4 ms·

The headlight vs. sun comparison (which I think was an edit?) is irrelevant because we're comparing the amount of energy deliverable over distance. The energy

The headlight vs. sun comparison (which I think was an edit?) is irrelevant because we're comparing the amount of energy deliverable over distance. The energy delivered by the sun (at a tenable band) vs. the energy delivered by the remote transmitter on earth, after the 'link budget' has been applied (taking into account distance, atmospheric attenuation, and so on) are the two things that need to be compared.

h2odragon 5y ago
I beg you pardon, im not arguing for the idea of a earth to moon microwave power link as viable. or sensible. I think it's beautifully insane, i have severe doubts about the actual practicality of such a thing, etc. But thats the thing: now i want to do a mad max maser on a truck with maybe dozens of magnetrons if i could tow a generator... It fits with my "Orbital Slingshot" project so well, too.
- hereforphone 5y ago
  What is your Orbital Slingshot project?
  - h2odragon 5y ago
    I'm glad you asked :) It's a totally silly idea to built a big ass slingshot that throws things as high as possible. I figure calling it an "Orbital Slingshot" makes it at least as viable and investment worthy as some of the other efforts [1] and [2] forex. If I can get my daughter to do some artwork I might fire up a web page for it finally. [1] https://www.space.com/23015-slingatron-reusable-launch-system.html https://www.space.com/23015-slingatron-reusable-launch-syste... [2] https://www.nextbigfuture.com/2018/02/spinlaunch-is-using-large-centrifuges-to-accelerate-to-payloads-into-space-target-500000-per-launch.html https://www.nextbigfuture.com/2018/02/spinlaunch-is-using-la...
deleted 5y ago
[deleted]
rrss 5y ago
Ok, check my math. basics: solar constant: 1.36 kW / m^2 earth-to-moon range: 400 km parameters from the article: frequency: 5 GHz -> wavelength: 6cm earth antenna array linear dimension: 200 km transmit power density: 100 W/m^2 Let's assume that the earth antenna array elements are 50m wide, and spaced out such that they cover 1% of the total 200km * 50m area, for a total antenna aperture of 1e5 square meters (10% of the SKA). Combining the stated transmit power density of 100 W/m^2 with the antenna area, we get a total transmit power of 10 MW. Throw it at Friis: power density at moon = transmit power * earth antenna area / (range^2 * wavelength^2) = 10e6 watts * 1e5 m^2 / ( 400e3^2 m^2 * 0.06^2 m^2) = 1.73 kW / m^2 Atmospheric attenuation at 5 GHz is pretty minimal. If we conservatively assume 20% loss, I think we still end up with a higher power density at a single frequency than from the sun across the entire spectrum. I don't think anything like this will ever be built, but I don't see why it is impossible. Where's the mistake?
- inglor_cz 5y ago
  > earth-to-moon range: 400 km Three zeros seem to be missing.
  - rrss 5y ago
    yikes, thank you

h2odragon 5y ago

I beg you pardon, im not arguing for the idea of a earth to moon microwave power link as viable. or sensible. I think it's beautifully insane, i have severe doubts about the actual practicality of such a thing, etc. But thats the thing: now i want to do a mad max maser on a truck with maybe dozens of magnetrons if i could tow a generator... It fits with my "Orbital Slingshot" project so well, too.

hereforphone 5y ago
What is your Orbital Slingshot project?
- h2odragon 5y ago
  I'm glad you asked :) It's a totally silly idea to built a big ass slingshot that throws things as high as possible. I figure calling it an "Orbital Slingshot" makes it at least as viable and investment worthy as some of the other efforts [1] and [2] forex. If I can get my daughter to do some artwork I might fire up a web page for it finally. [1] https://www.space.com/23015-slingatron-reusable-launch-system.html https://www.space.com/23015-slingatron-reusable-launch-syste... [2] https://www.nextbigfuture.com/2018/02/spinlaunch-is-using-large-centrifuges-to-accelerate-to-payloads-into-space-target-500000-per-launch.html https://www.nextbigfuture.com/2018/02/spinlaunch-is-using-la...

deleted 5y ago

[deleted]

rrss 5y ago

Ok, check my math. basics: solar constant: 1.36 kW / m^2 earth-to-moon range: 400 km parameters from the article: frequency: 5 GHz -> wavelength: 6cm earth antenna array linear dimension: 200 km transmit power density: 100 W/m^2 Let's assume that the earth antenna array elements are 50m wide, and spaced out such that they cover 1% of the total 200km * 50m area, for a total antenna aperture of 1e5 square meters (10% of the SKA). Combining the stated transmit power density of 100 W/m^2 with the antenna area, we get a total transmit power of 10 MW. Throw it at Friis: power density at moon = transmit power * earth antenna area / (range^2 * wavelength^2) = 10e6 watts * 1e5 m^2 / ( 400e3^2 m^2 * 0.06^2 m^2) = 1.73 kW / m^2 Atmospheric attenuation at 5 GHz is pretty minimal. If we conservatively assume 20% loss, I think we still end up with a higher power density at a single frequency than from the sun across the entire spectrum. I don't think anything like this will ever be built, but I don't see why it is impossible. Where's the mistake?

inglor_cz 5y ago
> earth-to-moon range: 400 km Three zeros seem to be missing.
- rrss 5y ago
  yikes, thank you