No abstract

In a space mission design, the goal of the thermal control subsystem is to ensure that all components of the satellite stay within their operating temperature ranges. The problem becomes more critical if the mission involves nano-satellites with an astrophysics payload requiring a dedicated thermal design to keep it at low temperature, as in the case of the HERMES mission. Therefore, a thermal analysis is performed using ESATAN, one of the most used software packages among those suggested by ECSS. This gives a good overview of the temperature fields but many geometrical simplifications must be introduced in the model and all thermal interfaces must be checked. In order to asses the effect of the latter, the ESATAN results are cross-checked with those obtained using another software, OpenFOAM, in which the geometry is created directly from the CAD model of the satellite, resulting in a very accurate geometrical representation. By first comparing the view factors calculations against analytical test cases some issues emerged. These are thoroughly analyzed and discussed and it is finally shown that they do not affect the temperature field. The high level of detail of OpenFOAM highlighted interesting possible improvements in the thermal configuration of the satellite.

Scientific payloads onboard CubeSats usually have complex geometries and occasionally narrower allowed temperature ranges with respect to the rest of the spacecraft. In these cases, the capability to correctly predict the thermal behaviour of the payload once in orbit is mandatory. To achieve this ability, a thermal balance test is required to correctly identify the thermal model of the payload. The test consists in the application of different external thermal boundary conditions together with the addition of heat dissipation to simulate the thermal load produced by active electronics during operation. Those experimental data are fundamental to validate the numerical thermal model and make its predictions reliable. This paper presents the configuration and procedures of the thermal balance test performed on the Demonstration Model of the payload to be embarked on each satellite of the HERMES constellation. The test data is compared with the results of a finite volume thermal model of the payload, proving the application of this method to be reliable for space thermal analyses. The obtained test results show the temperature jumps caused by the heat dissipation applied to active components. A weak correlation between the payload interface and internal equipment has been observed, thus proving that the payload is almost decoupled from the Service Module temperature variations. Based on test outcomes, some modifications in the payload design have been implemented, with the aim to lower the operative temperature on critical, temperature-sensitive equipment.