Astronautical hygiene
Encyclopedia
Astronautical hygiene is the application of science and technology to the recognition and evaluation of hazard
Hazard
A hazard is a situation that poses a level of threat to life, health, property, or environment. Most hazards are dormant or potential, with only a theoretical risk of harm; however, once a hazard becomes "active", it can create an emergency situation. A hazard does not exist when it is not...

s, and the prevention or control of risks to health, while working in low-gravity
Weightlessness
Weightlessness is the condition that exists for an object or person when they experience little or no acceleration except the acceleration that defines their inertial trajectory, or the trajectory of pure free-fall...

 environments.

Space medicine
Space medicine
Space medicine is the practice of medicine on astronauts in outer space whereas astronautical hygiene is the application of science and technology to the prevention or control of exposure to the hazards that may cause astronaut ill health. Both these sciences work together to ensure that...

 has developed as a science since 1948 when Dr. Hubertus Strughold
Hubertus Strughold
Dr. Hubertus Strughold was a German doctor and prominent medical researcher during the early twentieth century. An emigre to the United States after World War II, he is also known as "The Father of Space Medicine". He was the author of over 180 papers in the field of space medicine...

 predicted many of the medical problems of working in low gravity for example, neurovestibular disturbances, red blood cell changes. The discipline of astronautical hygiene includes such topics as the use and maintenance of life support
Life support
Life support, in medicine is a broad term that applies to any therapy used to sustain a patient's life while they are critically ill or injured. There are many therapies and techniques that may be used by clinicians to achieve the goal of sustaining life...

 systems, the risks of extravehicular activity
Extra-vehicular activity
Extra-vehicular activity is work done by an astronaut away from the Earth, and outside of a spacecraft. The term most commonly applies to an EVA made outside a craft orbiting Earth , but also applies to an EVA made on the surface of the Moon...

, the risks of exposure to chemicals or radiation, the characterisation of hazards, human factor issues and the development of risk management
Risk management
Risk management is the identification, assessment, and prioritization of risks followed by coordinated and economical application of resources to minimize, monitor, and control the probability and/or impact of unfortunate events or to maximize the realization of opportunities...

 strategies. Astronautical hygiene works side by side with space medicine
Space medicine
Space medicine is the practice of medicine on astronauts in outer space whereas astronautical hygiene is the application of science and technology to the prevention or control of exposure to the hazards that may cause astronaut ill health. Both these sciences work together to ensure that...

 to ensure that astronaut
Astronaut
An astronaut or cosmonaut is a person trained by a human spaceflight program to command, pilot, or serve as a crew member of a spacecraft....

s will be healthy and safe when working in space. This is especially critical with the planned manned expeditions to the Moon and Mars.

Overview

When astronauts return to the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 and travel farther to Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

, or even other planets, they will be exposed to a number of hazards e.g. radiation, microbes in the spacecraft, planetary surface toxic dust. An "astronautical hygienist" or an astronaut with knowledge of the discipline would provide invaluable data during the voyage on for example, how to assess the risks to health from exposure to chemicals within the spacecraft and the appropriate measures to mitigate exposure. Once on the surface of the Moon or planet the astronautical hygienist would provide information on the nature of the dust, measure the potential levels of exposure while exploring the surface terrain, assess the likely risks to health and thereby determine how to prevent or control exposure. Applying astronautical hygiene knowledge and expertise from the gathered intelligence during the journey would ensure that the health of the astronauts was protected at all time.

The Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...

 is to be replaced in 2014 by a new spacecraft the Orion
Orion (spacecraft)
Orion is a spacecraft designed by Lockheed Martin for NASA, the space agency of the United States. Orion development began in 2005 as part of the Constellation program, where Orion would fulfill the function of a Crew Exploration Vehicle....

 to carry astronauts to the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...

. Orion will contain potentially hazardous material such as ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

, hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...

, freon, nitrogen tetroxide, volatile 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 and individual United Kingdom astronautical hygienists and space medicine experts are developing the measures that will mitigate exposure to these substances.

Dr. John R. Cain (a United Kingdom government expert) was the first scientist to define this new discipline. He is a fellow of the Institute of Biology
Institute of Biology
The Institute of Biology was a professional body for biologists, primarily those working in the United Kingdom. The Institute was founded in 1950 by the Biological Council: the then umbrella body for Britain's many learned biological societies...

, a fellow of the British Interplanetary Society
British Interplanetary Society
The British Interplanetary Society founded in 1933 by Philip E. Cleator, is the oldest space advocacy organisation in the world whose aim is exclusively to support and promote astronautics and space exploration.-Structure:...

