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Resultados científicos revolucionarios en la estación espacial de 2023

What we learned from scientific investigations on the space station in 2022, melissa l. gaskill.

Lee esta historia en español aquí .

The International Space Station, in its third decade of continuous human presence, has far-reaching impact as a microgravity lab hosting technology demonstrations and scientific investigations from a range of fields. Between Oct. 1, 2021 and Sept. 30, 2022, researchers published more than 400 scientific papers based on studies conducted aboard the space station.

Read highlights of some of the groundbreaking space station science published this past year below. For more space station research achievements and additional information about the findings mentioned here, check out the 2022 Annual Highlights of Results .

Tracking unique strains of microbes

Microbial Observatory-1 monitored the microbes present on the space station, identifying hundreds of microbial species. Researchers report finding three novel strains of Agrobacterium , a genus known for disease-causing characteristics. Results suggest that these strains could colonize habitats with fewer nutrients, giving them an advantage over those that need richer environments. The study of microbes offers insight to support development of mitigation strategies for maintaining safe living spaces for astronauts in spaceflight and for humans on Earth.

Protecting crew members’ brains

ISS Medical Monitoring regularly collects crew member health data that measures spaceflight’s effects on the human body. This information also is used for additional research studies. Researchers from ESA (European Space Agency) and State Space Corporation ROSCOSMOS used crew member blood samples taken before and after extended exposure to microgravity to assess brain tissue biomarkers. They report an increase in blood-based biomarkers of inflammation that could indicate potential risk to long-duration spaceflight crews. Additional studies with larger samples are needed to clarify these findings.

Measuring magnetars

NICER studies the extraordinary physics of neutron stars, which are glowing cinders left behind by supernovas, or the explosions of massive stars. Researchers report the classification of a recently discovered astronomical object, Swift J1555.2-5402, as a magnetar. Magnetars are highly magnetized neutron stars that release an enormous amount of magnetic energy through irregular outbursts of X- and gamma-rays. Observations of these outbursts help scientists address a wide range of astronomical topics, increasing understanding of some of the most extreme conditions in the universe.

Cyanobacteria rock extreme environments

EXPOSE R-2 BIOMEX, an investigation from ESA, measures the survival of terrestrial organisms in extreme environments, which could provide insight into the characteristics that extraterrestrial life would need to survive in space. Researchers exposed the desert cyanobacterium Chroococcidiopsis to simulated Mars-like conditions in space and on the ground. They report no increased genetic variants in the space strain, suggesting that the strain retained its ability to repair accumulated DNA lesions caused by radiation exposure. Cyanobacteria have potential for use in artificial bioregenerative life support systems to provide oxygen and food in space and for fuel, fertilizers, marine farming, and pharmaceuticals on Earth.

How plants sense gravity

Gravity acts as an important influence on plant development on Earth. Plant Gravity Sensing, an investigation from the Japan Aerospace Exploration Agency (JAXA), studies whether plants grown in microgravity can sense changes in gravity. Researchers report that Arabidopsis seeds cultured on a nylon lace mesh in microgravity had coiled roots and increased root entanglement with the mesh compared to those in Earth’s gravity. This observation suggests that gravity influences root coiling. Understanding how gravity affects plant growth could help scientists develop new ways to grow plants in space and lead to development of new plant varieties on Earth.

Archaeology in orbit

More than 332,000 items have been sent to the space station during its 20-plus years of human habitation. SQuARE, an investigation sponsored by the ISS National Lab, examined what happened to these objects and their possible symbolic and social meanings for crew members. Researchers report their observations on the processes developed to return research, commercial, and personal items to Earth and the meanings and associations of the objects that return. This research provides insights into the nature of life on the station and could inform design of future space habitats by expanding our understanding of how different objects and spaces are used over time. The paper’s authors received an Award for Outstanding Work in Digital Archaeology from the Archaeological Institute of America.

Microanalysis of Martian meteorite

Mochii is a miniature scanning electron microscope (SEM) that conducts real-time imaging and measurements of specimens on the space station. Such particles can interfere with equipment or affect crew health. To test the accuracy of the technology, researchers analyzed a fragment of a Martian meteorite found in Antarctica in 1984. They compared results using a standard SEM on the ground and Mochii on the space station, noting good agreement between the results that indicates accurate functioning of the microscope in space. Mochii could support novel, real-time scientific investigations and technology testing in microgravity to benefit space travelers and humans on Earth.

Watching water use from above

ECOSTRESS measures the temperature of the surface of Earth to help answer questions about water availability, vegetation water stress, and agricultural water use. Researchers used data from the investigation to study the water use efficiency (WUE) values within and among regions with different plant functional types, such as grassland and forest. WUE provides a direct measure of the link between plant carbon uptake and water loss and shows how ecosystem function varies with climate.

Ultracold bubbles

The space station’s Cold Atom Lab (CAL) produces clouds of chilled atoms that allow scientists to study fundamental behaviors and quantum characteristics that are difficult to probe at higher temperatures on Earth. Researchers report creation and measurements of bubbles of these ultracold atoms. Their observations could inform future microgravity studies exploring the fundamental nature of the condensed bubble state and advancing understanding of quantum systems.

Radio program notches 7th continent

The ISS Ham Radio program reached every continent on Earth when astronaut Kjell Lindgren spoke via amateur radio with students at a school in Argentina’s Esperanza Base in Antarctica. These sessions engage students, teachers, parents, and other members of the community and help inspire interest in science, technology, engineering, and math. Esperanza Base is a permanent, year-round Argentine research station in Hope Bay on the Trinity Peninsula, one of only two civilian settlements in Antarctica.

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• Clin Neuropsychiatry
• v.18(5); 2021 Oct

The Burden of Space Exploration on the Mental Health of Astronauts: A Narrative Review

Alessandro arone.

1 Department of Clinical and Experimental Medicine Section of Psychiatry, University of Pisa, 56100 Pisa, Italy

Konstantin Loganovsky

3 Department of Radiation Psychoneurology, Institute for Clinical Radiology, State Institution “National Research Centre for Radiation Medicine, National Academy of Medical Sciences of Ukraine”

Stefania Palermo

Elisabetta parra, walter flamini, donatella marazziti.

2 Unicamillus—Saint Camillus International University of Medical and Health Sciences, 00131 Rome, Italy

Space travel, a topic of global interest, has always been a fascinating matter, as its potential appears to be infinite. The development of advanced technologies has made it possible to achieve objectives previously considered dreams and to widen more and more the limits that the human species can overcome. The dangers that astronauts may face are not minimal, and the impacts on physical and mental health may be significant. Specifically, symptoms of emotional dysregulation, cognitive dysfunction, disruption of sleep-wake rhythms, visual phenomena and significant changes in body weight, along with morphological brain changes, are some of the most frequently reported occurrences during space missions.

Given the renewed interest and investment on space explorations, the aim of this paper was thus to summarize the evidence of the currently available literature, and to offer an overview of the factors that might impair the psychological well-being and mental health of astronauts.

To achieve the goal of this paper, the authors accessed some of the main databases of scientific literature and collected evidence from articles that successfully fulfilled the purpose of this work.

