Space-Based Solar Power

a public discussion sponsored by the Space Frontier Foundation

“Why is the DoD interested in this?” Security at all levels!

Posted by Coyote on September 1, 2007

Yesterday at one of my alternate work locations (okay…another one of D.C.’s Irish pubs) a space skeptic asked me to write down all the security reasons that explain why the DoD is interested in space-based solar power. Fair enough. So this is what I wrote on the bar napkin: (I share it with you because that’s what I do!)

Immediate military tactical and operational needs:

  1. Dramatically reduce the energy logistics train to forward operating bases and reduce the need to secure massive energy convoys and stores in:
    1. Disaster relief efforts
    2. Nation building efforts
    3. Combat zones
  2. Beam power directly to vehicles in all operating media for the following reasons
    1. Reduce weight of carrying fuel
    2. Increase range and loiter time
    3. Eliminate need for refueling and reduce the need for refueling vehicles
    4. Reduce the need for consuming local energy supplies
    5. Reduce size and signature
  3. Use SSP for liquifaction of carbon-neutral fuels for current generation of liquid-fueled systems
    1. Continue to exploit current liquid fuel infrastructure, using carbon neutral fuels
    2. Gain independence from foreign liquid fuel providers

Urgent national security strategic goals:

  1. Assist in achieving national energy independence from current liquid fuel providers
    1. Reduce level of national interest in unstable regions
    2. Reduce national dependence on unfriendly foreign governments
    3. Reduce the risk of energy competition wars in the 21st Century
  2. Assist allies in achieving their national energy independence
    1. Develop and strengthen broad international partnerships
    2. Participate in international energy consortia and alliances
  3. Economic: Become an energy exporter
    1. Increase national ability to influence or avoid geopolitical events
    2. Increase GNP, wealth of the nation, and increase tax revenue
    3. Use energy earnings to pay off national debt
  4. Environmental: Dramatically reduce carbon emissions into the atmosphere
    1. Prevent food wars which might happen if global warming continues
    2. Enhance soft power and green credibility around the world
    3. Lead the international clean energy movement by example

So you can see, this is a disruptive technology for security operations, but far more importantly, it will redefine geopolitical relationships and removes energy competition as the major driver for wars. Personally, I think war prevention is the highest form of security.

The other key to improving security with this concept is moving it quickly into the commercial sector at the earliest possible time. The DoD merely wants to be a customer of a commercially available product–energy. We do NOT want to trigger false security dilemmas. This will drive multinational partnering and international engagement, which is called for in our National Space Policy. This is one of the key reasons why we initiated this study on the Internet and in the media–to provide openness.

Your comments???


42 Responses to ““Why is the DoD interested in this?” Security at all levels!”

  1. There is a much better and easier way to provide power to remote locations, and beam it to mobile vehicles, than to do it with space solar power:

    About 35,950 km closer and 100 times more intense, available day and night in the mid-latitudes.

  2. Coyote said


    That’s an interesting concept that needs to be looked at more closely. Remember, we favor the development of ALL clean energy sources. From my flying days I remember that winds aloft, even the jet stream, are very unpredictable, hence sometimes when you fly you have a tailwind, other times you don’t, so consistency of power will probably be a factor.

    Still we need a system that can broadcast power into combat zones that doesn’t hang an easy target for the adversary to strike and that doesn’t mess up the flow of our air forces. Moreover, the article mentions hanging these airborne windmills at 15,000 feet. That would give such systems only a few miles slant range to broadcast to surface vehicles. Also, the article seems to imply that the power would travel by wire down the tether. It doesn’t indicate that power beaming will be part of such a system. The added weight of microwave or laser broadcasters would change their depicted design dramatically.

    Just some thoughts, but definitely another option to consider.

  3. admin said

    wow! that must be an unusually large bar napkin! Can you please provide a photograph of the actual bar napkin with all those compelling reasons scrawled on it?

  4. scot4space said

    As a way of proving the concept of power beaming in space, have you considered having a ground station on earth and beaming it off a reflector in space. From what I know large inflatable reflectors in space have been looked at, with present day satellite station keeping technology available to keep it pointing in the right direction, with you able to measure overall losses to a ground based receiver. You also have the option of having a series of relatively low cost lightweight reflectors in space beaming it round the earth and down to the required location, which leaves all the heavyweight power generation and transmission requirements on earth.
    The Proton launch vehicle has the possibility of a 500kg piggyback payload to a geostationary orbit, which could be a cost effective option for proof of concept.


