Myths

Safety

The use of microwave transmission of power has been the most controversial issue in considering any SPS design, but any thought that anything which strays into the beam's path will be incinerated is an extreme misconception. Consider that quite similar microwave relay beams have long been in use by telecommunications companies world wide without such problems.

At the earth's surface, a suggested microwave beam would have a maximum intensity, at its center, of 23 mW/cm² (less than 1/4 the solar irradiation constant), and an intensity of less than 1 mW/cm² outside of the rectenna fenceline^[41] (10 mW/cm² is the current United States maximum microwave exposure standard). In the United States, the workplace exposure limit (10 mW/cm²) is at present, per the Occupational Safety and Health Act (OSHA)^[53], expressed in voluntary language and has been ruled unenforceable for Federal OSHA enforcement.

The beam's most intense section (more or less, at its center) is far below dangerous levels even for an exposure which is prolonged indefinitely. ^[54] Furthermore, exposure to the center of the beam can easily be controlled on the ground (eg, via fencing), and typical aircraft flying through the beam provide passengers with a protective metal shell (ie, a Faraday Cage), which will intercept the microwaves. Other aircraft (balloons, ultralight, etc) can avoid exposure by observing airflight control spaces, as is currently done for military and other controlled airspace. Over 95% of the beam energy will fall on the rectenna. The remaining microwave energy will be absorbed and dispersed well within standards currently imposed upon microwave emissions around the world.^[55]

The microwave beam intensity at ground level in the center of the beam would be designed and physically built into the system; simply, the transmitter would be too far away and too small to be able to increase the intensity to unsafe death ray levels, even in principle.

In addition, a design constraint is that the microwave beam must not be so intense as to injure wildlife, particularly birds. Experiments with deliberate microwave irradiation at reasonable levels have failed to show negative effects even over multiple generations. ^[56]

Some have suggested locating rectennas offshore ^[57][58], but this presents serious problems, including corrosion, mechanical stresses, and biological contamination.

A commonly proposed approach to ensuring fail-safe beam targeting is to use a retrodirective phased array antenna/rectenna. A "pilot" microwave beam emitted from the center of the rectenna on the ground establishes a phase front at the transmitting antenna. There, circuits in each of the antenna's subarrays compare the pilot beam's phase front with an internal clock phase to control the phase of the outgoing signal. This forces the transmitted beam to be centered precisely on the rectenna and to have a high degree of phase uniformity; if the pilot beam is lost for any reason (if the transmitting antenna is turned away from the rectenna, for example) the phase control value fails and the microwave power beam is automatically defocused.^[59] Such a system would be physically incapable of focusing its power beam anywhere that did not have a pilot beam transmitter.

It is important for system efficiency that as much of the microwave radiation as possible be focused on the rectenna. Outside of the rectenna, microwave intensities would rapidly decrease, so nearby towns or other human activity should be completely unaffected.^[59]

The long-term effects of beaming power through the ionosphere in the form of microwaves has yet to be studied, but nothing has been suggested which might lead to any significant effect.

[edit] Atmospheric damage due to launches

When rockets launch through the atmosphere the hot rocket exhaust reacts with the atmospheric nitrogen and can form nitrogen compounds. In particular these nitrogen compounds are problematic when they form in the the stratosphere as they can damage the ozone layer. However, the environmental effect of rocket launches is negligible compared to higher volume polluters, such as airplanes and automobiles.

[edit] Increased global warming

The entire point of a solar power satellite is to increase the amount of solar energy reaching earth. This extra energy will eventually be dissipated as heat. Depending on the scale of operations, this might or might not have a significant effect. No theories to date claim that waste heat from human power generation are a significant cause of global warming, nor would it be for the foreseeable future. The most widely promoted theory connecting human activity to global warming is that increased greenhouse gases (e.g. carbon dioxide and methane) are causing the natural heat from the Sun to be trapped so it cannot radiate to space, thus increasing the temperature of the planet. Space solar power would contribute greatly to reduction of greenhouse gases.

Rectenna power conversion efficiency would be better than 90%, so waste heat from the rectennas would be considerably less than from most other common power sources, e.g. nuclear and fossil fuels which generate much more waste heat.

[edit] In fiction

• Space stations transmitting solar power have appeared in science-fiction works like Isaac Asimov's Reason (1941), that centers around the troubles caused by the robots operating the station.
• Solar Power Satellites have also been seen in the work of author Ben Bova's novels "Powersat" and "Colony".
• In Sid Meier's Alpha Centauri, an endgame 'building' that fulfills the same function as an SPS is the 'Orbital Power Transmitter' which provides every city that you own with a unit of energy per satellite launched, providing the city has an Aerospace Command building or your faction controls the Space Elevator. Building multiple Orbital Power Transmitters provides massive bonuses to energy generation and soon pay for themselves many times over.
• Much of the conflict in the anime series Mobile Suit Gundam 00 arose from the construction of three space-based solar power systems and orbital elevators in a post-fossil fuels society.
• In both SimCity 2000 and 3000, plants that improvised solar satellite technology called microwave powerplants were available in the future. The plant was discontinued in SimCity 4 but several fan-made microwave powerplants were available on various SimCity 4 fan-sites.
• Solar Sats are used in the online browser-based game ogame. They are a means to supply power to planet production.