The science objectives of increasingly ambitious space missions require meeting stringent contamination requirements. The process of outgassing under vacuum exposure is often a primary source of spacecraft molecular contamination. Materials, such as cabling insulation and structural adhesives, evolve molecules that can be transported to and deposit on contamination -sensitive surfaces. Such deposition can negatively impact spacecraft performance : contaminant films may compromise scientific observations made by optical instruments, and may degrade the efficiency of radiators or solar arrays. The design of spacecraft and their mission operations is informed by contamination modeling, an engineering discipline combining empirical data and established science principles. Empirical data obtained from short-duration ASTM E1559 testing is used to determine outgassing rates from source materials. Scaling laws, based on Fick’s law of diffusion and Arrhenius factors to account for temperature variations, are used to extrapolate outgassing test data to mission conditions and durations. Outgassing contamination transport processes in vacuum are modeled as free molecular transport using a view factor formulation. Data from a thermo-gravimetric assessment performed at the conclusion of the ASTM E1559 test is used to estimate contamination condensation on spacecraft surfaces. Examples describing the contamination model — incorporating source outgassing, free molecular transport, and condensation onto spacecraft surfaces—are presented.

During launch operations, mission critical hardware and materials are encapsulated in a fairing prior to deployment. Depressurization can induce particle removal from fairing walls and redistribute them onto the payload. This poses serious challenges for current and future missions. This includes organic, inorganic, and biological material which can contaminate the surrounding environment. Given the risks associated with these events, efforts have been made to perform predictive simulations of particle contamination and redistribution. This work outlines the modeling efforts related to adhesion and aerodynamic removal of particles for prediction of redistribution in fairing environments. Physics-based models for adhesion and removal mechanisms are discussed. This includes the application of existing particle and spore adhesion models. Validation is performed for simplified canonical flow configurations. Future work regarding model improvements and extensions to large scale simulations is also discussed.

NASA’s Europa Clipper mission aims to conduct detailed reconnaissance of Jupiter’s icy moon Europa and to investigate whether the moon could harbor conditions suitable for life. Europa Clipper carries with it the Plasma Instrument for Magnetic Sounding, or PIMS, which will study the density, temperature, and flow of plasma near Europa. The instrument plays a key role in determining Europa’s ice shell thickness, ocean depth, and conductivity. There is both an Upper PIMS instrument and a Lower PIMS instrument.Radiation induced outgassing testing led by the JPL Contamination Control group indicates that a high level of outgassing is expected from Clipper’s Stamet Coated Kapton blankets in the Jovian radiation environment. A recent change to the Europa Clipper design has led to the Launch Vehicle Adapter (LVA) remaining with Clipper throughout the mission lifetime. This change introduces both a direct contamination source and a contamination reflection point for radiation induced outgassed contamination from Clipper’s thermal blankets to deposit on the Lower PIMS instrument. Free molecular flow analysis performed by the JPL Contamination group showed the expected molecular contamination deposition level on Lower PIMS drastically increases with inclusion of the LVA on Clipper, pushing the deposition on Lower PIMS over the requirement provided by the instrument. The contamination exceedance could significantly impact the science return from the PIMS instrument.A working group was formed with JPL Contamination Control, Mechanical, Materials and Processes, Thermal, and Systems teams to develop mitigations. The primary approach investigated was the implementation of a contamination shield on PIMS to block contamination from transporting to PIMS Lower. Other mitigations investigated include a contamination shield to block contamination from reaching the LVA and blanketing key locations on the spacecraft with a metallic MLI that outgasses less under radiation. The PIMS team was consulted to ensure the approaches did not cause harm to PIMS and to provide final review of the proposed solution. In the end CC analysis showed that with a PIMS shield implemented the flight system will meet PIMS’s End of Life (EOL) requirement for molecular contamination deposition. This approach shows a method by which Contamination Control identifies a contamination concern with a late-breaking spacecraft configuration change and functions with a multi-disciplinary working group to address and mitigate the concern.