  5. Coyote said

    Kirk: I am trying to figure out how to post or link those powerpoint slides that you provided to me yesterday, but so far I am not having any luck. Are they already posted somewhere that we can simply insert a link to? For everyone’s info, Kirk provided slides that addressed some of my specific concerns. And absolutely YES, we’d like to see such capabilities studied, demonstrated, and employed as yet another clean energy option for everyone to consider.

    Admin: Fighter pilot rules apply to bar napkin use! Both sides of the napkin were used and words were abbreviated as much as possible. Since you mentioned it, back when I was in Skunk Works (2001-2003, when I wasn’t deployed) I used to give a series of briefings to the generals on the Air Staff every Friday afternoon called “The Bar Napkin Series.” It was meant to be a time for the generals to relax a bit and simply build their personal relations,which is a good thing! Many of those briefings were literally scanned images of bar napkins that I collected during the week during interesting discussions at various alternate work locations. You would be amazed at how many ideas have gone from bar napkin to reality. Hmmm. Maybe I should write a book about that.

    Scot4space: Concept testing will be a very big consideration once this project is off and running. Much of this has already been done, but using different frequencies and much lower power. We need to assess the scalability of these concepts. Using satellites to relay power comes with a whole host of additional problems, such as doubling the path loss of 1/r2, heat issues at the relay, and transference loss at the relay. But keep in mind that another goal is to create an entirely new source of energy, not simply using current systems differently.

  6. allen said

    Hey Kirk, how does the skywindpower design handle power transmission?

    It seems to me that if you’re going to generate 2.5 megawatts you’re going to have to have very high voltage to get the power to the ground without a cable that has a large cross-sectional are and thus a lot of weight.

    Also, what about bad weather contingencies? A cable like that would develop some serious loading from winds and thunderstorms even if those phenomena occurred well beneath the altitude of the generator assembly. There’s also icing as a potential problem as well. And lightening.

  7. Tom N. said

    Any comment on the Space Prizes blog comment about having the DoD offer a SBSP-related power beaming competition?

  8. Coyote said

    Tom N.: That’s an interesting thought. I’m rather confident that the DoD will be glad to write fat checks to anyone who can demonstrate reliability in broadcasting 5 megawatts of power to a military base inside the continental US from a satellite system on orbit…then 10 megawatts. After that the commercial applications for 2-5 gigawatt satellites will be obvious.

  9. Charles F. Radley said


    DOD is already awarding prizes, specifically, the DARPA Challenge :-

  10. Coyote: there was a post recently that talked about how a 5 MWe SSP is a non-starter. You want to go to gigawatt-level power or the thing isn’t worth doing.

    Allen: I presume they plan to use the tether itself for power transmission. Bad weather certainly will have to be an issue to be dealt with. Nevertheless, the whole thing looks orders-of-magnitude more feasible than SSP for delivering power to remote sites, day and night. I saw an article on CNN on the topic:

  11. Edawg said

    What would be the tonnage of an 10 megawatt orbital ssp array?

  12. Tom N. said

    There are different models for prizes. The X-Prize has had the “do X within Y years” model. The Spaceward Foundation has the “do X better than Z each year” model. The first one seems to be for massive improvements. The second one goes for noticeable demonstrations with regular improvement. Not sure which is more appropriate for SBSP. I could envision useful intermediate steps, such as beaming 5 kW to a satellite (to demonstrate power over hundreds of kilometers, with a reasonably fast-slewing target). Certainly an area to look at, once the program gets funding.

  13. Sir,
    i am real glad the DoD is heading the project on this but what i
    am looking for to see is if the DoD has had any study on the environmental aspect of this gigantic project.
    when the time comes for you to be sending all this gigantic Launch of Rockets (one after another)and more of the future when
    you start beaming all this energy to earth daily with hundred and or thousnad times on thousand upon thousands of different
    Satellites. How would it or what would it do to the earth atmosphere (Ozone)….
    For the DoD to also Lead the way to this study would be benificial.. yes maybe bias but it will start for the civilian sector to do thier study …. i am sure of it.
    IS THERE ALSO A WAY TO GET ALL THIS RAW(CLEAN)ENERGY TO LIQUID FORM,since earthlings are still into this state of dependency into carbon liquid energy??????
    We are grateful to the DOD on this leadership.
    Thank YOU.
    Sirwill Stoneage

  14. Edawg said

    Tom:You cant close the business model if you dont have some simple raw data or “guesstimates” like weight for the variables..Whats the tonnage of x? And then y?

