How do you perform thermal balance analysis for spacecraft design?

Thermal balance equates heat inputs with heat outputs at each node/zone. Heat inputs: Solar flux (direct, Earth albedo ~0.3, Earth IR ~240 W/m2), Internal dissipation (electronics, heaters), and Conduction from adjacent zones. Heat outputs: Radiation to space (epsilon*sigma*A*T^4), Conduction to adjacent zones. Analysis approach: Define thermal network (nodes, conductors, capacitors), Calculate view factors for radiation exchange, Apply orbital environmental heating (varies with attitude, orbit position), and Solve energy balance for steady-state or transient temperatures. Tools: SINDA/FLUINT, Thermal Desktop, ESATAN. Hot case (maximum solar, maximum dissipation, end-of-life coatings) and cold case (eclipse, minimum dissipation, beginning-of-life) bound the design. Margins ensure temperatures remain within limits across mission.