Editing Human spaceflight (section)

=== Environmental hazards ===
{{See also|Bioastronautics|Space habitat|Effect of spaceflight on the human body|Locomotion in Space}}

Planners of human spaceflight missions face a number of safety concerns.

==== Life support ====
{{Main| Life support system}}

The basic needs for breathable air and drinkable water are addressed by the [[life support system]] of the spacecraft.

{{See also|Astronautical hygiene}}

==== Medical issues ====
{{See also|Effect of spaceflight on the human body|Sleep in space|Space medicine}}

Astronauts may not be able to quickly return to Earth or receive medical supplies, equipment, or personnel if a medical emergency occurs. The astronauts may have to rely for long periods on limited resources and medical advice from the ground.

The possibility of [[blindness]] and of [[Bone Loss|bone loss]] have been associated with human [[space flight]].<ref name="NYT-20140127">{{cite news |last=Chang |first=Kenneth |title=Beings Not Made for Space |url=https://www.nytimes.com/2014/01/28/science/bodies-not-made-for-space.html |date=27 January 2014 |work=[[The New York Times]] |access-date=27 January 2014 }}</ref><ref name="Wired-20120723">{{cite magazine |last=Mann |first=Adam |title=Blindness, Bone Loss, and Space Farts: Astronaut Medical Oddities |url=https://www.wired.com/wiredscience/2012/07/medicine-psychology-space/ |date=23 July 2012 |magazine=[[Wired (magazine)|Wired]] |access-date=23 July 2012 }}</ref>

On 31 December 2012, a [[NASA]]-supported study reported that spaceflight may harm the brains of [[astronauts]] and accelerate the onset of [[Alzheimer's disease]].<ref name="PLOS-20121231">{{cite journal |last1=Cherry |first1=Jonathan D. |last2=Frost |first2=Jeffrey L. |last3=Lemere |first3=Cynthia A. |last4=Williams |first4=Jacqueline P. |last5=Olschowka |first5=John A. |last6=O'Banion |first6=M. Kerry |title=Galactic Cosmic Radiation Leads to Cognitive Impairment and Increased Aβ Plaque Accumulation in a Mouse Model of Alzheimer's Disease |doi=10.1371/journal.pone.0053275 |volume=7 |issue=12 |page=e53275 |journal=[[PLoS ONE]]  |pmid=23300905 |date=2012 |pmc=3534034|bibcode=2012PLoSO...753275C |doi-access=free }}</ref><ref name="SpaceRef-20130101">{{cite web |title=Study Shows that Space Travel is Harmful to the Brain and Could Accelerate Onset of Alzheimer's |url=http://spaceref.com/news/viewpr.html?pid=39650 |date=1 January 2013 |publisher=SpaceRef |access-date=7 January 2013 |archive-date=21 May 2020 |archive-url=https://web.archive.org/web/20200521052054/http://spaceref.com/news/viewpr.html?pid=39650/ |url-status=dead }}</ref><ref name="NasaWatch-20130103">{{cite web |last=Cowing |first=Keith |author-link=Keith Cowing |title=Important Research Results NASA Is Not Talking About (Update) |url=http://nasawatch.com/archives/2013/01/important-resea.html |date=3 January 2013 |publisher=NASA Watch |access-date=7 January 2013 }}</ref>

In October 2015, the [[NASA Office of Inspector General]] issued a [[Effect of spaceflight on the human body|health hazards report]] related to [[space exploration]], which included the potential hazards of a [[human mission to Mars]].<ref name="AP-20151029">{{cite news |last=Dunn |first=Marcia |title=Report: NASA needs better handle on health hazards for Mars |url=http://apnews.excite.com/article/20151029/us-sci-space-travel-health-6dfd5b2c76.html |date=29 October 2015 |agency=Associated Press |access-date=30 October 2015 }}</ref><ref name="NASA-20151029oig">{{cite web |author=Staff |title=NASA's Efforts to Manage Health and Human Performance Risks for Space Exploration (IG-16-003) |url=https://oig.nasa.gov/audits/reports/FY16/IG-16-003.pdf |date=29 October 2015 |work=[[NASA]] |access-date=29 October 2015 |archive-date=30 October 2015 |archive-url=https://web.archive.org/web/20151030161330/https://oig.nasa.gov/audits/reports/FY16/IG-16-003.pdf |url-status=dead }}</ref>

