• Some satellites will always be in orbit with one side of their body facing the sun and one side facing the cold of space
• The side of the satellite facing space would be several hundred degrees colder than the side facing the sun
• Thermal blanketing is used to keep satellite cooler or warmer, depending on what is needed
• It acts like the insulation in your house: when it's hot outside, insulation keeps cool air inside, and when it's cold outside, insulation keeps warm air inside
• Mylar a very good material for thermal blanketing
• Mylar is the trademark name for a polyester film plastic discovered and manufactured by the company DuPont
• Mylar has many uses, including insulation, backing for magnet tape, balloons, and as a polyester film used to cover a metallic yarn
• Mylar is also used for insulation in space suits
• It is moderately expensive, and moderately durable
• As part of preliminary testing for early communications, ECHO I was a 30 meter in diameter helium-filled Mylar ballon that was coated in thin aluminum - this was allowed to float high into the atmosphere, and then communications signals were bounced off it