This PDF file contains the front matter associated with SPIE Proceedings Volume 11489, including the Title Page, Copyright information and Table of contents.

If all goes according to plan, in February 2021, NASA will land the Mars 2020 Rover on the surface of Mars. Mars 2020 is the latest in a series of unmanned Martian robotic rover missions that are part of NASA’s Mars Exploration Program, a long-term effort of robotic exploration of the planet. The mission seeks to address high-priority goals for Mars exploration, including answering questions about the potential for past life on Mars. Mars 2020 will look for evidence of habitable conditions on Mars in the ancient past, as well as look for signs of past microbial life itself. The mission also seeks to understanding the geological history and evolution of the planet, and to prepare for future robotic and human exploration. The Mars 2020 spacecraft and rover borrow heavily from the Mars Science Laboratory (MSL) mission and Curiosity rover which landed on Mars in 2012. This reliance on proven technology helps reduce mission risk and cost. Mars 2020 does contain new technology, including a drill for coring samples from Martian rock and soil and a Sample Caching System for gathering, storing and preserving samples for possible future return to Earth. In this paper, we will review the primary goals of the Mars 2020 Mission and look at the reasons for choosing Jezero Crater as the landing site. We will discuss the design and build of the Mars 2020 Spacecraft system and its similarities and differences with Mars Science Laboratory and the Curiosity Rover. We will also review the Mars 2020 Scientific Instrument Suite and their goals. Finally, we will review the Return Sample Contamination Control requirements and the design choices that were made to facilitate meeting these requirements.

One of the Mars 2020 mission’s primary science objectives is to seek out traces of past life on Mars – the rover’s sample caching system (SCS) will collect and store rock cores and regolith samples for possible return to Earth for analysis by a future mission. These samples must be contaminated with fewer than 10 parts-per-billion (PPB) total organic carbon (TOC) of terrestrial origin to permit an unambiguous detection of Martian organic signatures; this 10 PPB threshold translates to less than a monolayer of adsorbed contaminant molecules on the inside surfaces of sample tubes. Achieving such a stringent requirement has necessitated some of the strictest contamination control protocols ever enacted in NASA’s history. Throughout all phases of the mission, sources of terrestrial organic carbon can contaminate samples and sample caching hardware through a variety of transport mechanisms in free-molecular and continuum flow regimes. Predicting and mitigating the contamination of future returned samples requires a comprehensive understanding and cataloging of contaminant sources, transport mechanisms, and adsorption characteristics. Therefore, JPL Contamination Control has developed a novel multispecies model based on experimental measurements of Mars 2020 flight hardware, which has been applied in characterizing organic carbon contaminant sources, species compositions, and outgassing rate dependences on temperature. These are the boundary conditions for an end-to-end modeling framework in which the transport and deposition of contaminant species are calculated for each mission phase, culminating in a prediction of the total quantity of terrestrial organic carbon within future returned samples.

The Mars Helicopter, developed by the Jet Propulsion Laboratory and attached to the M2020 rover, aims to be the first aircraft to fly on another planet. It is a high-risk, high-reward project with the objective to prove that autonomous, controlled flight can be executed in the extremely thin Martian atmosphere. Testing the Helicopter on Earth required a vacuum chamber both capable of reaching Mars atmosphere conditions and large enough to accommodate the Helicopter’s test flights. The only available option was the JPL solar simulator, a 47’ tall, 25’ diameter vacuum chamber meant to provide environmental testing for JPL’s largest spacecraft. The solar simulator includes a 23’ diameter focusing mirror suspended 4 stories above ground level to direct energy onto spacecraft in the chamber. If this mirror is contaminated, JPL loses its capability to provide solar simulating capability to its largest spacecraft until the mirror is pulled down and carefully cleaned. The sensitivity of the solar simulator at JPL necessitates careful vetting of materials entering into the chamber. For most flight projects, the major assemblies entering the chamber are made of vacuum-compatible materials. The Mars Helicopter project constructed a wind tunnel in the solar simulator to provide airflow over the Helicopter engineering model in a Mars pressure environment. The wind-tunnel assembly was constructed from Commercial Off The Shelf (COTS) components without clear material documentation. The JPL Contamination Control group analyzed all major materials with Direct Analysis Real Time Mass Spectrometer (DART-MS), measured component outgassing after bakeout with a quartz crystal microbalance (QCMs), and estimated contamination impact to the solar simulator from the wind tunnel assembly. Contamination Control also implemented mitigation steps for COTS components, including material substitution, bakeouts, and cleaning. This approach overcame long-standing rules of thumb about the type of components that can enter the solar simulator, and can be used as an example when vetting COTS components for use in a vacuum environment with contamination sensitive surfaces.

