to judge my content decisions for themselves, and/or to restore anything they feel I shouldn't have removed, here are links to the last revisions of each page prior to my editing them:
 * Space-based solar power
 * Solar power satellite
 * Regardless of what you may think I did right or wrong, I do feel a merge and major cleanup is still necessary, especially as the topic is coming a bit more to the scientific forefront now than it has before. I'm fine with criticism of my methods, but in that case I'd also appreciate some constructive discussion on what should be done instead, because I think we can agree something does need to be done.  Equazcion •✗/C • 19:10, 20 Feb 2009 (UTC)


 * The merge was proposed ages ago, and I don't remember anyone objecting. It seems reasonable to me; the two articles mostly duplicated content, and I'm glad to see that somebody took the trouble to actually do it.  If you think that material was lost in the merge that was important, why not edit it in?  Geoffrey.landis (talk) 23:27, 21 February 2009 (UTC)
 * As a solution to the merge (treating the merge as a fait accompli) this has the considerable disadvantage of requiring considerable effort from someone. Apparently me. Since i've not sufficient time to do it, material of value will have been lost for the accidental reason of my lack of availability for such a project. As a default choice, this is unfortunate. ww (talk) 19:11, 28 February 2009 (UTC)
 * I can't help but feel a little unappreciated as a result of your comments, Ww. I didn't just slap this together. I combed through the content and made decisions to the best of my ability, which took me about 2 hours. The articles were long and I didn't want to deal with the headache, but I did it because I felt it needed to be done. I needed to make tough decisions. If you're unsatisfied with those decisions, that is unfortunate, but you shouldn't sit here complaining about other people's work on something you aren't willing to work on yourself. Being that no one, including yourself, seemed willing or able to perform the merge in the year since it was proposed, it doesn't seem logical to complain about the result now that someone took the initiative. As I said I'm fine with discussing the restoration of whatever content you feel shouldn't have been removed. If you're still unwilling to work yourself on fixing whatever problems you've determined to exist, then I can't help you.  Equazcion •✗/C • 19:56, 28 Feb 2009 (UTC)
 * This version is so much better than the original it's not even funny. Thanks!  The meandering comparisons to this-and-that, which, strangely enough, happened to mention only aspects of this-and-that favorable to the SBSP POV, are gone.  Thanks!
 * There's a little bit of advocacy in the introduction, and a bit subtly in the advantages/disadvantages section: note that the disadvantages all have rebuttals. Is the preferred fix to add the obvious rebuttals to the advantages, or remove them from the disadvantages?
 * In any case, thanks again. You've noticeably improved the quality of this article. -Dmh (talk) 05:54, 4 April 2009 (UTC)

Energy in global winters
This section should go. First, half of it is spent telling us a supervolcano event would be catastrophic. That's already in the linked article on volcanic winter. The rest asserts that SBSP could somehow save us. This assumes, without proof, that
 * 1) SBSP would still work through a volcanic haze.  I'm guessing it would, but who knows?
 * 2) Any kind of electric power, space-based or otherwise, would be useful and deployable on a large enough scale quick enough to enable food to grow.  We're talking a lot of ... I don't know, grow lights, maybe?
 * 3) There would be anywhere near enough SBSP available to do the job.

In previous versions of this article, the answer would have been to add some speculation along those lines, and maybe speculate more about rebuttals and rebut those rebuttals with more speculation. Let's not do that.

If someone has written this scenario up credibly, reference that. Otherwise, yank the whole section. -Dmh (talk) 06:12, 4 April 2009 (UTC)


 * On further consideration, and after a brief attempt at editing, I've taken this section out. The clincher was chasing the links to the actual articles on volcanic and nuclear winters and realizing that during the winters in question, the sun is shining almost normally.  Somewhat less sunlight is reaching the earth, enough to make a difference in the climate, but by no means is it pitch black and by no means would other renewable sources fail to work.  Given that no one has come forward with any citations on how an SBSP would make a measurable difference, there doesn't seem to be any reason to keep this -Dmh (talk) 21:07, 18 April 2009 (UTC)

Parenthesis
Do you think there are enough parenthesis (in the article)? They seem to (in my humble opinion) make some of the sentences (and sections) hard to read! 216.255.104.61 (talk) 17:16, 14 April 2009 (UTC)

watts per square meter
Is it too much to ask for someone to state how much watts per square meter an object receives in Earth Orbit?98.165.6.225 (talk) 18:12, 17 May 2009 (UTC)


 * 1366 W/m^2 is given here Solar_constant and this is cited: []  Keith Henson (talk) 21:30, 8 June 2009 (UTC)

The Oil Drum
The Oil Drum seems to have been cited as a good secondary source in a number of places on Wikipedia.

There is a new article here http://www.theoildrum.com/node/5485 on this subject. Since I wrote the article, I don't want edit this one to include it. Keith Henson (talk) 04:59, 17 June 2009 (UTC)

Increased global warming
User: 69.140.224.14 removed the "Increased global warming" section as possible original research. I know that it is not original since I have read discussion of the matter in other places. The question is whether there are reliable sources for this material. I can add finding such sources to my to do list, but do not wait for me. If anyone can save that matterial, go for it.--Fartherred (talk) 03:40, 9 November 2009 (UTC)

Weaponization
Offering a steady constant supply of energy can aid weaponization efforts and offer advanced shielding systems. —Preceding unsigned comment added by 209.195.79.169 (talk) 22:57, 10 December 2009 (UTC)

PV pushing?
Why is it, aside from a few throwaway references, no attention is paid to the solar thermal engine design? (Since the article seems ignorant of it, let me explain: a 1km2 Mylar mirror, helium reservoir, boiler, & turbine.) It's a) simpler, b) lighter, & c) could be flown right now with existing lifters. Except, nobody seems to give a damn... And USG is busy throwing billions down the fusion rathole, instead of supporting a system that works, & (unlike the dreams of the green zealots) won't put millions of km2 into permanent shadow (boy, that's eco-friendly!) to provide less power than SPS...

On an unrelated point, I was looking for a comparo with terrestrial solar, but there doesn't seem to be one. Given a 50MW SPS, then, how much delivered power is there? This says terrestrial 50 MW produces 87.6 GWh/yr. TREKphiler  any time you're ready, Uhura  00:04, 18 December 2009 (UTC)
 * I am not sure I understand TREKphiler's complaint about the article. The use of a heat engine in a solar power satellite is mentioned in the article.  In the SERT section it is noted that, subject to studies, SERT proposed both a photovoltaic system and solar dynamic engines to convert solar flux into electricity.  The Design section again refers to solar cells or a heat engine.  The Solar energy conversion section refers to both photovoltaic and solar dynamic conversion.  A solar power satellite could be launched completely with currently developed technology, but I recall mention by a reliable source that the launch costs are about 1000 times what is required for economic operation.  I cannot cite the source off the top of my head, but I do not see TREKphiler citing any source for a system that "could be flown right now with existing lifters."
 * Personally I prefer something like Gerard K. O'Neill's "New Routes to Manufacturing in Space," as given in the references. The article carefully states that the proposal suffers from a lack of the automated systems called for.  For twenty years engineers have been beating their heads up against a wall of launch costs, because they love being paid to do so.  It is people with the political clout to arrange that they get paid for this futile activity who are responsible for our space program being no closer to a SPS than it was twenty years ago.  No show stoppers have been identified for the task of producing the remotely operated devices which would allow people on Earth to mine the moon, ship the stuff to GEO and build SPSs there.  The problems are that it would take a long time and the task has not been examined well enough to be sure there are no showstoppers.  People are hesitant to get into a project that takes so long that the working plans become obsolete before the project is half done.  This objection does not apply to examining the lunar resources to see just how available they are to industrial processes.  It might be necessary to go through a few design iterations in the process of doing the project, but I still think doing the whole thing with lunar materials remotely from Earth is the way to go.--Fartherred (talk) 00:17, 22 December 2009 (UTC)


 * The thing about needing 1000x cheaper launch costs is complete nonsense. The breakeven point for this is a launch cost of about $300/kg. The current price is about $5000/kg. But economies of scale give you that kind of reduction anyway at the kind of launch rate you would need- and rockets are not actually much harder to build than turbocharged cars, it's just that the normal production rate is under ten a year so they're very expensive right now; but if you build a big factory...