The results of this review demonstrated how the psychological and psychiatric problems occurring during space missions are manifold and related to a multiplicity of variables, thus requiring further attention from the scientific community as new challenges lie ahead, and prevention of mental health of space travelers should be carefully considered.

Introduction

Since its first steps on Earth, the human species has evolved by adapting and shaping the surrounding environment to its needs. Yet nowadays, in a modern era marked by pandemics, social inequalities, wars and in which men still have much to discover despite enormous advances in science and other fields, some environments represent a huge challenge. This is due to some of their features, to the point of being defined as "extreme environments", as they often require challenging physical and mental efforts ( Paulus et al., 2009 ; Ilardo & Nielsen, 2018 ). Extreme environments are manifold, and they include prolonged and marked isolation experiences on Earth, such as polar environments and submarine explorations, but they can also be found beyond our planet’s boundaries, in the case of space. The adjustment from Earth to an environment characterized by the lack of gravity naturally raises the need for physical adaptation primarily, but it may also lead to the search for new horizons and to stimulation of creative thinking ( Amabile & Gryskiewicz, 1987 ; Runco & Charles, 1993 ), thus determining the exploitation of mental resource that, however, in this process as fascinating as rich in implications, must be preserved. Over the decades, the public and scientific interest in space missions has progressively revealed the risks and dangers to health behind this project, in particular in the case of long-duration space missions, as several space hazards, such as microgravity and radiation, can sharp different organs and systems by altering the human physiology ( Clément & Slenzka, 2006 ). From cell damages ( Huang et al., 2009 ; Kawahara et al., 2009 ) to the alteration of the processes maintaining the health of bones and muscles ( Ilyina-Kakueva & Burkovskaya, 1991 ; Kaplansky et al., 1991 ; Davidson et al., 1999 ; Willey et al., 2011 ), the immune system ( Gridley et al., 2009 ), heart and vessels ( Fritsch-Yelle et al., 1996 ; Diedrich al., 2007 ; Boerma et al., 2015 ) and central nervous system (CNS) ( Souvestre et al., 2008 ), space also increases the risk of carcinogenesis ( Kennedy, 2014 ), thus urging the search for drugs and compounds able to prevent or mitigate it ( Burns et al., 2001 ; Zhang et al., 2006 ; Kennedy & Wan, 2011 ). Space missions, particularly of long duration, can put a strain on maintaining an adequate mental well-being, and the role of some personal and interpersonal factors has long been discussed ( Kanas, 1998 ; Flynn, 2005 ; Barr et al., 2007 ; Kalb & Solomon, 2007; Trappe et al., 2009 ; Fitts et al., 2010 ; Kandarpa et al., 2019 ; Marazziti et al., 2021 ). Both individually and in synergy, such factors may determine the onset of mood symptoms ( Gushin et al., 1993 ; Tafforin et al., 2015 ), cognitive issues ( Britten et al., 2012 ; 2016; Rabin et al., 2014 ; Acharya et al., 2019 ; Cacao & Cucinotta, 2019 ; Moore et al., 2019 ), sleep disturbances ( Putcha et al., 1999 ; Barger et al., 2014 ; Wotring, 2015 ) and others. Finally, space missions may cause some significant neuroanatomical effects, with most of the data available coming from magnetic resonance imaging (MRI) studies, and will then be briefly discussed herein.

Therefore, this paper was conceived as a narrative review with the aim of commenting on the current literature on the main psychological conditions affecting astronauts in the course of space missions. We also investigated the possible aetiology of such issues, with a focus on the psychosocial and physical factors involved.

Materials and Methods

The following databases were accessed in order to research and gather data from articles that were published only in English language from 1 January 1963 to 31 August 2021: PubMed, Scopus, Embase, PsycINFO and Google Scholar. Free text terms and MeSH headings were combined as follows: “(space missions OR space travels OR astronauts) AND (psychological OR psychiatric OR psychosocial OR issues OR symptoms)”. All the authors agreed to include in the review conference abstracts, posters and case reports if published in indexed journals. All the authors equally contributed in identifying potential information specific to this topic amongst the titles and abstracts evaluated.

The first selection excluded 2176 titles because: a) duplicates; b) not concerning the scope of the paper; c) not informative enough. The second selection excluded 435 abstracts after being read and reviewed, as the information presented did not fulfill the scope of our paper and/or did not appear to be relevant to the topic of interest. Subsequently, 114 more publications were excluded after further reading and evaluation, as they did not provide enough information and/or resulted sufficiently in line with our review. Finally, 100 papers were included in this paper ( figure 1 ).

Health issues

It has long been known that the health of space travelers can be endangered by various space factors, to the point that the National Aeronautics and Space Administration (NASA) recognized the existence of a new branch of science called “bioastronautics”, aimed at the study of the biological effects on the astronauts’ bodies ( Charles, 2005 ). In particular, most of the gathered evidence to this day suggests that space microgravity and radiation stand among the most known space perils ( table 1 ).

Physical factors in space and their effects on health

Several studies have pointed out how microgravity may alter cell physiology by compromising its structure or its survival ( Crawford-Young, 2006 ; Huang et al., 2009 ; Kawahara et al., 2009 ). Furthermore, a relationship has been described between microgravity and the immune system ( Woods & Chapes, 1994 ; Sonnenfeld, 2002 ; Gridley et al., 2009 ) that might lead to the onset of infections, immune disorders and CNS alterations that might affect the health of astronauts, with the consequent impairment of the positive mission’s outcome. Microgravity may also negatively impact the mechanisms of tissue repair in skeletal muscles and bones ( Ilyina-Kakueva & Burkovskaya, 1991 ; Kaplansky et al., 1991 ; Davidson et al., 1999 ). The cardiovascular system may be affected as well, since several studies showed an important decrease in heart rate during spaceflights ( Fuller, 1985 ), the possible onset of potentially fatal dysrhythmias ( Fritsch-Yelle et al., 1996 ) and several changes in blood and plasma volume ( Bao et al., 2007 ; Diedrich al., 2007 ). Post-flight orthostatic intolerance has been frequently reported in astronauts ( Fritsch-Yelle et al., 1996 ). Finally, the sensory-motor system appears to be deeply affected by microgravity. Indeed, the CNS needs to adapt to microgravity since different spatial information, such as somatosensory, visual and vestibular stimuli, has to be elaborated ( Souvestre et al., 2008 ). A syndrome known as space adaptation syndrome (SAS) may occur as a consequence of a sensory conflict between inputs from visual and tactile senses and vestibular organs ( Lackner & Dizio, 2006 ). The eye is another organ that may be affected by the effects of microgravity, with damages to either its structure and/or its functions. Optic nerve swelling, flattening of the posterior globe, periorbital edema and increased intraocular pressure have all been reported ( West, 2000 ; Kramer et al., 2012 ). Hypobaric hypoxia, a microgravity-induced condition caused by a decreased partial pressure of oxygen in space, may also occur, potentially causing further eye diseases such as retinal and vitreous hemorrhages or papilledema ( Russo et al., 2014 ).