The Gateway space station will operate both as a lunar outpost and a hub for space exploration missions in support of a long-term human presence on the Moon, and is under development by NASA in collaboration with ESA, CSA, JAXA, and international commercial partners. Gateway will experience induced molecular contamination from sources including materials outgassing, venting, and the nominal operation of its chemical and electric propulsion systems. The degradation effects of molecular contamination on spacecraft are well-documented and understood, and predictive modeling tools have been developed to aid in the mitigation of such contamination effects in the mission design phase. Therefore, the Gateway Induced Environments and Thermal teams have worked with JPL Contamination Control to develop modular simulation tools for the prediction of molecular contaminant depositions across the mission life, and for use in requirements derivation and sensitivity assessments. Free-molecular transport and deposition of outgassing products onto sensitive Gateway receiver surfaces is calculated using a viewfactor matrix approach, while International Space Station (ISS)-heritage bipropellant plume models are used to evaluate contaminant fluxes generated by the operation of thrusters on Gateway modules and the Orion spacecraft. The alteration of optical properties, e.g. the solar absorptance, of contaminated surfaces is likewise calculated using an ISS-heritage semi-empirical model premised on flight and laboratory testing data. This framework is intended to support early identification of potential integration issues and establish a baseline for incorporating improved analysis and test data as the Gateway design matures.

Powered landings onto airless bodies like the Moon generate rarefied gas dynamic environments composed of engine plume flows and surface materials including mobilized dusts. These induced atmospheres can cause harmful degradations of spacecraft performance. In particular, lunar dust can cause severe operational problems for human and cargo landing systems, astronauts, and deployed scientific observatories as was observed during the Apollo program. The need to understand and quantify the effects of plume-surface interactions during powered landings onto airless bodies has motivated the development of physics-based modeling approaches at NASA’s Jet Propulsion Laboratory. JPL incorporates inputs from Blue Origin and literature surveys of lunar regolith and applies computational fluid dynamics, direct simulation Monte Carlo, and Lagrangian particle-tracing simulation methodologies to model the plume exhaust flowfields generated by the Blue Moon descent engines during the final meters of landing, as well as the effects of that plume flow in eroding, entraining, and transporting lunar regolith to the descent element. The effects of dust deposition onto thermal control system radiators are of primary interest in this work, but other detrimental effects can include deposition onto landing sensors and optical systems during and after landing; damage induced by dust impact or subsequent abrasion within exposed lander cavities; and the performance degradation of solar arrays and scientific payload instruments. Plume interactions will also result in lunar dust clouds which may obscure visibility during landing, and may cause mechanical erosion of surfaces downstream of the plume-surface interaction.

The search for biosignatures on other solar system bodies drives the scientific objectives of many ongoing and proposed exploration missions, including the Europa Lander mission concept.[1] The detection of trace and unfamiliar biosignatures in extreme environments necessitates state-of-the-art scientific instrumentation with extraordinary sensitivity – and often, extraordinary susceptibility to terrestrial and spacecraft self-induced contamination vectors.[2] While instruments can be carefully designed to operate remotely at high performance, in situ scientific measurements can only analyze the samples they’re given: samples or sample handling hardware that have been inadvertently tainted by outgassed organic molecules, thruster plume effluents, or other common sources of spacecraft contamination may yield ambiguous or false results. Maintaining and verifying the purity of collected samples and the cleanliness of sample handling hardware throughout the lifecycle of biosignature detection missions like Europa Lander is a primary responsibility of the Contamination Control group at JPL.