, a member of the Faculty of Occupational Hygiene and a member of the United Kingdom Space Biomedicine Association. For many years, he has been working to develop the discipline of astronautical hygiene with the goal of establishing a school of space medicine and astronautical hygiene in Britain linked with a major university. The establishing of the UK Space Agency
UK Space Agency
The UK Space Agency is a United Kingdom government agency responsible for its civil space programme. It was established on 1 April 2010 to replace the British National Space Centre and took over responsibility for government policy and key budgets for space and represents the UK in all negotiations...

 to promote and develop space science is one step in achieving this goal.

Hygiene in space

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. Since surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...

 causes water and soap bubbles to adhere to the skin, very little water is needed. Special non-rinsing soap is used, as well as special non-rinsing shampoos. Since a flush toilet would not work in low gravity environments, a special toilet was designed, that has suction capability. 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. The current toilet model was first flown on STS-54
STS-54
-Mission parameters:*Mass:**Orbiter landing with payload: **Payload: *Perigee: *Apogee: *Inclination: 28.5°*Period: 90.6 min-Space walks:* Harbaugh and Runco – EVA 1*EVA 1 Start: 17 January 1993...

 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.

Control of gases in spacecraft

Toxic gases are produced as an off-gassing from the astronauts, non-metallic materials e.g. surface coatings, adhesives, elastomers, solvents, cleaning agents, heat exchanger liquids etc. The gases if inhaled above specific concentrations could affect the ability of the crew to carry out their duties effectively

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.

Exposure limits are based on:
  • "Normal" spacecraft operating conditions.
  • An "emergency" situation.


In the normal conditions there are found trace contaminant gases such as ammonia from normal off-gassing at ambient temperatures and at 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
Ethylene glycol
Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...

) and from the pyrolysis
Pyrolysis
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...

 of non-metallic components. Carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 is a major concern for space crews; this was evident during the Apollo missions. The emitted trace gases can be controlled using lithium hydroxide
Lithium hydroxide
Lithium hydroxide is an inorganic compound with the formula LiOH. It is a white hygroscopic crystalline material. It is soluble in water and slightly soluble in ethanol...

 filter
Filter (chemistry)
In chemistry and common usage, a filter is a device that is designed to physically block certain objects or substances while letting others through. Filters are often used to remove solid substances suspended in fluids, for example to remove air pollution, to make water drinkable, and to prepare...

s to trap carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 and activated carbon
Activated carbon
Activated carbon, also called activated charcoal, activated coal or carbo activatus, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions.The word activated in the name is sometimes replaced...

 filters to trap other gases.

Gases in the cabin can be tested using gas chromatography, mass spectrometry
Mass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...

 and infra-red spectrophotometry
Infrared spectroscopy
Infrared spectroscopy is the spectroscopy that deals with the infrared region of the electromagnetic spectrum, that is light with a longer wavelength and lower frequency than visible light. It covers a range of techniques, mostly based on absorption spectroscopy. As with all spectroscopic...

. Samples of air from the spacecraft are examined both before and after flight for 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 on-going sampling of the hazardous substances is essential so that appropriate action can be taken if exposure is high.

A large number of volatile substances have been detected during flight mostly within their threshold limit values and NASA Spacecraft Maximum Allowable Concentration Limits. 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.

Spacecraft maximum allowable concentrations

SMACs provide guidance on chemical exposures during normal as well as emergency operations aboard spacecraft. Short-term SMACs refer to concentrations of airborne substances such as a gas and vapor that will not comprise 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 crews performance under continuous exposure to chemicals for as long as 180 days.

Astronautical hygiene data needed for developing the SMACs include:
  • chemical-physical characterization of the toxic chemical
  • animal toxicity studies
  • human clinical studies
  • accidental human exposures
  • epidemiological studies
  • in-vitro toxicity studies

Hazard

Lunar dust
Lunar soil
Lunar soil is the fine fraction of the regolith found on the surface of the Moon. Its properties can differ significantly from those of terrestrial soil...

 or regolith is the layer of particles on the Moon's surface and is <100 um. 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) and electrostatically
Electrostatics
Electrostatics is the branch of physics that deals with the phenomena and properties of stationary or slow-moving electric charges....

. During Apollo, the dust was found to cause wear in the fabric of the spacesuit.

Evaluation of risks

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 and charge and its plasma
Plasma (physics)
In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms , thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions...

 characteristics.

Control

The use of high-gradient magnetic separation
Magnetic separation
Magnetic separation is a process in which magnetically susceptible material is extracted from a mixture using a magnetic force. This separation technique can be useful in mining iron as it is attracted to a magnet....

 techniques should be developed to remove dust from the spacesuits following exploration as the fine fraction of the lunar dust is magnetic. Furthermore, vacuums can be used to remove dust from spacesuits.

Mass spectrometry

Mass spectrometry
Mass spectrometry
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...

 has been used to monitor spacecraft cabin air quality. 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.

Deposition of inhaled particles of lunar dust

The extent of the inflammatory response in the lung will depend on where the lunar dust particles are deposited. In 1G deposition in 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.

