The outgassing contamination of a satellite can induce severe degradation of surfaces or sensitive devices. Return information from flight ( LDEF, …) or others have shown the effects of outgassing contamination on many surfaces. In order to minimise these contaminating effects, the material used on a spacecraft are carefully selected from their TML (Total Mass Loss) and CVCM (Collected Volatile Condensable Material). The list of the materials used on a satellite is identified and their characteristics verified. Nevertheless, the material outgassing remains to be carefully analysed for most of the spacecraft.
The OUTGASSING software was developed to predict the contamination due to the material outgassing and its effect on the spacecraft in term of contamination.
The OUTGASSING software allows to compute from the material characteristics, the evolution of the contaminants deposits with time. It allows also to compute the column density related to the contaminant cloud around the spacecraft.
The geometry of the satellite is entered using the SYSTEMA framework, based on simple shapes. The material properties are specified in a specific material file.
The main assumption of the computation is that the flow regime in the outgassing cloud is free molecular (only few collisions). Then, the molecules are supposed to move following lines between the surfaces. Three contamination phenomena are considered :
The OUTGASSING software is mainly used to model the outgassing processes on sensitive satellites dedicated to the earth observation (SPOT series) or scientific missions (SOHO). It is used to predicts the contamination of the external surfaces and around the spacecraft or the internal part of sensitive instruments (telescopes).
For validation, on ground experiments have been modelled and the results have been correlated (well) with the measurements.
The main problem encountered during an outgassing analysis is the definition of the material characteristics. In the case where the data are not known, specific experimental measurements of outgassing properties have to be performed. The accuracy of the OUTGASSING results is often linked to the quality of the measured input parameters.
ESA, CNES, ....