Health professionals have long been warned about the negative and potentially catastrophic consequences for the human body following radiation exposure ( Meyers, 2000 ) and, in the course of space missions, different organs may be deeply affected by radiation. Bone loss and fractures may occur as a consequence of a disruption of the skeleton ( Willey et al., 2011 ). The cardiovascular system is also at risk, since it was found to be particularly sensitive to the effect of ionizing radiation ( Boerma et al., 2015 ). Nevertheless, when it comes to radiation, the focus is primarily on the risk of carcinogenesis, with the focus being shifted over the years to the search of potential surrogate endpoint biomarkers (SEBs) to explain this phenomenon ( Kennedy, 2014 ). Regardless, it has been suggested that radiation exposure may lead to oxidative stress, which in turn may be behind the mechanisms of carcinogenesis ( Kennedy & Wan, 2011 ). Therefore, unsurprisingly, antioxidants, along with protease inhibitors and retinoids, have been proposed as chemopreventive agents to oppose the risk of carcinogenesis ( Burns et al., 2001 ; Zhang et al., 2006 ; Kennedy & Wan, 2011 ), albeit further studies on the field are required to draw definitive conclusions.

Psychological and psychiatric problems

Emotional and interpersonal issues.

Emotion regulation seems to need appropriate countermeasures during long-duration space flights, as emotion training can play an important role in the success and safety of missions ( Liu et al., 2016 ). Mood issues of the astronauts have long been reported, and they may also compromise the fulfillment of the mission task, as in the case of the abrupt abort of the Soyuz T14-Salyut 7 mission in 1985, which was suggested to have been partly caused by crew's depression ( Morris, 2014 ). Symptoms of reduced resilience may occur, ranging from decreased drive and energy levels to passiveness ( Gushin et al., 1993 ). Anxiety symptoms have been reported and linked to negative interpersonal interactions, as well ( Tafforin et al., 2015 ). Indeed, the heterogeneity of the space crew in terms of size, ethnic background, languages and roles may result in tension and communication issues among the crew members ( Kanas, 1998 ). Prolonged isolation from loved ones and routine on Earth also pose a risk for the mental wellbeing of cosmonauts ( Kandarpa et al., 2019 ), along with sharing a confined environment with the same people around ( Harrison et al., 1989 ). Indeed, isolation may lead to monotony, which has been conceptualized as a three-fold model of spatio-temporal, sensory and social isolation and has been proven to be potentially detrimental for the success of the mission ( Peldszus et al., 2014 ). Evidence from space analogues would also suggest that such factors may be responsible for a wide range of symptoms, including fatigue, altered circadian rhythms, sleep disturbance and neurocognitive impairments ( Pagel & Choukèr, 2016 ; Deming & Vasterling, 2017 ). Moreover, the features of the spacecraft, which constitute the so-called “habitability” ( Musso et al., 2018 ) represent a fundamental element of space missions, for reasons exceeding far beyond its sole role as a means of transport, and may represent another stressor to the overall well-being of the astronauts. According to Kanas and Manzey (2008) , these include light, noise, vibration and temperature. As for the light, since it represents the main stimulus of the circadian rhythms, its excessive exposure may then lead to a deep alteration of the latter. Therefore, it has been suggested how either its removal from the settings and the spaces dedicated to sleep or the creation of an environment where alternating light and dark in the spaces shared by the astronauts may be desirable ( Caddick et al., 2017 ). Excessive exposure to noise, mainly due to the equipment and the crew activities, may represent a further stress factor for cosmonauts. Both wakefulness and sleeping may be compromised, to the point that cosmonauts have been instructed to wear protection devices to counteract the potential damages induced by high levels of noise ( Limardo et al., 2017 ).

Finally, habitability includes the need for privacy that, considering the spaces available and the peculiar environment, may not be always sufficiently respected, thus leading to possible psychological effects ( Winisdoerffer & Soulez-Larivière, 1992 ).

Cognitive problems

Although fascinating, space poses as a seriously stressful environment, and may therefore represent a danger to cognitive functions that, along with motor performances, have long been known to undergo some kind of deterioration under stress conditions ( Hockey, 1983 ; Albery & Goodyear, 1989 ; Lieberman et al., 2002 ).

Space radiation is one of the factors most involved in the onset of these issues, and its potential biological effects are broad, even at a low-dose rate exposure, that has been demonstrated to induce significant neurocognitive complications associated with an impairment in neurotransmission ( Acharya et al., 2019 ).

Originally, back to the 1960s, the general assumption was that the brain is not sensitive to the effect of cosmic radiation, and even the consequences on other body areas, such as the lens of the eye, were thought to be minimal ( Curtis, 1963 ). However, a few decades after the original assumptions of Curtis (1963) , it was demonstrated that high linear energy transfer (LET) particle irradiation of the brain may cause capillary hemorrhages, and that both neuroglia and blood-brain barrier may be vulnerable to damage following ionizing radiation. Since DNA repair in neural cells has a certain amount of mispair, such damages may produce different notable effects, including myelin degeneration, a reduction in local metabolism, and alterations in both synaptic density and microcirculation. Scientists and health professionals have long warned about adverse consequences following radiation exposure ( Meyers, 2000 ), as well as many secondary effects in cognition and mood due to a decrease in neuronal structural complexity ( Parihar et al., 2015 ; 2016).

As a result, it is not surprising that the radiation matter has gone under the lens of NASA, since the safety of space travellers and the success of missions may indeed be compromised by the neurocognitive effects induced by radiation ( Cucinotta et al., 2014 ). Indeed, radiation exposure is massive during space missions. The estimated average astronaut’s radiation exposure to Mars per year is equivalent to a cumulative dose of 672 millisieverts (mSv), and, in International Space Station (ISS) orbit, around 182.5 mSv. In order to get an estimate of the extent of such numbers, it should be highlighted that the average background radiation exposure on Earth per year is, instead, of 3 mSv ( Jones et al., 2012 ).

A large amount of data on the matter comes from rodent models strongly, suggesting potentially significant consequences of radiation on cognition ( Britten et al., 2012 ; 2016; Rabin et al., 2014 ; Cacao & Cucinotta, 2019 ). Furthermore, other researchers recently demonstrated that several alterations in the intrinsic electrophysiological features of CA1 superficial layer pyramidal neurons in the dorsal hippocampus may represent a consequence of the exposure to a prolonged 18 cGy dose of neutron radiation. These changes may persist after six months from the completion of irradiation ( Acharya et al., 2019 ). They also found that chronic (6 months) radiation exposure to low-dose (18 cGy) and dose rate (1 mGy/day) exposures to a mix of neutrons and photons caused an impairment in cellular signaling both in the prefrontal cortex and the hippocampus. This caused learning and memory impairment, and was linked to the potential increase of anxiety behaviors, thus also indicating damage to the amygdala ( Acharya et al., 2019 ). Some studies pointed out a significant reduction in dendritic complexity and spine density not only in the hippocampal but also in cortical neurons ( Parihar et al., 2015 ; 2016). Moreover, astronauts may undergo deficits in executive functions due to a functional loss in several areas of the brain, such as the medial prefrontal cortex, posterior cingulate, anterior cingulate and basal forebrain ( Lonart et al., 2012 ). Decision-making may also be affected ( Acharya et al., 2019 ). Indeed, it is a common assumption that one out of five astronauts taking part in a long space mission would experience similar behaviors, and out of three would instead face struggles in memory processes ( Acharya et al., 2019 ). Dopamine levels may be another key factor in neurobehavioral response to radiation ( Hienz et al., 2010 ), ando also gender, as murine models showed how male mice displayed an increased susceptibility to behavioral decrements secondary to radiation ( Krukowski et al., 2018 ). Different male susceptibility to cognitive processes to irradiation may be due to mechanisms related to memory formation ( Greene-Schloesser et al., 2012 ; Balentova & Adamkov, 2015 ). Therefore, it is evident that such effects need to be adequately studied in the future planning of interplanetary space fights.

