he subject of this book is stratospheric balloons used for scientific observations and for the development of space technology and balloons that are used for aerological observations. These balloons attain flight altitudes more than three times those of passenger planes. They transport payloads ranging from several hundred kilograms up to several tons into the earth?? stratosphere. The density of the atmosphere at these altitudes is less than 1% that at the earth?? surface. In addition, as part of planetary exploration, this book includes planetary balloons sent to float over other planets that have atmospheres, such as Mars and Venus. The general term used to describe these sorts of activities is scientific ballooning.