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ExoMars is a Russian-European Mars exploration mission currently under development by the European Space Agency (ESA) and the Russian Space Agency (Roscosmos), with a significant contribution by NASA, which plans to send a lander to release a rover on the surface of Mars in 2020.
Within this mission, Comecer Group has been commissioned to develop a 7-metre long multi-chamber isolator consisting of 4 contiguous Glove Boxes, inside which the technical-scientific heart of the ExoMars rover will be assembled.
To assure mission success in fact, the equipment which will be released on the surface of the planet Mars must be free from any contamination of terrestrial origin.
Therefore, handling and assembly of the instruments must be performed under conditions that assure no microbiological and particle contamination at all and with volatile organic components (VOC) contamination reduced to the minimum possible levels, never before reached in commercial and experimental isolators.
The rover’s technological heart is a set of sophisticated instruments able to pick up materials, through core samples at various depths in the Martian surface, to analyse their chemical composition in real time and detect any presence of organic compounds or other biological markers. The objective of the ExoMars mission is in fact to analyse whether there are or were in the past any life forms on Mars. For this reason, it is not acceptable for the instruments designated for these analyses to be affected by even the smallest presence of terrestrial organic substances.
An additional reason for the extreme attention required by the ExoMars project to avoid any sort of biological and chemical contamination of the Martian soil, is dictated by the requirement of safeguarding the planet under study, which is guaranteed by a designated agency, the Planetary Protection Office, within the European Space Agency ESA.
The goal of the isolator is therefore to prevent organic contamination to the order of nanograms and assure total absence of micro-organisms on the rover’s instruments, during the entire assembly stage.
Both assembly and integration of the most critical and clean components of the Analytical Laboratory Drawer (ALD), is to be performed inside the isolator.
ALD is a true “portable” chemical laboratory, containing various instruments which enable various techniques to be applied on site, such as:
The isolator is a solution designed on Thales Alenia Space Italia specifications, which ESA has commissioned for a crucial part of the entire project, and is made possible thanks to Comecer’s know-how, currently used in producing isolators for sterile processes and large-scale pharmaceutical production. Additionally, thanks to the contribution of Comecer’s R&D department, innovative technologies have been used in this project, integrated thanks to the partnership network with companies and laboratories in this field.
The final objective has been to reach an absolute level of cleanliness, below the part-per-trillion (PPT), corresponding to an isolator in ISO3 particle class and AMC-9 (or) molecular contamination, therefore with respect to a defined set of organic contaminants.
This result has been made possible thanks to designated design and use of unique components, specifically developed for this purpose, among which:
The isolator is currently in use for the testing stage at the Thales Alenia Space Italia facility in Turin and is a unique, outstanding solution in the worldwide arena of Isolation Technology.
The level of in air molecular contamination is classified as Airborne Molecular Contamination (AMC) and represents chemical contamination in steam or aerosol form.
The AMC level has been codified within ISO standard 14644-8 and is usually expressed as total mass of contaminants contained per m3.
Table 1 – Molecular contaminant levels classification
The target sectors with the greatest need to monitor and remove AMCs are essentially the aerospace, semiconductors industry, and the sector of ultra-precision chemical analyses.
The issue has been analysed in depth within these fields, leading to identifying the sources of molecular contamination and the most widespread substances to be monitored and avoided.
Molecular contamination may be found outside of the isolated context, i.e. it is conveyed by the air entering the system, as well as inside the isolated context, for example deriving from the very materials found in the isolator.
In this project, the assessment of the connection between internal and external contamination sources, has led to some fundamental technical choices, such as the need for a complete extraction solution in the isolator ventilation, the type and quantity of filters in the system, the analysis and selection of non-metallic materials used.
The ventilation system, with operation at full extraction, has been designed and sized to enable unidirectional airflow on the work areas and the air changes required to maintain the ISO3 cleanliness class for each of the 4 Glove Boxes (GB). Additionally, positive pressure with respect to the exterior and to the previous GB is maintained inside each GB, to promote protection of the interior. For this purpose, a pressure and flow balancing system has been introduced, assured by the presence of a dual inlet and outlet fan and of proportional valves.
The system thus allows the increasingly restrictive requirements along the line to be complied with, depending on the unidirectional process which requires the material to be inserted into GB 1, the following assembly steps in GB2 and GB 3, until complete assembly of the instrumentation in GB 4. GB4 and GB3 are in fact defined as Ultra Clean Zones (UCZ).
Definition of the filter to be used has required considerable effort and it has been developed in partnership with the manufacturer Camfil.
