How do you plan and execute thermal vacuum testing for spacecraft qualification?

Thermal vacuum testing validates thermal design and workmanship in space-like environment. Test planning: Define hot/cold case temperatures from thermal analysis, Determine dwell durations for thermal equilibrium and workmanship, Plan transition rates and cycles (typically 4-8 thermal cycles), and Identify functional testing at temperature extremes. Test execution: Pump chamber to <10^-5 torr (simulates space vacuum), Control temperatures using shroud heating/cooling and chamber LN2 panels, Shroud provides sink temperature for spacecraft radiation. Test phases: Thermal balance (steady-state verification), Thermal cycling (workmanship), and Hot/cold functional testing. Measurements: Thermocouples (100+ locations typical), Heater power consumption, and Component performance parameters. Correlation: Compare measured temperatures to model predictions, Update model thermal properties and contact conductances, Generate correlated model for flight predictions. Issues discovered: Manufacturing defects, Design margin adequacy, and Thermal runaway conditions.