    Coyote: that sounds like a very good idea for a book ,its amazing how many productive ideas come from bar napkins

  15. Gary Oleson said

    On the future markets side of the issue, I suggest looking at the South Pacific. See:

  16. Dan Lantz said

    Kirk #10:

    “While each FEG would cost an estimated $2,260,000 to build, maintain and support, arrays of FEGS would, in the long term, prove extremely cost effective, generating electricity at about 2 cents per kilowatt hour, as opposed to the 3-5 cents of conventional generating methods”-from

    “Dinkin: When will the price of electricity start to drop if you were given the money today?

    Criswell: Approximately 15 years after the start of an Apollo-priority program the cost of electricity would drop beneath $0.10/kilowatt electricity hour (kWe-h). By 2040 the cost would be a fraction of a cent per kWe-h.

    When the LSP system delivers 20 TWe and the energy is sold at $0.01/kWe-h then the profit is approximately $1.6 trillion/year…

    Dinkin: That is fantastic. That is a huge source of clean power beckoning. Are you saddened by all of the deaths related to pollution and wars when we could have lunar solar today if we had stayed on the Moon with a 15-person research base in the 70s?

    Criswell: Of course. The daily global lost of life due to the lack of low-cost energy is the order of the deaths from the Indonesian tsunami.” -from

  17. allen said

    Kirk: Some parts of the idea are certainly more feasible and easily-achievable then SPSS but some other parts look kind of prickly.

    Leaving aside the problems of wind- and ice-loading on the tether the really thorny problem is how to get the power down the tether if you plan to move 2.5 megawatts.

    In order to keep the cross-section of the cable reasonable the voltage has to be, no pun intended, sky-high.

    At 100,000 volts you’ve got to have a cable that’ll handle 25 amps with acceptable power loss. But voltages that high create a number of problems in the solving of others. For instance, how do you get to that 100,000 volts without incurring the weight penalty of a transformer capable of handling 2.5 megawatts? Is there a generation technology that’ll produce ultra-high voltage electricity, at the required power levels, directly?

    I like the idea because it doesn’t appear to require the development of an entirely new industrial base which SPSS would. Deployment’s also, obviously, easier and cheaper as is maintenance and upgrade.

    Looking through the site I don’t see any coverage of power-transmission considerations. I’ve e-mailed my questions to skywindpower. If anyone’s interested I’ll summarize whatever response I get.


  18. Edawg said

    Where does the old bear Russia fit in to ssp and commercial space plans?I can think of several launch systems that will throw the current geo-political balance out of whack..I hear that the russkies got velocities of up mach 27 with their test for gun to orbit systems

  19. We keep bouncing back and forth on this forum as far as what we’re talking about. A little while back Coyote said that economics didn’t matter because he was paying some awful amount to ship fuel to a forward operating base in Iraq and that SSP would be a viable contender at whatever price. That was what motivated me to post the FEG link. I think the idea is intriguing–I don’t know if it will work or not, but I think it’s worthy of investigation.

    I’m not proposing Sky WindPower as the solution to the global energy crisis, nor necessarily saying that it will be cost-competitive in other markets. Maybe it is, maybe it isn’t. My experience with space solar power leads me to strongly believe that FEGs are a better investment of effort than SSP, and infinitely better than Criswell’s lunar-solar ideas.

  20. allen said

    The one-line reply was that high voltage generators are a specialty item.

    Anybody have a clue about the availability, cost, supplier, reality of a 100,000 volt/.75 megawatt generator?

  21. allen said

    Kevin, I’m not trying to throw cold water, I just want to know if there are any stoppers to the use of the idea.

    For instance, you can’t push 2.5 megawatts down a power line unless the voltage is pretty high. The problem is compounded when the first couple of miles of transmission line are hanging from the generator.

    So the per/unit weight of the tether has an upper limit. Since current capacity is a function of cross-sectional area and conductivity someone with more knowledge about this stuff could calculate conductor cross-section for various current levels. From that you can calculate weight/unit length and then the total weight of the tether.