Cognitive issues may also arise due to the effects of microgravity. Indeed, a reduction in different motor functions, such as dual-tasking, motion perception and manual dexterity, following a six-month period spent on ISS was recently demonstrated. However, it should be noted that these cognitive deficits were resolved in four days after landing. In any case, although this research is affected by a major bias that is the small sample size including eight astronauts only ( Moore et al., 2019 ), these effects may be a cue of relevant changes in brain structure ( Roberts et al., 2019 ). On the other hand, it has been suggested that microgravity may actually improve cognitive functions when taken out of a stress context that, instead, may represent the cause itself of cognitive impairment ( Wollseiffen et al., 2016 ).

Sleep disturbances

In the course of space missions, the achievement and maintenance of an adequate sleep quality is far from being an easy goal. Whether due to disturbances or its interruption, sleep alterations may in turn lead to tiredness, difficulties in maintaining the focus and, thus, to errors of different kind, which may result, in the worst case scenarios, to the extreme possibility of loss of life ( Buckey, 2006 ; Pandi-Perumal & Gonfalone, 2016 ).

Different factors may be involved, either individually or in combination, to sleep alterations, such as the uncomfortableness of sleeping bags, loud noises and different room temperatures ( Gundel et al., 1997 ; Stuster, 2000 ). The absence of gravity also seems to play an important role, as it may in particular shorten the duration of sleep ( Gonfalone, 2016 ).

In particular, recreational and mission-related activities tend to delay turning off the lights and going to bed, which could explain the delay in the onset of the sleep episode that was noted ( Dijk et al., 2001 ). In addition, a study of a group of astronauts in space over eight days showed an average of 4.6 awakenings per night and an average waking time during sleep of 6.5 minutes. The most frequent cause of these nocturnal awakenings was muscle stiffness as a result of trying to find a comfortable position in the sleeping bag ( Gundel et al., 1993 ). In parallel, a change in the structure of the cosmonauts' sleep was also observed, with changes in both REM sleep and the amount of slow-wave sleep ( Gundel et al., 1993 ).

In order to study the sleep-wake dynamics in a ground-based simulation of a mission to Mars, six individuals were isolated for 520 days. Most subjects experienced one or more problems, such as recurrent reductions in perceived sleep quality, interrupted sleep-wake periodicity, performance deficits associated with chronic partial sleep deprivation and increased sleep displacement in the daytime period ( Basner et al., 2013 ). These occurred at the start of the experiment and persisted throughout the duration of the simulation ( Basner et al., 2013 ). This reduction in sleep during space missions seems to be present even during a pre-flight training interval of 3 months, as revealed in another study of 64 astronauts ( Barger et al., 2014 ). Although derived from two studies only, these findings further suggest that maintaining good sleep patterns and quality is essential to prevent and/or reduce performance impairments.

In spite of chronic sleep deprivation, astronauts may frequently resort to the use of hypno-inducing drugs. In a report study of Barger et al. (2014) , about 75% of the crew members had taken a hypno-inducer, with drug take being reported on 52% of nights and the use of two doses of such drugs in around 17% of cases. The most frequently used medications were zolpidem and controlled-release zolpidem; others were temazepam, eszopiclone, melatonin and quetiapine fumarate. Furthermore, different drug combinations were reported, the most common being zolpidem and zaleplon and zolpidem and melatonin ( Barger et al., 2014 ). Another study looked at medication used during flight and found that 94% of astronauts were taking some medication, 45% for sleep disorders. In this case, the most frequently used sleep medications were temazepam (67%), triazolam (10%), flurazepam (7.5%), and zolpidem (10%) ( Putcha et al., 1999 ). In another research, the use of sleep medications was found to be about 10 times higher during spaceflight missions, 71% of the crew members in one study reported using medications to induce or maintain sleep and the most commonly were zolpidem, zaleplon, ot both ( Wotring, 2015 ).

However, hypnic dysregulation should not be considered separately from other medical issues that may arise in the course of space missions. Indeed, it may be subsequential to anxiety, depression and personality changes, interpersonal problems (i.e. intra-crew conflicts), and physiological reactions to a new environment, such as muscle atrophy, a reduced immune response and changes in regards to cardiovascular system. All those factors may indeed alter the sleep pattern, which may in turn aggravate psychological and physical stress in a vicious cycle ( Kanas & Manzey, 2008 ).

Visual phenomena

Visual disturbances may also represent a critical issue to space flights, and radiation exposure plays a key role in their genesis, likely along with the effects of intracerebral pressure changes. This is critical since visual impairment may compromise the fulfillment of the space missions goals and potentially lead to long-term consequences on the cosmonauts’ life quality upon their return to home. Despite playing a key role in the functioning of vision, the retina and the retinal vasculature have not been considerably studied in regards to radiation exposure during space travel. A recent paper would indicate that different types of examined radiation might cause significant differences in the responses of endothelial cells to such harmful factors. Indeed, low doses of 160 enhanced apoptosis in the endothelial cells of the retina, with the most significant changes observed following 0.1 Gy irradiation, whilst 160-induced apoptosis was found to be more frequent than apoptosis caused by protons ( Mao et al., 2018 ).

Moreover, during the Apollo, Skylab and MIR missions, astronauts observed flashes of light, of different shapes, moving across the visual field ( Sannita et al., 2006 ). Such flashes are more often present before sleep, predominantly white, with elongated shapes and often accompanied by a sense of movement perceived as lateral, diagonal or in-out ( Fuglesang et al., 2006 ). It has been suggested how these phosphenes can be a consequence of an alteration in perception caused by ionizing radiation on the eye ( Narici, 2008 ). In particular, temporarily increased biophoton emission has been proposed as a key process which may give an accurate description of the matter ( Bókkon, 2008 ). Indeed, the ionizing radiation impacting in the eye generates radicals, some of these generated in rod lipids undergo lipid peroxidation that leads to chemiluminescence and photon emission. At this point, the photon bleaches a nearby rhodopsin and the phototransduction cascade is initiated, which can lead then to the perception of flashes of light ( Bókkon, 2008 ; Narici et al., 2009 ), giving the impression that light is visible where it is not present and thus posing as a new potential hazard tied to space radiation. Nevertheless, whether this represents a reversible or persistent phenomenon is still an unsolved question, requiring future research. However, it should be mentioned that the effects of radiation exposure on sight are well documented, as they may even lead to impairing medical conditions such as posterior subcapsular cataract ( Khan et al., 2017 ).

