Microorganisms are present in all occupied indoor environments, including homes on Earth and within specialized systems like the International Space Station (ISS). Microbes when exposed to excess moisture, such as from an unexpected ventilation system failure, can undergo growth that is associated with material degradation and negative health effects. However, we do not yet understand how exposure of these microbes to excess moisture alters their function. A de novo metatranscriptomic study was performed using dust collected from the US air filtration system of the ISS and incubated in laboratory chambers on Earth at different equilibrium relative humidity (ERH) levels. Changes in fungal function (gene expression) were significantly associated with moisture (adonis2 p = 0.0001). Secondary metabolism and fungal growth genes were upregulated (FDR-adjusted p ≤ 0.001, log2FC ≥ 2) at elevated ERH compared to 50% ERH. Elevated moisture conditions showed upregulation of aflatoxin and fungal allergen genes such as Asp f 4 (log2FC = 26.4, upregulated at 85% ERH compared to 50%) and Alt a 7 (log2FC = 2.98, upregulated at 100% ERH compared to 50%). Our results demonstrate that understanding microbial functional changes in response to elevated moisture will help develop more robust microbial monitoring standards for spacecraft environments to protect astronaut health and spacecraft integrity in low-Earth orbit and beyond.

In the pursuit of human space exploration, the safety of the crew is paramount. Environmental Control and Life Support Systems are a unique aspect of human spaceflight that contribute to the myriad of problems requiring engineering solutions. Before being able to solve these problems, the first step is to properly define their boundaries. As with all human rated vehicles, the Artemis program, and by extension the Habitation And Logistics Outpost (HALO), will need to address fire detection. Though the approach to fire detection is complex, frequently smoke detection is a useful and necessary aspect of the solution. However, smoke detection in zero-G is not simple; It’s a multi-faceted problem dependent on numerous variables, ensuring that there is no “one size fits all” answer to the problem. In the development of HALO’s smoke detection solution, it was quickly identified that there is little guidance available for properly scoping the needs of a smoke detection device. This paper looks at existing documentation published from past experiments at the Glenn Research Center and, using the data from those papers, identifies a method for determining an acceptable smoke particulate concentration at which a smoke detector should alert. The approach is intended to identify a threshold at which smoke detectors can alert smoke presence in a defined cabin volume before crew health is jeopardized by the hazardous smoke by-products generated from smoke events, as defined by the NASA Spacecraft Maximum Allowable Concentration (SMAC) tables.

Fire is an imminent risk in space activities. Toxic gas and particle emissions can quickly reach dangerous levels in sealed environments. To improve smoke detection, protection, and post-fire cleanup, understanding the emissions from the pyrolysis of spacecraft-relevant materials is crucial. This study investigated the pyrolysis of four common spacecraft materials, including Kapton, polytetrafluoroethylene (PTFE), Teflon/Kapton/Teflon (TKT) wire insulation, and VelcroTM, to identify, evaluate, and quantify their gaseous and particulate emissions. Kapton emitted high levels of carbon monoxide and hydrogen cyanide, PTFE and TKT emitted multiple toxic fluorinebased gases including carbonyl fluoride and hydrogen fluoride, while VelcroTM had the highest PM2.5 emission factor. Most particles were in the submicron size range, with mode diameter peaked in the 100-200 nm range. The particles were nearly electrically neutral, carrying less than 0.15 net elementary charges per particle. Organic compounds predominated in the particle compositions.

Smoke detection in any space vehicle or habitat is fundamental for safety and mission assurance. If early warning of a fire scenario fails, the contingency may progress to catastrophic outcomes, including loss of crew, loss of vehicle, and loss of mission. Operational experience with smoke detection in spacecraft is currently limited to low Earth orbit, but space missions to farther destinations have different concepts of operations and more extreme environments that levy additional requirements on the hardware. Smoke detection on missions to the Moon and Mars will be particularly challenging as lunar and Martian dust will inevitably enter vehicles and habitats via human activities, despite the best mitigation techniques. Typical spacecraft cabin dust that is airborne in low Earth orbit has been an ongoing challenge, causing false alarms and requiring operational controls, such as turning off smoke detectors during housekeeping. This practice has been acceptable in low Earth orbit but should not be the norm for dusty destinations. This paper will present background information on smoke detection and airborne particulate matter in spacecraft, limitations of existing technologies, and scenarios for false alarms. Further discussion will look at future mission environments with more stringent requirements, including vehicle autonomy and cabin pressures. A previous paper introduced a smoke detector to prevent false alarms in lunar missions by smoke-dust discrimination (ICES-2020-125), and this paper augments the technology summary with engineering hardware considerations for future missions.