    If the lift of the platform can be calculated then you know if it’ll fly.

    The only way to lighten the conductors in the tether is to drop the resistance of the conductors or raise the transmission voltage.

    I don’t think superconducting transmission lines are a viable option at their current state of development so that leaves raising voltage which creates its own problems.

    Obviously, transformers big enough to handle the power and raise the voltage sufficiently aren’t going to be light but the platform’s already carrying the weight of the tether.

    How much does a transformer capable of handling 2.5 megawatts and raising it to, arbitrarily, 100,000 volts weigh? Beats me but I know that anything that flies is sensitive to excess weight.

    The only other way to deal with the situation is a generator that generates the electricity at 100,000 volts obviating the need for voltage step-up gadgetry.

    Is there such a thing as a 100,000 volt, .625 mega-watt generator (the platform needs four generators I’m guessing) that’s light enough to let this idea fly? Seems unlikely but I could be wrong about that as well.

    I’m not calling bullshit but there are real questions that have to have answers before this idea can be considered commercially viable. The site answers some question forthrightly, some vaguely and some not at all.

    Found a site that has info about wire sizes necessary for different current capacities:

    12 gauge carries 40 amps at 30 degrees C. if insulated with flourinated ethylene propylene so if the insulation is up to the job of handling high voltages, it looks like conductors smaller then I’d thought, could work for transmission. That still leaves the high-voltage generators though.

  22. This article has a lot of technical discussion of how the Sky Wind Power idea works:

    Harnessing High Altitude Wind Power

    They mention a transmission voltage of 15 kV down an aluminum tether and have some discussion of power generation:

    “Conventional ground-based wind energy systems harvest only about 30% availability. Flying electric generators, in single units of 20 MW or more, can achieve about 80% availability with suitable siting at land or sea locations. These generators at altitude involve power transmission over lengths of between 4 and 8 km. Flying generator/tether voltages between 11 kV and 25 kV ac could be used on units of 30 MW at the most extreme altitudes. Also there are recent modern innovations, which use powerformers / motorformersTM [15,16]. The latter, being developed by equipment suppliers such as ABB, Siemens, Mitsubishi, etc., would allow polymeric cable stators and tether voltages at say 33 kVac or more. Grid interfacing would then be easier at bulk energy levels.”

  23. allen said

    Thanks Kirk. Using “powerformers” as a search term I found a press release by ABB – – that goes into a bit of detail. The line that jumped out at me, and answers my questions is:

    > The Powerformer can generate electricity at voltages between 20
    > kilovolts (kV) and 400 kV.

    Obviously, if you can reach 400 kV directly from the generator then sending 20 megawatts down the tether seems doable to my uneducated eye. Nothing about power-to-weight ratio though, which is understandable.

    I’m sure the Powerformer wasn’t designed to fly but with commercial production under way, albeit not designed for use in this application, another objection is knocked down.

    I wish the project well. The idea has an unlikelyness that I find appealing. Probably it’s that I associate the generation of electricity with the word “massive”. Great, big things like dams, nuclear and conventional power plants in which weight isn’t a consideration. The notion that a kite, albeit a great, big, sophisticated kit could compete with them is somehow gratifying.

  24. MervynKellum said

    Edawg Says:
    September 5th, 2007 at 1:26 pm
    What would be the tonnage of an 10 megawatt orbital ssp array?

    i calculate about 45,000 kg.

  25. E Norton said

    The involvement of the Dept of Defense in this idea tends to make me wonder about the possibility of using these SBSP satellites as weapons. Will the energy that is being beamed down to Earth be in a form that could actually kill people if aimed at them?

    I don’t think that such worries are necessarily a point against the development of the SBSP, I’m just curious. I’m sure a lot of foreign countries will be leery if America is going to be putting a large fleet of satellites up that could possibly be used as weapons.