On 2 November 2017, scientists reported, based on [[Magnetic resonance imaging|MRI studies]], that significant changes in the position and structure of the brain have been found in astronauts who have taken [[Effect of spaceflight on the human body|trips in space]]. Astronauts on longer space trips were affected by greater brain changes.<ref name="NEJM-20171102">{{cite journal |author=Roberts, Donna R. |display-authors=etal |title=Effects of Spaceflight on Astronaut Brain Structure as Indicated on MRI |date=2 November 2017 |journal=[[New England Journal of Medicine]] |volume=377 |issue=18 |pages=1746–1753  |doi=10.1056/NEJMoa1705129 |pmid=29091569 |s2cid=205102116 |doi-access=free }}</ref><ref name="QTZ-20171103">{{cite web |last=Foley |first=Katherine Ellen |title=Astronauts who take long trips to space return with brains that have floated to the top of their skulls |url=https://qz.com/1119668/space-travel-changes-astronauts-brains/ |date=3 November 2017 |work=[[Quartz (publication)|Quartz]] |access-date=3 November 2017 }}</ref>

Researchers in 2018 reported, after detecting the presence on the [[International Space Station]] (ISS) of five ''[[Enterobacter|Enterobacter bugandensis]]'' bacterial strains, none [[pathogen]]ic to humans, that [[microorganism]]s on ISS should be carefully monitored to assure a healthy environment for [[astronaut]]s.<ref name="EA-20181122">{{cite web |author=BioMed Central |title=ISS microbes should be monitored to avoid threat to astronaut health |url=https://www.eurekalert.org/pub_releases/2018-11/bc-ims112018.php |date=22 November 2018 |work=[[EurekAlert!]] |access-date=25 November 2018 |archive-date=26 November 2018 |archive-url=https://web.archive.org/web/20181126005739/https://www.eurekalert.org/pub_releases/2018-11/bc-ims112018.php |url-status=dead }}</ref><ref name="BMC-20181123">{{cite journal |author=Singh, Nitin K. |display-authors=etal |title=Multi-drug resistant Enterobacter bugandensis species isolated from the International Space Station and comparative genomic analyses with human pathogenic strains |date=23 November 2018 |journal=[[BMC Microbiology]] |volume=18 |issue=1 |page=175 |doi=10.1186/s12866-018-1325-2 |pmid=30466389 |pmc=6251167 |doi-access=free |bibcode=2018BMCMb..18..175S }}</ref>

In March 2019, NASA reported that latent [[virus]]es in humans may be activated during space missions, possibly adding more risk to astronauts in future deep-space missions.<ref name="EA-20190315">{{cite news |author=Staff |title=Dormant viruses activate during spaceflight – NASA investigates - The stress of spaceflight gives viruses a holiday from immune surveillance, putting future deep-space missions in jeopardy |url=https://www.eurekalert.org/pub_releases/2019-03/f-dva031519.php |date=15 March 2019 |work=[[EurekAlert!]] |access-date=16 March 2019 |archive-date=18 March 2019 |archive-url=https://web.archive.org/web/20190318230153/https://www.eurekalert.org/pub_releases/2019-03/f-dva031519.php |url-status=dead }}</ref>

On 25 September 2021, [[CNN]] reported that an alarm had sounded during the [[Inspiration4]] Earth-orbital journey on the [[SpaceX Dragon 2]]. The alarm signal was found to be associated with an apparent toilet malfunction.<ref name="CNN-20210925">{{cite news |last=Wattles |first=Jackie |title=An alarm went off on SpaceX's all-tourist space flight. The problem was the toilet |url=https://www.cnn.com/2021/09/25/tech/spacex-toilet-waste-management-system-scn/index.html |date=25 September 2021 |work=[[CNN]] |access-date=25 September 2021 }}</ref>

===== Microgravity =====
{{See also|Weightlessness}}
[[File:Space fluid shift.gif|thumb|The effects of microgravity on fluid distribution around the body (greatly exaggerated)]]

Medical data from astronauts in low Earth orbits for long periods, dating back to the 1970s, show several adverse effects of a microgravity environment: loss of [[bone]] density, decreased muscle strength and endurance, postural instability, and reductions in aerobic capacity. Over time these [[deconditioning]] effects can impair astronauts' performance or increase their risk of injury.<ref>
{{cite web|url=http://exploration.grc.nasa.gov/Exploration/Advanced/Human/Exercise/ |title=Exploration Systems Human Research Program – Exercise Countermeasures |work=NASA |url-status=dead |archive-url=https://web.archive.org/web/20081011052437/http://exploration.grc.nasa.gov/Exploration/Advanced/Human/Exercise/ |archive-date=11 October 2008 }}</ref>