Microbial hazards in space

During spaceflight there will be the transfer of microbes
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...

 between crew members. Microbial exchange commonly occurs amongst astronauts. Several bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

l associated diseases were experienced by the crew in Skylab 1
Skylab
Skylab was a space station launched and operated by NASA, the space agency of the United States. Skylab orbited the Earth from 1973 to 1979, and included a workshop, a solar observatory, and other systems. It was launched unmanned by a modified Saturn V rocket, with a mass of...

. The microbial contamination in the Skylab was found to be very high. Staphylococcus aureus
Staphylococcus aureus
Staphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently found as part of the normal skin flora on the skin and nasal passages. It is estimated that 20% of the human population are long-term carriers of S. aureus. S. aureus is the most common species of...

and Aspergillus
Aspergillus
Aspergillus is a genus consisting of several hundred mold species found in various climates worldwide. Aspergillus was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli...

spp have commonly been isolated from the air and surfaces during several space missions. The microbes do not sediment in microgravity which results in persisting airborne aerosol
Aerosol
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...

s 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 of fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

 and pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

ic streptococci were found.

Proteus mirabilis
Proteus mirabilis
Proteus mirabilis is a Gram-negative, facultatively anaerobic, rod shaped bacterium. It shows swarming motility, and urease activity. P. mirabilis causes 90% of all Proteus infections in humans.-Diagnosis:...

, an organism commonly isolated from patients with urinary tract infection
Urinary tract infection
A urinary tract infection is a bacterial infection that affects any part of the urinary tract. Symptoms include frequent feeling and/or need to urinate, pain during urination, and cloudy urine. The main causal agent is Escherichia coli...

, tends to build up on the urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...

 collection devices. This could be a serious problem during the trip to Mars especially as some of the astronauts may be susceptible to urinary infection. In Apollo 13, the lunar module pilot suffered an acute urinary tract infection which required two weeks of antibiotic therapy to resolve.

Biofilm
Biofilm
A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance...

 that may contain a mixture of bacteria and fungi have the potential to damage electronic equipment by oxidising various components e.g. copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 cables. Such organisms flourish because they survive on the organic matter
Organic matter
Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds...

 released from the astronaut's skin. Organic acids produced by microbes, 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 microbial mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

s.

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 it is important that the risks are assessed and where appropriate the levels of microbial growth controlled by the use of good astronautical hygiene. For example, by frequently sampling the spacecabin 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 manned missions to the Moon and Mars that the risks from microbial contamination will be underestimated unless the principles of good astronautical hygiene practice are applied. Further research in this field is therefore especially important so that the risks of exposure can be evaluated and the necessary measures to mitigate microbial growth are developed.

Microbes and microgravity in space

There are over one hundred strains of bacteria and fungi that have been identified from manned space missions. These microorganisms survive and propagate in space. 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 as ethylene oxide
Ethylene oxide
Ethylene oxide, also called oxirane, is the organic compound with the formula . It is a cyclic ether. This means that it is composed of two alkyl groups attached to an oxygen atom in a cyclic shape . This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered...

 and methyl chloride
Chloromethane
Chloromethane, also called methyl chloride, R-40 or HCC 40, is a chemical compound of the group of organic compounds called haloalkanes. It was once widely used as a refrigerant. It is a colorless extremely flammable gas with a minorly sweet odor, which is, however, detected at possibly toxic levels...

; and astronauts are quarantine
Quarantine
Quarantine is compulsory isolation, typically to contain the spread of something considered dangerous, often but not always disease. The word comes from the Italian quarantena, meaning forty-day period....

d for several days prior to a mission. However, these measures only reduce the 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 are immunocompromised
Immunodeficiency
Immunodeficiency is a state in which the immune system's ability to fight infectious disease is compromised or entirely absent. Immunodeficiency may also decrease cancer immunosurveillance. Most cases of immunodeficiency are acquired but some people are born with defects in their immune system,...

, are not affected.

Humans in space

The work of Cain ("Spaceflight" Dec 2007) and others 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 the body 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 be psychosocial
Psychosocial
For a concept to be psychosocial means it relates to one's psychological development in, and interaction with, a social environment. The individual needs not be fully aware of this relationship with his or her environment. It was first commonly used by psychologist Erik Erikson in his stages of...

 changes caused by traveling in the confined space of a spacecraft. Astronautical hygiene (and space medicine) needs to address these issues in particular the likely behavioral 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 for contact dermatitis
Contact dermatitis
Contact dermatitis is a term for a skin reaction resulting from exposure to allergens or irritants . Phototoxic dermatitis occurs when the allergen or irritant is activated by sunlight....

 to develop in particular if there is exposure to skin sensitisers such as acrylate
Acrylate
The acrylate ion is the ion of acrylic acid.Acrylates are the salts and esters of acrylic acid. They are also known as propenoates ....

s. 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.

