4 ms·

The atmosphere is fairly transparent to microwaves, so the loss shouldn't be much worse. The book The Case for Space Solar Panel cited net efficiency of 40% wit

The atmosphere is fairly transparent to microwaves, so the loss shouldn't be much worse. The book The Case for Space Solar Panel cited net efficiency of 40% with the tech at the time it was written, with a theoretical maximum of 60%. It's a pretty good deal given that a panel in geostationary collects five times as much energy in 24 hours as the same panel on the ground, and the power flows 24/7 for most of the year with no need for storage.

scythe 5y ago
We're a long way from geostationary orbit with this tech, though. They got 1 km, now you need 35,000.
- giantg2 5y ago
  I guess it depends on how tight the maser beam stays. Most of that 35k km has little to no atmosphere, so that part is a little less important.
  - scythe 5y ago
    There's an equation for that. The effective range of a Gaussian beam is roughly equal to (beam width)^2 / wavelength. I'm not sure what wavelength or beam width they used here, though.
    - engineer_22 5y ago
      10Ghz from the article, and photo of the target appears to be 3 meters square
      - scythe 5y ago
        That means they're right at the Rayleigh length. You'd need a significantly wider beam or higher frequency to send power from orbit. https://en.wikipedia.org/wiki/Rayleigh_length https://en.wikipedia.org/wiki/Rayleigh_length
        DennisP 5y ago
        In fact, SPS designs involve receivers measured in square kilometers. But they'd be mostly wire and would only contribute about 0.7 cents/kWh to the cost.
  - deleted 5y ago
    [deleted]
  - pfdietz 5y ago
    Why do you think it's a maser? High power microwave beams are a thing in radar. We don't use masers to make them. We don't use masers in microwave ovens, either, or in industrial applications requiring high power microwaves.
walrus01 5y ago
I'd question whether anyone writing "the atmosphere is fairly transparent to microwaves" has calculated the link budget, then implemented in the real world an FCC part 101 licensed microwave radio system (example: 1024QAM modulation, 11 GHz standard FDD band plan, +16 Tx power, 80 MHz channels H&V dual linear, 35 km, 180 cm high performance dishes both ends) and seen the path loss in reality. I think anyone that's done terrestrial point to point microwave telecom professionally will take a very skeptical view of things like 10 GHz band, 1 km power "beams". the reality is that the atmosphere absolutely eats microwave, and when it's not eating it, you have temperature inversions, ducting and diffraction effects to take into account at long distances as well. this is why their demo only works at 1.0 km.
- DennisP 5y ago
  Indeed. Such a writer may, however, have read up on studies on expected losses for the frequencies proposed for SPS. The book I mentioned covers a lot, but a paper I just googled is available on scihub at your discretion. Here's the abstract: https://www.tandfonline.com/doi/abs/10.1080/00222739.1970.11688771 https://www.tandfonline.com/doi/abs/10.1080/00222739.1970.11... The paper is published in the Journal of Microwave Power, proposes using a wavelength around 10 cm, and with a vertical beam calculates a loss of 1% in clear skies and up to 10% loss with rain.

scythe 5y ago

We're a long way from geostationary orbit with this tech, though. They got 1 km, now you need 35,000.

giantg2 5y ago
I guess it depends on how tight the maser beam stays. Most of that 35k km has little to no atmosphere, so that part is a little less important.
- scythe 5y ago
  There's an equation for that. The effective range of a Gaussian beam is roughly equal to (beam width)^2 / wavelength. I'm not sure what wavelength or beam width they used here, though.
  - engineer_22 5y ago
    10Ghz from the article, and photo of the target appears to be 3 meters square
    - scythe 5y ago
      That means they're right at the Rayleigh length. You'd need a significantly wider beam or higher frequency to send power from orbit. https://en.wikipedia.org/wiki/Rayleigh_length https://en.wikipedia.org/wiki/Rayleigh_length
      - DennisP 5y ago
        In fact, SPS designs involve receivers measured in square kilometers. But they'd be mostly wire and would only contribute about 0.7 cents/kWh to the cost.
- deleted 5y ago
  [deleted]
- pfdietz 5y ago
  Why do you think it's a maser? High power microwave beams are a thing in radar. We don't use masers to make them. We don't use masers in microwave ovens, either, or in industrial applications requiring high power microwaves.

walrus01 5y ago

I'd question whether anyone writing "the atmosphere is fairly transparent to microwaves" has calculated the link budget, then implemented in the real world an FCC part 101 licensed microwave radio system (example: 1024QAM modulation, 11 GHz standard FDD band plan, +16 Tx power, 80 MHz channels H&V dual linear, 35 km, 180 cm high performance dishes both ends) and seen the path loss in reality. I think anyone that's done terrestrial point to point microwave telecom professionally will take a very skeptical view of things like 10 GHz band, 1 km power "beams". the reality is that the atmosphere absolutely eats microwave, and when it's not eating it, you have temperature inversions, ducting and diffraction effects to take into account at long distances as well. this is why their demo only works at 1.0 km.

DennisP 5y ago
Indeed. Such a writer may, however, have read up on studies on expected losses for the frequencies proposed for SPS. The book I mentioned covers a lot, but a paper I just googled is available on scihub at your discretion. Here's the abstract: https://www.tandfonline.com/doi/abs/10.1080/00222739.1970.11688771 https://www.tandfonline.com/doi/abs/10.1080/00222739.1970.11... The paper is published in the Journal of Microwave Power, proposes using a wavelength around 10 cm, and with a vertical beam calculates a loss of 1% in clear skies and up to 10% loss with rain.