 * The reason breakeven is about $300/kg is because that's what the PVs cost in extreme quantity. In other words, when you launch PVs into space they see at *least* 3x more sun (for some places like Britain, Northern Europe more like 6-8x more sun in winter when you need it), but the launch costs are about the same as the cost of the panels, and you lose about 1/3 of the energy in beaming losses.


 * So for somebody on the equator, it's not worth it- just stick them on the ground, it costs the same/kWh. Further North or South it becomes increasingly worth it.- Wolfkeeper  00:43, 22 December 2009 (UTC)


 * Anyway, if you have a reference, we'll probably have to add it in the article, but I would expect we'd find references that are more like what I just wrote.- Wolfkeeper  00:44, 22 December 2009 (UTC)


 * I'll admit I may not have read every detail, but what I saw was a lot of attention to PV & slim coverage of the "solar furnace" option (if I can call it that). Sourced for flying now? No, admitted: how much does a 1km Mylar mirror weigh? How much a 10kW (or so) turbine, which a 1km Mylar mirror would support? Can a 10kW turbine fit in an STS payload bay? AFAIK, the answers are all "yes", which ="can be flown now". (Note, I'm not suggesting that be actually put in the article, so my inability to actually source it is irrelevant. If, however, somebody has access to a Toshiba Industrial catalog...?)
 * As for "economic operation", allow me to suggest Wolfkeeper's right: the first one will be hideously expensive; the 100th wouldn't be much/any more than existing 20GW plants (which are power industry standard, IIRC). And if the eco-nuts are right & this is the "defining moment for mankind" (which I doubt, but why not use them for leverage?), cost shouldn't be a deal-breaker. It wasn't for Hoover Dam or Tennessee Valley Authority--or Apollo... And is it more economic to go terrestrial in the tropics? Not against the potential output growth; terrestrial maxes out at about 10% of solar "coverage" (only 10% total energy/m2 actually reaches the surface), against over 90% in L4/L5, so even allowing for transmission losses, terrestrial is stupid. Not to mention inducing permanent shadow...
 * And can we please stop offering Luna as the resource option? Spending so much delta-V on Lunar resources is stupid. There are thousands of NEAs with lower delta-V that can be trapped, moved to L4/L5, & mined.  TREKphiler   any time you're ready, Uhura  04:59, 22 December 2009 (UTC)
 * The reference is NASA official Dr. Pete Worden speaking on thespaceshow.com for the edition of the 23rd day of March in the 2009th year of our Lord. He refers to space based solar power as being five orders of magnitude more expensive than solar power based in a desert near California.  Supporting this claim he refers to transportation of solar panels to the desert as being two or three orders of magnitude cheaper than putting them in geosynchronous Earth orbit.  He also refers to greater costs for the panels themselves when they are engineered for the hostile space environment which he claims to have some familiarity with.  Dr. Worden also refers to the high cost of maintaining anything in space giving as example the servicing of things in space using the space shuttle.  Listen to the man.  Take notes.  I intend to listen to him a couple of times yet when I have the time.  In sum he claims that there is no business case for space based solar power, and there won't be for a few decades at least.  He admits that after a few decades the situation might change.--Fartherred (talk) 22:25, 14 January 2010 (UTC)
 * Servicing? Solar panels? Space shuttle? (Which will be out of service pretty soon...) All of which seems to ignore the proposed helium turbine system... "five orders of magnitude more expensive"? Only if NASA is doing it.  TREKphiler   any time you're ready, Uhura  01:08, 15 January 2010 (UTC)
 * User Trekphiler seems to suggest that the article should mention a 10kW turbine based electrical power plant in space that uses a helium working fluid, on the basis that as far as he knows it is possible. It will not be mentioned without a reliable source to indicate that it is notable.  Unless user Trekphiler finds a source, I cannot think of anyone who is going to look for one.  Then user Trekphiler writes that he does not suggest putting such a concept into the article.  This discussion page is for improving the article, not loose talk about space based solar power, as indicated in the heading.  So if the discussion "seems to ignore" loose talk, it does so as a matter of policy, and the only reason to bring it up is to point out the failure to follow policy.
 * Though I know that David Criswell suggested transmitting power by microwave beam to the Earth from the Moon, which is just as difficult on the basis of distance as transmission from L4/L5. I would not put such a suggestion into the article because I do not believe that practicality was well supported by plans.  Others can include such suggestions if they find the sources.  User Trekphiler disparages "spending so much" delta-V on lunar resources.  As pointed out in the launch costs section of Colonization of the Moon, the amount electrical power projected to be used to supply that delta-V to a kilogram would cost an Earthly residential customer about $0.16 and, given a sufficient market for industrial power on the Moon, the cost of producing it there is projected to become much less.  Though it would be nice to avoid even a 16 cent per kilogram launch cost for building materials, the artificial intelligence necessary for robot operations on distant asteroids does not yet exist and sending a human crew to bring back an asteroid is beyond current capabilities.  Neither advances in AI nor a human crew is necessary to remotely operate a lunar mining operation.  Humans would be employed there just because their services become so valuable and their upkeep so much easier when industrial facilities have been sufficiently developed.
 * Still, the opinions of reliable sources to the contrary are welcome. I would like to know if heat engine electric proposals include a mirrored zigzag path through a micrometeor shield for the concentrated sunlight or the radiated infrared.  Do they plan many trips to orbit with replacement working fluid?
 * There is certainly much bashing of NASA for being economically wasteful. NASA makes it so easy that anyone can do it.  However, all the costs that Dr. Worden mentioned are still applicable, costs such as transportation to space relating to heat engines as much as to solar cells.--Fartherred (talk) 22:46, 16 January 2010 (UTC)
 * •I don't suggest I am going to, given no WP:RS. You, OTOH, don't even suggesting improvements, just criticisms of the SPS idea. Offhand, I recall Gerry O'Neill suggesting the turbine in 3d Industrial Revolution & Jerry Pournelle covered it, IIRC, in A Step Farther Out (which I can't find any publication data on...), neither of which I have copies of. (I wish.) I suspect they would fail to pass.
 * •"many trips to orbit with replacement working fluid?" Never heard of closed cycles? Even so, I'd presume a design would allow for replenishment periodically; how much does a Delta 3 cost? Not for NASA to fly it, just to buy 1. And how many replacements would be needed in its service lifetime? Factor that against the extraordinarily low power cost, & the great edge in power delivery, cost, & environmental benefit against terrestrial solar (not least, not putting thousands of hectares into permanent shadow), SPS still wins hands down.
 * •"the amount electrical power projected to be used to supply that delta-V to a kilogram would cost an Earthly residential customer about $0.16" Pay attention. It's not the cost/kW that's the issue, it's the delta-V. It's cheaper by at least 4km/s not to lauch from Luna, & use NEAs, instead, & it's got to be created somehow. Every km/s not used is one better employed elsewhere. Neither did I suggest "artificial intelligence". How hard is it to put a lander on an asteroid, deploy a mass driver, & point it to deliver a payload to LEO? Surely if we can send independent rovers to Mars, we can accomplish that.
 * •Notice I never even raised the Lunar power idea; it's ridiculous on its face. The cost of landings (especially manned landings!), construction in gravity, & lunar night, not to mention the needless complication of added pointing difficulties, & moonquakes, all count heavily against, compared to L5/L4.  TREKphiler   any time you're ready, Uhura  00:13, 17 January 2010 (UTC)
 * Well, let us not get side tracked into discussing who is the bigger violator of policy. I actually do want to improve the article.  As I wrote: "...I still think doing the whole thing with lunar materials remotely from Earth is the way to go."  The idea is supported by "The high frontier: human colonies is space" which O'Neill wrote in 1977, but the idea has been expanded upon since then.  Bootstrapping industry on Luna could have started twenty-five years ago, but the leadership at NASA, our presidents, congress, and the space enthusiasts that convinced them decided to go with reducing the cost of access to space to be able to implement a quicker plan.  The future came and revealed that their plans for cheap reliable access to space were based to a considerable extent upon wishful thinking.  Some people still say: "This (CRATS) is, of course, an absolute requirement of space solar power."  I would change the article to say that driving down the costs of ETO transportation is a requirement for space solar power only if the materials and work crew are lifted up from Earth.  We will never get back the wasted twenty-five years, but we do not need to keep repeating the same wrong-headed strategy over and over again, blindly ignoring the physical limitations that have made this effort futile.  Establishing industry remotely in orbit and on Luna could make Earth orbit and Luna into places where people could be maintained economically do worthwhile work, and reduce the cost of space access.  NASA, however, stubbornly insists on putting people on top of a rocket as soon as is physically possible for the purpose of demonstrating technical know-how instead of availing themselves of the opportunity to actually do something economically significant.  Where the article states: "of course" in support of CRATS based entirely on launch vehicle technology, this is a substitute for considering alternatives.  NASA's devotion to its beloved near term objectives in the manned program is religious rather than reasoned, a religion backed by paying money to the same interests that have been employed by the manned program in the past.  The scariest thing about a long term investment in space infrastructure is that NASA would need to do things differently than before.  Bureaucrats hate change.  It's almost like admitting that they have made a mistake. The article should also state that there are no current plans for any space transportation system which is projected to result in the kind of cost reduction that would allow the assembly of an economic SPS with materials and work crews sent up from Earth.  Any engineers saying, "We are working on it." mean that they are cashing their paychecks.
 * By the way, I disagree with user Trekphiler's figure for saving on delta V by not launching from Luna. A projectile launched from Luna at 2400 meters per second could reach L2 with velocity to spare.  The collecting depot could maintain position by internal mass shifting and ride the small upward thrust of incoming cargo while the electromagnetic catcher generates electricity from regenerative braking. Leaving L2 by even one meter per second could allow a spacecraft to hit the Earth, hit the moon, or escape to independent solar orbit by judicious choice of direction.  This is a result of the chaotic nature of the three body problem.  Since we do not have infinite time to play around with, I allow 200 meters per second for leaving L2 and maneuvering.  Following a somewhat complex 3 body orbit, the inter-orbit transfer vehicle would end up sailing by the moon as it crosses the Earth's equator and use the gravitational interaction to accomplish change of plane while entering a transfer orbit to GEO.  At the SPS construction site another electromagnetic catcher would give the transfer vehicle a circularizing impulse of about 1250 meters per second again generating electricity.  The construction site would use a large high specific impulse electrical thruster to maintain momentum, with no need to change the velocity of the engine.  A ten thousand meter per second exhaust velocity with oxygen as a reaction mass should be possible.  When I add that up it comes out to 3850 meters per second total mission delta V.  From where can stuff be shipped to GEO to save 4000 meters per second compared to that?
 * The materials for heat engines could be shipped from Luna with oxygen for a working fluid. If the artificial intelligence can be managed, carbon from the asteroids or Mars could go into carbon monoxide as a working fluid.  Photovoltaic cells could work too.
 * I cannot answer user Trekphiler as to how hard it is to deploy a mass driver on an asteroid, I just point out that it would be harder than the Phoenix spacecraft scooping up dirt and delivering it to an analyzer. That was done by intelligence sent from Earth by radio because artificial intelligence was not up to the task.--Fartherred (talk) 00:29, 19 January 2010 (UTC)