In a weightless environment, astronauts put almost no weight on the back [[muscle]]s or leg muscles used for standing up, which causes the muscles to weaken and get smaller. Astronauts can lose up to twenty per cent of their muscle mass on spaceflights lasting five to eleven days. The consequent loss of strength could be a serious problem in case of a landing emergency.<ref>{{cite web|url = https://www.nasa.gov/pdf/64249main_ffs_factsheets_hbp_atrophy.pdf|title = NASA Information: Muscle Atrophy|access-date = 20 November 2015|website = NASA|archive-date = 22 July 2020|archive-url = https://web.archive.org/web/20200722232908/https://www.nasa.gov/pdf/64249main_ffs_factsheets_hbp_atrophy.pdf|url-status = dead}}</ref> Upon returning to Earth from [[long-duration spaceflight|long-duration]] flights, astronauts are considerably weakened and are not allowed to drive a car for twenty-one days.<ref>{{cite web|title = Earth Living Is Tough for Astronaut Used to Space|url = http://www.space.com/21413-hadfield-astronaut-health-return-earth.html|website = Space.com|date = 3 June 2013|access-date = 21 November 2015}}</ref>

Astronauts experiencing weightlessness will often lose their orientation, get [[motion sickness]], and lose their sense of direction as their bodies try to get used to a weightless environment. When they get back to Earth, they have to readjust and may have problems standing up, focusing their gaze, walking, and turning. Importantly, those motor disturbances only get worse the longer the exposure to weightlessness.<ref>{{cite news | url=https://abcnews.go.com/Technology/story?id=3830060&page=1 | last=Watson | first=Traci | date=11 November 2007 | title=Readjusting to gravity anti-fun for astronauts | publisher=ABC News | access-date=14 February 2020}}</ref> These changes can affect the ability to perform tasks required for approach and landing, docking, remote manipulation, and emergencies that may occur while landing.<ref>{{Cite journal|last1=Eddy|first1=D. R.|last2=Schiflett|first2=S. G.|last3=Schlegel|first3=R. E.|last4=Shehab|first4=R. L.|date=August 1998|title=Cognitive performance aboard the life and microgravity spacelab|url=https://pubmed.ncbi.nlm.nih.gov/11541924|journal=Acta Astronautica|volume=43|issue=3–6|pages=193–210|doi=10.1016/s0094-5765(98)00154-4|issn=0094-5765|pmid=11541924|bibcode=1998AcAau..43..193E}}</ref>

In addition, after long [[space flight]] missions, male astronauts may experience severe [[visual system|eyesight]] problems, which may be a major concern for future deep space flight missions, including a [[crewed mission]] to the planet [[Mars]].<ref name="Mader-2011">{{cite journal|author=Mader, T. H. |display-authors=etal |title=Optic Disc Edema, Globe Flattening, Choroidal Folds, and Hyperopic Shifts Observed in Astronauts after Long-duration Space Flight|date=2011 |journal=[[Ophthalmology (journal)|Ophthalmology]] |volume=118 |issue=10|pages=2058–2069 |doi=10.1016/j.ophtha.2011.06.021 |pmid=21849212|s2cid=13965518 |url=http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1068&context=nasapub }}</ref><ref name="Puiu-20111109">{{cite web |last=Puiu |first=Tibi |title=Astronauts' vision severely affected during long space missions|url=http://www.zmescience.com/medicine/astronaut-eyesight-damage-weightlessness-3214143/|date=9 November 2011 |publisher=zmescience.com |access-date=9 February 2012 }}</ref><ref name="CNN-20120109">[http://www.cnn.com/video/#/video/us/2012/02/09/pkg-zarrella-astronaut-vision.cnnCNN News (CNN-TV, 02/09/2012) – Video (02:14) – Male Astronauts Return With Eye Problems]. CNN (9 February 2012). Retrieved on 22 November 2016.</ref><ref name="Space-20120313">{{cite web|title=Spaceflight Bad for Astronauts' Vision, Study Suggests |url=http://www.space.com/14876-astronaut-spaceflight-vision-problems.html |date=13 March 2012 |publisher=[[Space.com]] |access-date=14 March 2012 }}</ref><ref name="Radiology-20120313">{{cite journal |author=Kramer, Larry A. |display-authors=etal |title=Orbital and Intracranial Effects of Microgravity: Findings at 3-T MR Imaging |journal=[[Radiology (journal)|Radiology]] |volume=263 |issue=3 |pages=819–27 |doi=10.1148/radiol.12111986 |pmid=22416248 |date=13 March 2012 }}</ref><ref name="WIRED-20140212">{{cite magazine |author=Kevin Fong MD  |title=The Strange, Deadly Effects Mars Would Have on Your Body |url=https://www.wired.com/opinion/2014/02/happens-body-mars/ |date=12 February 2014 |magazine=[[Wired (magazine)|Wired]] |access-date=12 February 2014 }}</ref> Long space flights can also alter a space traveler's eye movements.<ref>{{cite journal |last1=Alexander |first1=Robert |last2=Macknik |first2=Stephen |last3=Martinez-Conde |first3=Susana |title=Microsaccades in applied environments: Real-world applications of fixational eye movement measurements |journal=Journal of Eye Movement Research |date=2020 |volume=12 |issue=6 |doi=10.16910/jemr.12.6.15 |pmid=33828760 |pmc=7962687 |doi-access=free }}</ref>

