How does Multi-Layer Insulation (MLI) work and how is it designed?

MLI reduces radiative heat transfer using multiple reflective layers separated by low-conductance spacers. Construction: Outer cover (Beta cloth, Kapton for durability), Multiple reflector layers (aluminized Mylar or Kapton, typically 10-30 layers), Spacer material (Dacron netting) between layers, and Inner cover. Thermal performance: Effective emissivity 0.01-0.05 (compared to single layer 0.8+). Heat transfer reduced by factor of (1 + number of layers). Design considerations: Layer count (diminishing returns above ~20), Seams and penetrations (major heat leak paths), Venting for launch depressurization, Grounding for electrostatic discharge, and Handling (easily damaged). MLI protects against solar flux and cold space. Used on most external surfaces except radiators. Ground testing validates effective emissivity. Weight: ~0.5-1.0 kg/m2 typical.