 * •Agreed, I'm not looking for a fight over whose more wrong. ;p
 * •Substuting waldoes for men may be more economically reasonable, but it's also the arguement used by opponents of spaceflight, which troubles me. Can an asteroid capture be done remotely, or by combination of AI & waldo? Certainly (& I'd start with that, absent a better way). The problem is, without some kind of infrastructure in L4/L5, some of the rationale for building SPS is undermined, & with the ability to do it without manned flights makes that worse. The trouble seems to be in NASA, not in manned flight per se (as I suggested above); JEP, I think, mentioned a "space DC-3" able to cut the costs way down, if there was a demand for really cheap manned flights to LEO & above, which SPS might offer. (This would also address in some measure the trouble of servicing missions, which could be, & far more sensibly should be, from L4/5.
 * •The delta-V from Luna presupposes some kind of mining on Luna. Establishing it will absorb a lot more than 2.4km/s. The same mining by capture of NEA means the whole mission can be done within that 2.4km/s budget.
 * •The mass driver Q was a bit rhetorical. We've already put a spacecraft around an asteroid (hitting it can't be much harder), built a "smart" lander able to do science (the mass driver is simpler & much dumber), & depolyed a lander (the mass driver is simpler to depoly & operate). We can, therefore, already perform the NEA capture mission.  TREKphiler   any time you're ready, Uhura  01:10, 19 January 2010 (UTC)
 * There are certainly published suggestions of bringing an asteroid or a big chunk of one to cislunar space and capturing it, so such a suggestion could go in the article. I will not put it in the article because I perceive that people are more interested in keeping a safe distance from Apophis than capturing a big chunk of it.  As noble an idea as it is to represent all notable opinion regarding the acquisition of material to build a space-based solar power system, I do not want to include information that will scare people.  If it came to funding an asteroid capture mission, someone would say that it is possible that the control system might fail so that we end up with no communication with the asteroid being captured in a slightly different orbit than planned.  This opens the possibility that the chaotic three body problem will dump the asteroid chunk on Beijing.  However remote the possibility, it will make funding impossible for the next twenty years at least.  Building materials from Luna or Mars would be moved around in small enough batches that they can be made fail safe.  That is, if control systems failed so that the shipment crashed into Earth, the inter-orbit transfer vehicle could be designed to break up and dump its cargo in batches which would in turn break up and burn harmlessly.--Fartherred (talk) 04:41, 19 January 2010 (UTC)
 * If people really want to establish human colonies at L5, Luna and Mars; the best strategy is to establish industry on the Moon by remote control first. The international space station is just convincing people that no profit can ever come from activities in outer space.  We might get a big technological advance that allows a vehicle that really works as its supporters said the space shuttle would, but I would not want the future of humanity to depend upon such an unpredictable possible development.--Fartherred (talk) 05:17, 19 January 2010 (UTC)
 * It may be Lunar industry needs to come first; given a choice, I wouldn't do it, for the reasons noted. As for the potential hazard, I think you overstate; orbital mechanics isn't a mug's game, & the error'd have to be pretty large to miss L4/5 by enough to put any NEA on an impact trajectory (a miss of, what, 200Kkm?). And the flaws of the Shuttle have damn all to do with the technology, & a lot to do with the politics of the funding, & (yet again) we are back to NASA. Get NASA out of the way, however.... Then we're back to the unmanned v manned argument, & if we accept your R/C industry, the demand for a manned vehicle drops fairly dramatically...  TREKphiler   any time you're ready, Uhura  05:27, 19 January 2010 (UTC)
 * Wolfkeeper suggested about a 17 fold reduction in launch costs from economies of scale if a larger launch market develops. This is not necessarily so.  There are also diseconomies of scale in resources becoming more expensive when there is a need to develop new sources of supply such as new air liquefaction plants if the total market for liquid oxygen increases enough or new launch sites becoming more expensive as the cheaper sites have already been taken.  Wolfkeeper does not allow anything for the cost of launching the microwave antenna or the equipment for generating microwave.  Trekphiler does not mention the difficulty of providing the radiators for a heat engine in space.  I see no evidence that launching a power plant from Earth to orbit will be competitive with an Earth bound plant in the foreseeable future.  Trekphiler refers to the extraordinarily low power cost & the great edge in power delivery cost ... against terrestrial solar.  That is exactly what launching power plants from Earth does not provide, as Dr. Pete Worden pointed out.  The sunlight is free.  Turning it into power that can be sold requires equipment.
 * Liquid oxygen is already produced in million tonne quantities annually. I fail to see how this is a disincentive; indeed, I don't think that propellant costs are even worth talking about; the fact that you raise them suggests you don't understand cost-modelling of space hardware; they are insignificant cost drivers. The cost of microwave antenna is not particularly significant; it can be a parabolic shape predominately made of aluminium foil or similar, and the transmitter electronics does not seem an issue either.- Wolfkeeper  19:42, 25 January 2010 (UTC)
 * My best guess from the various things Trekphiler writes is that Trekphiler does not support space based solar power because it has economic potential but rather because it provides jobs for colonists at L4/L5. Then Trekphiler writes: "....Then we're back to the unmanned v manned argument..."  It is not a case of manned versus unmanned space flight.  It is a case of putting hundreds of people into space through the life of the program just to show that we can do so versus an economic program that could lead to a million people a year being launched into orbit with the industrial and economic infrastructure that could be developed remotely in space.   Continually ignoring the economics of space travel in the government manned space program will lead only to its continuing to be an appropriations absorption program indefinitely.  Dinky little space power programs like the solar arrays on the ISS can be produced at excessive cost, but it will not lead to generating power that can be sold to cover its costs.  Current manned space flight is an impediment to the development of an economic SPS.
 * Here is the sequence to follow: first, robotic exploration of Luna by orbiting spacecraft (this is mostly done); second, robotic exploration in detail by rovers on the lunar surface; third robotic development of infrastructure (second and third somewhat overlap since exploring robots can benefit from infrastructure such as a nuclear power plant); fourth people come to Luna to put their hands on problems that people are uniquely qualified to handle (This includes repairing robotic equipment while isolated from the non oxidizing dry atmosphere that the equipment requires by wearing an isolated atmosphere suit.); fifth start building the space-based solar power stations from lunar materials; sixth start building orbiting space ports that will allow shuttles (two ton craft) that can reach orbital altitude to acquire orbital velocity from the space port's electromagnetic catcher (a electrically driven rail car that matches velocity with incoming craft).  People can run with that plan for the next couple of centuries.  Other plans can be acceptable.  Switching from one plan to another can cost less than the benefit of the better plan.  Efforts must fit into some plan or another to make sense.  Just planning to have people on the ISS to do whatever they can do there is the worst of plans.
