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.
KEYWORDS: Diffusion, Physics, Chemical species, Data modeling, Chemical analysis, Temperature metrology, Standards development, Mass spectrometry, Epoxies, Data processing
Progress was performed recently on the separation and characterization of the chemical species outgassed by space materials, relying on the assessment of thermogravimetric analysis (TGA) peaks by mass spectrometry (MS). A companion communication reports on this experimental technique and the first level processing of these MS data, which often allows determining which are the outgassed species, and their MS spectra. This communication focusses more on the second analysis step, i.e. the study of the MS data acquired during the initial outgassing phase. Ancient simpler outgassing analyses based on total mass measurements only, most of the time on quartz crystal microbalances (QCMs), cannot realistically determine the separate contribution of different species, even though some models consider the contribution of several species, which are indeed more “mathematical species” than physical ones. In contrast, this new approach, also taking into account the MS measurements during the outgassing, and known species spectra (from the TGA/MS analysis done previously), allows a more realistic determination of the contribution of each real chemical species to the total outgassing. Even though results are not yet final and perfect, measured outgassing fluxes from several species and materials are presented. Their physical analysis, through comparison and fit by diffusion or other possible outgassing laws are also presented. At this level, they clearly point to diffusion laws, rather than to any other outgassing law, although not necessarily always Fickian diffusion. This method was applied to typical US or European outgassing approaches, with either isothermal ASTM-1559 outgassing tests or multi-temperature VBQC-type tests.
Well-established procedures for the characterization of contamination during outgassing usually involve total mass measurements through quartz crystal microbalance (QCM). Recently, the addition of mass spectrometry (MS) measurements to these data has become more common. The combination of both high sensitivity QCM and MS data may lead to a better understanding of the physics taking place during outgassing contamination processes. The way to do so is to complement the basic measurements of total mass loss on QCMs by the identification of each species and the quantitative determination of each species contribution. In a first characterization step, the thermogravimetric analysis of contaminants deposited on QCMs allows a partial species separation that helps exploiting mass spectrometry data. In return, these data permit a finer species separation. The key to these measurements is to obtain sufficient signal to noise ratio in the mass spectrometer. Though outgassing of space materials is not done the same way in Europe (multi-temperature steps, ECSS-Q-TM-70-52A) and in the US (isothermal, ASTM E-1559-09), both tests could be used to perform a first species separation, as reported here. Most species outgassed by a few common materials were identified (and quantified) through TGA and MS coupling. As reported in a companion paper, the knowledge of these species’ spectra then allows the analysis of the MS data during the initial outgassing phase, determining the quantitative outgassing of each species and leading to the improved comprehension of the physical laws ruling outgassing.
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 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.
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.
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