Development and validation of a new return flux model for the International Space Station

This paper documents the development and validation of a new return flux model for the International Space Station (ISS). This model has been developed to augment current ISS external contamination modeling tool capabilities. The model is capable of characterizing return flux from ISS molecular emission sources. These sources include materials outgassing, vacuum venting, propellant purging and thruster firings. The BGK method (named after its authors: Bhatnagar, Gross and Krook1) was selected for modeling ambient scatter. This method was used to reduce computational times, as the ISS geometric models used for external contamination modeling may contain up to 40,000 surface elements. The model has been validated by comparison with analytical results and with results from the ESA COMOVA software. Validation with on-orbit flight experiment data will be conducted when adequate experimental data is available. Previously flown experiments (i.e., REFLEX) have not produced data with high enough fidelity to validate this model. The model has been applied to the ISS to characterize return flux from the European Columbus module onto its own payload locations. Analysis results indicate the return flux contribution to ESA payload surfaces will be small, but not negligible.