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If I am not mistaken, global energy consumption is an exponential function of increase in world population * expansion of 'western lifestyle' * increases in energy-intensiveness of western consumer technology (flatscreen tvs). One resource LEO offers in principle is 24hour 1400 W/m2. What cold water can be poured on whether or not solar power harnessing will work within the next 3-4 decades? I'd like to hear some show-stopping numbers.
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one word. Costs. Orbital solar power satellites will needs to be huge. even with economies of scale when launching large numbers of high mass objects will not make it cheap. Orbital solar will be so much more expensive than the alternatives like gen III/IV nuclear, that nuclear is by far a cheaper option for powering the world. at least in the short to mid term. only with massive lunar infrastructure can Orbital solar start to compete.
Established Member
"only with massive lunar infrastructure can Orbital solar start to compete"
Do you mean that a most economical source for competitive LEO solar collectors would have to be pertinent lunar in situ resources, lunar manufacture, and lunar launch back to LEO, all which would imply / require 'massive lunar infrastructure'?
LEO solar is just an obvious and nearby objective. I'm hoping to see if there is any consensus on optimal sequence of steps from 2010 to BEO.
Established Member
Don't get me wrong. I'm a big fan of industrializing space. but it's incredibly costly. at least with current launch costs. if any government was to build such a facility the amount of mass launched for just one such orbital power station would seriously alter the economy of launching stuff into space. but in order to supply base-load power to the entire world we would need around 15 terrawatts worth of power beamed down continuously. and that is just to maintain the current world power needs. To maintain such a large fleet of what can only be called immense power satellites would require hundreds of launches annually.
Spending that much on power is somewhat strange when an investment an order of magnitude smaller can deliver the same amount of power down on the ground trough nuclear technologies. technologies that can supply that much power for thousands of years before we even have to worry about running out again.
The current stockpile of so called nuclear waste is enough to power the world for quite some time if it was put into a Gen IV full burnup reactor like LFTR or something similar.
Order of Kilopi
Do you mean that a most economical source for competitive LEO solar collectors would have to be pertinent lunar in situ resources, lunar manufacture, and lunar launch back to LEO, all which would imply / require 'massive lunar infrastructure'?
If you're talking LEO solar collectors, then your calculations are seriously flawed. In the first place, they wouldn't have 24 hours of sunlight a day in LEO - more like 12 hours. Not only that, but a LEO satellite is in the line of sight of a given ground station for only a few minutes at a time. You'd need many satellites in the constellation to have a continuous line of sight to a ground station.
If you move the satellite out to GEO, then you'll have 24 hours of sunlight for most of the year. The exceptions would be during the eclipse seasons centered on the vernal and autnumal equinoxes. At zero degrees inclination, the longest eclipse is 72 minutes. Eclipse season starts a few weeks before an equinox and lasts a few weeks afterwards and the duration of each eclipse resembles a bell-shaped curve.
Getting a solar power satellite to GEO is an expensive proposition but it'd have the advantage of constantly being in view of the supporting ground station. For the foreseeable future, the high costs of solar electric power don't make this an economically viable option for large scale energy production. The military has done some research on using solar electric power for supplying power to geographically isolated areas with high logistics costs (e.g. Afghanistan) but I have not seen anything come of it.
Banned
With computer-controlled phased-arrary transmitting antennas and a series of SPSes in co-orbit, it's a fairly simple matter to maintain lock on the receiving array, and to jump to the next receiving array in the same split-second the trailing satellite jumps to the one being left.
Having said that, it's a heck of a lot cheaper per kW-hr to build solar power stations on the ground!
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@Larry Jacks:
Or build two separate stations on the ground with a total surface area of a little more then twice as the earth orbiting station on opposite sides of the planet. Considering that solar panels have to be replaced after a few decades, the expense of, at present, getting things into orbit, the losses from beaming power, and I think this would be cheaper, especially if you built it in two areas that were almost ALWAYS sunny at the equator.
Established Member
A startup company is apparently putting their $ where their mouth is.
Interview with Solaren CEO Gary Spirnak http://www.next100.com/2009/04/inter...en-ceo-gar.php
My favorite thing to hear from this paper is that space solar can be redirected onto land solar arrays during the night.
Reinventing the Solar Power Satellite http://gltrs.grc.nasa.gov/reports/20...004-212743.pdf
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One big issue for space solar power is that it doesn't scale down well. You need a large diameter transmitter in order to get a narrow enough beam, so it's something of an "all or nothing" investment.
Thanks for that link! My favorite thing to hear from this paper is the analysis which suggests it makes more sense to beam power onto hybrid arrays in the morning and afternoon, rather than at night.Originally Posted by Hernalt
I do wonder if Landis's concept could be improved by using a Molniya orbit instead of GEO. A "slab" power satellite in a Molniya orbit could provide morning or afternoon power to two different markets (e.g. New York, Tokyo) so it gets twice as much utilization. Also, it is only 63% the distance of GEO, so the minimum size of the satellite is only 40% the area or mass of the GEO satellite.
So, for example, a Molniya "slab" satellite could provide morning power to New York, and then half a day later it provides morning power to Tokyo. A second such satellite could provide afternoon power to the same markets.
If, someday, night power becomes more economically desirable, then a third satellite could provide New York/Tokyo power at night.
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I do wonder if Landis's concept could be improved by using a Molniya orbit instead of GEO. A "slab" power satellite in a Molniya orbit could provide morning or afternoon power to two different markets (e.g. New York, Tokyo) so it gets twice as much utilization. Also, it is only 63% the distance of GEO, so the minimum size of the satellite is only 40% the area or mass of the GEO satellite.