NASA's Europa Clipper mission aims to conduct detailed reconnaissance of Jupiter's icy moon Europa and to investigate whether the moon could harbor conditions suitable for life. To perform these tasks Clipper will carry a suite of state-of-the-art scientific instruments, many of which are susceptible to the effects of molecular contamination and to interactions with the natural Jovian radiation environment. Recent ground testing conducted by the JPL Contamination Control group in the JPL Dynamitron particle accelerator (high-energy radiation source) has demonstrated that many common spacecraft materials exhibit significantly increased rates of molecular outgassing under exposure to high-energy radiation characteristic of the Europan environment [1]. This includes materials to be used in Clipper's thermal blankets and solar arrays, and subsequent free-molecular transport analyses showed that the increases in expected outgassing attributable to radiation would lead to exceedances of molecular deposition requirements for several of Clipper's instruments during the planned mission. The JPL Contamination Control group and the Europa Clipper project investigated testing and analysis refines in parallel with project mitigations strategies to protect Clipper's instruments. Refinements included improving the outgassing testing configuration and performing higher fidelity free-molecular flow analyses of instrument interiors. The project mitigations investigated include developing and testing alternate thermal blanket materials with a lower outgassing response under radiation and developing contamination shields that block line-of-sight between outgassing source surfaces and sensitive instrument surfaces. These mitigations were considered and coordinated with the impacted instrument teams such that any updates to the instrument requirements, available operation mitigations, or science robustness could be considered holistically. A combination of these strategies applied uniquely to each instrument proved most effective at mitigating predicted increases in molecular deposition caused by radiation induced outgassing. This approach demonstrates a novel method of identifying, assessing, and mitigating radiation induced outgassing that will be relevant to future space exploration missions with exposure to high-radiation environments.

Psyche is a NASA Discovery-class mission that is designed to visit the metallic asteroid (16) Psyche to determine its origin and conditions of formation and to understand whether parallels between the asteroid and the cores of terrestrial planets can be drawn. [1] The Psyche instrument suite consists of a magnetometer, a gamma ray and neutron spectrometer (GRNS), the Psyche Multispectral Imagers (PMI) and the Deep Space Optical Communications (DSOC) technology demonstration payload. PMI and DSOC drive the overall contamination sensitivity of the Psyche mission. Unique contamination analysis challenges for the Psyche mission included: developing a novel molecular contamination transport model for parametric assessments of outgassing risk [2]; implementing a contamination-induced optical throughput degradation model; justifying the need for a T-0 purge and deployable aperture cover for DSOC; and modelling the sputtering and transport of contaminants due to electric propulsion system plume impingement. Contamination control implementation challenges on Psyche included: using a commercial telecommunications satellite bus to host scientific instruments; interfacing with a new spacecraft contractor; and creating a "chamber inside a chamber" for spacecraft TVAC to protect JPL's 25ft Space Simulator. [3] This work describes JPL's Contamination Control program for the Psyche mission, including the planning and execution of strategies to resolve those mission-unique challenges in preparation for launch.

The Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) is a Jet Propulsion Laboratory (JPL) and Caltech led mission which will perform the first near-infrared all-sky survey to address the goals of NASA's astrophysics division. SPHEREx accomplishes these surveys of the entire celestial sphere with an infrared telescope cooled to cryogenic temperatures by a passive thermal system. Because the SPHEREx payload has both an optical telescope and a passive thermal system, it is highly sensitive to particulate contamination In this work the JPL Contamination Control (CC) group develops a computational physics framework to model particulate transport contamination from the fairing environment during launch, which is the largest particulate contamination source for most missions. Even with strict contamination control during ground processing, the launch environment can induce enough particulate contamination to exceed the scientific requirements of sensitive missions. For SPHEREx, particulate contamination in the telescope has a direct impact on the quality of the scientific data gathered during the surveys. Additionally, particulate contamination of the thermal system has a detrimental effect on its ability to cool the instrument to its cryogenic operating temperatures and maintain temperature stability. Due to these sensitivities it is imperative for SPHEREx that the particulate contamination from launch be comprehensively understood and mitigated wherever possible. The computational physics framework developed in this work is used to obtain precise estimates of particulate contamination on the SPHEREx payload and provides mitigations to ensure the mission meets its scientific requirements.

