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Astronautical hygiene evaluates, and mitigates,hazards and health risks to those working inlow-gravity environments.[1] The discipline of astronautical hygiene includes such topics as the use and maintenance oflife support systems, the risks of theextravehicular activity, the risks of exposure to chemicals or radiation, the characterization of hazards, human factor issues, and the development ofrisk management strategies. Astronautical hygiene works side by side withspace medicine to ensure thatastronauts are healthy and safe when working in space.[citation needed]
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When astronauts travel in space, they are exposed to numerous hazards, such as radiation, microbes in the spacecraft, and planetary surface toxic dust, etc.[2] During a space voyage, astronautical hygienists work on collecting data concerning a multitude of subjects. Once the data has been collected, they then analyze the data to determine, among other things, the risks to human health due to exposure to the various chemicals within the spacecraft as well as other toxins during their flight. From that, the hygienists can determine the appropriate measures to take to mitigate exposure of the astronauts to the harmful chemicals.
Once on the surface of a moon or planet, the astronautical hygienist would also collect data on the nature of the dust, and the levels of radiation on the surface. From this analysis, they would determine the risks to the astronauts' health and will conclude how to prevent or control exposure.
The main roles of the astronautical hygienist are as follows:[3][4]
TheOrion spacecraft (orMulti-Purpose Crew Vehicle) is an American-European interplanetaryspacecraft intended to carry a crew of four astronauts[5] to destinations at or beyondlow Earth orbit (LEO). Currently under development by the National Aeronautics and Space Administration (NASA) and theEuropean Space Agency (ESA) for launch on theSpace Launch System.[6][7] Orion will contain potentially hazardous material such asammonia,hydrazine,freon,nitrogen tetroxide, andvolatile organic compounds and it will be necessary to prevent or control exposure to these substances during flight. Astronautical hygienists in the United States together with colleagues in the European Union, individual United Kingdom astronautical hygienists and space medicine experts are developing measures that will mitigate exposure to these substances.[citation needed]
Dr. John R. Cain (a UK government health risk management expert) was the first scientist to define the new discipline of astronautical hygiene. The establishment of theUK Space Agency and the UK Space Life and Biomedical Sciences Association (UK Space LABS) see the development and application of the principles of astronautical hygiene as an important means to protect the health of astronauts working (and eventually living) in space.
Cleaning and waste disposal issues arise when dealing with low gravity environments. On the International Space Station, there are no showers, and astronauts instead take short sponge baths, with one cloth used to wash, and another used to rinse. Sincesurface tension causes water and soap bubbles to adhere to the skin, very little water is needed.[8][9] Special non-rinsing soap is used, as well as special non-rinsing shampoos.[10] Since a flush toilet would not work in low gravity environments, a special toilet was designed, that has suction capability.[11] While the design is nearly the same, the concept uses the flow of air, rather than water. In the case of the space shuttle, waste water is vented overboard into space, and solid waste is compressed, and removed from the storage area once the shuttle returns to Earth.[12] The current toilet model was first flown onSTS-54 in 1993, and features an unlimited storage capacity, compared to only 14-day capacity of the original shuttle toilets, and the new model has an odor-free environment.[10]
Inside the ISS, astronauts wear ordinary clothes. The clothes are not washed, and are typically worn until being considered too dirty, at which point they are taken back to Earth as rubbish, or ejected as waste to burn up in the atmosphere. In 2020, per agreement between NASA andProcter & Gamble, research into space-usable detergents began;[13] in 2021, an experimental detergent was launched aboardSpaceX CRS-24.
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Toxic gases are produced as anoff-gassing from the astronauts and non-metallic materials e.g. surface coatings, adhesives, elastomers, solvents, cleaning agents, heat exchanger liquids, etc.[14] Above specific concentrations, if inhaled, the gases could affect the ability of the crew to carry out their duties effectively.[15]
Most of the toxicological data on gas exposure is based on the 8-hour work period of the terrestrial worker and is therefore unsuitable for spacecraft work. New exposure times (astronautical hygiene data) have had to be established for space missions where exposure can be uninterrupted for up to 2 weeks or longer with no daily or weekend periods.[14]
Exposure limits are based on:
In normal conditions, there are trace contaminant gases such as ammonia from normal off-gassing at ambient temperatures and elevated temperatures. Other gases arise from the breathing gas supply reservoirs and crew members themselves. In emergencies, gases can arise from overheating, spills, a rupture in the coolant loop (ethylene glycol) and from thepyrolysis of non-metallic components.Carbon monoxide is a major concern for space crews; this was evident during theApollo missions.[16][17] The emitted trace gases can be controlled usinglithium hydroxidefilters to trapcarbon dioxide andactivated carbon filters to trap other gases.
Gases in the cabin can be tested usinggas chromatography,mass spectrometry andinfra-red spectrophotometry. Samples of air from the spacecraft are examined both before and after flight for their gas concentrations. The activated carbon filters can be examined for evidence of trace gases. The concentrations measured can be compared with the appropriate exposure limits. If the exposures are high then the risks to health increase. The ongoing sampling of the hazardous substances is essential so that appropriate action can be taken if exposure is high.
