Thermal Louvers: Passive Bimetallic Radiator Control

Many spacecraft keep sensitive electronics at a steady temperature without a single sensor or line of control software: a bimetallic coil spring behind each radiator louver blade senses the baseplate temperature directly and rotates the blade open or closed, throttling the radiator's effective emissivity. This simulator models that closed loop in a 2D cross-section — an orbiting spacecraft swings between full sunlight and Earth's shadow, its internal heat load and the sun's contribution drive a baseplate energy balance, and the louvers respond with a first-order spring lag to hold temperature inside a safe band. Adjust the internal heat load, the spring's set-point temperature and its response time, or lock the louvers fully open or fully closed to see how much of the temperature stability is actually being done by this purely mechanical thermostat. Drag the orbit dial to scrub through a full orbit and watch the strip chart track the resulting temperature swing.