Understanding the physical and chemical properties of extraterrestrial dust is crucial for extended human and robotic exploration on the Moon or Mars. Lunar and Martian dust can affect everything from equipment and spacesuits to habitable spaces in the lunar modules and may also serve as a potential resource for future space missions. Due to limited availability of lunar dust from the Apollo missions, simulant materials have been manufactured to replicate specific properties of the dust for testing on Earth. A total of 8 commercial and government-based simulants provided by NASA, SolySys Mining, and Space Resource Technologies were analyzed by automated particle analysis using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). The focus of the analysis was on the fine fraction of particles less than 20 micrometers. The fine size fraction has not been studied as extensively as the coarse fraction, but an understanding of the fine particle characteristics is essential for dust mitigation strategies. The behavior of dust particles in the small size fractions is vastly different than particles in the visible range. Transport and adhesion of particles below 20 micrometers pose risks to hardware and human health, and specialized microscopic characterization techniques are warranted. The automated SEM-EDS analysis provided data on size, shape, and elemental composition. Particle size distributions by number were determined as well as particle type concentrations based on elemental compositions. Optical and SEM relocation were also performed on the larger fraction of particles to correlate the color, surface morphology, and elemental composition. A comparison of the particle size distribution, elemental composition, and particle morphology was made between the lunar dust simulants and published data from Apollo mission studies.

Human occupied built environments are no longer confined to Earth. In fact, there have been humans living and working in low-Earth orbit on the International Space Station (ISS) since November 2000. With NASA’s Artemis missions and the age of commercial space stations set to begin, more human-occupied spacecraft than ever will be in Earth’s orbit and beyond. On Earth and in the ISS, microbes, especially fungi, can be found in dust and grow when unexpected, elevated moisture conditions occur. However, we do not yet know how indoor microbiomes in Earth-based homes and in the ISS differ due to their unique set of environmental conditions. Here we show that bacterial and fungal communities are different in dust collected from vacuum bags on Earth and the ISS, with Earth-based homes being more diverse (465 fungal OTUs and 237 bacterial ASVs) compared to the ISS (102 fungal OTUs and 102 bacterial ASVs). When dust from these locations were exposed to varying equilibrium relative humidity conditions (ERH), there were also significant fungal community composition changes as ERH and time elevated increased (Bray Curtis: R2 = 0.35, P = 0.001). These findings can inform future spacecraft design to promote healthy indoor microbiomes that support crew health, spacecraft integrity, and planetary protection.

Background The commercialization of space travel will soon lead to many more people living and working in unique built environments similar to the International Space Station, which is a specialized closed environment that contains its own indoor microbiome. Unintended microbial growth can occur in this environment as in building on Earth from elevated moisture, such as from a temporary ventilation system failure. This growth can drive negative health outcomes and degrade building materials. We need a predictive approach for modeling microbial growth in these critical indoor spaces. Results Here we demonstrate that even short exposures to varying elevated relative humidity can facilitate rapid microbial growth and microbial community composition changes in dust from spacecraft. We modeled fungal growth in dust from the International Space Station using the time-of-wetness framework with activation and deactivation limited growth occurring at 85% and 100% relative humidity, respectively. Fungal concentrations ranged from an average of 4.4 x 106 spore equivalents per mg dust in original dust with no exposure to relative humidity to up to 2.1 x 1010 when exposed to 100% relative humidity for 2-weeks. As relative humidity and time elevated increased, fungal diversity was significantly reduced for both alpha (Q < 0.05) and beta (R2 = 0.307, P = 0.001) diversity metrics. Bacteria were unable to be modeled using the time-of-wetness framework. However, bacterial communities did changes based on constant relative humidity incubations for both beta (R2 = 0.22, P = 0.001) and alpha diversity decreasing with increasing moisture starting at 85% relative humidity (Q < 0.05). Conclusion Our results demonstrate moisture conditions can be used to develop predict changes in fungal growth and composition onboard human-occupied spacecraft. This predictive model can be expanded upon to include other spacecraft environmental factors such as microgravity, elevated carbon dioxide conditions, and radiation exposure. Understanding microbial growth in spacecraft can help better protect astronaut health, fortify spacecraft integrity, and promote planetary protection as human activity increases in low-Earth orbit, the moon, Mars, and beyond.

Polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCDD), "novel" brominated flame retardants (NBFRs), organophosphate esters (OPEs), polycyclic aromatic hydrocarbons (PAH), perfluoroalkyl substances (PFAS), and polychlorinated biphenyls (PCBs) were measured in a composite sample of dust from the International Space Station (ISS). Notwithstanding the unique environment from which the dust originated, while concentrations of all target compound classes frequently exceeded the median values in terrestrial indoor microenvironments in the US and western Europe, ISS dust concentrations were generally within the terrestrial range. The relative abundance of the three HBCDD diastereomers is dominated by γ-HBCDD (96.6% ΣHBCDD). This matches very closely with the commercial mixture added to materials and contrasts with the diastereomer distribution observed in most terrestrial indoor dust samples (in which γ-HBCDD is typically ∼60-70% ΣHBCDD). This suggests conditions inside the ISS do not favor the previously reported photolytically mediated formation in dust of α-HBCDD. Also of note, the concentration of perfluorooctanoic acid (PFOA) in ISS dust (3300 ng/g) exceeds the maximum reported (1960 ng/g) in a 2008 survey of dust from US child daycare centers and homes. This may reflect the widespread use of waterproofing treatments in the ISS to prevent microbial growth. Our findings can inform future material choices for manned spacecraft such as the ISS.

Fire is a very serious threat in any confined volume but particularly so when a crew is confined in a spacecraft far from Earth, where there is little or no possibility of receiving aid or being rescued. Therefore, every measure must be taken to prevent a fire from happening. Even with material controls and other fire prevention measures, fire detection, suppression, and clean-up systems must be provided on spacecraft to allow the crew to respond to a fire. Unlike flames in normal gravity, fires in low gravity are not supported by the strong pumping of oxidizer and fuel into the flame zone and the subsequent pumping of the reactants out of the reaction zone. The lack of buoyancy allows a flame to propagate at lower air velocities than on Earth that changes the transport of oxygen into the flame, heat transfer to the fuel surface, and transport of heat out of the reaction zone. Under these conditions, the flame spread can occur at conditions and with characteristics that are not duplicated readily in normal gravity because of the large buoyant flows generated by the flame. Differences in flame characteristics also impact requirements for fire detection and suppression of spacecraft fires. Of course, any fire response protocol must be compatible with the other spacecraft systems such as the Environmental Control and Life Support System (ECLSS).

To reduce transportation costs for building a lunar base station, it is important to utilise in-situ resources like lunar regolith. Lunar regolith can be used to create a concrete-like material by means of geopolymerization. For application of geopolymerizing mixtures, the rheology of the slurry must be known in advance. This article investigates the rheology of mixtures of lunar dust simulants with water, NaOH (as alkaline agent) and urea (as superplasticizer). The rheology of all the mixtures can be approximated with the Bingham Model. Aging has a dramatic effect on the rheology of the water + simulant mixture and, after 2 days, the yield stress decreases by six times. The presence of NaOH, on the contrary, increases both the apparent viscosity and the yield stress as it promotes geopolymerization. The addition of urea reduces the viscosity by 25%, but it has a limited effect on the yield stress. These findings can enable the design of construction 3D printers on the moon. (C) 2021 COSPAR. Published by Elsevier B.V. All rights reserved.

Air quality on board the International Space Station (ISS) is a significant concern for the long-term health of astronauts living on the station. Aerosolized particles are generated from a variety of sources, such as on-board equipment, electronics, and the astronauts themselves. Airborne particles can remain suspended for significant amounts of time due to the absence of gravitational settling. In this work, we examine the particulate matter on board the ISS through scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX) and single-particle multi-element inductively coupled plasma time-of-flight mass spectrometry (sp-ICP) analysis of two vacuum bag dust samples collected with a handheld vacuum cleaner used to clean surfaces and filter faces inside the ISS. SEM/EDX analysis shows that many large particles were collected. These particles are most commonly clothing fibers or of biological origin, along with smaller numbers of carbonaceous particles that may be from polymer and halopolymer materials. sp-ICP analysis quantitatively determined metal concentrations in particles approximately <10 µm in diameter and was able to identify several distinct particle compositions. Some of these, such as stainless steel (Fe-Cr-Ni-Mn), antiperspirant (Al-Zr), silver (Ag), and titanium oxide (Ti) particles, are consistent with particle types identified through past aerosol and vacuum bag sampling and analyses. Other types, including Fe-Al and other types of Al and Zr particles, do not have a clear origin consistent with past work. SEM/EDX and sp-ICP provide different but complementary information regarding the composition of particles obtained from vacuum bag dust samples. The material analyzed was obtained through the Divert Unwanted Space Trash (DUST) experiment on ISS, which returned vacuum bags to Earth for the purpose of understanding airborne particles in the unique ISS environment. Copyright © 2021 American Association for Aerosol Research

