This limitation is far more critical than the ANSI standard. It is because this assumption ignores many physiological and physical parameters such as the beam scattering in the eye and the nystagmus. Therefore, the ANSI standard based on epidemiological and pathological data is more practical in this case. Under a condition based on the ANSI standard, a laser beam must be expanded to less than about 10'3 [mW/cm2] on the ground. Then, 10 MW power transmission requires at least 103 [km2]. Though this size of receiver is almost the same as the predicted size of the rectenna which will receive microwaves of comparable power, this light receiver must not have any slit or hole nor any obstacles in it. Therefore, this time, the existence of so large a receiver (more than 30 [km] x 30 [km]) will cause ecological problems, because it will affect the local climates in some aspects such as humidity, wind speed, local reflection rate of solar light, and so on. The Thermal Effect of the Laser Beam On average, the human body surface emits 100 W energy over time. In case of exposure to the laser beam from the beaming satellite, if he or she is naked, the person's body receives the beam only on half of the body surface, which bears 50 W of daily heat emission. The energy of visible light is absorbed mainly in the skin surface. This is the most different feature of laser beams in comparison to microwaves. The peak power production of the human body is around 1 kW but its duration is not long. Therefore, human skin can tolerate heating up to 10 times of the internal heat production, for a while. In this case, half the body surface receives 500 W radiation and estimating the body cross section area as 0.3 m2, the allowable radiation density is : This is about 1.4 times the solar constant and is tolerable to the human body in short duration. The use of protection suits to reflect visible light is recommended for humans. But of course, no animal can use their eye under the laser radiation of this power because even the scattering light is harmful to their retina. However, the area of the receiver can be reduced to several square kilometers. Conclusion and Advice about the Usage of Laser Beam If we want to avoid any kind of biological hazard caused by misdirection of beaming, the power density should be less than 10'6 [W/cm2] to prevent damage on animal retina in the case of misdirection of the laser beam. In this case, the size of the receiver becomes so large that it should be divided into small pieces scattered over large area on the Earth to avoid ecological effects. If it is possible to ignore the effects on unprotected animal eyes, we can use a much stronger beam (up to 10'1 [W/cm2]). This time, we must consider the possibility of local biome change caused by the additional heating, up to the solar constant power. And the misdirecting of the beam onto animals will cause the loss of visual ability in a large part of the visual field and decrease the survival rate of the animal (including humans). The decrease or increase of some kinds of insects will also affect the plant composition in the area. The excess heat effect changing the local biome depends on the efficiency of the receiver. Energy Emission in and from the Rectenna Site Whether the energy from the power satellite is conveyed on the Earth by laser or microwaves, all the additional energy which has failed to be converted at the receiver or the rectenna is exhausted as heat into the atmosphere. At the highest level, this effect can be classified into the following three groups. 1) If the amount of excess energy is small enough, there is no effect on biota. 2) If it is not strong enough to perish the whole of the ecosystem, new biota which is adapted to the existence of the beam will emerge. 3) If it is strong enough, complete death of the ecological system in the area will occur. One of the problems of the energy transportation system design is which condition among the three above should be selected. The answer will be different depending on the scale of the total system of the rectenna site. If it is an experimental or preliminary system which can be done in a small
RkJQdWJsaXNoZXIy MTU5NjU0Mg==