Thermal control of the PLM is passive (i.e. radiators and MLI) and supplemented by heaters.
These are the main elements of the thermal control:
- Multi-Layer-Insulation (MLI)
- flexible Second Surface Mirror Radiators
- thermal doublers to spread the heat of high dissipating units
- black paint on inner side of PLM panels
- hardware controlled heaters
- software controlled heaters
- monitoring thermistors
Hardware controlled heaters use thermostats and maintain minimum non-operating temperatures to allow immediate activation of the:
- Payload Module Computer (PMC)
- Thermal Control Unit (TCU)
- Power Distribution Unit (PDU)
- Power Control Unit (PCU)
Software controlled heaters are controlled by the PMC on the basis of thermistor readings and defined temperature limits. They are used for warm-up and for control of operational temperatures.
Most instruments have their own thermal control and are thermally de-coupled from the PLM structure. For the Advanced Very High Resolution Radiometer (AVHRR), High Resolution Infra-Red Sounder (HIRS) and the Search and Rescue Repeater (SARR) instruments, baseplate temperatures are controlled by the PLM.