We have selected a number of materials used in construction of space instruments and spacecraft that require a bakeout to reduce outgassing under vacuum in view of the environment of the Solar Orbiter mission. Most of the materials were used in the PHI instrument on board Solar Orbiter. We subjected the samples to the bakeout process using a quartz crystal microbalance (TQCM) monitor and, for a similar duration, using a much simpler setup with a vacuum oven, equipped with a rough vacuum pump, called “purged bakeout process”. We compared the residual outgassing of those samples after the bakeout process and compared the efficiencies of the two methods. We find that the bakeout in a vacuum oven with clean gas purging is equally efficient as the high-vacuum bakeout with TQCM monitor for those samples with simple geometry of the material such that purging is efficiently accessing all surfaces, whereas complex structures like honeycomb panels will not be well enough purged under rough vacuum conditions.

The Jet Propulsion Laboratory (JPL) has pursued a multi-disciplinary effort to experimentally characterize and computationally simulate the effects of powered descent onto the Europan surface. As part of the proposed Europa Lander technology development and maturation activities, JPL Contamination Control and the German Aerospace Center (DLR) are conducting a test program to characterize monopropellant plume-induced contamination, the preliminary results of which are showcased in this presentation. These measurements have been used in the further development of JPL’s computational physics simulations of descent engine plumes interacting with the Europan surface with direct simulation Monte Carlo (DSMC) techniques, and in broader support of contamination control strategies for the proposed Europa Lander mission.

ESA Sentinel-4 mission will monitor trace gas concentrations and aerosols in the Earth’s atmosphere with a 1-hour revisit frequency and unprecedented spatial resolution. Initial performance predictions, relying on literature/historical values for optical absorption coefficients, revealed considerable losses at the end of the mission lifetime caused mainly by high levels of absorption of light due to molecular contamination spread over the 39 optical surfaces of the UVIS channel. This publication describes the significant effort undertaken by Sentinel-4 team to establish more reliable and accurate performance predictions, and the importance of performing measurements under representative conditions of the instrument’s contamination environment. The refined performance prediction analysis was the final step of the activity, demonstrating that the end of life performance requirements of Sentinel-4 will be met.

Scientific exploration of space is dramatically changing as a result of increasing participation by commercial and private space industries. Missions utilizing SmallSats and CubeSats for exploration are proliferating, and crewed missions to the Moon and Mars are anticipated in the near future. In 2020, NASA will release revisions to policy documents governing planetary protection to reflect the new multi-stakeholder community. These policy documents establish the foundation for practices to control forward contamination during exploration of extraterrestrial solar system bodies and to prevent backward contamination of the Earth/Moon system when extraterrestrial samples are returned to Earth for study. This paper will inform contamination control and planetary protection practitioners about these policy changes, which will clarify planetary protection standards and streamline implementation and verification processes throughout mission life cycles.