Europa is a premier target for advancing both planetary science and astrobiology, as well as for opening a new window into the burgeoning field of comparative oceanography. The potentially habitable subsurface ocean of Europa may harbor life, and the globally young and comparatively thin ice shell of Europa may contain biosignatures that are readily accessible to a surface lander. Europa's icy shell also offers the opportunity to study tectonics and geologic cycles across a range of mechanisms and compositions. Here we detail the goals and mission architecture of the Europa Lander mission concept, as developed from 2015 through 2020. The science was developed by the 2016 Europa Lander Science Definition Team (SDT), and the mission architecture was developed by the preproject engineering team, in close collaboration with the SDT. In 2017 and 2018, the mission concept passed its mission concept review and delta-mission concept review, respectively. Since that time, the preproject has been advancing the technologies, and developing the hardware and software, needed to retire risks associated with technology, science, cost, and schedule.

A novel computational technique was used to simulate eruptions from Io's Tvashtar Catena region to better understand the origin of the visible structure of the gas/particulate plumes observed by the New Horizons spacecraft in its 2007 flyby of the Jovian system. The direct simulation Monte Carlo (DSMC) method was used to produce number density, temperature, and velocity fields for SO2 gas erupting from rectangular vents of aspect ratio 1:1, 3:1, 10:1, and 15:1. Simulations of eruptions of visible particles entrained in the gas were subsequently conducted in a separate MATLAB simulation by injecting particles at the vent and propagating them through the plume by interpolating the gas velocity fields. The temperature and number density fields were used to implement a particle growth model in which the grains grow/shrink via condensation/sublimation. With these simulations, we investigated the plume's lack of a prominent spout, how particulate structures in the vent are transformed as they move through the plume and how this could produce filamentary structure, and the origin of the traveling canopy wave observed in some of the images. Simulations showed that the presence of an observable spout in a given plume image can depend on several factors including vent aspect ratio, observer vantage point, particulate size, and eruption frequency. Several possible explanations for the lack of an observable spout in the Tvashtar images were explored, and the most plausible is that the particles are pulsed from the vent infrequently rather than being emitted in a continuous spray. The transformation of particulate structures in the vent as they travel through the plume depends primarily on vent aspect ratio and the structure's region of origin in the vent. Simulations showed that the continuous emission of particles from concentrated regions in the vent can produce filamentary structures similar to those seen in Tvashtar images, but the appearance of such structures is highly dependent on the observer's vantage point. The traveling canopy wave was replicated in simulations, to varying degrees, with two different mass flux functions: a traveling wave in the vent and the pulsing of particles out of thin cracks parallel to the vent's long axis. With a pulsing frequency of 10-15 min, the latter mass flux function was able to replicate, in a broad sense, much of the plume's interesting structure including the filaments, the traveling canopy wave, and the lack of an observable spout.

The New Horizons flyby of the Jovian system yielded multiple images of the erupting Pele-class volcanic plume, Tvashtar. These images include a unique five-frame sequence or "movie" taken over 8 min that revealed short-term dynamical activity in the form of a traveling wave and evolving plume structure. The high-latitude Tvashtar plume was observed from various aspects during the flyby to exhibit a canopy shock and a depositional ring with thermal vent emission. The movie frames and other high-resolution images of Io taken during the New Horizons flyby by the Long Range Reconnaissance Imager (LORRI) were deconvolved to aid analysis of the plume dynamics. While our previous work (Hoey et al., 2016) modeled this plume's gas field in its steady state with rarefied gas dynamic methods, Tvashtar's virtual vent conditions were underconstrained by observation. Therefore, to constrain thermodynamic and geometric parameters at the virtual vent, we extend our models of the Tvashtar plume to perform a parametric series of 3-D simulations at much improved resolution. These simulations vary virtual vent aspect ratio and stagnation temperature, and implement new models for gas opacity in SO2 flows and for the condensation and sublimation of particles entrained in the plume. We arrive at a set of virtual vent conditions that incorporate or satisfy all available observational constraints and several novel ones, including the gas canopy height and aspect ratio and the depositional ring extent and orientation. The 2007 Tvashtar gas plume is shown to be consistent with a virtual vent of aspect ratio less than or equal to 3; stagnation temperature 1287 K; area 30 km(2); and mass flow rate 2.0 x 10(5) kg/s SO2. Alternate canopy shock and depositional ring configurations are evaluated across a range of vent aspect ratios from 1 to 15 with results that will help to constrain the sources of other observed gas plumes. Finally, we develop an alternate hypothesis for the New Horizons observations of canopy unsteadiness in the Tvashtar plume; namely, that transient perturbations in the structure of the gas canopy shock itself produce a traveling notch-like structure that may even grow unstable, inducing temporary canopy collapse. This is as opposed to a high-amplitude density pulse at the source, or to source-entrained dust in a condensate model coupled to steady gas-field solutions.

