It is desired to make the spacecraft such that it can survive in the extreme conditions of universe. Thus the subsystems, which are designed to protect the components of spacecraft from extreme thermal vibrations and other space hazards, are called environment subsystem.
Passive cooling: The use of painting, shading, reflectors and other techniques to cool a spacecraft. Internal components are typically painted black to radiate heat more efficiently.
Active heating: The use of resistive electric heaters or radioisotope heaters to keep spacecraft components above their minimum allowable temperatures. Electric heaters can be controlled either autonomously or via command, while radioisotope heaters are used where it is necessary to provide components with a permanent supply of heat.
Life support: Life support functions include crew compartment pressure, cabin air revitalization, water-cooling, temperature control, water supply, waste collection, airlock support and crew altitude protection.