Chemical propulsion is still widely present within the space industry especially when it comes to exploration or earth observation missions. Despite its historical usage, some questions concerning plume induced contamination remain open. Plus, the complexity of the future missions, especially within OHB, leads to configurations where the plume is a driving key for satellite design. In fact, the thrusters could theoretically impinge all kind of optical components such as cameras, telescopes, mirrors or even radiators. However, impinging a surface does not necessarily mean possible troubles: depending on the angle, velocity and the nature of the contaminants, the performance loss can be either consequent or insignificant. Despite this hot topic, few data^{1, 2} or in-orbit observations³ are available. This is probably due to the complexity of a direct observation of such a phenomena. These data are very useful to calibrate the numerical modelling even if some questions are still unanswered. Meanwhile, the numerical tools progressed and computation capabilities today are far more developed than in the beginning of the investigations. Within OHB, the open source tool “openPlume” have been developed the last year based on the ray-tracing technique and by connecting the CFD calculations to the far field. This provides to the System Engineers quick, reliable and robust answers to the questions regarding the plume induced thermal fluxes or forces and torques. After the last years progress⁴, the extension of the tool continues to tackle contamination. This paper presents the roadmap of the “openPlumeCP contamination module” that already provides the gases distribution and implement the droplets distribution. The CFD modelling take into account each gases species after that the preliminary combustion products properties have been generated by the CEA code. The transport properties such as the viscosity and the specific heat capacities are then injected into the thruster mesh thanks to openFOAM. Once the gases distribution on the near field of the thruster is performed, the extrapolation to the far field relies on the ray-tracing algorithm. The droplets are simply injected according to an analytical formula relying on on-orbit observation. An empirical comparison with the Trinks experiments was performed and gave encouraging results for the species distribution. Thanks to this preliminary work, a first glimpse can be provided by openPlumeCP regarding the possible impact on the spacecraft surfaces. The backflow modelling remains tricky and need to be handled differently: a specific DSMC method relying on DS3V⁵ is used for the near field impingement. Nevertheless, the thruster lip influences the species distribution in the near field and the CFD method need to be modified. Investigations are on-going by trying to couple the CFD simulation and the DSMC part next to the lip.

The performance of contamination sensitive components—such as optical components—can be degraded by particulate matter depositing on the surfaces. Particles can accumulate during manufacturing, handling and operation. For a space-based system, particles can shed from the fairing and redistribute onto sensitive surfaces during launch. An engineering modeling approach has been developed for modeling particle migration during launch. The approach involves particle detachment from the fairing, particle transport through the venting atmosphere inside the fairing, and attachment to the receiving surface. Particle size and amounts on the fairing surface can be modeled using distributions from standards, such as IEST-STDCC1246E, as well as from empirical data obtained from tape lifts. Surface interactions are modeled using theoretical as well as empirical data. Commercial computational fluid dynamics codes are used to calculate the gas flow in the fairing during depressurization during launch. This approach not only provides insight into particle redistribution during launch but also can be used to establish fairing cleanliness requirements.

Prediction of the contamination deposits from the Total Mass Loss (TML) via a novel technique is presented. This predictive methodology, based on the multi-step dynamic outgassing test complemented with a thermogravimetric analysis (TGA), allows assigning outgassed species according to their sticking coefficients to a collector's surface. The proposed approach enables to identify major chemical species outgassed from the tested material and calculate sticking coefficients in a broad temperature range (-175 to+80°C). The preliminary results show that this method could be used as an improved procedure for predictions of deposition and reemission levels.

As usually known, the physics in space have a tendency to behave differently from the physics on earth. In fact, Free Molecular Flow are an important hurdle to cross in order to completely gasp molecules behaviors. Outgassing for example is one of these phenomena that deeply impacts satellite performances and remains complex to model regardless of the numerous successful optical satellites missions. Despite the efforts spent last years, on-ground outgassing testing still gives little information about the driving mechanism of outgassing. Is it controlled by desorption? By diffusion? Is it a mix of both? And once extracted from the material bulk, what are these molecules? Are they carbon based molecules? Are they a mix of different species? And once they leave the materials, how the molecules condensate on the sensitive surface? How are they reemitted? Is it governed by reflection or by a residence time? In addition, the configuration on a spacecraft is far more complicated than in a simple set-up: huge temperature gradients exists, a material with low outgassing criteria (TML, RML, CVCM) can still be a threat to the whole mission if it is located next to a sensitive optical surface… Meanwhile, OHB conducted several numerical investigations that this article will summarize. Based on latest JAXA1 and ONERA² experiences, a diffusion model have been implemented and connected to the view factors calculations of a closed cavity. The model is based on the Fick’s law and a numerical calculation was performed thanks to an Euler/Crank-Nicolson method. Compared to the desorption modelling, the diffusion results showed quite important differences especially in the starting of the outgassing. To able to judge between the two approaches, the numerical model have been confronted to an outgassing set-up called the “CNES mock-up”. To make things more complicated, the “reemission” part is also challenging. Depending on the configuration to model, reflection of molecules can be the driving mechanism and the residence time approach is too slow to catch up with the real observed behavior. Concrete examples will be presented in this article to open the discussion on possible approaches to better model and understand outgassing.

