powersat recalc.

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no_way

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lets do the powersat calculations again, just for fun <img src="/images/icons/smile.gif" /><br />Based on this:<br />http://www.powerfilmsolar.com/products/oem_components/modspecs/rc7275psa.htm<br /><br />I get about 325grams per square meter, or 325 tons per square kilometer.<br />about 40 watts per square meter, or 40 megawatts per square kilometer.<br />I believe i have seen 10 megawatt "demo" designs proposed, that would be "only" roughly hundred tons to launch just counting the film material.<br />The film is rollable, so deployment shouldnt be complicated, but how to make it rigid, inflatables ? Or maybe there wouldnt be any need to make it rigid, just add stationkeeping solar-electric thrusters at the corners that pull the "fabric" under constant small tension, and if this isnt enough, weave tethers through it.<br /><br />Cooling be a major obstacle though, i have no idea how much sunlight this would absorb as heat at full incident angle in GEO, and how much would need to be dissipated.<br /><br />This is just a BOTE calc based on the commercially available current product. There are always other thin-film products coming on market, could be that some of them weigh significantly less.
 
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chriscdc

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Well a mylar collector would allow more light to be collected allowing an optimum collection. There might be a fancy optical way to deal with infra red info. Perhaps a surface with a plasmon resonance thing going on. Guide the plasmons through a small hole in the film were they re-emit the unwanted energy on the other side. It's been done with optical frequencies but don't know about Infra red.<br /><br />A slight rotation should keep it taught.
 
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no_way

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You mean something like that ?<br />http://www.openenergycorp.com/suncone/suncone.php<br /><br />The problem i see with that : after concentration you still need something to turn the heat into electric and then to microwave. <br />In theory, a Stirling engine with a generator could do electric conversion at 80% efficiency or so, but this involves moving parts. Maybe it wouldnt be a showstopper with proper engineering. The Stirlings, however, arent known for their best power density, so getting a megawatt-scale one up there would be a tough challenge.<br /><br />Inflatable mylar cones for heating would be ideal for lunar soil processing though, as oxygen extraction and other regolith refinement processes require mostly heat input.
 
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thereiwas

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40 W per square meter isn't a lot - I have an amorphous panel that does way better than that at Earth's surface where incident energy is something like 1 KW/sq m. Weight and bulk have to be enough better to make it worthwhile. I wonder how this stuff stands up to multiple micrometiorite punctures?
 
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no_way

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<blockquote><font class="small">In reply to:</font><hr /><p>I have an amorphous panel that does way better<p><hr /></p></p></blockquote><br />have you weighed it ? <br />The thing with thin-film is, its lightweight and flexible. Which means its at least theorethicall feasible to launch square kilometers of it. Silicon cells are just too heavy.
 
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gunsandrockets

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Interesting data, thanx!<br /><br />I don't find the powersat application interesting though, because even visionaries like Elon Musk don't believe it is economically viable.<br /><br />But I do find your data interesting because of how it might describe spacecraft applications, such as Solar Electric Propulsion (SEP).
 
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thereiwas

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The early proposals assumed a mechanically stiffened collector and phased array antennas. If you change the collector to a spin-stiffened collector you need to use circularly polarized antennas, in orbit and on the ground, which are more complicated. Also I don't know how such a large structure spinning so close to earth would work out - you would want the collector to stay face-on to the sun, and the spin would help it do that, but any such large structure is also going to experience tidal and/or magnetic lock forces from the planet, and these two influences will fight each other. <br /><br />
 
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kelvinzero

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gunsandrockets:<br /><blockquote><font class="small">In reply to:</font><hr /><p><br />Interesting data, thanx! <br /><br />I don't find the powersat application interesting though, because even visionaries like Elon Musk don't believe it is economically viable. <br /><p><hr /></p></p></blockquote><br /><br />Hi.. all the stuff I have read agrees SSP is not viable yet, and is waiting on some breakthrough such as luna resources or a magically cheaper launch system. Is this what you mean?<br /><br />I love the idea of SSP because it suggests the possibility of an open ended space industry unlike communications and tourism, but certainly the fact it probably requres some as yet unknown tech to reach maturity puts it a fair way in the future. Fortunately we have other reasons to keep pushing for cheaper launch, better cells and better beamed power so unlike fusion power all the necessary components will be getting lots of development whether or not SSP looks viable. In the meantime it is fun to watch the numbers.<br /><br />
 