 * If people would have the nerve to catch Apophis rather than deflect it, the development schedule could be shortened. I do not expect that to happen.
 * Trekphiler points out the high cost of manned landings on the Moon. Lunar development can lower the cost of these too, when they are called for.  There is an article titled "Lunar Rocket-sled to Orbit" on http://www.lunarpedia.org that tells how the cost could be reduced.  I only wish I had a reliable source for an LRSTO.--Fartherred (talk) 15:48, 25 January 2010 (UTC)
 * I suppose Trekphiler would like to know how colonies at L4/L5 fit into my SPS plan. That would be in the sixth step along with the orbiting space ports and the other space habitats.--Fartherred (talk) 17:39, 25 January 2010 (UTC)
 * •Actually, I'm on both sides of the argument, Fartherred. Within the confines of the page, I'd say, "get it there fastest", & worry less about "Does it create jobs?" or "Is it economical?". As part of an actual program, IMO Gerry O'Neill & Jerry Pournelle are right: L5 hab first, which means manned flight, 'cause I'm not entirely convinced waldoes can do it (& because I'm damn sure the ability to do it with waldoes would lead to efforts to stop manned flights entirely). Also, IMO SPS & L5 habs are drivers for manned flight for the spinoffs from actually building them. If it was up to me alone, I'd happily accept waldo-built & -operated SPS by lunar resources (tho I'd use NEAs for the reasons mentioned, & go through a power relay satellite phase, 1st with a tie into OTEC to power linac lifters); my opposition to it in the real world is what I see as the probable outcome, namely, an end to the program altogether. If you could guarantee otherwise, I'd happily side with you, but I don't see how you can. (Worries about impacts are overblown. There are thousands of NEAs in stable orbits now, any of which can be easily & safely redirected; as noted, you have to miss by a lot for it to be a problem. We've already demonstrated the ability to point spacecraft better than that outbound; I see no reason pointing should get orders of magnitude worse on an inbound package.)
 * •Do I support SPS as an economic power source? Absolutely. And I vastly prefer it to terrestrial solar. Even if the initial cost is higher, because the long-run cost drops precipitously, & the benefit climbs almost as much. In short, I'm saying, "Build it, prove it works, cost be damned." After it's proven viable, the economics will work themselves out, IMO. ("Build it, & they will come"? ;p) Unfortunately, with so much political support for terrestrial solar & fusion, & so little for any variety of SPS, it's probably a pipedream regardless.   TREKphiler   any time you're ready, Uhura  19:19, 25 January 2010 (UTC)
 * Am I dumb sometimes, or what? ;p I just realized, Fartherred, everything you've said about lunar mining by waldo applies equally to NEAs in situ, so the hazard is zero & the cost is 'way lower. See this.  TREKphiler   any time you're ready, Uhura  23:04, 30 January 2010 (UTC)
 * Liquid oxygen cost $15 a ton in 1983, a year for which I happen to have data. The stoichiometric ratio for burning kerosene is about 3.5 pounds oxygen to 1 pound of kerosene.  I do not know the exact ratio for combustion in the Saturn V, but considering that the F-1 engine burned fuel rich and used film cooling for the engine wall, 2.4 to 1 is probably close.  So, of the more than 2000 metric tons of fuel and oxidizer carried, that is about $23,000.00 worth of liquid oxygen.  It put about 47,000 pounds into Lunar transfer orbit, or nearly that much to GEO.  That $23,000.00 may seem a very minor portion of the Apollo budget, but it would not be sneered at by someone hauling the equipment of a solar power plant 170 miles east of Los Angeles on US 10 in a pickup truck.  For the $46,000.00 represented by the LOX for two launches he could buy the truck, the gasoline for the 47 trips hauling 2000 pounds per load, a hundred roadside meals, haul as much cargo as the two Saturn V launches, and have money left over.  For what is an "insignificant" portion of the cost of launching to GEO, you could pay for much the costs of transporting the same cargo to the Arizona desert and only have two months wages for the driver and insurance yet to pay.  Since most of the cost of transporting a power plant to the desert in a pickup truck (The example used by Dr. Worden) is only the cost of one of the "insignificant cost drivers"(as Wolfkeeper said) of space transportation, it seems the launch-from-Earth option is far and away overpriced.
 * The cost of a microwave antenna is significant in a solar power satellite. This is not one of those parabolic horns that are sometimes on microwave relay towers.  What is called for in the Space-based solar power article is a steerable phased array of dipoles that is a one kilometer diameter rigid disk that must remain flat to within a reasonably small fraction of the dipole length.  It might be necessary to keep it all in the shade so that it does not warp with differential heating when partially in the sunlight, as will occur when it is constantly pointed at the Earthside receiving antenna and the Earth rotates so the transmitting antenna is edge on to the sun.  On page 7, figure #4 of G. M. Hanley's "Satellite Power Systems Concept Definition Study" (referenced in the article) calls for arrays of about 66 square kilometers with about half of the array area filled with solar cells and half filled with mirrors providing a two for one concentration of sunlight.  (One rather limited scale experiment with concentrating the sunlight on solar cells resulted in the cells having a shorter life time so the full benefit of the concentration was not realized.)  The antenna occupies only about 0.79 square kilometers, but those are important square kilometers because the microwave radiation is much more concentrated there than at the receiving antenna.  I do not have a good estimate for the cost of the transmitting antenna, so I will compare it to the BMEWS antennas, another phased steerable dipole array.  It is about 129 times the area of a BMEWS antenna.  The BMEWS system transmitted and received with a phased array.  The SPS only transmits.  So I will count the SPS as only half the cost per unit area of the BMEWS.  Since the BMEWS cost $115 million each that would put the SPS at about $7 billion.  Admittedly that is very unreliable synthesis, but can anyone get a handle on how much an SPS transmitting antenna or the klystrons ought to cost?--Fartherred (talk) 00:36, 31 January 2010 (UTC)
 * This is still all nonsense. LOX makes up about 2/3 of the takeoff mass of the rocket, and the payload is about 2-3%. LOX costs pennies- the fuel costs about a dollar per kg. You can trivially calculate that the cost of the propellant is about ~$10 per kg of payload... but the payload, PV panels cost more like 300-$1000/kg. Meanwhile the body of the rocket right now costs $10,000/kg!!! The trick is, that rockets get cheaper fairly quickly as you mass produce them (because they are produced in low quantities right now, so you are doubling many-fold the production quantities.) And PV panels also get cheaper somewhat, but they are being produced in reasonably large quantities already, so the effect is less pronounced.- Wolfkeeper  01:45, 31 January 2010 (UTC)
 * As to the thermal issues of parabolic dishes; I expect that spinning them solves most problems; but they are not high precision objects, they have to be accurate to only about a centimetre or so (1/4 wavelength.) I refuse to believe that an object that is in sunlight practically 24x7 is difficult to keep at a reasonably stable temperature.- Wolfkeeper  01:45, 31 January 2010 (UTC)