Regardless, illusions and hallucinations also frequently appeared in some reports of space missions, possibly as a result of isolation or sensory deprivation ( Gushin et al., 1993 ).

Anorexia in space

Caloric intake may be lower than recommended in the course of space flights, thus leading to the so-called anorexia in space. Caloric deficits up to 1330 kcal per 70 kg astronaut per day may follow, with potential drops in the performances of the astronauts ( Da Silva et al., 2002 ). The causes of this phenomenon are likely related to the continuous light environment of space missions rather than to issues linked to the availability of food or energy expenditure ( Varma et al., 2000 ), with several neurochemical mediators (i.e. hormones and cytokines) involved ( Da Silva et al., 2002 ). The food intake of mice exposed to 24 hours of continuous light for 7 days was assessed and a significant reduction in meal numbers was found, resulting in increased concentrations of dopamine and serotonin in the ventromedial nucleus and lateral hypothalamic area, plasma cortisol and leptin, and decreased levels of insulin, tumour necrosis factor (TNF), oestradiol and testosterone. The results of this study make it possible to hypothezise an action of continuous light on the suprachiasmatic nucleus and ventromedial nucleus, resulting in endocrine and neurochemical changes ( Varma et al., 2000 ). Ionizing radiation may also play an important role in spatial anorexia by causing taste aversion and vomiting. Similarly, microgravity may be involved ( Da Silva et al., 2002 )

Nevertheless, it should be noted that current evidence suggests that anorexia in space is a reversible phenomenon, as cosmonauts’ body mass and caloric intake were comparable to those before the missions upon their return on Earth ( Da Silva et al., 2002 ).

Neuroanatomical correlates

Data gathered from studies using different neuroimaging techniques seem to suggest that different areas of the CNS and the peripheral nervous system (PNS) may be affected by the consequences of space travel ( table 2 ).

Neuroanatomical consequences of space travel

Some studies with magnetic resonance imaging (MRI) revealed some significant changes in the neuroanatomical configuration of the brain and cerebrospinal fluid (CSF) provoked by space flight. A narrowing of the central sulcus, an upward shift of the brain, narrowing of CSF spaces and optic-disk edema were found in post-flight scans of a small sample of astronauts ( Roberts et al., 2017 ). Further evidence derives from a functional MRI (fMRI) research involving a single cosmonaut over a period of 6 months subsequently to microgravity exposure. The authors reported significant changes in both vestibular and motor-related regions that, according to them, might underlie the alteration of the vestibular function and of the motor control skills after return on Earth ( Demertzi et al., 2016 ). Instead, a study employing quantitative MRI detected multiple grey and white matter alterations in a sample of 19 astronauts, such as thinning of the cerebral cortex of the right occipital lobe and of bilateral fusiform gyri, a decreased left thalamus size and an expansion of lateral ventricle ( Riascos et al., 2019 ). An increase in periventricular white matter hyperintensity was found in another research performed in a sample of 17 astronauts who had either taken part to a long-duration mission on ISS or a short-duration mission on the Space Shuttle ( Alperin et al., 2017 ). This finding was further linked to an expansion of ventricular CSF volume in the ISS group ( Alperin et al., 2017 ). More recently, an increase was found in summated brain and CSF volumes, a considerable deformation of the pituitary gland and an enhancement of aqueductal CSF hydrodynamics following long-term spaceflight ( Kramer et al., 2020 ). The cerebellum, along with cortical sensorimotor and somatosensory areas, as well as pathways related to the vestibular system, may also be subjected to significant changes in both their structural and functional component, mainly under the influence of microgravity, as proved in a recent research performed with the use of fMRI ( Buoite Stella et al., 2021 ).

Therefore, further studies with MRI or other imaging techniques carried out with larger samples are necessary to deepen these preliminary data that pose the crucial questions of the reversibility or not of the reported changes.

Conclusions

Space exploration was born as one of the most ground-breaking events that mark the history of the human species, that continues to this day to be a primary interest of the scientific community and beyond. Since the success of the launch of the first artificial object, the notorious V2 rocket, to reach outer space, the objectives of space missions have gradually begun to extend, asking the question of how far man is able to go. However, the development of increasingly refined technologies has revealed the risks that space travelers are forced to face and which, for a long time, have not received the right attention. Anecdotes, reports and scientific research have brought to light the dramatic burden on the mental well-being of space travellers, thus leading to a massive effort put in the selection and preparation of both astronauts and space missions and with the choice of specific countermeasures of psychological and/or psychiatric support. Nevertheless, attention should not be limited to the problems that have arisen during space missions, as the resumption of life on Earth may prove to be an equally arduous task. Over the years, it is likely that new aspects of medical interest on the matter will arise, a challenge that the scientific community must be ready to accept, for the success and safety of space travel.

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• Published: 18 January 2024

The effect of space travel on human reproductive health: a systematic review

• Marta Gimunová   ORCID: orcid.org/0000-0001-7284-2678 1 ,
• Ana Carolina Paludo 2 ,
• Martina Bernaciková 1 &
• Julie Bienertova-Vasku 1  

npj Microgravity volume  10 , Article number:  10 ( 2024 ) Cite this article

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With increasing possibilities of multi-year missions in deep space, colonizing other planets, and space tourism, it is important to investigate the effects of space travel on human reproduction. This study aimed to systematically review and summarize the results of available literature on space travel, microgravity, and space radiation, or Earth-based spaceflight analogues impact on female and male reproductive functions in humans. This systematic review was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and Space Biomedicine Systematic Review methods. The search was performed using three databases: PubMed, Web of Science, and Medline Complete. During the database search, 364 studies were identified. After the study selection process, 16 studies were included in the review. Five studies included female participants, and the findings show an increased risk of thromboembolism in combined oral contraceptive users, decreased decidualization, functional insufficiency of corpus luteum, and decreased progesterone and LH levels related to space travel or its simulation. Male participants were included in 13 studies. In males, reproductive health considerations focused on the decrease in testosterone and sex hormone-binding globulin levels, the ratio of male offspring, sperm motility, sperm vitality, and the increase in sperm DNA fragmentation related to space travel or its simulation. Results of this systematic review highlight the need to focus more on the astronaut’s reproductive health in future research, as only 16 studies were found during the literature search, and many more research questions related to reproductive health in astronauts still need to be answered.

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Introduction.

To undertake multi-year missions in deep space, colonize other planets, and/or prepare appropriate safety measures for space tourism, it is important to investigate the possible effects of space travel on human reproduction. During space travel, astronauts are exposed to several hazardous factors, such as alterations in gravitation forces, including hypogravity and hypergravity, or ionizing radiation 1 , 2 . Exposure to microgravity has been demonstrated to impair the endocrine system in males 3 , muscle mass, and bone mass 4 , 5 ; it also leads to altered fluid and electrolyte balance, cardiovascular changes, or increased glomerular filtration rate in both genders 2 . Experimental bed rest studies are typically used in humans to simulate spaceflight microgravity 6 . For in vitro samples, clinostat or random positioning machines are used to simulate microgravity by randomization of the gravity direction over time. In animal studies, hindlimb suspension is usually used to stimulate the physiological effects of microgravity 2 . Ionizing radiation, which is about 500 times greater in space compared to Earth conditions, was observed to cause DNA damage, apoptosis in ovarian follicles, and sperm DNA fragmentation in animal models 1 , 2 , 7 , 8 .

