Orbital Power Plant Dummies' Guide

* Solar radiation, radio waves, microwaves and lasers are all forms of electromagnetic energy. They're distinguished by wavelength and frequency: long wavelengths equal short frequencies. Also, the shorter the frequency, the higher the energy per unit time (because more waves will arrive per second, for example).

* Radio waves have the longest wavelengths, followed by microwaves. Solar radiation is made up of infrared, visible and ultraviolet light, at intermediate wavelengths. Finally, X-rays and gamma rays have very short wavelengths and high frequencies.

* Electromagnetic waves of any frequency will transmit energy to a surface by heating it, providing that surface absorbs those wavelengths. For example, in the visible spectrum, white objects are white because they reflect all wavelengths of light and they do not therefore experience much heating from visible wavelengths. Black items, on the other hand, absorb all wavelengths and therefore absorb heat much more efficiently.

* Solar radiation is made up of infrared radiation (52 percent), ultraviolet radiation (9 percent) and visible light (38 percent) plus tiny amounts at other wavelengths. This distribution occurs at the top of the atmosphere, as well as in space; it is also the distribution of wavelengths that any space solar system must take advantage of.

* As solar radiation encounters the atmosphere, it interacts with various molecules and particles in a variety of ways, which changes the proportion of wavelengths of the total radiation received on the ground (or at any altitude in between).

* Two main processes are molecular absorption — whereby certain wavelengths are absorbed by certain molecules and gases; and scattering — which is when light of a certain wavelength is reflected or refracted by particles that have a diameter very close to that wavelength.

* Ultraviolet radiation interacts particularly with ozone, by molecular absorption. Thanks to ozone, the harmful effects of UV radiation are limited to sunburn in most cases, though skin cancer could become more of a problem if ozone continues to be depleted near the poles.

* Visible light is affected by the same processes, but in general, more of it gets through. The sky is blue because the wavelength of blue light happens to be close to the size of many particles in the air — nitrogen and oxygen molecules — so it is scattered.

* Other scattering effects explain why sunsets are red, and clouds are white. Other wavelengths are also selectively absorbed and scattered, but much of the visible light gets through to the surface. However, on cloudy days, there is a lot more scattering — of both visible and infrared wavelengths — so it gets colder on the ground (and solar panels don't receive as much energy).

* Therefore, the balance of wavelengths received at the surface is completely different from the balance in space. Essentially, a lot more infrared radiation is available in space, whereas on Earth's surface the bulk of radiation is in the visible band.