  26. Dee Illuminati said

    I think that Coyote needs to think about Arecibo in reverse, or Stirling dish concentrators or trough concentrators uploading microwaves to a GOES type platform that can then download microwaves at different efficiencies to different lattitudes. That might not be the most efficient means of supplying energy to forward command, but better than none and the real possibility that the ground based system could be used on-grid when less efficient transmission was not required. Now go ahead and play the part of a neanderthal andrun a sword through me as I’m scribbling and you romans are dreaming~~ I guess the question is this, what is total transmission loss of an uplink and a downlink if say the permanent position was the badlands in the US southwest and the recipient foci in Baghdad? And in closing, I see that “According to model calculations, a simple updraft power plant with an output of 200 MW would need a collector 7 kilometres in diameter.” With atmospheric loss how much energy could be delivered if an optimum Stirling dish concentrator was excavated in say Nevadad near Nulles and that energy redirected to baghdad if the excavation had a 7 kilometres footprint?

  27. Neil Cox said

    I’ve been excited about alternative uses of FEG = flying electric generators for several years. We need to start buiding them. True the losses in the tether are large, but that will prevent ice build up. Initially they need to be located where lightening is rare. Superconductors will cut the losses sharply, but lightening will produce a strong magnetic field which will make the superconductor line resistive long enough to vasporize the tether. We should not wait for superconductors which can tolerate magnetic pulse.
    I think we can order 5000 volt dc generators today. 13,000 volts should be available a year after it is clear there are customers for them. The 2.5 megawatt FEG has 8 rotors thus 8 generators = series connection 100,000 volts. 25 amps should be easy with high temperature insulation. A hot tether means no ice. So what if the pilot model uses half the power output heating the tether? The real value of the FEG is attached to balloon supported platform at 35,000 feet or more. 4 FEG can supply the platform with ten megawatts. If one of the 4 balloon fails, the FEG can run as a heliocoptor and keep the platform level. Neil

  28. Neil Cox said

    Even if the solar power satelite is in LEO = low earth orbit the transmitting antenna is huge to produce deadly beam density. A huge transmitting antenna will make the solar power satellite much more costly. The one kilowatt per square meter = 0.1 watt per square centimeter generally proposed will have only minor harrassment effects on humans, which can be reduced by wearing a tinfoil hat. Aluminum foil works even better. Neil

  29. Neil Cox said

    Neither Flying electric generators nor solar power satellites, impact the envirornment significantly until we get to a million megawatts = 1000 gigawatts. Even then the effects will likely be tiny. ie warming a millionth part of Earth’s statosphere a millionth of a degree c. The airline industry has a much larger impact. Neil

  30. Neil Cox said has some detailed analysis on sending power by laser. It is costly at present, and the CNT = carbon nano tubes are not yet strong enough to make the space elevator practical. As cyote suggessted, cost is a minor problem in modern warfare and in dealing with terrorists. Neil

  31. Neil Cox said

    Some experts think Lunar solar should be done near the North pole as a few mountain tops have continous sunlight for most of an Earth year which I think is about as long as a lunar year. In between polar mountains is twilight 3/4? of the year. Polar temperature is less extreem than the rest of the moon, so this may be a better place for base and colony. The power grid can be a single wire at the top of tall poles carying as much as ten million volts. I don’t know how you convert that to 240 volts 60 hertz ac center taped (except 9000 inverters with their inputs in series) but several very high voltage dc power lines are operational on Earth, so apparently there is an ecconomical conversion method. If you have any details, please tell us.
    SBSP is not a problem as a million or so, laser diodes can be operated in series.
    All of North America (except Mexico and farther South) is above the horizon about 1/3 of the time from higher Luner polar locations, so North America, Europe and Asia need a different power source than the Moon’s North pole about 2/3ds of the time. The Equitorial Zone, and Southern Hemisphere of Earth can be served only rarely by Lunar SBSP in the Northpolar region of our moon. In theory we can also build a Southpole lunar grid and SBSP, but the mountains are less tall, so solar power will be available less than 2/3 ds of the year for bases and colonys near the moon’s South Pole.
    Earth receiving sites for Lunar SBSP may cover thousands of square kilometers because of beam spreading over the almost 400,000 kilometers beam path. What is the probability of using ultraviolet diode lasers, which would reduce beam spreading? I don’t think SBSP is possible with microwaves from the Moon to Earth.
    Bases, colonies and SBSP near the Lunar equator would require a power line grid that circled the moon’s Equator to have solar electricity always, except during an eclipse of the moon. I think you will agree a power line about 10,000 kilometers long would be a massive project on the Moon.
    Lunar satelites are not sychronous with the moon’s surface, except at Earth-moon L1 and L2. L2 wanders considerably due to the sun’s gravity and the great distance of L2 from the moon.
    Please correct, embellish and/or refute. Neil