Camfil has a highly qualified R&D department which, during this highly technical-scientific design stage, has guided and supported Comecer in the technical decisions to achieve real effectiveness in removing the molecules identified as critical.
The list of AMC molecules of organic origin whose presence must be avoided inside the isolator has been directly supplied among TAS-I requirements, and during definition of the filtration system, the focus has been on these specific substances identified as VOC (Volatile Organic Components). These VOC are found in ambient air and, in the context of an isolator, they may be released from the plastic materials and chemicals used.
Therefore, the initial steps taken during the analysis stage were:
For finalisation of steps 1 and 2 we have been supported by specialised chemical laboratories, able to identify the most effective analytical method for the purpose, and to perform sampling and subsequent analysis.
Once VOC mapping data were obtained and analysed, taking into account the ventilation system designed by Comecer for the isolator and thanks to the partnership with Camfil, it has been possible to identify and quantify the type of filtering material needed to meet and maintain the requirement.
Additionally, this approach has enabled us to identify the method of analysis to be used for validation of the filtering system upon completion and activation of the system, i.e. gas-chromatography analysis and GC-MS mass spectrometry based on thermal desorbtion with tenax tube.
The result has been the development of a canister of considerable size, containing 3 tonnes of filtering active carbon, selected and produced for the specific VOC contaminants selected, and a subsequent low out-gassing filtering stage.
Specifically, an air filtering system has been designed entailing two key components:
This filtering system allows the molecular contaminants and particles found in the air entering the entire isolator to be immediately removed, as well as further reduction of residual particles entering each individual GB.
Adding absolute filtration is essential to achieve ISO 3 class as well as being an AMC-9 (or) requirement, since many of the molecular contaminants are conveyed together with the micro-particle charge.
The VOC organic molecular contaminants may be released via out-gassing (removal of inert gas from the materials), mainly by various plastic substances, lubricants and chemical solvents.
However, not all substances have the same out-gassing index: high-silicone content plastics for example release high amounts of VOC, while materials with different chemical composition such as EPDM and FKM (Viton) show minimal out-gassing.
Solvents may also release VOC – the significance of the out-gassing phenomenon varies depending on their chemical composition and concentrations of the various components.
The substance release phenomenon generally diminishes over time, until it virtually disappears.
A known method to promote VOC release by the material is prolonged exposure to heat, called bake-out. By exposing the plastic materials to high temperatures for several consecutive hours, they release most of the residual volatile substances, both during and immediately post-treatment. Obviously, the thermal treatment must take into account the heat resistance of the material, in order to prevent its deterioration with resulting out-gassing increase.
The acceleration of VOC release induced by the treatment ensures the phenomenon then quickly decreases, until it becomes negligible.
For this reason Comecer has performed an in-depth analysis of these aspects, employing considerable time and resources.
The steps taken during this analysis consist of:
The final internal cleaning procedure of the isolator has been performed at Thales Alenia Space Italia, and has been designed to minimise the use of solvents and VOC release materials, while assuring a high level of cleanliness. The procedure has been drawn up after an analysis of the specific project requirements and of the available literature, by the same operators who then implemented it. For this reason, only isopropyl alcohol (IPA) and low particle release cloths have been used, and well-defined cleaning steps.
The procedure has been performed at the end of the installation stage.
This activity has enabled the release of VOC by the elements inside and forming the isolator to be further minimised, in order to contribute to achieving a controlled environment in compliance with the requirements.
Also for the decontamination stage of this project, great attention has also been paid to the critical aspects, essentially consisting of the molecular contamination risk and the need for absolute sterilisation.
For this reason, all stages and relative components/substances used have been analysed, in order to minimise the risk of VOC release, while assuring the maximum possible level of cleanliness.
The results of integration of the various aspects analysed have led to a number of measures, including:
Comecer’s goal is to always remain open to new technological challenges, while assuring the design and implementation of its isolation systems are in compliance with regulatory requirements and with the highest quality standards.
Compliance with high construction standards and the pursuit of continuous innovation in the field of isolation technology, grant Comecer a considerable advantage in dealing with its customers. This, in fact, not only assures joint intentions and goals, but promotes the achievement of the desired results and the success of the project.
Evidently, Comecer’s approach is to explore the different and possible applications which require an isolation system, thus allowing it to grow in terms of skills and to continuously evolve.
This project represents a clear example of how isolation technology, if appropriately implemented, enables innovative projects to be developed, including extremely specific processes and highly restrictive requirements, otherwise difficult to achieve.