Particulate contamination is a source of potential risk for spacecraft systems [1]. Cleanliness engineering aims to control contamination during manufacturing and in-orbit delivery. The major uncertainties are related to the environment seen after encapsulation in the fairings and the launch phase. A significant increase in particle deposition occurs at the launch position [2]. These uncertainties strongly affect the contamination control process and may lead to highly demanding and costly constraints which are potentially unjustified.

Simulation results of particulate contamination inside fairings can be found, e.g., in [3]. However, a worst-case scenario is often assumed, with the detachment of all particles from the fairings. Here, a similar analysis uses sophisticated particle-wall interaction models, showing the fraction of particles that detach under certain conditions.

In the studied case (ESA's Euclid mission), the simulation results obtained using DUSTFLOW software show that only the largest particles detach from the fairings. Different scenarios indicate that the flow induced by depressurisation has a limited influence on detaching particles: shocks, acceleration, and vibration are the critical phenomena that allow previously attached particles to resuspend and thus be free to be transported elsewhere. Results show that only particles with higher mass/diameter are detached in this case. Therefore, even a very low number of such particles may significantly increase the obscuration of sensitive surfaces.

A counter-intuitive flow effect can be observed during the depressurisation process: a swirl is observed around the payload (see Fig. 1). Thus, the particles from the bottom can migrate to the upper elements of the payload. On the other hand, a similar case for different fairing and payload (see Fig. 2) does not show such flow features.

The presentation will cover the software design and validation approach and present simulation results for test cases already utilised by the European Space Agency.