Until now, limited research has focused on the effect of space travel on the reproductive system and its function, along with endocrine regulation of reproduction or prenatal development. Endocrine regulation of sex hormones is the most investigated as it also impacts musculoskeletal health and skeletal muscle protein metabolism (e.g. 9 , 10 ). Most of this research is based on animal models 1 , 2 .

Female mouse models show that microgravity affects embryonic stem cell growth and differentiation 11 , resulting in impaired decidualization of the endometrium needed for implantation and maintaining pregnancy 12 . Data from therapeutic radiation on ovaries suggests that space radiation exposure during a typical Mars mission may reduce the ovarian reserve by 50% by destroying some of the primordial follicles. Furthermore, space radiation may lead to a decreased time interval to menopause, leading to a decreased reproductive capacity of the female astronaut 13 . Exposure to total body radiation of 15 Gy leads to the loss of ovarian function in humans 14 .

In males, the microgravity exposure was observed to reduce the total sperm count in mice models 15 , decrease testes weight, and decrease testosterone concentrations in male rats 2 , 16 . Exposure to ionizing radiation increases sperm DNA fragmentation in Echinogammarus marinus models 7 , affecting the male reproductive health. Data from therapeutic radiation on testes in humans show that a dose higher than 1 Gy might result in azoospermia and risk for hereditary disorders 17 . Furthermore, decreased serum testosterone levels were observed in men treated with radiotherapy for rectal cancer when testes are exposed to direct or scattered radiation 18 .

As described in The Impact of Sex and Gender on Adaptation to Space: A NASA Decadal Review 19 , reproductive demographics of female and male US astronauts significantly differ based on biological processes and gender roles for parents. Women are usually the primary caregivers (e.g., ref. 20 ) and are often required to take an extended family leave from their career when having a child (e.g., ref. 21 ). A smaller number of female astronauts (44.7%) have at least one child compared to the male astronauts (83.9%). Female astronauts also significantly delay reproduction, on average, by 5.6 years compared to males. It was hypothesized that the delayed reproduction in female astronauts is related to the required extensive space travel training time 19 . A new NASA decadal review is expected next year, adding more current data on the topic. However, not only delayed reproduction but also the impact of the potential acceleration of aging and gonadal radiation exposure related to space travel might be other factors affecting the reproduction capacity in female astronauts 19 . Therefore, the aim of this study was to systematically review and summarize the results of available literature on space travel, microgravity, and space radiation’s impact on female and male reproductive functions in humans.

Characteristics of included studies

During the database search, 364 studies were identified (Pubmed: 121 articles; Medline Complete: 142 articles; Web of Science: 101 articles). After the duplicate removal ( n  = 160), studies involving animal samples ( n  = 45), different methodologies, or non-English language articles (e.g., conference paper, book chapter; n  = 12), 147 studies were screened based on title and abstract in which 120 studies were excluded. In the last stage, 27 studies remained, followed by the exclusion of 5 studies due to no full-text being available and eight studies because the outcomes needed to match the topic. Via another method (accidental find), two studies focusing on ionizing radiation’s effect on male reproductive health were found 22 , 23 . A total of 16 studies were included in the systematic review.

The methodological quality of the included studies (Table 1 ) ranged from 70.0% 24 to 90.9% 25 , suggesting good methodological quality 26 . The most common methodological deficits consisted of not reporting the study’s hypothesis clearly, not reporting the probability values, and the lack of representativeness of the source population. The methodological quality of the included studies is shown in Supplementary Table 1 .

Six of the included studies used bed rest study design. Bed rest studies’ methodological quality (Table 2 ) ranged between 2 27 to 7 points 28 . No study indicated a prohibition of sunlight exposure. Four studies did not indicate a set wake/sleep time 6 , 10 , 29 , 30 . One study design allowed a limited ambulation time (to shower and toilet) 29 . In three of the included studies, the recommended 6° head-down tilt was not used 6 , 27 , 29 .

Articles meeting the inclusion criteria included four articles from USA (25%), two articles from China (12, 5%), two articles from Russia (12, 5%), one article from Poland (6, 25%), one article from Italy (6, 25%), one article from South Korea (6, 25%), one article from India (6, 25%), one article from Japan (6, 25%), one article from Spain (6, 25%), one article from Austria (6, 25%), and one article from Germany (6, 25%) 6 , 10 , 12 , 22 , 23 , 24 , 25 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 .

As shown in Table 3 , in most of the included studies, only male participants were analyzed (11 studies; 68, 75% 6 , 10 , 22 , 23 , 25 , 28 , 29 , 30 , 31 , 33 , 35 ), three studies focused on female participants (18, 75% 12 , 24 , 32 ), and two studies included a mixed sample (12, 5% 27 , 34 ).

Thirteen articles reported data from the experiments on Earth. Simulated microgravity by parabolic flight was used in two studies 31 , 35 and by clinostat system in one study 12 ; in two studies ionizing radiation occupational exposure was used 22 , 23 , head-down bed rest was performed in four studies 10 , 27 , 28 , 30 , bed rest was conducted in two studies 6 , 29 , in two studies dry immersion was used 24 , 32 , and in one study data from water submersion were reported 25 . Three articles reported data on space exposure 30 , 33 , 34 . Eight of included studies focused on endocrine changes after the space flight or its simulation 10 , 25 , 6 , 27 , 28 , 29 , 30 ; four studies focused on sperms 22 , 23 , 31 , 35 ; two studies focused on menstrual cycle changes 24 , 32 ; one study focused on endometrial stromal cells 12 , one study focus of the venous thromboembolism risk 34 , and one study focused on offspring sex ratio in male astronauts 33 .

Female and mixed studies

Three studies, including female participants, and two studies, including mixed samples, were identified during the study selection process. Their characteristics are shown in Table 4 . One study used a clinostat system to simulate the microgravity of in vitro samples of human endometrial stromal cells (PSCs) from the uterus 12 . Two studies used dry immersion to simulate microgravity; in both studies, participants were allowed 30 min/day to spend outside the immersion bath for hygiene procedures 24 , 32 . Tomilovskaya et al. 32 described the first female dry immersion study, and their participants were involved in their study for two menstrual cycles. The three-day dry immersion occurred between day 7 and day 10 of participants’ menstrual cycles 32 . In a study by Gorbacheva et al. 24 , two menstrual cycles were followed; the 5-day-long dry immersion was performed between day 10 and day 15 of participants’ menstrual cycles. One study used one hour-long -12° head-down bed rest to simulate microgravity and analyze endocrine parameter changes 27 . In one study, spaceflight exposure was used to analyze proteins involved in clotting cascade from blood samples obtained twice before spaceflight, five times during the flight, and twice after flight 34 .