 * Contrast the AZ example: it has to be at least 15x as big as the equivalent SPS, thanx to atmospheric attenuation, & night.... Then, remove the mass of PV cells (which was my initial complaint) for aluminized ("mirror") Mylar, which hardly weighs anything. (A quick Google produces a cost estimate for 1km2 of about US$65K.) How much does a 5GW turbine weigh? Or, if you'll accept a lower-power prototype, cut the mirror size, output, & cost, by five & weight by, what, half for a smaller turbine? Can it be done within the throw weight of a single Proton? Then multiply by 15 or so, & tell me the terrestrial is competitive. Then look at putting (conservatively) thousands of hectares into permanent shadow, & tell me that's "green"... As for BMEWS, don't forget, that's built to milspec; commercial needn't meet such stringent standards, so you could cut the cost by, oh, half. And nobody I know suggests only building one; how much did the prototype Model T cost, including factory & tooling? Hell, how much did the first production example cost? (IIRC, US$1250...) How much did the last Model T cost? Around US$250.... Figure the second SPS will cost about 10% what the first one did (if Pournelle's estimate is right, & IIRC).  TREKphiler   any time you're ready, Uhura  02:04, 31 January 2010 (UTC)
 * Most NEAs get farther from Earth than Mars. They all have considerable maximum round trip communications delay and their the trajectory for sending cargo from them to Earth is always changing.  So NEAs do not have the level of remote control convenience or the perpetual window for launching to Earth that is available on Luna.  Also expect varying trip times from an NEA to Earth to go from a month to two years.  An electric inter-orbit tug would not be delivering cargos very frequently on the average, making its per trip capital expense much more than for one used for transportation from Luna, where it would be possible for an inter-orbit tug to start a trip to GEO from L2 at the same time every month.  I expect the round trip to be less than two years for a low delta V trajectory, or just two months for somewhat higher delta V.
 * Wolfkeeper repeats that LOX is cheap per pound in thousand ton lots. No one contests this.  The whole point is that most of the transportation costs for shipping something out to the desert equals what is a trivial part of the expense of the transportation from Earth to GEO.
 * People have for many years been pointing out the potential savings in launch costs that could be obtained by mass producing rockets and frequent routine launches. Even if ten times cost reductions were obtained, the desert would still be a much cheaper site.  One problem with the mass production frequent launch strategy is that the high traffic volume must be there before the mass production and routine launch can be accomplished.  Another problem is the frequent launch failures that Earth to orbit vehicles have experienced so far.  If a pickup truck had a one chance in a thousand of blowing up when the key was turned to ignition, the maker would be out of business and lawyers would be fighting over the corporate remains in court.  An Earth to orbit launcher that only blows up once in a thousand times would be showcased for its safety record.
 * It seems that Wolfkeeper errs in continuing to refer to a parabolic dish for a transmitting antenna of an SPS. Where is such a thing suggested?  The idea of spinning an SPS transmitting antenna for even heat distribution seems impractical.  This thing should be a kilometer or more in diameter to provide a tight enough beam to get 95% of the beam energy into a ten kilometer diameter beam Earthside.  Spinning it would not be trivial.  There are problems with heat distribution in Space that are different than what we are familiar with on Earth.  On earth everything in close proximity to a particular spot has about the same temperature because of heat transfer by convection.  Is space things in sunlight and out of sunlight go to very different equilibrium temperatures.  One part of a large structure in space shading another can be a problem if one wants the whole to be of one temperature.
 * Out in the desert East of Los Angeles one can still get sunlight 41 percent of the day in the middle of winter. Its average strength is half of that at full noon. By arranging parabolic troughs for heat engines in East West rows they can be turned to focus on a tubular central boiler all day.  By leaving enough space between the rows they won't shade each other.  The noon sun is 69 percent of that in space.  So, combining factors, space-based has only slightly better than a 7 times advantage in average radiation.  Besides the cheaper transportation on Earth, there is water available from mountain streams to be used in a cooling tower for the condenser and no micrometeoroids smashing into the boiler and radiator causing numerous small leaks.  The 7 times radiation strength does not make up for the enormous transportation costs from Earth, the lack of cooling water and the micrometeoroid problem.
 * With twenty cent a pound dirt from Luna people might be able to remotely manufacture something that would work. NEAs might be able to supply material, but unless a big chunk is captured by loosing energy swinging around Luna, Luna would be the cheapest source.  There are disadvantages with Luna.  Bootstrapping industry to make the transportation infrastructure on a shoestring will take a long time.  I guess thirty or forty years before the mass driver cargo deliveries.  Also the low costs will not be realized except with large scale transportation.  I guess a few hundred thousand tons a year would start things going.--Fartherred (talk) 03:11, 2 February 2010 (UTC)