===== Radiation =====
{{See also|Health threat from cosmic rays}}
[[File:PIA17601-Comparisons-RadiationExposure-MarsTrip-20131209.png|thumb|right|Comparison of Radiation Doses – includes the amount detected on the trip from Earth to Mars by the [[Radiation assessment detector|RAD]] on the [[Mars Science Laboratory|MSL]] (2011–2013)<ref name="SCI-20130531a">{{cite journal |last=Kerr |first=Richard |title=Radiation Will Make Astronauts' Trip to Mars Even Riskier |date=31 May 2013 |journal=[[Science (journal)|Science]] |volume=340 |issue=6136 |page=1031 |doi=10.1126/science.340.6136.1031 |pmid=23723213 |bibcode=2013Sci...340.1031K}}</ref>]]

Without proper shielding, the crews of missions beyond low Earth orbit might be at risk from high-energy protons emitted by [[solar particle event]]s (SPEs) associated with [[solar flare]]s. If estimated correctly, the amount of radiation that astronauts would be exposed to from a solar storm similar to that of the most powerful in recorded history, the [[Carrington Event]], would result in [[acute radiation sickness]] at least, and could even be fatal "in a poorly shielded spacecraft".<ref>{{cite web |url=https://www.newscientist.com/article/dn7142 |title= Superflares could kill unprotected astronauts|work=New Scientist |date=21 March 2005 |first=Stephen |last=Battersby}}</ref>{{better source needed|reason=Citation does not differentiate between solar flares and solar particle events.|date=December 2021}} Another storm that could have inflicted a potentially lethal dose of radiation on astronauts outside Earth's protective [[magnetosphere]] occurred during the [[Space Age]], shortly after [[Apollo 16]] landed and before [[Apollo 17]] launched.<ref>{{cite journal |author1 = Mike Lockwood |author2 = M. Hapgood |title = The Rough Guide to the Moon and Mars |journal = Astron. Geophys. |volume = 48 |issue = 6 |pages = 11–17 |date = 2007 |doi = 10.1111/j.1468-4004.2007.48611.x |bibcode = 2007A&G....48f..11L |doi-access = free }}</ref> This solar storm, [[August 1972 solar storm|which occurred in August 1972]], could potentially have caused any astronauts who were exposed to it to suffer from acute radiation sickness, and may even have been lethal for those engaged in [[extravehicular activity]] or on the lunar surface.<ref>{{cite journal |author1 = Jennifer L. Parsons |author2 = L. W. Townsend |title = Interplanetary Crew Dose Rates for the August 1972 Solar Particle Event |journal = Radiat. Res. |volume = 153 |issue = 6 |pages = 729–733 |date = 2000 |doi = 10.1667/0033-7587(2000)153[0729:ICDRFT]2.0.CO;2 |pmid = 10825747 |bibcode = 2000RadR..153..729P |s2cid = 25250687 }}</ref>

Another type of radiation, galactic [[cosmic ray]]s, presents further challenges to human spaceflight beyond low Earth orbit.<ref>{{cite book|isbn=978-0-309-10264-3|url=http://www.nap.edu/catalog.php?record_id=11760 |title=Space Radiation Hazards and the Vision for Space Exploration |publisher=NAP |date=2006| doi=10.17226/11760 }}</ref>