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no_way

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<blockquote><font class="small">In reply to:</font><hr /><p>all the stuff I have read agrees SSP is not viable yet, and is waiting on some breakthrough<p><hr /></p></p></blockquote><br />What stuff have you been reading ? Everyone says that the basic technology is there, what does not add up is economic viability, largely due to huge upfront investment costs, in the order of billions of dollars as calculated above.<br /><br />Technological and economical feasibilities are entirely separate issues.<br /><br />However, large terrestrial powerstations always cost in the order of billions, and do not break even for quite some years.<br /><br />Read the latest complete overview materials here:<br />http://www.nss.org/settlement/ssp/library/index.htm<br />Especially the bottom one, 2006 URSI whitepaper.<br /><br />The whitepaper summary is also available as HTML here:<br />http://www.ursi.org/WP/WP-SPS%20final.htm<br /><br />Note that the assumptions in the paper are far less than current state of the art, i.e. they assume 13% solar cell efficiency, whereas over 40% has been demonstrated already.<br />And a very appropriate summary:<br /><blockquote><font class="small">In reply to:</font><hr /><p>Only some parts of these questions can be addressed by laboratory work, simulations, or system analyses. Tests of the large structures (solar-cell arrays, transmitting antenna, mirrors) in space are mandatory. After successful testing, launching a pilot SPS unit as an operational demonstrator project – presumably with broad international consensus – may be a suitable way to assess the remaining questions.<p><hr /></p></p></blockquote><br /><br />Read: this is a concept that needs testing and be put on public conciousness. ASAP. IMO, it should receive at least tenth of the funding and attention that goes into fusion development.<br /><br />
 
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kelvinzero

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Hi, that is a cool looking link.<br />I couldnt judge the viablility from the science though, I am just referring to studies on viability eg by NASA, Space.com articles and wikipedia, both of which were probably quoting NASA <img src="/images/icons/smile.gif" /><br /><br />All I meant by breakthrough is much lower masses or more likely much cheaper $/kg to orbit, eg luna resources. I can't justify that. I am just quoting what I have read.<br /><br />I do support serious effort applied to making SSP work, since it would inevitably lead to a massive money spinning space industry. <br /><br />Oh here is a quote.. it is from 2000 I think:<br />http://spacefuture.com/archive/a_fresh_look_at_space_solar_power_new_architectures_concepts_and_technologies.shtml :<br /><blockquote><font class="small">In reply to:</font><hr /><p>The economic viability of such systems depends, of course, on many factors and the successful development of various new technologies - not least of which is the availability of exceptionally low cost access to space. However, the same can be said of many other advanced power technologies options. Space solar power may well emerge as a serious candidate among the options for meeting the energy demands of the 21st century. <br /><p><hr /></p></p></blockquote> <br /><br />I also support those studies you mention, and I expect much work will continue since beamed power has uses before even SSP for earth becomes viable.
 
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no_way

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my point in opening the thread above was : there are new technologies coming online fast, like thin-film solar cells, that change the variables of economics in SSP development. Thats the reason why SSP concept should be under continuous review and study.<br /><br />The one NASA source you quote, "Fresh study", was published in 1997. Thats ten years ago, thats hardly Fresh anymore. A lot of variables have changed since then.<br /><br />I havent plugged new numbers into the old models, but im fairly confident that even at present, solar power satellite would have shorter payback time on investment than a new nuclear plant, especially when you take waste handling into account.<br /><br />By the way, Japanese have been working on this the whole time, low-profile and modest goals, but Kyoto university is the one single research department that has done most in advancing microwave power transmission and the overal SSP conept. Look at their english webages here:<br />http://energy.coe21.kyoto-u.ac.jp/eng/task-solar/<br /><br />The problem with Japanese is that they are very conservative, so despite all their research results, the first actual space hardware test has been pushed back and back.<br />
 
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kelvinzero

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Well Im certainly prepared to be convinced. My impression really just came from the wiki article.<br />http://en.wikipedia.org/wiki/Solar_power_satellite<br /> and the nasa and space.com articles.. and Im not claiming to have understood all of that either.<br /><br />I would say go for it if its merely at the break-even stage, ie funding its own construction but not actually giving any return. zero seems a small price to pay for gaining a massive space industry <img src="/images/icons/wink.gif" /><br /><br />Have there been any more recent external evaluations on its current state of readyness? .. I guess that was your point with this thread of course.
 
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no_way

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just doing a bit of further calcs.<br /><br />325 tons is 16 Proton launches ( to LEO )<br />Proton price is reported roughly $60M per launch.<br />thats a $billion per square kilometer of thin film launched to LEO ( neglecting any support mass like tethers and so on, but also neglecting any price savings of such a huge number of launches )<br /><br />thats not too bad for a 40MW pilot power plant. Especially considering what a nice demand you can create for cheaper launches this way.
 
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nexium

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40 megawatts is almost one gigawatt hour per day = 360 gigawatt hours per year worth $18 million dollars per year at 5 cents per kilowatt hour which is an average wholesale price at most locations where we could put a rectenna. That is a 56 year pay back on just the billion dollar launch cost. There are some other non trivial costs such as the square kilometer of photovolaic film and the cost of the rectenna. I agree we should do this as it will advance space technology. On the optimistic side I think better than 40 megawatts per square kilometer may soon be available even for the very thin photovoltaic film. Neil
 
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no_way

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the thing is, my 40MW calculation is based on terrestrial output. at full incident angle at ground level, and ThinFilm product isnt particularly efficient ( i think around 12% ) or so.<br /><br />SpectroLab recently announced their triple junction cells that are demonstrated over 40% efficient, and can theorethically go to 58%.<br /><br />IIRC the output in space at GEO is roughly four times more, and if you manage to get the three times more efficient cells then you have multiplied the output to 480MW.<br /><br />All that of course is beside the point for prototype, ITER is built without any payoff being in sight. Its also designed for 500MW output, and costs over 10 billion.<br />
 
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