  32. Neil Cox said

    45,000 kg is very optimistic with technology likely to be mass produced by 2010. If thin film photovoltaic has a mass of one gram per square meter and produces 100 watts per square meter = 8% efficiency: 10 million watts is 100,000 square meters = 100,000 grams = 100 kilograms. Quilted heavy duty aluminum foil has a mass of 10? grams per square meter. We need about 1/2 square kilometer welded into a honey comb to produce slight ridigity = 5000 kilograms. We do need to turn the panel to keep it facing the sun, so slight rigidity is necesary. 100 kilograms for the ion engines or equivelent. We need several ion engines to distribute the turning stress. 1000 kilograms of ejection mass/fuel for the ion engines, except for the thin film times two for the laser diode array . 100 kilograms for the flexible power cord (very high voltage insulation) 5000 kilgrams for the stifening structure that holds the 200,000 laser diodes and their optics. This must not change shape, or the beam will get wider, thus requiring a wider rectenna, which will be impractical for a moving vehicle powered by an energy receiving aray. 30,000 kilograms for the 200,000 laser diodes and their optics. 41,300 kilograms, but I added 3 stiffening structures when we only need two, but surely there will be 5000 kilograms of miscelanous. I got a bit less mass than you, but I likely forgot some massive items and the one gram per square meter, including the metal that interconnects the millions of individual photovoltaic cells is very optimistic. Neil

  33. Alienthe said

    In theory we can also build a Southpole lunar grid and SBSP, but the mountains are less tall, so solar power will be available less than 2/3 ds of the year for bases and colonys near the moon’s South Pole.

    This depends on whether or not there truly are any Peaks of Eternal Light on the Moon. The Wikipedia-article is full of contradictions so there is little point in looking there.

    From what I can see from elsewhere on the net the lunar south pole has a number of promising places that could be PELs. Some are on the edge of the Shackleton crater within which the lunar south pole point is located and thus is a potential source of water ice. Helium 3 is also suspected to be found in these areas and the value of 3 billion USD/tonne is not to be overlooked, especially in these times with high oil prices.

    All in all this place looks like the hottest property on the Moon and I believe most forward looking countries would like to “occupy” it. Technically speaking you cannot own real estate on the Moon but just as the case is for Earth’s south pole just being there is controlling it and is as close to owning it as you need.

  34. Steve said

    I just stumbled up this discussion from and this is really my first exposure to both technologies. I wanted to ask if it would be possible to couple the ideas.

    Is it feasible to Generate power via the FEG but project it via the mechanism proposed for SBSP?

    This would eliminated the need for a conductive tether and possibly eliminate the need for a tether at all.

    This is quite a fascinating discussion.

  35. John G. said

    Have we ever considered rather than FEG Building underground wind tunnels that replicate the jet stream? This would cancel out many of the obstacles to FEG. Space based solar panels. Would it be possible to transmit that power via radio waves similar to a cell phone signal times x. Also would light beams from the solar panels at varying strengths strategically pointed at different sections of an NEO be sufficient to alter the trajectory of the NEO?

  36. Neil Cox said

    We have been transmitting power from space for 50 years. Perhaps we need to build a one square kilometer rectenna and see if we can get more or less than one milliwatt? Perhaps it is already built. Does Aricibo radio telescope pick up a milliwatt, if tuned for very broadband?
    Assuming we can get a milliwatt, of the megawatt being presently broadcast at Earth = one part per billion; we can aim a satellite or two at the Arecibo antenna to be sure the output increases measurably. We should likely repeat the experiment at several other radiotelescopes around the world. Next we build a 100 meter antenna array in low Earth orbit to send two kilowatts in a very narrow beam to Arecibo and other radio telescopes. If less than one kilowatt is received, we need to find a better way, as we need to lose less than half the signal to make SBSP = space based solar power practical.