Please remember everybody; this is NOT a forum for discussion of the article's topic!!!- Wolfkeeper  03:38, 2 February 2010 (UTC)


 * Which I was trying to do... Who said anything about "multiple launches"? The whole point of the helium turbine system is to reduce weight, & so the demand for repeat lauches... And "a few hundred thousand tons" is a preposterous figure for the mass of even a few thousand satellites.  TREKphiler   any time you're ready, Uhura  04:40, 2 February 2010 (UTC)


 * Citation needed.- Wolfkeeper  16:27, 2 February 2010 (UTC)

Efficiency errors
In the Goldstone demonstration the efficiency of the rectenna was 84%. The article implies strongly that the total end to end efficiency was 84%. This is wrong. The you tube video on the experiment claims a 500 kw transmitter was used and 34 kw was received. That would be only 6.8% efficient. The video does not state the transmit power used and cannot be used for end to end calculations. The video does state that the 82.5% number is based on the flux of the power hitting the array. It also goes on to say that 54% was the best end to end they achieved in the lab.

In the reference to the Caltech experiment the absorption efficiency is given as if it were the conversion efficiency. The conversion efficiency is always a much lower number. Conversion efficiency is unknown because it is not a working cell. It is my understanding that silicons max efficiency is in the neighborhood of 40% and that the Caltech numbers would work out to be 85% of 40% or a 34% efficient cell. I don't recall the reference for that 40% number sorry.

I don't mean to be nit-picky but as this is an encyclopedia this seems to be a material difference.

Blturner3 (talk) 21:56, 28 May 2010 (UTC)


 * I looked up the "Wireless Power Transmission for Solar Power Satellite (SPS)..." source. Table 1.1 gave collector efficiencies of 96.5%, 86%, 87% and 89%.  Now one must also consider the inefficiency caused by beam spread, which plans try to minimize by using large diameter sending and receiving antennas, but the big loss comes from generating the electricity in the first place.  I think I have read about solar cells of from 10% to 40% efficiency in converting light energy to electricity.  There is the inefficiency of converting electricity to microwave, which I think is a small loss.  If you can multiply all of the efficiencies together, I guess that is what you mean by an end to end efficiency, then that would be something to add to the article.  I am not sure whether all of the relevant efficiencies are in sources already given in the article or some of them must come from other sources.  Go to it.  Then I will see if I can nit-pick your contributions, all for the good of Wikipedia.--Fartherred (talk) 00:54, 29 May 2010 (UTC)
 * FWIW, Pournelle quoted a DC-DC efficiency of 65% in A Step Farther Out, IIRC. I don't, however, have a copy...  TREKphiler   any time you're ready, Uhura  11:18, 29 May 2010 (UTC)
 * Well, thanks TREKphiler, I do have a copy of [A STEP FARTHER OUT], but it has no index. Taking your DC-DC efficiency times a 40% efficiency for sunlight to electric, we get 26% efficiency from sunlight to the grid distributing power on Earth, which I hope to put in the article when I can document it. --Fartherred (talk) 18:59, 3 June 2010 (UTC)
 * Sorry guys, but i do not buy a microwave transmission efficiency (calculated (electric power fead into the terrestrial grid) / (electric power on the sattelite)) higher than single-digit. —Preceding unsigned comment added by 84.11.16.250 (talk) 09:52, 21 December 2010 (UTC)

Launch costs
The section on dealing with launch costs mentions that the total cost of launching a 4 GW satellite weighing 4,000,000 kg would be as little as $11 billion, depending on the launch system used. I don't see any citations for that figure (and I've marked the article as such). Furthermore, I don't think the math works out. Here's a list of heavy lift launch systems. The cheapest launch system mentioned on that list is the Falcon 9 heavy, which comes at a cost of $3,273/kg if you want to launch something into LEO, though that comes with a citation needed tag, and it mentions that they haven't made any successful launches yet. Even here, $3273/kg * 4,000,000 kg comes out to $13 billion, not $11 billion.

Furthermore, I was under the impression that that section was only talking about GEO, it doesn't say anything about putting a satellite into LEO. If we're talking about GEO, then, we can go back to the list and we find the lowest cost for GEO goes with the Proton rocket. Here, the cost is $18,359/kg to GEO, and $18,359/kg * 4,000,000 kg comes out to $73 billion, not $11 billion.

So, how exactly did the person who added that $11 billion figure get that result? Are we talking about using a microwave-powered scramjet to get cargo to LEO and some 'tugboats' with ion engines to get cargo from LEO to GEO at low cost? Or is there some other extremely cheap HLLV I don't know about? --NorsemanII (talk) 16:38, 30 May 2010 (UTC)
 * The $11 billion figure came from User:148.104.248.225, revision # 324913820 on the 10th of November 2009, rounding the previous $11.3 billion figure with no explanation. The $11.3 figure came from User:148.104.248.223, revision # 298585560 on the 25th of June with the claim in the edit summary that the amount was based upon projected Falcon 9 Heavy costs.  User:148.104.248.223 made his last contribution from that IP address on the 17th of August 2009.  The only thing on the user talk page is an unanswered welcome from the 14th of July.  In summary I write that the launch cost figures constitute no information, and ought to be removed.  If someone wants to reinstate them, they can add the references.  --Fartherred (talk) 11:18, 31 May 2010 (UTC)

Launch cost prediction
At 01:38 on the 2nd of October Trekphiler added that reusable launch systems are predicted to provide lower launch costs. Who predicts that? Fartherred (talk) 04:32, 2 October 2010 (UTC)
 * That's rewording what was previously said, based (apparently) on what the website in the footnote claims, minus the advert for the method.  TREKphiler  <sup style="color:#1034A6;"> any time you're ready, Uhura  23:21, 2 October 2010 (UTC)
 * The next footnote after "lower launch costs" is, Case For Space Based Solar Power Development.  The most I saw stated about lower launch costs was: "Lower launch costs is a major goal of all space advocates.  The X Prize contenders, Musk's Space-X even the major aerospace "EELV" program all have the intention of significantly reducing launch costs."  That does not seem to support the statement that you restored.  It is also false.  I am a space advocate and I do not support research and development efforts aimed at markedly improving the state of the art in lowering the cost of launching rockets from Earth.  Many billions have been wasted this way already.  I support using the currently available technology for as low cost launch as can reasonably be achieved on a somewhat regular schedule for space programs that make sense with such a launch cost.  I suggest the claim that some unnamed agent predicts lower launch costs should be removed.  For predictions I have read of lower launch costs, the problem as my foggy memory indicates is that they are quite unreliable predictions.  It is good that those predictions are not here.  If there is support for a prediction of lower launch costs, I cannot find it.  --Fartherred (talk) 20:08, 3 October 2010 (UTC)
 * Why is there a paucity of reliable predictions for lower launch costs? Because there will not be any markedly lower launch costs in the next couple of decades.  Why will there not be lower launch costs?  It results from two main causes.  First, the launch market is not cost driven.  It is driven by desire to promote national prestige and national security.  This prevents one launch system from serving the whole market and thus gaining improved economies of scale.  A common factor in all proposals to lower launch cost that I have seen is dependence on large market size to reduce unit cost.  Second, research and development aimed at lowering cost were government funded attempts two hire invention.  You can hire development along a known line of inquiry, but you cannot hire inspiration.  So if there are any reliable predictions of lower launch costs, they can be posted in the article, but they will be wrong.  Whatever genius SpaceX has comes entirely from Elon Musk.  The direction of development indicates only modest improvement in costs.  Musk is in the same bind as the government.  Sufficient genius cannot be hired.  No expert can say it cannot be done, but there is absolutely no evidence that it can be done. --Fartherred (talk) 23:16, 5 October 2010 (UTC)
 * I restored the lower launch cost prediction with a reliable source, Dr. Lee Valentine. The man has a lot of nerve, and he is wrong, but he is a reliable source.  --Fartherred (talk) 06:07, 13 November 2010 (UTC)

Advantages - military
It does not seem appropriate that the article talks about advantages for the American military. If there are military advantages to the technology, they should be expressed more abstractly - not how many lives of Amercian servicemen could possibly have been saved in an extremely controversial war.