In Table 5 , results from female and mixed samples studies are shown. In female in vitr o samples, exposure to microgravity was observed to decrease decidualization (the process of endometrial cells in preparation for, or during pregnancy) by decreasing proliferation and migration and endometrial stromal cells growth rate through Akt/MMP and FOXO3a/autophagic flux 12 . Two studies reported that menstrual cycle length stayed intact after dry immersion exposure 24 , 32 . Gorbacheva et al. 24 observed decreased luteinizing hormone (LH), progesterone, and ovarian volume at day 9 of the menstrual cycle after the immersion. On the other hand, an increase in dominant follicle diameter and no change in uterus size and endometrial thickness were reported 24 . The mixed sample study focused on venous thromboembolism risk in male and female astronauts, showing an increased risk in females taking combined oral contraceptives 34 . A head-down bed rest mixed sample study reported no statistically significant change in oestradiol, testosterone, and LH levels after the rest 27 .

Male studies

Eleven studies focused on male participants were identified during the study selection process. In Table 6 , the male studies’ characteristics are summarized. In the study by Little et al. 33 , retrospective data from astronauts’ biographies were included in the analysis of offspring ratio. A study by Smith et al. 30 focused on the effect of long- and short-duration space flight and −6° head-down bed rest on testosterone levels. In two studies, parabolic flights were used to simulate short-duration microgravity 31 , 35 . In a study by Boada et al. 35 , twenty parabolic flight maneuvers (8.5 s of microgravity for each parabola) were used for frozen sperm samples. In a study by Ikeuchi et al. 31 , fresh sperm samples underwent ten parabolic flight maneuvers (20 to 25 s of microgravity for each parabola). Occupational low-dose exposure to ionizing radiation while working with radiation in a hospital on sperm characteristics was analyzed in two studies 22 , 23 . Four studies analyzed the effect of bed rest or −6° head-down bed rest on testosterone levels 10 , 6 , 28 , 29 . Studies by Belavy et al. 6 , Liang et al. 28 , and Zachwieja et al. 10 applied a strict bed rest. Study design by Smorawinski et al. 29 provided 20 min/day to ambulate (to shower and toilet). In one study, the effect of water submersion on testosterone levels was analyzed 25 . In the study by Loder et al. 25 , divers were allowed to emerge for less than 20 min every 4 hours to urinate, defecate, drink, or undergo medical checks.

One of the studies including male participants in the space study setting (Table 7 ) focused on the offspring sex ratio, showing a decreased ratio of male offspring (43.75%) in male astronauts 33 . Furthermore, the study by Little et al. 33 observed a decreased male offspring ratio of 38.41% in high G pilots compared to 50.34% in low G pilots. The second study using the space study setting focused on endocrine changes, showing no statistically significant changes in testosterone and sex hormone-binding globulin (SHBG) during or after the short and long-duration space flight. A decrease in total, free, and bioavailable testosterone was observed only on the landing day after the space flight, probably as the transient effect of flight 30 . One study observed decreased sperm motility after microgravity exposure 31 , and another study by Boada et al. 35 observed no statistically significant change in sperm motility, vitality, or sperm DNA fragmentation after exposure to microgravity. Occupational ionizing radiation exposure was observed to decrease sperm motility, vitality, and concentration and to increase sperm DNA fragmentation in comparison with non-exposed controls 22 , 23 . Bed rest and head-down bed rest studies show no statistically significant change in testosterone and prolactin after the rest 10 , 28 , 29 , 30 . SHBG was observed to decrease after the bed rest 6 . After the water submersion, a decrease in plasma testosterone was observed 25 .

The aim of this study was to systematically review and summarize the results of available literature on space travel, microgravity, and space radiation impact on female and male reproductive functions in humans. The reproductive health consideration of space travel differs for female and male astronauts. In female astronauts, they include oral contraceptive use 34 , progesterone and LH levels 27 , ovarian and uterus changes 24 , decidualization, and endometrial stromal cell growth rate 12 . In males, reproductive health considerations focus on testosterone and SHBG levels 10 , 25 , 6 , 27 , 28 , 29 , 30 , the ratio of male offspring 33 , sperm motility 22 , 23 , 31 , 35 , sperm vitality 22 , 35 , and sperm DNA fragmentation 22 , 23 , 35 . To support those considering these options, it might be helpful to explore assisted reproductive technologies such as oocyte and sperm cryopreservation, along with reproductive counseling possibilities, as suggested by Rose 13 and Ronca et al. 36 .

In female astronauts, the endocrine regulation of the menstrual cycle involves the hypothalamic release of gonadotropin-releasing hormone, which stimulates the pituitary gland to produce follicle-stimulating hormone and luteinizing hormone, which peaks mid-cycle and invokes ovulation 37 . The developing ovum in ovaries produces estrogen, and the corpus luteum , which forms after ovulation, produces progesterone. Animal models show a decrease in luteinizing hormone related to 37 days-long spaceflights; however, no changes in estrous cycle stages were observed 38 . In naturally cycling women, simulated microgravity by dry immersion led to a decrease in luteinizing hormone by 12% and progesterone by 52%, showing functional insufficiency of corpus luteum 24 . The menstrual cycle length was not altered after 3 and 5 days of dry immersion 24 , 32 . One hour of −12° head-down bed rest did not induce any significant changes in the endocrine regulation of the cycle, suggesting that longer microgravity exposure is needed to affect the endocrine regulation of the menstrual cycle 27 . Despite the fact that abnormal uterine bleeding is a common complaint among reproductive-aged women 39 , uterine bleeding changes were not analyzed in any of the included studies.

As the menstrual bleeding flow management during space flight training and the space flight can be challenging, medically induced amenorrhea using combined oral contraceptives is often used by female astronauts 40 . However, combined (progestin and estrogen) oral contraceptives were associated with lower circulating concentrations of albumin, higher concentrations of transferrin, and elevated markers of inflammation, which can contribute to an increased risk of venous thromboembolism event during space travel 34 . The occlusive deep venous thrombosis was diagnosed in one female astronaut during a long-duration spaceflight 41 , highlighting the need to carefully consider the type of combined oral contraceptives used before and during flight 34 .

Human pregnancy is currently contradicted during space flight as a safety measure to protect the fetus 13 , 42 , 43 . Multi-year duration space flights and colonization will require understanding the impact of space flight on pregnancy, and simulation studies will try to provide better insight into reproduction in space. Fetal development, long-term effects on gestation under space conditions, and monitoring the development and function of offspring conceived and developed in space are some of the potential priorities for future space programs as described in a European perspective of human development and reproduction in space by Jain et al. 43 . The study by Cho et al. 12 showed that exposure to simulated microgravity leads to decreased decidualization and endometrial stromal cells growth rate due to decrease in Akt activity and FOX03a expression leading to an unreceptive endometrium. Furthermore, if microgravity and space radiation alter the pro-oxidant/antioxidant balance during pregnancy, it can increase the risk of miscarriage, preterm birth, or fetal growth restriction 44 . The absence of gravitational loading during the last trimester of gestation may cause hypotrophy of muscles and osteopenia in the trunk and legs, leading to delayed acquisition of developmental milestones such as sitting or walking of the fetus developed in space 45 . Animal models show increased perinatal morbidity for the rats that spent 9 to 20 days in spaceflight during their gestation. In surviving offspring, no delay in walking acquisition was observed 46 .