There is also some scientific concern that extended spaceflight might slow down the body's ability to protect itself against diseases,<ref>{{cite journal|doi=10.1189/jlb.0309167 |title=Could spaceflight-associated immune system weakening preclude the expansion of human presence beyond Earth's orbit|date=2009|last1=Gueguinou|first1=N.|last2=Huin-Schohn|first2=C.|last3=Bascove|first3=M.|last4=Bueb|first4=J.-L.|last5=Tschirhart|first5=E.|last6=Legrand-Frossi|first6=C.|last7=Frippiat|first7=J.-P.|journal=Journal of Leukocyte Biology|volume=86|issue=5|pages=1027–1038|pmid=19690292|doi-access=}}</ref> resulting in a weakened [[immune system]] and the activation of dormant [[virus]]es in the body. [[Radiation]] can cause both short- and long-term consequences to the bone marrow stem cells from which blood and immune-system cells are created. Because the interior of a spacecraft is so small, a weakened immune system and more active viruses in the body can lead to a fast spread of infection.<ref>{{cite web |last1=Sohn |first1=Rebecca |title=How do viruses affect astronauts in space? |url=https://www.space.com/viruses-in-space-astronaut-health-impacts |website=Space.com |date=7 March 2022 |publisher=Future US |access-date=20 October 2022}}</ref>

===== Isolation =====
{{Further|Effect of spaceflight on the human body#Psychological effects|Psychological and sociological effects of spaceflight}}

During long missions, astronauts are isolated and confined in small spaces. [[Depression (mood)|Depression]], anxiety, [[cabin fever]], and other psychological problems may occur more than for an average person and could impact the crew's safety and mission success.<ref>{{Cite journal|last=Flynn|first=Christopher F.|date=1 June 2005|title=An Operational Approach to Long-Duration Mission Behavioral Health and Performance Factors|url=http://www.ingentaconnect.com/contentone/asma/asem/2005/00000076/A00106s1/art00007|journal=Aviation, Space, and Environmental Medicine|volume=76|issue=6|pages=B42–B51|pmid=15943194}}</ref> NASA spends millions of dollars on psychological treatments for astronauts and former astronauts.<ref>{{Cite book |title=Space psychology and psychiatry |date=2008 |publisher=Springer |last1=Kanas |first1=Nick |last2=Manzey |first2=Dietrich |isbn=9781402067709 |edition=2nd |location=Dordrecht |oclc=233972618}}</ref> To date, there is no way to prevent or reduce mental problems caused by extended periods of stay in space.

Due to these mental disorders, the efficiency of astronauts' work is impaired; and sometimes they are brought back to Earth, incurring the expense of their mission being aborted.<ref>{{Cite news |url=https://www.theguardian.com/science/2014/oct/05/hallucinations-isolation-astronauts-mental-health-space-missions|title=Isolation and hallucinations: the mental health challenges faced by astronauts |last=Bell|first=Vaughan|date=5 October 2014|work=The Observer|access-date=2019-02-01|language=en-GB |issn=0029-7712}}</ref> A Russian expedition to space in 1976 was returned to Earth after the cosmonauts reported a strong odor that resulted in a fear of fluid leakage; but after a thorough investigation, it became clear that there was no leakage or technical malfunction. It was concluded by NASA that the cosmonauts most likely had [[Phantosmia|hallucinated the smell]].

It is possible that the mental health of astronauts can be affected by the changes in the sensory systems while in prolonged space travel.

===== Sensory systems =====
During astronauts' spaceflight, they are in an extreme environment. This, and the fact that little change is taking place in the environment, will result in the weakening of sensory input to the astronauts' seven senses.
* [[Hearing]] – In the space station and spacecraft there are no noises from the outside, as there is no medium that can transmit sound waves. Although there are other team members who can talk to each other, their voices become familiar and do not stimulate the sense of hearing as much. Mechanical noises become familiar, as well.
* [[Sight]] – Because of weightlessness, the body's liquids attain an equilibrium that is different from what it is on the Earth. For this reason, an astronaut's face swells and presses on the eyes; and therefore their vision is impaired. The landscape surrounding the astronauts is constant, which lessens visual stimulations. Due to cosmic rays, astronauts may see flashes, even with their eyelids closed.
* [[Sense of smell|Smell]] – The space station has a permanent odor described as the smell of gunpowder. Due to the zero gravity, the bodily fluids rise to the face and prevent the sinuses from drying up, which dulls the sense of smell.
* [[Taste]] – The sense of taste is directly affected by the sense of smell and therefore when the sense of smell is dulled, the sense of taste is also. The astronauts' food is bland, and there are only certain foods that can be eaten. The food comes only once every few months, when supplies arrive, and there is little or no variety.
* [[Somatosensory system|Touch]] – There are almost no stimulating changes in physical contact. There is almost no human physical contact during the journey.
* The [[vestibular system]] (motion and equilibrium system) – Due to the lack of gravity, all the movements required of the astronauts are changed, and the vestibular system is damaged by the extreme change.
* The [[Proprioception|proprioception system]] (the sense of the relative position of one's own parts of the body and strength of effort being employed in movement) – As a result of weightlessness, few forces are exerted on the astronauts' muscles; and there is less stimulus to this system.