The numerical assessment of in-flight contamination is a global process, which needs consistent numerical processing of elementary ground tests and global modeling of in-orbit situations. If the traditional physical approach of Europe is followed, both sides must make use of consistent physical models, and upgrade them consistently. This article presents recent progress performed at ONERA, in collaboration with CNES, in this respect. For this physical approach, elementary material outgassing tests aim at characterizing each chemical species independently, based on TGA / MS coupling for in situ characterization. Processing large data sets of mass peaks versus time, and interpreting them as resulting from a few outgassed chemical species, each one with its own mass spectrum, requires heavy computations and smart algorithms. The first results shown here are very promising. QCM and mass spec data acquired during TGAs where fitted with very convincing models for deposit reemission and mass spectra for the reemitted species that were identified with database spectra. This makes us confident in the next step consisting in similarly interpreting outgassing QCM + MS measurements in term of discriminated species, although they are all outgassed simultaneously in that case.
Contamination modeling has struggled with the challenge of species separation. Without the capabiliity to physically identify the chemical nature of contaminants and their contributions, the realistic correspondence between a chosen model and its underlying physics is very difficult to demonstrate. With the development of TGA/MS coupling experimental techniques and specific data treatments, a species separation was achieved on the ScotchWeld EC2216 adhesive. After a detailed exposure of the species separation need, this paper presents the experimental facility and the numerical procedure to effectively get contaminants identification and differentiate their contribution in a mixture.
Space instruments such as solar arrays, radiators, or optics can be strongly impacted by molecular contaminants outgassed from spacecraft materials. For optics, transmittance and reflectance performances could indeed be modified by the deposit of contaminants. We report the transmittance measurements and predictions in the ultraviolet–visible–near-infrared range of contaminated optics from the outgassing of a mixture of two common materials used in space industry: EC2216 material (epoxy compound) and RTVS691 material (silicone compound). The Swanepoel model, commonly used in many fields, was employed for the first time in such conditions to easily and quickly predict transmittance. Transmittance was fully recovered at 20°C; a decontamination plan could be based on heating at this temperature at least during a duration depending on the silicone/epoxy contaminants layer thickness.
Contamination modeling in Europe has long been based on physical mechanisms, such as desorption. However other physical mechanisms, such as diffusion, evaporation or mixing effects exist. These alternative mechanisms were experimentally evaluated and modelled. It was yet observed that, without an experimental capability to reliably separate the (re)emitted chemical species, it is very difficult to determine whether the modeling and its underlying physical mechanisms are representative of reality, or simply a mathematical fit of reality. This is the reason why in the last years emphasis was put on the experimental separation of species, mostly through TGA/MS coupling. This paper presents a review of these efforts and promising results on species separation to reach a really physical modeling of outgassing, deposition/reemission and UV synergy.