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Solar power satellites are a hypothetical future technology that could provide abundant free energy to the people of Earth. The concept involves placing large (50-100 km2) solar panels in high earth orbit to gather sunlight there and beam it down to a rectenna on the Earth, from which it can be distributed and used. Since the shadow of the Earth would rarely obscure the sun from such satellites, and are located outside of out photon-blocking atmosphere, a given square kilometer of solar panel in space would gather about 5 times more power than a panel exploiting the same area on Earth.
According to calculations performed thus far, it is estimated that solar satellites would provide about a gigawatt of power per 10 square kilometers (3.86 square miles) of panel. The availability of nuclear power makes it dubious that solar satellites will ever really be necessary, but the concept is still interesting for consideration. Thinking about such concepts helps us get creative when it comes to energy.
Solar satellites would need actuators to keep them pointed towards the sun at all times. Autonomous robotics to provide maintenance could be useful. A substantial obstacle to the deployment of solar satellites are present-day launch costs: they are too darn high. At $3,000 US Dollars (USD) per one pound (0.45 kg), a solar satellite weighing hundreds or thousands of tons is a non-starter. There are two plausible workarounds: lowered launch costs, which could bring down the price of launch such that putting the satellite up there is economically sane, or space-based manufacturing with local materials, such as lunar regolith or near-earth asteroids (NEOs). Turning NEOs into solar satellites and space colonies would be a good way to ensure that they don't crash uncontrollably into the Earth one day.
One reason why people may be even more testy about solar satellites as a source of power than they are about nuclear plants is that a suitably constructed solar satellite could be used as a weapon. The means of power conveyance from space to Earth is through a microwave beam. If made diffuse enough, such a beam would be completely harmless. You could stand right in it without any ill effects. But if owned or taken control of by an unscrupulous regime, a solar satellite could be turned into a wave cannon of doom.
If constructed closer to the Sun, solar satellites could extract even more power. The intensity of light increases exponentially as you move closer to the center of the Solar System. One day solar satellites could be built in huge numbers around the Sun, forming the beginnings of a Dyson sphere.
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