Mirrors in the sky: Status, sustainability, and some supporting materials experiments

This paper critically reviews the state of the art of an approach to supply energy to earth from space mirrors that would be placed in orbit with angle control to reflect solar radiation to specific sites on earth for illumination, and also presents our (i) optical and mechanical tests to examine the property changes at a cryogenic temperature of thin film mirror that we manufactured, (ii) economic analysis related to several applications, and (iii) leading issues that must be taken into account in the sustainability analysis of the concept. The space mirrors were proposed to be of the order of a square kilometer or more each, planned to be made of thin plastic reflective films, which are launched to some optimal orbit around the Earth. One could, for example, thereby provide night or emergency illumination to cities and other locations, or illuminate agricultural production areas to lengthen the growing season, or to illuminate photovoltaic or thermal collectors on earth for producing electricity or heat. Proposals were also made for using such mirrors for weather modification, and we added here the possibility of using the space mirrors for shading the earth to reduce global warming. Experiments with space mirrors were conducted in the past by the former Soviet Union. Without (yet) consideration of environmental and social impact externalities, our economic analysis agrees with past studies that if transportation costs to mirror orbit are reduced to a few hundred $/kg, as planned, the use of orbiting space mirrors for providing energy to earth is an investment with a good rate of return and a cost effective alternative to other power sources. This energy concept is very appealing relative to other options for addressing the severe energy and global warming problems that we face, and deserves much and urgent R&D attention.