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.

NASA's proposed Europa Lander Project would deliver an autonomous robotic lander with a suite of scientific equipment to the icy moon's surface in order to excavate surface samples and search for bio-signatures. This mission concept would land on the Europan surface using JPL's iconic Sky Crane technique, by which a powered descent vehicle is propelled and maneuvered into a hovering position with eight monopropellant hydrazine engines before lowering its lander. [1] The gas plumes of these engines would expand rapidly into Europa's near-vacuum surface conditions and impinge upon the moon's surface, the lander, and descent vehicle to potentially detrimental effect. Engine plumes induce torques and heating of spacecraft and can transport gas and liquid propellant byproducts to contaminate sensitive instrument surfaces, impacting science collection. [1]–[6] Major interactions of concern include surface contamination with, and subsurface penetration of, propellant byproducts; the removal and transport of particulates from plume-induced pressure gradients; and the sublimation of surface ices. Therefore it is critical to understand and characterize the proposed Europa Lander's engine plumes. Landings onto Europa and other airless bodies - i.e. those without collisional atmospheres, a class including Enceladus, Earth's moon, and many asteroids - will generate engine plume flow-fields that transition through continuum, rarefied gas-dynamic, and free-molecular regimes. Such complex, non-equilibrium flow-fields require hybrid solution schemes. A one-way-coupled continuum-to-rarefied hybrid scheme has been demonstrated, validated, and deployed for the simulation of single-engine, steady-state lander plumes impinging onto both the Earth's moon and Europa in a multidisciplinary effort at JPL. [2] The present work extends that hybrid framework to model the complex interactions of the full set of four Europa Lander descent engine plumes, each canted at 30°, generated during the final Sky Crane bridled descent. We report resultant surface pressure, heating, and contaminant depositions, and we demonstrate a framework that can be applied to model realistically-rough Europa-like surface morphologies. Likewise, we report the pressures, heat fluxes, and contaminant depositions induced by transient descent engine plumes onto both the Europa Lander and descent vehicle envelopes during landing, and we propose and outline several detailed campaigns of future work to the benefit of Europa Lander's engineering and science teams.

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.

Spacecraft orbiting Jupiter and performing flybys or landing on Jovian moons, such as Europa, experience an environment with high radiation levels. A Radiation Induced Outgassing Test (RIOT) campaign was initiated to study of radiation effects on contamination products evolving from spacecraft materials. Materials were irradiated with a flux of 2.6×10 10 electrons/cm 2 /s at an energy of 1.5 MeV. Preliminary results from the ongoing test campaign include determining species produced by radiation scissioning of silicones, as well as measuring outgassing rates from the material. A physics based outgassing model has been developed to explain the observed experimental results. Material outgassing rates measured during, and subsequent to radiation exposure, can be modeled using a simple diffusion model. Use of Fick's law with a source term during irradiation, and without a source term when the radiation is turned off, can explain some of the experimental results. However, not all of the experimental results can be explained by this model. The observed discrepancies can be due to a combination of radiation interference with the test instrumentation and also due to radiation interaction with the test sample surface. Although additional work is needed, the experimental results can provide a basis for extrapolating experimentally measured outgassing rates to predict contamination outgassing as a function of the radiation levels encountered during a mission at Jupiter.

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.