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Respectfully, I believe you are inaccurate on both accounts, sun synchronous orbits (SSO) only have no eclipse if their orbital plane is within a very degrees o

Respectfully, I believe you are inaccurate on both accounts, sun synchronous orbits (SSO) only have no eclipse if their orbital plane is within a very degrees of the terminator, this of course widens with altitude but there exists far more possible SSOs with eclipses than without. Secondly with GEOs as with any very high altitude orbit the eclipse time trends towards zero so effectively at a GEO the eclipse time is minimal compared to the illuminated time. Of note the length for the eclipse time of GEO varies throughout the year.

spacemark 3y ago
Respectfully, you are not correct that eclipse in Geo is insignificant. It drives many engineering constraints for spacecraft systems. Look I get why people are excited about space space solar power, but I've been in this industry for 15 years and when you dig into the numbers and understand the realities of spacecraft engineering, SBSP just seems like a fool's errand. It may not always be that way, but the technical challenges are extreme and costs are still nowhere near what would be required to make it work. You can chalk my comments up to a grumpy engineer tired of the cyclical SBSP pushes that never go anywhere.
- mecko23 3y ago
  Hmm, well I totally understand how it drives spacecraft design and I don’t know off the top of my head the length of greatest eclipse but it cannot be greater than a small fraction of the period (upwards of 1/12). This is significant for a spacecraft itself but as far as a regionally integrated power grid is concerned it is a clear improvement over current solar PV systems. I get that there maybe some fatigue here with the idea and blue sky optimism that comes with SBSP, I think there are valid criticisms to level at it orbit selection and corresponding ground tracks and eclipses are not one.
- mlyle 3y ago
  > It drives many engineering constraints for spacecraft systems. Here the only thing it's going to drive are thermal requirements-- which are admittedly significant problems. There's no need to continue to use large amounts of power for comms, etc, like on most GEO birds. And, of course, the grid needs to deal with the power disappearing for an hour in the middle of the night for short periods of the year.
  - spacemark 3y ago
    It drives electrical and battery system requirements more than anything else. Thermal effects impact pointing/ADCS, which impacts propulsion, etc.
    - mlyle 3y ago
      There's no real intrinsic electrical or battery system requirements for a giant solar power satellite. The energy use is comparably trivial: no big transponders to run in eclipse like a comsat. But you do need everything to survive the cold and thermal cycling.
      - giantrobot 3y ago
        Not just thermal cycling but a giant solar collector is literally a giant solar sail. There would be significant force applied to a giant collector. You'd need propulsion to maintain position and orientation. You'd also need a number of propulsion units to balance solar pressure gradients as the collector entered and existed the Earth's shadow as well as the thermal expansion/contraction of the structure. It's likely not a lot of power but a non-trivial amount of fuel.
        mlyle 3y ago
        You probably maintain orientation with a control moment gyro and periodically desaturate it with thrust. You also use thrust to reboost and stay in orbital slot. High-impulse ion engines, etc, are a good match for this task.
        dabluecaboose 3y ago
        This is exactly how the NOAA GOES sats work. Every day at a proscribed time we used to desaturate the reaction wheels, so they could more or less keep running constantly and keep the satellite pointing where it should be.

spacemark 3y ago

Respectfully, you are not correct that eclipse in Geo is insignificant. It drives many engineering constraints for spacecraft systems. Look I get why people are excited about space space solar power, but I've been in this industry for 15 years and when you dig into the numbers and understand the realities of spacecraft engineering, SBSP just seems like a fool's errand. It may not always be that way, but the technical challenges are extreme and costs are still nowhere near what would be required to make it work. You can chalk my comments up to a grumpy engineer tired of the cyclical SBSP pushes that never go anywhere.

mecko23 3y ago
Hmm, well I totally understand how it drives spacecraft design and I don’t know off the top of my head the length of greatest eclipse but it cannot be greater than a small fraction of the period (upwards of 1/12). This is significant for a spacecraft itself but as far as a regionally integrated power grid is concerned it is a clear improvement over current solar PV systems. I get that there maybe some fatigue here with the idea and blue sky optimism that comes with SBSP, I think there are valid criticisms to level at it orbit selection and corresponding ground tracks and eclipses are not one.
mlyle 3y ago
> It drives many engineering constraints for spacecraft systems. Here the only thing it's going to drive are thermal requirements-- which are admittedly significant problems. There's no need to continue to use large amounts of power for comms, etc, like on most GEO birds. And, of course, the grid needs to deal with the power disappearing for an hour in the middle of the night for short periods of the year.
- spacemark 3y ago
  It drives electrical and battery system requirements more than anything else. Thermal effects impact pointing/ADCS, which impacts propulsion, etc.
  - mlyle 3y ago
    There's no real intrinsic electrical or battery system requirements for a giant solar power satellite. The energy use is comparably trivial: no big transponders to run in eclipse like a comsat. But you do need everything to survive the cold and thermal cycling.
    - giantrobot 3y ago
      Not just thermal cycling but a giant solar collector is literally a giant solar sail. There would be significant force applied to a giant collector. You'd need propulsion to maintain position and orientation. You'd also need a number of propulsion units to balance solar pressure gradients as the collector entered and existed the Earth's shadow as well as the thermal expansion/contraction of the structure. It's likely not a lot of power but a non-trivial amount of fuel.
      - mlyle 3y ago
        You probably maintain orientation with a control moment gyro and periodically desaturate it with thrust. You also use thrust to reboost and stay in orbital slot. High-impulse ion engines, etc, are a good match for this task.
        dabluecaboose 3y ago
        This is exactly how the NOAA GOES sats work. Every day at a proscribed time we used to desaturate the reaction wheels, so they could more or less keep running constantly and keep the satellite pointing where it should be.