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danielravennest t1_j1edfe7 wrote

Reply to comment by call_Back_Function in Northrop Grumman clears key hurdle for space-based solar power by PhyneasPhysicsPhrog

Terrestrial solar has the same first two steps (solar > electric). But satellites in space get 36% more solar energy per square meter because no atmospheric absorption, and 3-8 times the operating hours depending on location, because no night or weather.

So you are starting out with a big advantage. There are efficiency losses going to RF and back to electric, and then there is cost. Launching to space has been way too expensive to make this idea work.

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call_Back_Function t1_j1edtqa wrote

Don’t forget the inverse square law. The bigger the distance transmission the bigger receiver you need.

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danielravennest t1_j1eppyn wrote

The Raleigh Criterion (1.22 lambda/D) is what sets the beam angle. Lambda is the wavelength, and D is the transmitter diameter. The larger the transmitter, the tighter the beam.

Since the beam spreads as a circle and travels in a straight line, the diameter grows with distance, and beam area grows as distance squared. Total beam energy is constant at any distance till you hit the atmosphere.

The beam intensity goes as the inverse square because the area goes as the square and the total energy is constant. So that is a derived value from the physics.

For a reasonable size satellite and ground antenna, therefore you want the highest reasonable frequency and the lowest reasonable orbit.

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