Solar Power Satellites
CNN had an article up today that was a bit of a blast from the past.
How to harvest solar power? Beam it down from space!
This is something of a blast for me since I did a major report for school (High School I think) on the topic of solar power satellites. As the article says:
That would be during the last energy crisis. As it happens I read some of those reports for that report for school. Since this would have been written around 1992, we were deep in the throws of cheap oil. Desert Storm caused major oil spikes and crashes, but not the sustained high prices we've got going on right now.
As the article says, there are some major engineering challenges in getting solar power satellites (SPS) working. The first is on-orbit assembly. Our robotics are getting a heck of a lot better these days. Better enough that with a concerted effort we could create the technologies to launch modular sections of a larger SPS and have them lock together on orbit, probably within 10 years if we focus. That's just one of the major issues.
The second major issue is how to get the electrical power from orbit to the ground. A 22,000 mile long transmission cable is not in the cards, so you have to use some for of wireless method. The method identified in those 1970's reports was a form of microwave transmission. Like regular sunlight, it does suffer atmospheric losses as it transits the atmosphere, around 7% on clear day if I remember right. Clouds do affect the microwave transmission, though not nearly to the level of visible light.
Another thing to keep in mind is that this isn't the same microwaves you have in your kitchen. Those have been specifically tuned to a frequency that vibrates water. The frequency used to transmit satellite radio (Sirius and XM) is also a microwave, as are the frequencies used for WiFi networks. When the SPS idea gained some traction in the early 1980's environmentalists got up in arms about the idea of birds getting into the beam path and exploooooooding! This is a misunderstanding of how microwaves work, but the image stuck.
The effects of microwaves of that power-level, not frequency, has been studied. When I was writing that report, some studies done during WWII on military ships experimenting with RADAR inadvertently exposed certain people to very high levels of microwave radiation. These are not studies that can be done any more, scientific standards have increased markedly since then, but it is still data. More work needs to be done to fully quantify the effect of high power-level microwaves on mammals.
The third engineering challenge is the microwave receiver. These rectennas will have to receive a beam originated 22,000 miles away. While newer technology may mean that we can narrow the beam scatter more than was possible in the 70's, it still means a rectenna with a diameter measurable in kilometers. It is possible to construct rectennas that large, some of those early reports suggested farming would still be possible under them, but it does require a commercial aviation no-fly zone above the device.
One of the prime reason cited for putting large solar arrays into space is because light there isn't subjected to the same atmospheric scattering light here on the ground gets. Or at least, that was the reason cited back in the day. Now, better reasons are that solar arrays in space don't have to worry about night, clouds, or finding enough real-estate to plant them. The truly grandiose think on large scales, such as this quote from the article:
That "kilometer-wide band" would have to be a bit over 163,000 miles long. This is not feasible within my lifetime. I suspect this quote was used to illustrate the power available out there, and I strongly suspect their assumption was a 100% light to energy conversion ratio which we simply can't do right now.
In short, SPS are feasible if we focus on the technologies to bring them about. There will be environmental push-back due to the microwave beam required to transmit the energy to the ground, which will further limit their applicability. As we develop cheaper heavy lift capacity at our space-ports, it becomes easier to get the hardware up there in the first place. It'll take significant investment of funds by someone to do it, though.
How to harvest solar power? Beam it down from space!
This is something of a blast for me since I did a major report for school (High School I think) on the topic of solar power satellites. As the article says:
NASA and the United States Department of Energy studied the concept throughout the 1970s, concluding that although the technology was feasible, the price of putting it all together and sending it to outer space was not.
That would be during the last energy crisis. As it happens I read some of those reports for that report for school. Since this would have been written around 1992, we were deep in the throws of cheap oil. Desert Storm caused major oil spikes and crashes, but not the sustained high prices we've got going on right now.
As the article says, there are some major engineering challenges in getting solar power satellites (SPS) working. The first is on-orbit assembly. Our robotics are getting a heck of a lot better these days. Better enough that with a concerted effort we could create the technologies to launch modular sections of a larger SPS and have them lock together on orbit, probably within 10 years if we focus. That's just one of the major issues.
The second major issue is how to get the electrical power from orbit to the ground. A 22,000 mile long transmission cable is not in the cards, so you have to use some for of wireless method. The method identified in those 1970's reports was a form of microwave transmission. Like regular sunlight, it does suffer atmospheric losses as it transits the atmosphere, around 7% on clear day if I remember right. Clouds do affect the microwave transmission, though not nearly to the level of visible light.
Another thing to keep in mind is that this isn't the same microwaves you have in your kitchen. Those have been specifically tuned to a frequency that vibrates water. The frequency used to transmit satellite radio (Sirius and XM) is also a microwave, as are the frequencies used for WiFi networks. When the SPS idea gained some traction in the early 1980's environmentalists got up in arms about the idea of birds getting into the beam path and exploooooooding! This is a misunderstanding of how microwaves work, but the image stuck.
The effects of microwaves of that power-level, not frequency, has been studied. When I was writing that report, some studies done during WWII on military ships experimenting with RADAR inadvertently exposed certain people to very high levels of microwave radiation. These are not studies that can be done any more, scientific standards have increased markedly since then, but it is still data. More work needs to be done to fully quantify the effect of high power-level microwaves on mammals.
The third engineering challenge is the microwave receiver. These rectennas will have to receive a beam originated 22,000 miles away. While newer technology may mean that we can narrow the beam scatter more than was possible in the 70's, it still means a rectenna with a diameter measurable in kilometers. It is possible to construct rectennas that large, some of those early reports suggested farming would still be possible under them, but it does require a commercial aviation no-fly zone above the device.
One of the prime reason cited for putting large solar arrays into space is because light there isn't subjected to the same atmospheric scattering light here on the ground gets. Or at least, that was the reason cited back in the day. Now, better reasons are that solar arrays in space don't have to worry about night, clouds, or finding enough real-estate to plant them. The truly grandiose think on large scales, such as this quote from the article:
And so has a 2007 report released by the Pentagon's National Security Space Office, encouraging the U.S. government to spearhead the development of space power systems.
"A single kilometer-wide band of geosynchronous Earth orbit experiences enough solar flux in one year to nearly equal the amount of energy contained within all known recoverable conventional oil reserves on Earth today," the report said.
That "kilometer-wide band" would have to be a bit over 163,000 miles long. This is not feasible within my lifetime. I suspect this quote was used to illustrate the power available out there, and I strongly suspect their assumption was a 100% light to energy conversion ratio which we simply can't do right now.
In short, SPS are feasible if we focus on the technologies to bring them about. There will be environmental push-back due to the microwave beam required to transmit the energy to the ground, which will further limit their applicability. As we develop cheaper heavy lift capacity at our space-ports, it becomes easier to get the hardware up there in the first place. It'll take significant investment of funds by someone to do it, though.
posted by Corwin at 8:28 AM
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