In order to maintain electronic components in their operative optimal temperature ranges, to reduce drifts in bias and calibrations due to temperature changes, a thermal control system will be adopted to maintain the temperature inside the experiment box as constant as possible close to 0 °C. To maintain the internal temperature not below 0 °C, evaluation of the overall thermal dissipation from the experiment box to external environment that, in the worst case, can be as low as -90 °C is obtained through mathematical models and thermal test in thermal chamber.

Considering heat transfer that occurs by conduction through the walls of the experiment box, a value of the thermal power that flows out has been obtained considering a temperature difference between the inside and the outside of 90÷100 °C. Results shows that is necessary to provide a total thermal power of about 10 W in order to maintain the thermal gradient required. These calculations have been confirmed by experimental results, where a fixed amount of thermal power was supplied inside the experiment insulation box and the equilibrium temperature has been measured. Tests shows that a ∆T = 10 °C is obtained for every Watt provided, confirming the theoretical solution. However this occurs only in the worst condition and means that heater has to be controlled by the microprocessor, driving an on-off switch. The heater is placed above the component side of the electronic board.

Heat transfer by radiation has not been considered because we believe that will slightly lower the power need rather than increase it. Moreover, as the air flows out with increasing altitude, severe thermal gradient may occur due to the absence of free convection. Overheat problem has been considered for the early phase of the mission. Particularly, the heat generated by the experiment itself, can lead the internal temperature to rise while the balloon is still on the ground preparing to be launched. To avoid this event, a low power consumption mode is foreseen for the experiment during the launch preparation. However, tests demonstrate that even one to 2 W power do not heat up too much the experiment box.

The thermal control is obtained placing an heating plate above the PCB component side. Two independently driven resistors provide 10 W of power on an anodized aluminium plate. Anodized aluminium is used because of its high emissivity coefficient.

For more details about thermal tests, you can see the section Current Status.