This paragraph shows clear American bias and on something that is peripheral to subject of the article. —Preceding unsigned comment added by 92.234.37.5 (talk) 00:46, 2 February 2011 (UTC)

Launch costs and the lunar space elevator
An issue which I think could be revolutionary for SSP is the effect of the Pearson lunar cable (Jerome Pearson et al, 2005, Lunar Space Elevators for Cislunar Space Development Phase I Final Technical Report here) on capital costs. The huge problem with SSP, that has always daunted me, is launch cost to GSO from Earth, putting up thousands of tons of material. Now that we have the ISS in place and solar electric propulsion demonstrated, launch costs might be somewhat reduced, but still too big I think. But Pearson's lunar cable (for the Earth/Moon L1 case, first published in 1979) is clearly feasible with current material technology, being ~20x easier (in terms of the equivalent 1g potential height of the cable: 250 km for the Moon vs 5500 km for Earth GSO), if it can be built with lunar materials (using a small leader cable launched to L1 from Earth, as long done for suspension bridges) to hoist up the main mass. Then we could make photovoltaic cells with lunar silicon (one thing the Moon has plenty of), hoist them to L1, and then move them to GSO with solar electric drives. I think the economics need to be revisited with this in mind. We should be looking for reliable sources. The availability of lunar carbon for the cable may be an issue, but my guess is that enough carbon should be findable. This is probably a ~50 year project, on a par with nuclear fusion I believe. Wwheaton (talk) 15:44, 12 March 2011 (UTC)

Interesting, cool ideas but appears to be editorial synthesis for now. Joja lozzo  21:02, 12 March 2011 (UTC)
 * Yup, can't put it in the article at this point, just giving a heads-up to our editors to get the idea around, and keep an eye out for sources. I just noticed Pearson's 2005 study a few days ago.  I have not studied it yet, but I think SSP is not mentioned in there.  Wwheaton (talk) 22:03, 12 March 2011 (UTC)

Light Pollution
Does anyone have references to criticism for such a system due to potential for spectacular light pollution if done incorrectly? Satellite "flares" from specular surfaces on Iridium satellites (magnitude -9 from 1 m^2 antenna surfaces) and Hubble are well known. ISS is now the third brightest object in the sky and it is tiny compared to the surface area of some of these sytems proposed for LEO.

Surely this has been discussed and addressed. Geogene (talk) 16:05, 5 August 2009 (UTC)


 * Satellite flares can indeed be spectacular -- and few people have been fortunate enough to see one -- but they are short-lived and don't interfere with astronomy like general light pollution does. I would welcome a constellation of solar power satellites that regularly flares in my sky. GPS Pilot (talk) 18:08, 14 May 2011 (UTC)

Why are manufacturing facilities required?
User Trekphiler on the 27th of September added the question to "It would require establishing silicon mining and solar cell manufacturing facilities on the Moon." It seems to me that I read about mass drivers being built on the moon with lunar materials, and that would include solar cells, but I do not have the reference off hand. A space elevator from the moon to orbit would be a truly massive thing which would require extraterrestrial manufacturing facilities somewhere, but to put that in the article we should have a reference. I will replace the non rendered comment with a citation needed template, and hope to find some citation or another. --Fartherred (talk) 03:34, 29 October 2010 (UTC)
 * I would rather, if it can be found, see explanation of the connection. It's evident the mass drivers need power, & PV cells would be the reasonable approach. (Lunar nuclear power sounds like a pipedream.) I'd also guess shipping from Earth is too costly. However, adding a reason manufacturing is preferable (if it is...) would be good for the page, IMO.  TREKphiler  <sup style="color:#1034A6;"> any time you're ready, Uhura  22:23, 29 October 2010 (UTC)
 * The concern here is reducing cost. By original research I estimate the incremental cost of an established earth to Luna transportation system (supposing one is ever established) of 70,000 dollars a pound.  In order to use lunar materials for a space based solar power system there must be on Luna a mass driver, a to orbit elevator, or some rocket launch scheme that avoids the need for importing massive amounts of fuel.  Each of these might be possible, but lacking reliable sources that I can remember, I cannot put that in the article.  Also required for using lunar materials is the power generation needed by the launching system, the mining industry, any materials processing industry, and the payload preparation.  These industries themselves will require substantial capital equipment.  At 70,000 dollars a pound, there can be little alternative to manufacturing the capital equipment out of lunar materials if there is to be any reduction in cost compared to launching the SBSP from Earth.  This gets to be a long term complicated endeavor that might belong in the Colonization of the Moon article.  Silicon mining on Luna would be one thing that I would most doubt would be necessary.  Solar cells can get by with only a thin vapor deposited layer of silicon on the substrate and producing high purity silicon from sand is a complex industry.  There is also the possibility of heat engine generated power.
 * Meanwhile, anyone is justified in removing the claim that manufacturing facilities are required. Then such a claim could be restored when and if someone comes up with a source that is reliable according to the standards accepted for this article.
 * As for nuclear power, that is only distantly related to this article. It would be handy to have a source of power at the lunar poles that does not shut down during the local dark winter, and those peaks of eternal light might not be in the most navigable terrain for building infrastructure.  I should be able to get a reference for what NASA is doing about nuclear power but it is time to do other things now.  --Fartherred (talk) 17:41, 3 November 2010 (UTC)
 * A reference has been added to Colonization of the Moon as promised. I corrected a few typographical omissions by lazy fingers in my previous post.  Is the anti nuclear crowd really so politically powerful and so lacking in common sense as to block nuclear power on the Moon?  Give me your insight.  I am a little politically out of touch.  Perhaps we could add something to the article about politics. --Fartherred (talk) 02:15, 6 November 2010 (UTC)
 * Is the anti nuclear crowd really so politically powerful and so lacking in common sense as to block nuclear power on the Moon?
 * One would hope not; there are no tsunamis on the moon that can wreck a nuclear reactor, and even if there were, there are no winds that can carry fallout to any significant distance from the reactor. Yet, we should never underestimate their lack of common sense! GPS Pilot (talk) 18:19, 14 May 2011 (UTC)

Danger of NET energy gain in atmosphere !!!
This is probably not appropriate, but I am very concerned about the topic.

My belief is that if we implement this method of essentially increasing the solar surface area of the earth, we will completely overpower the earth with energy. The technology to make SBSP viable will work... however the ramifications of beaming energy to earth where it will not escape as quickly as it is added.

High power energy will be "beamed" to earth, the energy will be transmitted to the end users, where the energy will be dissipated as heat energy in very large quantities. This thermal energy will then be trapped in the atmosphere, and continue to accelerate global warming. The faster we implement this technology, the faster we will heat the atmosphere.

Ultimately, we will see the atmosphere swell exponentially, and be blown away by solar winds until the planet dries out, de gasses, and turns into an atmosphere similar to mars. If we adopt this technology, great care should be taken to determine the volume of our atmosphere, and maintain the delicate balance that remains. (if it is not too late) I believe solutions may include, using the energy to seqester greenhouse gasses, and reduce the atmospheric imbalances of global warming. Another possible scenario may include powering heat pumps and storing heat to be sent back into space some other way without loosing any of earths resources to space (radiation/beaming it back?)

I am really concerned about this as there is alot of short sighted thinking when it comes to energy, and the environment. This may be a larger pending disaster than any other we have faced. Lets face it, if we find a way to harness a large portion of the power of the sun, who is going to prevent the global catastrophe that will follow?

I am really an optimist, however I fear that short sightedness very easily could cause catastrophic problems that technology would not be able to solve.

