This lecture covers the radiation balance for spacecraft close to Earth, including the mean value of direct solar flux, albedo, and emitted radiation. It explains the Stefan-Boltzmann law, solar absorptivity, and infrared emissivity. The importance of these factors in estimating the temperature of a spacecraft is discussed, along with the properties of materials used in spacecraft design. Strategies for spacecraft design in the space environment, such as conducting surfaces, electronic component filtering, and surface ratios, are also presented.