Actually, the typical 12 hour Molniya orbit has an apogee out near GEO distances.
A Molniya orbit has many advantages over GEO for this application, but as always, there are also disadvantages. The advantages include less energy required to achieve the desired orbit by eliminating the circularization burn and especially the orbital plane change needed for GEO. This is one of the biggest reasons* why the Soviets invented the Molniya communications satellite constellations in the first place (along with better coverage of far northern latitudes). This represents a significant reduction in launch costs. The drawbacks include the need to have 3 satellites in the same orbital plane to provide 24 hour coverage, the need for tracking antennas on the ground instead of fixed antennas for GEO, and the need to design for a more harsh radiation environment because the satellites are crossing the van Allen radiation belts 4 times a day. A paper that discusses this is available here.
*Back in the early 1960s when they were wanting to implement communications satellites, the Soviets lacked a suitable booster to put a payload into GEO from their launch sites. The minimum inclination normally achieveable from Tyuratam (Balkinour) is just over 50 degrees so you have to spend a lot of energy lowing the inclination needed for geostationary satellites. Eventually, they developed their Proton booster with a powerful upper stage to do the job. I remember reading figures years ago that stated the base Proton could put 20 metric tons into LEO at 50 degrees inclination. Add the upper stage and you could put 2 metric tons into GEO, so the upper stage and propellant was 18 metric tons. The energy requirement for GEO was so extreme that they could actually use a Proton to send 5 metric tons to Mars compared to 2 metric tons to GEO.
More info on the Molniya orbit is available here.
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I think LEO tends to give closer to two-thirds than a half of a period of daylight.
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Thanks for the correction. I was trying to calculated it myself in my head, but I stopped calculating when I got to the semi-major axis calculation. Oops! Molniya is elliptical, of course.
Again, thanks for the info! I hadn't thought about the plane change needed for GEO. Am I right in thinking that if there were a suitable launch site on the equator, such a plane change wouldn't be needed?A Molniya orbit has many advantages over GEO for this application, but as always, there are also disadvantages. The advantages include less energy required to achieve the desired orbit by eliminating the circularization burn and especially the orbital plane change needed for GEO. This is one of the biggest reasons* why the Soviets invented the Molniya communications satellite constellations in the first place (along with better coverage of far northern latitudes). This represents a significant reduction in launch costs.
For Landis's proposal, each "slab" satellite only provides power for either the morning hours or afternoon hours anyway. So you don't need 24 hour coverage.The drawbacks include the need to have 3 satellites in the same orbital plane to provide 24 hour coverage, the need for tracking antennas on the ground instead of fixed antennas for GEO, and the need to design for a more harsh radiation environment because the satellites are crossing the van Allen radiation belts 4 times a day. A paper that discusses this is available here.
I'm not clear about whether there's a need for a tracking antenna on the ground. Rectennas should be able to receive power from a good range of angles, as long as the beam fits within the array, right?
The satellite would need an active phased array to aim the beam, though, rather than a simple fixed phased array.
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Again, thanks for the info! I hadn't thought about the plane change needed for GEO. Am I right in thinking that if there were a suitable launch site on the equator, such a plane change wouldn't be needed?
Correct, that's why the ESA launches satellites near the equator at their French Guiena launch site. That location offers a substancial advantage for payloads going to GEO.
I'm not clear about whether there's a need for a tracking antenna on the ground. Rectennas should be able to receive power from a good range of angles, as long as the beam fits within the array, right?
I not certain about the radiation pattern of the rectennass but I do know the narrower the beamwidth, the higher the gain. You can build an antenna to receive RF energy over a range of angles (beamwidth). However, a more narrowly focused beamwidth gives a greater amplification factor (gain). For a GEO satellite, the beam can be very narrow providing high gain. For a Molnitya orbit, the azimuth and elevation is constantly changing. You'd either want your rectennas to have sufficient beamwidth to handle all of the azimuth and elevation range (lower gain) or make the antennas track the satellite (higher gain but higher cost/complexity). The difference can easily exceed 10 dB (a factor of 10 amplification).
For Landis's proposal, each "slab" satellite only provides power for either the morning hours or afternoon hours anyway. So you don't need 24 hour coverage.
Given the cost of the satellites themselves, this would greatly lengthen the time required to recoup your investment. The satellites along with their launch costs are almost certainly the biggest expense in the whole enterprise, so it makes sense to get as much power from them as possible. That's why I liked the notion of a 12 hour Molniya orbit. You could sell power in two different locations (say the US and Asia) every day. Three satellites in the same orbit spaced 120 degrees apart would provide 24 hours of base power a day, giving you a greater opportunity to recoup your investment.
Banned
The beaty of phased array is that the sending and recieving antennas need not be on the same plane, or even artificially "synched" at the transmitter. While that's more efficient for minimizing beam dispersal, it's possible to synch each recentenna element for the incoming beam. It's costly, though, both in terms of electronics as well as power loss.
It's a simple matter to adjust the phase of the sending antenna such that it's received in phase on the ground by passively coupled elements.
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Phased array antennas are great things. I don't know if they'd provide the kind of gain that's possible with a form of tracking rectenna arrangement or not. That would be a good engineering trade study. The RF energy from a solar power satellite will be dispersed over a fairly wide area and will be pretty weak. Going from a 30 dB gain to 40 dB gain gives you 10 times the RF energy, so the extra complexity of the tracking array might be worth it. The greatest antenna gain that I've ever seen was on a 60 foot diameter dish antenna used for satellite command & control. It had a gain of 63 dB (factor of 2 million) but the beamwidth was only about 0.1 degree.
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