Concerned citizen of Earth, Chris Rohrer Kingston NH, USA. 75.68.4.237 (talk) 07:11, 26 January 2011 (UTC)
 * ♠It's just this kind of scare tactics that give the greens a bad name... Do you have the vaguest notion how much heat you'd have to add to expand the atmosphere of Earth at all? (I don't, but I'm guessing it's a pretty damned enormous lot.) Without even taking account of the changes in terrestrial factors, like cloud & weather, which will (automatically...) respond to increased heat? Not to mention the reductions in GHGs, which are already warming the planet? Quite aside the human response to heating, which will happen before it gets even into mass extinction territory (which is why we're discussing the issue: repsonse to global warming...), let alone "blown away by solar wind". Sheesh. :( :(
 * ♠And "great care to determine the volume of our atmosphere"? Seriously? It's, lets see, 100km deep by 4 pi r2, where r=half the diameter of Earth, or roughly 49,500 million km3. And you're treating it like it's a soap bubble... Sheesh. :( :(  TREKphiler  <sup style="color:#1034A6;"> any time you're ready, Uhura  09:13, 26 January 2011 (UTC)


 * To compute the "volume" of the atmosphere in a meaningful way, you have to think about the fact that its density declines exponentially with altitude. Of course you could go up 300 km (getting an even larger volume; there's still a little air there!), but the drop-off is about a factor of e (=2.718...) every 10 km in altitude, so 10 km is a more realistic number than 100 km for the effective thickness (since you really must think about the mass, not the volume of the atmosphere, and 10 km of sea-level density air would give you that mass).  Thus the atmosphere really is pretty thin, less than 1/500 of the radius.  Of course all fossil (and nuclear) power generation directly puts extra heat into the atmosphere, and SSP does too, but SSP (being thermally much more efficient) clearly puts in less heat per kW electric generated.  So if satellite solar power replaced all our fossil-fuel power generation it would help, plus the elimination of CO2 warming would help even more, and the combination would greatly ameliorate our global warming problems.  But not forever, of course.  I believe SSP would give us maybe another factor of ten or so in allowable energy use before we again get into trouble.  I think we could really use that extra 10× headroom, given the needs of the underdeveloped world. Wwheaton (talk) 08:13, 12 March 2011 (UTC)
 * Huh. So the volume isn't nearly as high as I thought. :( (OK, 5Mkm3 still makes the threat of expansion pretty ridiculous.) I totally agree, SSP will help enormously. The increase in energy availability would enable the 3d World to raise standards of living, & so reduce population growth, dramatically, which has tremendous benefits to reducing environmental degredation. Not to mention building that many SPSs would require launchers & orbital industry that would (finally!) enable us to move substantial portions of the world's population off the planet (with time...), & that would only be a good thing for the world.  TREKphiler  <sup style="color:#1034A6;"> any time you're ready, Uhura  09:22, 12 March 2011 (UTC)
 * The basic misunderstanding (which took me a while to realize also) is that the atmosphere is not the issue, it is the heat balance of the whole biosphere: atmosphere, ocean, and solid Earth combined, which exchange energy on various time scales ranging from days to centuries. (Note that the ociean is ~100× more massive than the atmosphere.)  On the decadal scale, the balance between heat input and heat loss seems to be the relevant factor, and I believe the current estimate for global warming is that the planet is out of balance by something +1 watt per square meter in the warming direction (~1/1000 of the ~1385 watt/sq meter solar flux input).  I agree that SSP would help a lot, although the direct heating problem will always be an issue to keep in mind in maintaining the balance.  Wwheaton (talk) 15:02, 12 March 2011 (UTC)
 * Oh, sure. That's why you hear the "humnan activity is limited by the biosphere" argument. It ignores our ability to leave... :(
 * The thing is, as I understand it, if we switch to SSP, we can generate & transmit power without all the losses in the system, all of which generate heat in 1 way/another. Reduction in overall heat generated means increased output per unit power, so there's more "slack" to allow increased production. Can we hit an upper limit on terrestrial output? Maybe; by the time energy output reaches that level, SSP or not, I'd expect we'd have the ability to move into LEO & the LaGrange points, so it'd be moot. (The sooner the better AFAI'm concerned!)  TREKphiler  <sup style="color:#1034A6;"> any time you're ready, Uhura  16:00, 12 March 2011 (UTC)
 * Chris Rohrer: yes, solar power satelllites would redirect solar energy and effectively increase the amount of solar energy that the earth "intercepts." However,
 * Think about the enormous cross-sectional area that the entire earth presents to the sun. Even if there were an unprecedented and decades-long industrial effort to build solar power satellites, we could not increase the effective cross-sectional area of the earth by any more than a negligible amount.
 * The rate at which a planet radiates energy back out into space is proportional to temperature to the fifth power. This means that after a solar power system is "switched on," any tiny increase in global temperature would result in a large increase in heat radiated back out into space, and things would quickly return to an equilibrium where energy escapes at the exact rate at which it is added.
 * Please think about things like that before you put ideas out there that endanger the wonderful concept of solar power satellites. You know that there are luddites who would seize on your idea, become kneejerk opponents to SPS, and endeavor to doom humankind to a miserable energy-scarce existence.  GPS Pilot (talk)  —Preceding undated comment added 18:01, 14 May 2011 (UTC).

mW or gW
Cite:

To give an idea of the scale of the problem, assuming a solar panel mass of 20 kg per kilowatt (without considering the mass of the supporting structure, antenna, or any significant mass reduction of any focusing mirrors) a 4 GW power station would weigh about 80,000 metric tons, all of which would, in current circumstances, be launched from the Earth. Very lightweight designs could likely achieve 1 kg/kW,[62] meaning 4,000 metric tons for the solar panels for the same 4 GW capacity station.

if 1 kg / 1 kw then 1 x 4000 kg / 1 x 4000 kW = 4mW and not 4gW or am i missing something?

.--190.21.130.248 (talk) 14:22, 26 April 2011 (UTC)--190.21.130.248 (talk) 14:22, 26 April 2011 (UTC)


 * The switch from kg to tonnes: 4 e3 t = 4 e6 kg --> 4 e6 kW = 4 GW.
 * —WWoods (talk) 15:35, 26 April 2011 (UTC)

Shorter transmission path: dubious advantage
The article says that SPSes in low earth orbit would have the advantage of a "shorter energy transmission path." But is this really an advantage? In the vacuum of space, long distances will not cause attenuation of a microwave beam. Maybe beam spread would be worse... maybe. If so, I'd like to see a citation. If not, the article should not claim a shorter transmission path as an advantage -- and lunar solar power becomes a more attractive option. GPS Pilot (talk) 18:42, 14 May 2011 (UTC)
 * "lunar solar power becomes a more attractive option" Nonsense. L4/L5 are thousands of miles closer, & don't suffer the problems of darkness or moonquakes, just to name the obvious. IDK where you think the SPS would be to claim otherwise.  TREKphiler   any time you're ready, Uhura  21:53, 14 May 2011 (UTC)
 * The minimum possible divergence of a microwave beam is given in the Beam divergence article. Theta=lambda/(pi*w) where theta is the angle of divergence, lambda is the wavelength and w is the beam diameter at the beam waist. I am not familiar with the details of the limitations of beam spot size but it is obvious that beams must diverge.  Take the best laser pointer that you can get and point it at a distant object at night.  You will see that the spot is larger than it is on you hand.  It is the same way with microwaves.  So a microwave beam from the moon, L4 or L5 would need much larger antennas than a beam from an antenna at geosynchronous orbit altitude.  A lower orbit beam would be able to use a more divergent beam and still hit a reasonably sized receiving antenna, so it could use a smaller transmiting antenna.  It would need to electrically steer the beam to point it at one after the other of a series of antennas.  Presumably several transmitting antennas would take turns illuminating one receiving antenna.  With all the complications I would not say low Earth orbit would be an advantageous place for SBSP.
 * The article refers to a 1 km wide antenna to produce the beam at GEO and a 10 km wide receiving antenna. There is a reference for that in the article.  These sizes were arrived at by trying to minimize beam spread and antenna diameter and accepting a trade off with the smaller antenna in space where it is more expensive.  The concept of unavoidable beam spread is basic physics.  There should not need to be a reference for that. Fartherred (talk) 09:19, 15 May 2011 (UTC)
 * "beam spread is basic physics. There should not need to be a reference for that." I'm afraid we may still see it tagged by the ignorant. :/
 * I wouldn't argue for SPS in LEO, by any means. Power relay satellites to distribute power, to & from points on the ground & from SPS in L4/L5, yes... Actually, PRS first makes a lot of sense, not least to make ops from LEO to GEO/L4/L5 easier.  TREKphiler   any time you're ready, Uhura  10:38, 15 May 2011 (UTC)