A large number of volatile substances detected during the flight are mostly within their threshold limit values and NASA Spacecraft Maximum Allowable Concentration Limits.[18] If spacecraft cabin exposure to specific chemicals is below their TLVs and SMACs then it is expected that the risks to health following inhalation exposure will be reduced.
SMACs guide chemical exposures during normal as well as emergency operations aboard spacecraft. Short-term SMACs refer to concentrations of airborne substances such as gas and vapour that will not compromise the performance of specific tasks by astronauts during emergency conditions or cause serious toxic effects. Long-term SMACs are intended to avoid adverse health effects and to prevent any noticeable changes in the crew's performance under continuous exposure to chemicals for as long as 180 days.[19]
Astronautical hygiene data needed for developing the SMACs include:[20]
Lunar dust or regolith is the layer of particles on the Moon's surface and is approximately <100 um.[21] The grain shapes tend to be elongated. Inhalation exposure to this dust can cause breathing difficulties because the dust is toxic. It can also cloud astronauts' visors when working on the Moon's surface. Furthermore, it adheres to spacesuits both mechanically (because of barbed shapes) andelectrostatically. During Apollo, the dust was found to cause wear in the fabric of the spacesuit.[22]
During lunar exploration, it will be necessary to evaluate the risks of exposure to the Moon dust and thereby instigate the appropriate exposure controls. Required measurements may include measuring exospheric-dust concentrations, surface electric fields, dust mass, velocity, charge, and itsplasma characteristics.[23][24][25]
The extent of the inflammatory response in the lung will depend on where the lunar dust particles are deposited. In the 1G deposition, the more central airways will reduce the transport of the fine particles to the lung periphery. On the Moon with fractional gravity, the inhaled fine particles will be deposited in more peripheral regions of the lung. Therefore, because of the reduced sedimentation rate in lunar gravity, fine particles of dust will deposit in the alveolar region of the lung. This will exacerbate the potential for lung damage.[26][27]
The use of high-gradientmagnetic separation techniques should be developed to remove dust from the spacesuits following exploration as the fine fraction of the lunar dust is magnetic.[28] Furthermore, vacuums can be used to remove dust from spacesuits.
Mass spectrometry has been used to monitor spacecraft cabin air quality.[29] The results obtained can then be used to assess the risks during spaceflight for example, by comparing the concentrations of VOCs with their SMACs. If the levels are too high then appropriate remedial action will be required to reduce the concentrations and the risks to health.
During spaceflight, there will be the transfer ofmicrobes between crew members. Severalbacterial associated diseases were experienced by the crew inSkylab 1. The microbial contamination in the Skylab was found to be very high.Staphylococcus aureus andAspergillus spp have commonly been isolated from the air and surfaces during several space missions. The microbes do not sediment inmicrogravity which results in persisting airborneaerosols and high microbial densities in-cabin air in particular if the cabin air filtering systems are not well maintained. During one mission, an increase in the number and spread offungi andpathogenic streptococci were found.[30]
Urine collection devices build up the bacteriumProteus mirabilis, which is associated withurinary tract infection. For this reason, astronauts may be susceptible tourinary tract infection. An example is theApollo 13 mission, during which theApollo Lunar Module pilot experienced an acute urinary tract infection which required two weeks ofantibiotic therapy to resolve.[31]
Biofilm that may contain a mixture of bacteria and fungi have the potential to damage electronic equipment by oxidising various components e.g.copper cables. Such organisms flourish because they survive on theorganic matter released from the astronaut's skin. Organic acids produced bymicrobes, in particular fungi, can corrode steel, glass and plastic. Furthermore, because of the increase in exposure to radiation on a spacecraft, there are likely to be more microbialmutations.
Because of the potential for microbes to cause infection in the astronauts and to be able to degrade various components that may be vital for the functioning of the spacecraft, the risks must be assessed and, where appropriate, manage the levels of microbial growth controlled by the use of good astronautical hygiene. For example, by frequently sampling the space-cabin air and surfaces to detect early signs of a rise in microbial contamination, keeping surfaces clean by the use of disinfected clothes, by ensuring that all equipment is well maintained in particular the life support systems and by regular vacuuming of the spacecraft to remove dust etc. It is likely that during the first crewed missions to Mars that the risks from microbial contamination could be underestimated unless the principles of good astronautical hygiene practice are applied. Further research in this field is therefore needed so that the risks of exposure can be evaluated and the necessary measures to mitigate microbial growth are developed.
