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.
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.
“NASA’s Mars 2020 mission … rover is being designed to seek signs of past life on Mars, collect and store a set of soil and rock samples that could be returned to Earth in the future.”1 The Mars 2020 Project has a top-level requirement that soil and rock samples contain less than 10 ppb Total Organic Carbon (TOC) of terrestrial
origin 2. The approach taken to meet this requirement is to identify and model for each Mars 2020 mission phase the TOC sources, model TOC transport from sources to sample contacting surfaces, and combine them into an end-to-end model that calculates the TOC in each sample during the mission. The calculations show that Mars 2020 can achieve the TOC sample cleanliness requirement because the project has adopted specific TOC mitigations strategies.
We present the results of a laboratory test to determine the effects of bulk-deposited DC-704 silicone-oil contaminant film on the transmittance properties of an anti-reflective (AR) coated fused-silica optical substrate. Testing and optical measurements were performed in vacuum in the Boeing Contamination Effects Test Facility (CETF). The test and measurement procedures are described herein. Measurement results are presented showing the change in transmittance characteristics as a function of contaminant deposit thickness and vacuum-ultraviolet (VUV) exposure levels. The results show an initial degradation in the transmittance of the contaminated sample. This is followed by a partial recovery in transmittance as the sample is exposed to additional VUV radiation. The results also show a loss of transmittance in the ultraviolet portion of the spectrum and an increase in transmittance in the infrared portion of the spectrum. Thin-film interference analysis indicates that some of the observed transmittance results can be successfully modeled, but only if the contaminant film is assumed to have the complex index of refraction of SiO2 rather than DC-704 silicone oil. Post-test Scanning Electron Microscope (SEM) scans of the test sample indicate the formation of contaminant islands and the presence of a thin uniform contaminant film on the sample.
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