Speaker
Description
Earth observation spacecrafts have seen a great interest and development in the past years and, still nowadays, it is one of the most prominent space markets thanks also to the miniaturization of the satellite platforms that allows to rapidly build constellations. In this presentation, the full development of a smallsats for Earth Observation is shown with a major focus on the thermal aspects. The case study is the HEO (Hawk for Earth Observation) spacecraft built for the first Argotec Earth Observation constellation, which will operate within the IRIDE constellation. IRIDE is an Earth observation satellite constellation developed on the initiative of the Italian government, with the support of the resources of the Italian National Recovery and Resilience Plan (PNRR). The work shown will start from the description of the first preliminary ESATAN thermal model (TMM and GMM) to the detailed ones, with insights on the numerical statistics and considerations on the differences in computational effort and modelling strategies. What has been noted is that an increase in TMM and GMM details does not always gives a justifiable results resolution increase wrt the increase in computational time and heaviness of the model. Considerations and results on modelling approaches to have the best trade-off between details and results worthiness are given. Then a description on how the TVC has been prepared and conducted to better replicate the worst cases orbital thermal maps of the spacecraft are shown, explaining how we were able to overcome test setup limitations. The satellite thermal map is mainly driven by the sun-pointing attitude of the satellite during most of its lifetime; hence the principal thermal gradient goes from spacecraft’s sun-side to anti-sun side. To replicate this behaviour without UV lamps or simulation chambers, a differential temperature control between thermal plate and shroud on the TVC has been used to heat up the sun-side and then, with the shroud, simulate the heatsink of the space environment. Limitations of this test setup relies in the impossibility to verify, for example, the solar absorptivity of the external surfaces. Eventually, the thermal model correlation results are shown with statistics evaluation of the results, considering checks also for the thermal inertia of the system, a major aspect for a satellite that works constantly in a transient thermal scenario. The last topic will be the description of the thermal control strategy foreseen to gain the focus on the optical payload. The capability to well observe the Earth surface strictly depends on the performance of this element and its capability to maintain optical focus during spacecraft’s nominal operations avoiding the use of a mechanical focuser. The use of the latter represents a single point of failure for the mission, hence the use of a proper TCS to keep the optical focus permits to relies on a more robust control system. Usually, optical payloads are designed to correctly perform in a narrow temperature range around 20°C, hence having the ability to maintain the payload within these temperature limits allows to guarantee the correct mechanical alignment of all the element in the optical path and then gain the focus. Finally, considerations on the effects of the thermal environment (solar flux, albedo and IR) are done and a final thermal control strategy for the optical payload focusing is described. A final short appendix will be added to show preliminary thermo-elastic results with the objective to study their effects on the relative positions between start trackers and optical payload during the orbit. These thermo-elastic displacement errors will be implemented on the ADCS to gain the best possible attitude control and then reduce also the pointing error on the Earth ground during the acquisition. The ESATAN output satellite thermal map is given as input on a FEM software to run static structural analysis that have temperature as load.