There are over one hundred strains of bacteria and fungi that have been identified from crewed space missions.[32] These microorganisms survive and propagate in space.[33] Much effort is being made to ensure that the risks from exposure to the microbes are significantly reduced. Spacecraft are sterilized as good control practice by flushing with antimicrobial agents such asethylene oxide andmethyl chloride, and astronauts arequarantined for several days before a mission. However, these measures only reduce microbe populations rather than eliminate them. Microgravity may increase the virulence of specific microbes. It is therefore important that the mechanisms responsible for this problem are studied and the appropriate controls are implemented to ensure that astronauts, in particular, those that areimmunocompromised, are not affected.[34]
The work of Cain (2007) and others[35] have seen the need to understand the hazards and risks of working in a low gravity environment. The general effects on the body of space flight or reduced gravity for example, as may occur on the Moon or during the exploration of Mars include changed physical factors such as decreased weight, fluid pressure, convection and sedimentation. These changes will affect thebody fluids, the gravity receptors and the weight-bearing structures. The body will adapt to these changes over the time spent in space. There will also bepsychosocial changes caused by travelling in the confined space of a spacecraft. Astronautical hygiene (and space medicine) needs to address these issues, in particular, the likely behavioural changes to the crew otherwise the measures developed to control the potential health hazards and risks will not be sustained. Any decrease in communication, performance and problem solving, for example, could have devastating effects.
During space exploration, there will be the potential forcontact dermatitis to develop in particular if there is exposure to skin sensitisers such asacrylates. Such skin disease could jeopardise a mission unless appropriate measures are taken to identify the source of the exposure, to assess the health risks, and thereby determine the means to mitigate exposure.[36]
Fans,compressors,motors,transformers,pumps etc. on theInternational Space Station (ISS) all generate noise. As more equipment is required on the space station, there is a potential for more noise. Astronaut Tom Jones indicated the noise was more of an issue in the earlier days of the space station when astronauts wore hearing protection. Today, hearing protection is not required and sleeping chambers are soundproofed.[37]
The Russian space program has never given a high priority to the noise levels experienced by itscosmonauts (e.g. onMir the noise levels reached 70–72 dB). Less than 75 decibels are unlikely to cause hearing loss.[38] Seenoise-induced hearing loss for more information. This could result in hazard warning alarms not being heard against the background noise. To reduce the noise risks NASA engineers built hardware with inbuilt noise reduction. A depressurized pump producing 100 dB can have the noise levels reduced to 60 dB by fitting four isolation mounts. The use of hearing protectors are not encouraged because they block out alarm signals. More research is necessary for this field as well as in other astronautical hygiene areas e.g. measures to reduce the risks of exposure to radiation, methods to create artificial gravity, more sensitive sensors to monitor hazardous substances, improved life support systems and more toxicological data on the Martian and lunar dust hazards.
Space radiation consists of high energy particles such asprotons,alpha and heavier particles originating from such sources asgalactic cosmic rays, energeticsolar particles fromsolar flares and trappedradiation belts. Space station crew exposures will be much higher than those on Earth and unshielded astronauts may experience serious health effects if unprotected. Galactic cosmic radiation is extremely penetrating and it may not be possible to build shields of sufficient depth to prevent or control exposure.
The Earth'smagnetic field is responsible for the formation of the trapped radiation belts that surround Earth. The ISS orbits at between 200 nautical miles (370 km) and 270 nautical miles (500 km), known as a Low Earth Orbit (LEO). Trapped radiation doses in LEO decrease duringsolar maximum and increase duringsolar minimum. Highest exposures occur in theSouth Atlantic Anomaly region.
This radiation originates from outside theSolar System and consists ofionized chargedatomic nuclei fromhydrogen,helium anduranium. Due to its energy, the galactic cosmic radiation is very penetrating. Thin to moderate shielding is effective in reducing the projected equivalent dose but as shield thickness increases, shield effectiveness drops.
These are injections of energeticelectrons,protons, alpha particles intointerplanetary space during solar flare eruptions. During periods of maximum solar activity, the frequency and intensity of solar flares will increase. Thesolar proton events generally occur only once or twice a solar cycle.
The intensity and spectral disruption of SPEs have a significant impact on shield effectiveness. The solar flares occur without much warning so they are difficult to predict. SPEs will pose the greatest threat to unprotected crews in polar,geo-stationary orinterplanetary orbits. Fortunately, most SPEs are short-lived (less than 1 to 2 days) which allows for small volume "storm shelters" to be feasible.
Radiation hazards may also come from man-made sources, for example, medical investigations,radio-isotopic power generators or from small experiments as on Earth. Lunar and Martian missions may include eithernuclear reactors for power or relatednuclear propulsion systems. Astronautical hygienists will need to assess the risks from these other sources of radiation and take appropriate action to mitigate exposure.
Laboratory tests reported in theJournal of Plasma Physics and Controlled Fusion[39] indicate that a magnetic "umbrella" could be developed to deflect harmful space radiation away from the spacecraft. Such an "umbrella" would protect astronauts from the super-fast charged particles that stream away from the Sun. It would provide a protective field around the spacecraft similar to themagnetosphere that envelops the Earth. This form of control againstsolar radiation will be necessary if humans are to explore the planets and reduce the health risks from exposure to the deadly effects of radiation. More research is necessary to develop and test a practical system.
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