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.

This paper discusses recent model improvements and performance optimization implemented in the Contamination Transport Simulation Program (CTSP). We start by discussing modification of the storage octree to utilize the space-filling Morton Z curve. We then discuss several enhancements to the input file format, such as the ability to utilize mathematical expressions and to combine several short steady-state solutions to cover a longer physical time frame. An HTML-based GUI is described. We then introduce a new molecular model based on materials- specific activation energy and the ability to use partial pressure curves to control material adhesion. Subcycling for particulate motion and a new model for particle surface adhesion are also covered. The paper finishes with a brief discussion of an ongoing experimental test campaign.

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.

In the past year, EUV lithography scanner systems have entered High-Volume Manufacturing for state-of-the-art Integrated Circuits (IC), with critical dimensions down to 10 nm. This technology uses 13.5 nm EUV radiation, which is shaped and transmitted through a near-vacuum H2 background gas. This gas is excited into a low-density H2 plasma by the energetic EUV and DUV radiation from the Laser-Produced Plasma (LPP) in the EUV Source. In the vicinity of the walls and mirrors within the scanner system, this creates an environment rather similar to that near the surfaces of objects in space, especially when considered in combination with trace species such as N2, O2, H2O and hydrocarbons. This paper will discuss how insights on electrostatics and charging from astrophysics have been used to build understanding of particulate and molecular contamination, and how these were translated into prevention and control schemes to achieve near-zero contamination levels on critical imaging surfaces, compatible with the stringent manufacturing requirements for 10 nm lithography.

Molecular contamination phenomena depend on temperature. For example, the morphology of a contaminant can change from a uniform film to droplets. The authors believe that the surface morphology of thin-film contamination affects optical transmittance and reflectance of camera lenses and other sensors, so it is important to gain a better understanding of the morphology of contamination. The authors investigated a simple measurement technique to determine molecular contamination morphology in a vacuum and at low temperatures using a CMOS camera sensor chip. The CMOS camera operates down to −60°C, which covers our range of interest (i.e., from −60°C to room temperature). Furthermore, using a combination of the camera sensor and the optical measurement setup in a vacuum chamber, the morphology and optical transmittance were measured simultaneously. The advantages of the technique are that the equipment is inexpensive and can be installed in many chambers now in use.

Newly developed space instruments are increasingly efficient and accurate. One of the main drawbacks is that they are consequently more and more sensitive to contamination. Once integrated, optics are continuously exposed to cleanroom environment. Most of the time, cleaning operations are risky or even impossible considering coatings fragility or accessibility constraints. Thus even in cleanrooms, with the use of specific covers and/or the implementation of purging, inducing altogether stringent operational constraints, molecular and particulate contamination deposition appears to be unavoidable. Hence, the use of a protection film on the most critical optics during manufacturing assembly and tests would allow a significant reduction of the overall contamination levels or the release of the operational constraints to reach the same cleanliness target. This study presents the results obtained in the frame of a test campaign aiming at identifying and evaluating the most promising protection films (including varnishes, adhesive tapes and electrostatic films) dedicated to space instruments optics. Impacts on both molecular and particulate contamination were investigated together with associated effects on protected substrates (aspect, spectral properties, …). The best solution has been qualified at Airbus and is currently implemented on flight hardware.