  37. Neil Cox said

    In theory using millimeter waves, instead of microwaves will provide a tighter = narrower beam, so nearly all the energy falls on the radio telescope.
    We can repeat the experiment with a two kilowatt transmitter, a large antenna kept aloft by a high altitude balloon, which tests part of Earth’s atmosphere. I’m sure these expariments have been done in the past for other reasons, but sometimes we are surprised when we do an experiment with a single result in mind, such as SBSP.
    I think we will decide that even millimeter waves cannot deliver ten kilowatts to one square meter, with a reasonable size antenna array, 36,000 kilometers away at GEO altitude. We may need to think ultraviolet laser diodes to get that tight a beam for military portable power reception from GEO altitude.
    We do not need, nor want that tight a beam for civilian very large fixed rectennas, so the millimeter waves may be the best option for large scale.
    My guess is we should forget millimeter waves and microwaves for the millitary application and go directly to laser diodes of the color presenty best. These can be tested from high flying balloons at much less cost, so my suggestion is to do that ASAP = as soon as possible. Neil

  38. Neil Cox said

    Hi John: All good ideas, except possibly the first two sentences. Air does move in underground tunnels, but I would think to get jet stream airspeeds, the tunnel would need to be about 10,000 kilometers long and have a volume of 1000 cubic kilometers. Even a millionth that big would be a huge engineering feat. Please give us more details.
    The SBSP is a lot like a celphone tower, but a bigger antenna, more power and a higher frequency = shorter wave length is better.
    The light beams we can produce now would move a NEO (near Earth object) minutely, but this might be practical, if we fund powerful light beam research. Particle beam generators would also deflect NEOs minutely. Laser diodes look promising as a very narrow beam is possible, which possibly could vaporize some of the surface of the NEO. This would behave like a jet engine which is likely more efficient than light pressure propulsion. Neil

  39. Neil Cox said

    Hi Steve: That might work very well. We won’t know unless we try. I reccomend ASAP = as soon as possible. The SBSP platform (tethered to several FEGs) should also have high altitude balloons as a back up for the FEG when the wind is weak.
    With no tether at all the FEGs would move down wind, but two FEGs conected by a long tether, would often be able to generate some power and move at least a little with respect to the down wind direction. So it seems to me. Neil

  40. Neil Cox said

    Hi alienthe: I hope you are correct. The lower peaks are likely easier for SBSP construction. The Moon polar peaks may be the best even if they only provide power 3/4 of the time. Perhaps we will send a probe to get close up photos of the polar peaks each day of the month from various angles.

    We can expect the price of HE3 to be much lower when it becomes clear we can supply a ton per week long term. Demand for helium 3 will remain low unless the price falls a lot, and availability improves. Neil

  41. Alienthe said

    @Neil Cox

    Post #31 and #37

    While ultraviolet light would provide less diffractive spreading you would get a lot of absorption in the ozone layer which already protects the ground from UV radiation. For that reason I am not sure UV lasers are worth the trouble. Also you would get only a small improvement over visible light.

    Having said that I would hesitate using blue light as it experiences a lot of scattering in the atmosphere, ref the blue skies of a clear day. Blue light has its place though, you could take advantage of the scattering and use it to provide night time illumination and dispose of street lighting. Something closer to green would be better for focused power delivery.

    Post #40

    The price of He3 is related to the value of it in terms of electricity produced, not the cost of obtaining the helium.

    Considering the increasing cost of electricity (and power in general) I would guess the price would increase, not decrease.

    All in all all indicators are that the Shackleton crater and its surroundings are extremely high value real estate.

  42. Neil Cox said

    Hi John G: October 7, 2007 at 5:19 am
    Sorry for the long delay. I was hoping someone who understood underground wind tunnels would respond. Can you give us more details? I presume air does move though tunnels hundreds of kilometers long which open to the surface at both ends, especially if we have one way vehicles moving through the tunnels in the prevailing wind direction. The tail wind would reduce fuel consumption for the vehicles, but it does not appear sufficient to justify the huge cost of the tunnels.
    The tunnels would be cheap, if the only humans who survived a world disater were enroute in one or more of these tunnels. They could repopulate Earth.
    Yes radio waves can be used as a way to transmit energy. Higher frequencies than cell phones are probably better as smaller antennas are needed to send a beam to a spot smaller than a few miles.
    Yes light beams (from lasers) can be focused on NEO = Near Earth asteroids to alter the trajectory of the NEO. Present lasers are too puny to change the trajectory by enough, but there is hope for better lasers soon, and yes the lasers can be powered by solar panels on SSPs. A laser SSP may save Earth from a deadly asteroid impact, in the future. Neil

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