Commercial space transportation must address air quality on flights in the same way that the commercial aircraft transportation industry has worked to ensure a standard of air cleanliness and breathability. There are multiple scenarios for future space transportation, ranging from multiyear exploration missions to suborbital flights on the order of minutes, and space tourism excursions with durations somewhere in-between these extremes. Written air quality standards do not exist for these scenarios at this time, but they will differ based on the mission duration and the level of life support equipment within the space vehicle. Once standards are written and implemented, the quantitative assessment of air quality must be communicated to the crew, without requiring interpretation and active management of this information. A tool to summarize pollution levels for spaceflight participants and crew members is of high importance. The most common approach for characterizing air pollution is the air quality index (AQI). The AQI system has been developed in different countries around the world, mainly for outdoor environments, based on the results of risk assessments, epidemiological studies, and current local air pollution standards. Earth-based AQIs cannot be extrapolated to microgravity indoor environments, so the objective of this work was to explore what will be required to formulate a space air quality index for future commercial spacecraft.

Fire detection faces challenges of increasing sensitivity, accuracy, and response speed while reducing false alarms. Air quality sensors measure fire emission signatures similar to smoke detectors but are often more sensitive. Recent advancement in air quality sensors provides an opportunity to improve fire detection. This study used low-cost and research-grade gas and particle sensors to detect and characterize emissions from laboratory smoldering and flaming tests of three spacecraft-relevant materials. The electrochemical carbon monoxide (CO) sensor sensitively detected fire emissions in all but a pyrolysis test, whereas the metal oxide volatile organic compound (VOC) sensor with cross sensitivity for CO detected fire emissions in all tested cases. Several low-cost particle sensors, although saturated at high concentrations, detected smoke at low concentrations. A combination of CO/VOC and particle sensors would provide sensitive fire detection distinct from non-combustion nuisance sources. In support of the ongoing Spacecraft Fire Safety Experiments (Saffire), the DustTrak DRX aerosol monitor was evaluated for smoke measurement. It measured particle concentrations over a wide range and its single particle counting provided additional size distribution data similar to that of an optical particle counter. However, the single particle counting accuracy degraded at high concentrations due to coincidence errors.

Exposure to bioaerosols can adversely influence human health through respiratory tract, eye, and skin irritation. Bioaerosol composition is unique on the International Space Station (ISS), where the size distribution of particles in the air differs from those on Earth. This is due to the lack of gravitational settling and sources of biological particles. However, we do not understand how microbes are influenced by particle size in this environment. We analyzed two types of samples from the ISS: (1) vacuum bag debris which had been sieved into five different size fractions and (2) passively collected particles on a tape substrate with a passive aerosol sampler. Using quantitative polymerase chain reaction (qPCR), the highest concentration of fungal spores was found in the 106–150 μm-sized sieved dust particles, while the highest concentration of bacterial cells was found in the 150–250 μm-sized sieved dust particles. Illumina MiSeq DNA sequencing revealed that particle size was associated with bacterial and fungal communities and statistically significant (p = 0.035, p = 0.036 respectively). Similar fungal and bacterial species were found within the passive aerosol sample and the sieved dust samples. The most abundant fungal species identified in the aerosol and sieved samples are commonly found in food and plant material. Abundant bacterial species were most associated with the oral microbiome and human upper respiratory tract. One limitation to this study was the suboptimal storage conditions of the sieved samples prior to analysis. Overall, our results indicate that microbial exposure in space may depend on particle size. This has implications for ventilation and filtration system design for future space vehicles and habitats.

Conventional spacecraft smoke detectors are not optimized for detecting space smoke, which differs from that on Earth due to the fuel materials, burning conditions, particle formation/transformation processes, and lack of gravity. More effective smoke detectors can be developed with knowledge of smoke chemical compositions, size distributions, optical properties, and emission factors specific to spacecraft-relevant materials, e.g., Poly(methyl methacrylate) (PMMA), cotton, and Nomex® fabric. In normal gravity testing it is found that carbon is the main smoke component, with elemental carbon constituting ∼90% of particle mass for flaming PMMA combustion and organic matter constituting ≳80% of particle mass for other fuels and test conditions. Particles emitted from flaming PMMA are fractal-like soot agglomerates, different from the near spherical particles found for other fuels and burning conditions. Particle size distributions vary during the combustion process. When particle concentrations are near maximum, smoldering cotton generates bimodal number size distributions, while other fuels and test conditions exhibit unimodal lognormal number size distributions. Smoke particles from flaming PMMA combustion are black with single scattering albedos <0.3, while particles from other burned materials demonstrate low light absorption, with single scattering albedos >0.9 at 405–781 nm. Mass extinction coefficients are 7.8 m2/g for flaming PMMA and 2.7–4.2 m2/g for smoldering combustions at 632.8 nm. CO and PM2.5 emission factors are higher for smoldering than for flaming combustions, while CO2 emission factors are higher for flaming combustions.