In the field of contamination control, many unknowns exist. Often, contamination control engineers have to utilize multiple spectroscopic, macroscopic, and microscopic tools to identify contamination sources when there is a potential contamination exposure to space flight hardware. Understanding the chemical composition of the molecular contamination provides an opportunity for contamination control engineers to determine if this contamination is problematic or benign. In this study, an existing witness plate program for monitoring space flight hardware during the assembly, integration, and testing phases is coupled with micro Raman spectroscopy analysis. The main goal of this study is to determine the limitations, reproducibility, and throughput of micro Raman spectroscopy for characterizing molecular contamination. Micro Raman Spectroscopy will be an additional tool used by contamination control engineers to monitor the cleanliness of space flight hardware.

A challenge present in assessing contamination accumulation on many missions is predicting fallout during ground processing given the multiple and various orientations possible for surfaces such as optics and instruments. The best practice assumption has been to quantify particle build up on vertical surfaces as approximately 1/10 that of horizontal surfaces. There is insufficient data to provide confidence in the 1/10 approximation, yet its use can have a significant effect on mission end of life contamination level predictions, leading to expenditures of precious resources to meet mission requirements. There are many variables influencing the relationship between fallout on vertical and horizontal wafers, including wafer position with respect to air flow, air changes in the facility, duration of exposure, and activity workload. The goal of this continuing study is to develop a tool to inform particulate accumulation predictions for future projects.

For system contamination control often cleanrooms or clean zones are used. Cleanrooms are classified for particles between ≥ 0.1 μm and ≥ 5 μm according to the ISO 14644-1:2015 classification table. In many applications air cleanliness for larger particles is more important. Especially in optical systems contamination by particles ≥ 20 μm is important. The present ISO 14644 cleanroom standards do not offer methods of controlling and monitoring of these particles. The new ISO 14644-17, of which the Draft International Standard is published in January 2020, covers the missing aspects of air cleanliness for macro-particles from ≥ 5 μm to ≥ 500 μm. The particle deposition rate gives a direct relation between air cleanliness and contamination risk. Particle deposition rate data predicts the contamination by particles during exposure, but the data also provides information on how to reduce the particle deposition rate if required. This paper discusses the specification and application of the particle deposition rate in clean controlled environments. As examples the production of a photo conductor and the assembly of a MEMS inkjet device is described.

It is reported that contaminants outgassed from these organic materials cause to degree the performance of optical systems mounted on spacecraft in orbit. We have been focusing on photocatalysts to solve this contamination problem. In this paper, photocatalytic activities of TiO₂ in vacuum were measured from frequency change of QCMs. The QCM frequencies increased during UV irradiation to TiO₂ on the QCM contaminated by oleamide and MR, which implied that TiO₂ can decompose oleamide and MR and their mass on TiO₂/QCM decreased in vacuum. We have succeeded to estimate photocatalytic activity from mass change. Moreover, this estimation method is effective to evaluate photocatalytic activity in vacuum.

Future space exploration missions will force contamination control requirements to become more strict to support increasingly sensitive instrumentation and search for life missions. Driving issues for these extremely clean requirements include increased instrument sensitivity, return sample science, and protecting ambitious mission science objectives. Preparing to meet these requirements mandates that contamination control provide new guidelines and more involved support for the cleanrooms during flight hardware assembly, including establishing better methods for setting cleanroom personnel limits to reduce particle fall out in cleanrooms. Limited literature exists for universal methods of determining cleanroom personnel limits, and what does exist includes mostly theory and assumptions on determining the limit. In this work, published method will be assessed against particle fall out data collected from the ISO 5 cleanrooms of the Mars 2020 Perseverance Rover assembly. Additional evaluations will assess contamination control required cleanroom protocols and the overall success of meeting strict cleanliness requirements of the Adaptive Caching Assembly (ACA) and sample tubes to safeguard future scientific endeavors.