Noise

Fans, compressor
Gas compressor
A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...

s, motor
Engine
An engine or motor is a machine designed to convert energy into useful mechanical motion. Heat engines, including internal combustion engines and external combustion engines burn a fuel to create heat which is then used to create motion...

s, transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

s, pump
Pump
A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...

s etc. on the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...

 (ISS) all generate considerable noise. As more equipment is required on the space station, then more noise will be generated.

The Russian space program has never given a high priority to the noise levels experienced by its cosmonauts (e.g. on Mir
Mir
Mir was a space station operated in low Earth orbit from 1986 to 2001, at first by the Soviet Union and then by Russia. Assembled in orbit from 1986 to 1996, Mir was the first modular space station and had a greater mass than that of any previous spacecraft, holding the record for the...

 the noise levels reached 70 - 72 dB. But they were exceeded as new components were brought on board. Such noise levels may cause a temporary reduction in hearing but not a full hearing loss. This could result in hazard warning alarms not being heard against the background noise. To reduce the noise risks NASA engineers are building 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. For future space programs it is essential that the noise levels are reduced. The use of hearing protectors are not encouraged because they block out alarm signals. More research is necessary in 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.

Hazards of radiation in space

Space radiation consists of high energy particles such as proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

s, alpha
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...

 and heavier particles originating from such sources as galactic cosmic rays
Galactic cosmic ray
Galactic cosmic rays are cosmic rays that have their origin inside our Galaxy. GCRs are high-energy charged particles, and are usually protons, electrons, and fully ionized nuclei of light elements...

, energetic solar particles
Solar Energetic Particles
Solar Energetic Particles are high-energy particles coming from the Sun which had been first observed in the early 1940s. They consist of protons, electrons and heavy ions with energy ranging from a few tens of keV to GeV...

 from solar flare
Solar flare
A solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy . The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day...

s and trapped radiation belt
Van Allen radiation belt
The Van Allen radiation belt is a torus of energetic charged particles around Earth, which is held in place by Earth's magnetic field. It is believed that most of the particles that form the belts come from solar wind, and other particles by cosmic rays. It is named after its discoverer, James...

s. 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.

Trapped radiation

The Earth's magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

 is responsible for the formation of the trapped radiation belts that surround Earth. The ISS orbits at between 200 nautical miles (370.4 km) and 270 nautical miles (500 km), known as a Low Earth Orbit (LEO). Trapped radiation doses in LEO decrease during solar maximum
Solar maximum
Solar maximum or solar max is the period of greatest solar activity in the solar cycle of the sun. During solar maximum, sunspots appear....

 and increase during solar minimum
Solar minimum
Solar minimum is the period of least solar activity in the solar cycle of the sun. During this time, sunspot and solar flare activity diminishes, and often does not occur for days at a time...

. Highest exposures occur in the South Atlantic Anomaly
South Atlantic Anomaly
The South Atlantic Anomaly is an area where the Earth's inner Van Allen radiation belt comes closest to the Earth's surface. This leads to an increased flux of energetic particles in this region and exposes orbiting satellites to higher than usual levels of radiation...

 region.

Galactic cosmic radiation

This radiation originates from outside the solar system and consists of ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

ized charged atomic nuclei
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...

 from hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

, helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

 and uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

. 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.

Solar Particle Events

These are injections of energetic electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s, proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

s, alpha particles into interplanetary space during solar flare eruptions. During periods of maximum solar activity, the frequency and intensity of solar flares will increase. The solar proton event
Solar proton event
A Solar proton event occurs when protons emitted by the Sun become accelerated to very high energies either close to the Sun during a solar flare or in interplanetary space by the shocks associated with coronal mass ejections. These high energy protons cause several effects. They can penetrate the...

s 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
Geostationary orbit
A geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...

 or interplanetary
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

 orbits. Fortunately, most SPEs are short lived (less than 1 to 2 days) which allows for small volume "storm shelters" to be feasible.

Other

Radiation hazards may also come from man-made sources for example, medical investigations, radio-isotopic
Radionuclide
A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...

 power generators or from small experiments as on Earth. Lunar and Martian missions may include either nuclear reactors for power or related nuclear propulsion
Nuclear propulsion
Nuclear propulsion includes a wide variety of propulsion methods that fulfil the promise of the Atomic Age by using some form of nuclear reaction as their primary power source.- Surface ships and submarines :...

 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 the Journal of Plasma Physics and Controlled Fusion 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 the magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...

 that envelops the Earth. This form of control against solar radiation
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

will be necessary if man is 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.

Sources

  • British Interplanetary Society (BIS) Spaceflight - Letters and emails (September 2006, p 353)
  • BIS Spaceflight - Letters and emails (December 2007, p 477)
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