DelFFi Thermal Subsystem

In contrast with Delfi-n3Xt, the outside of DelFFi is covered in solar cells, limiting the options of the thermal engineer. Using ESATAN-TMS, professional satellite thermal engineering software, it was investigated if active measures need be taken to control the temperature of DelFFi’s subsystems. A model was created, which will serve the successor thermal engineer in developing the final TCS that will be flown on the satellite.

A series of small tests was performed in order to investigate a number of assumptions made in previous thermal designs for the Delfi missions. The DelFFi team would like to thank EADS Dutch Space for providing heaters, insulation and tape to help facilitate the testing. The effects of the aluminium spacers and aluminium mid-plane stand-off’s employed by the structural subsystem were investigated, and shown to be in some cases significant. The structural system behaved thermally as predicted by theory. The new to DelFFi PC/104 connectors showed to have a very significant conductance, which altered the thermal behaviour of the subsystems significantly.

Using this test data, an extensive model was created in ESATAN-TMS. A variety of radiative cases and power-uses have been investigated together to ensure both hot case and cold case criteria, see table 1, can be satisfied. In this table, only the expected critical subsystems are displayed. The identified critical components are: the batteries, FIPEX’ boards (at the low end) and the propulsion unit (at the low end). Especially the batteries provided a difficult thermal analysis; their thermal range is approximately as wide as the allowed range after margins.

The first thermal design of DelFFi is now complete. Using the test data and the ESATAN model, it was determined that using the right thermal coatings and removing stack to structure conductances should suffice to keep the satellite in an appropriate thermal range. The first consists of applying Kapton and Aluminium tapes, the latter of making specific spacers out of steel or another low-conductivity material, and making mid-plane stand-off’s out of steel, and placing them strategically between spacers instead of on a PCB.

The inaccuracies in this stage of the modelling are high, because some details are unknown at the time. It is crucial for the successor thermal engineer, to reduce the uncertainties coupled with the early stage of the project. The large uncertainties are a danger to the project; a heater or an adaptation of power use in different operational modes may be considered. An increased thruster tank capacitance and high ADCS capacitance are both beneficial to the thermal performance, too.