Spacecraft struggle to cool down because there is no air in space to carry heat away.

Thermal management is one of the most critical challenges in aerospace engineering. On Earth, heat transfer occurs through conduction, convection, and radiation. However, the vacuum of space lacks the fluid medium necessary for convection, meaning heat cannot simply be blown away by a fan. This creates a 'thermos bottle' effect where internal heat from electronics and solar radiation builds up rapidly.To solve this, spacecraft use Passive Thermal Control Systems (PTCS) and Active Thermal Control Systems (ATCS). The iconic gold or silver film seen on satellites is Multi-Layer Insulation (MLI), typically made of Kapton or Mylar coated with aluminum. According to NASA's Jet Propulsion Laboratory, MLI works by reflecting solar radiation and trapping internal heat when needed, acting as a high-tech thermal barrier.For cooling, spacecraft use radiators that emit thermal energy as infrared radiation into the cold sink of deep space, which sits at about 2.7 Kelvin. The International Space Station (ISS) utilizes a complex External Active Thermal Control System (EATCS) that circulates liquid ammonia through massive 23-meter-long radiator panels. This system is essential because, without it, the sun-facing side of the station would bake at 121°C while the dark side freezes at -157°C.Modern research from institutions like the Goddard Space Flight Center continues to refine these systems using phase-change materials and heat pipes. These technologies allow for precise temperature regulation of sensitive scientific instruments, such as those on the James Webb Space Telescope. By balancing absorbed solar energy with emitted infrared radiation, engineers ensure that spacecraft remain operational in the most extreme environment known to man.