High-altitude airplane flights, e.g., transatlantic flights, constitute trivial cosmic radiation exposure for casual travelers. Pregnant pilots, flight attendants, and frequent flyers may exceed the recommended radiation exposure 47 . During transatlantic air travel in the third trimester of pregnancy, most of the pregnant women report no change in fetal movements during take-off or flight 48 . A study by Grajewski et al. 49 focusing on miscarriage risk among flight attendants shows that cosmic radiation exposure of 0,1 mGy or more may be associated with an increased risk of miscarriage in weeks 9 to 13. However, the miscarriage risk was also associated with other factors such as work during sleep hours and high physical demands, and the miscarriage risk was not increased among flight attendants compared to a control group of teachers 49 . Maternal stress and exposure to stressful events during pregnancy were observed to impact the infant’s physical health 50 , premature birth, and low birth weight 51 , suggesting a possible negative effect of space travel-related stress on the fetus.

Space travel may increase the carcinogenic risk to reproductive organs. This risk was proposed to be higher in women as they have a higher incidence of radiation-induced cancers, as widely discussed in Market al. 19 . Still, the low number of female astronauts does not allow for assessment of the risk of spaceflight on gynecological cancer 36 .

In expert opinion by Rose 13 , significantly reduced ovarian reserve and consequent decrease in the reproductive capacity and decreased time interval to menopause caused by space radiation was suggested in female astronauts. Unfortunately, no original article showing the data about reproductive capacity or age of menopause in astronauts was found during the literature search in this systematic review.

Testosterone is the key hormone in the development of the male reproductive system and promotes muscle and bone mass 52 . Testosterone has been, therefore, often considered as a potential countermeasure for musculoskeletal losses related to space flight (e.g. 10 ). The testosterone level seems unchanged by the space flight or bed rest study settings 9 , 10 , 6 , 27 , 28 , 30 apart from the transient effects after flight 30 . A decrease in testosterone levels was observed in a short-term water submersion (41 h) study by Loder et al. 25 . Similarly, it was hypothesized that the decrease is related to stress effect 25 . The self-rated sexual drive was reported to temporarily decrease during space flight in male astronauts parallelly to urinary, plasma, and salivary testosterone levels in a study by Strollo et al. 53 . Similarly, animal studies show a decrease in testosterone levels in simulated microgravity studies caused by a reduction in testicular blood flow related to body fluid shift 1 .

Prolactin and LH levels did not change during the analog bed rest study 27 , 6 . Similarly, no LH and FSH levels change was observed after a 6-week hindlimb suspension in animal models 54 . Serum SHBG levels were observed to decrease during bed rest in inactive participants. The physical activity load during the bed rest led to stable SHBG levels 6 . Similarly, no change during or after the space flight in the level of SHBG was observed by Smith et al. 30

Results observed by Ikeuchi et al. 31 using fresh semen suggest that sperm motility is reduced by microgravity. In a study by Boada et al. 35 using frozen semen, no significant change in sperm motility, vitality, or sperm DNA fragmentation was observed compared to Earth condition after a similar parabolic flight experiment as used by Ikeuchi et al. 31 . These results suggest that the sperm integrity may be protected by cryopreservation during the space flight when transporting male human gametes into space 35 . Still, chronic occupational exposure to ionizing radiation was observed to have a detrimental effect on sperm motility, vitality, concentration, and DNA fragmentation 22 , 23 . Similarly, ionizing radiation and microgravity were observed to increase sperm DNA fragmentation in animal studies 1 . Furthermore, a decreased sex ratio of male offspring by male astronauts exposed to high G forces was reported by Little et al. 33 . The authors hypothesized that sperm sex differences in sperm motility and longevity, smaller size, and cytoplasm content in Y sperm were the reason of decreased sex ratio of male offspring as higher G forces may accelerate metabolism in sperm subtracting energy available for travel to the ovum 33 . However, current knowledge shows no morphological differences between X and Y sperms in humans 55 . Still, X and Y sperms differences in genetic content may lead to differences in their stress response 56 . The study by You et al. 57 reported that the viability of human Y spermatozoa was lower after exposure to stress (e.g., different temperatures and culture periods) compared to X spermatozoa, which may result in a shift of the offspring sex ratio as observed by Little et al. 33 . Similarly, low male sex offspring ratio associated with occupational testicular radiation exposure was observed in a previous study 58 . On the other hand, no association between offspring sex ratio and gonadal irradiation was observed in childhood cancer survivors in a study by Reulen et al. 59

Future studies on the effect of space radiation on both fresh and frozen semen samples are needed to assess the possibility of creating a human sperm bank outside the Earth. A study by Wakayama et al. 60 analyzed the effect of space radiation on mouse freeze-dried spermatozoa stored for almost six years on the International Space Station. The sperm DNA and fertility were not affected after the storage outside the Earth compared to control preserved on Earth, and the current data show the possibility of storing freeze-dried spermatozoa for more than 200 years in space 60 .

Among potential priorities identified by Jain et al. 43 for future research regarding reproductive aspects of space flight were topics similar to those covered in this systematic review. Additionally, the effect of space travel on libido and the possibility of pregnancy and birth in space were proposed 43 . Results of this systematic review highlight the need to focus more on both female and male astronauts’ reproductive health in future research, as only 16 studies were found during the literature search, and many more research questions related to reproductive health in female and male astronauts still need to be answered.

There are several limitations of this systematic review. The main limitation is the few included studies and the wide range of reproductive health parameters they focused on. The small sample sizes, different types of populations (healthy volunteers, astronauts), and different methodologies need to be considered when comparing or generalizing the results. The limited number of studies addressing these health concerns underscores the imperative need for future research dedicated to reproductive health in both female and male astronauts.

Eligibility criteria for selecting studies

A systematic review of the effect of space travel or its simulation, e.g., bed rest studies, microgravity simulation, or dry immersion, on reproductive health in human females and males was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines 61 and according the Space Biomedicine Systematic Review methods ( https://sites.google.com/view/sr-methods/home ). The search was performed using three databases, PubMed, Web of Science, and Medline Complete, on the 29 th of April 2023 by one researcher (MG). The eligibility criteria included: (1) astronauts, space travel, or space simulation; (2) experimental or retrospective studies performed on human participants (animal studies were excluded); (3) description of reproductive health parameters.

Search strategy and selection process

The following terms with Boolean operators were used for the search: (“infertility” OR “birth outcomes” OR “amenorrhea” OR “menstrual” OR “menstrual cycle” OR “follicular phase” OR “luteal phase” OR “menstruation” OR “ovarian cycle” OR “ovulation” OR “anovulation” OR “reproduct*” OR “obstetric*” OR “gynecolog*” OR “maternal” OR “pregnan*” OR “contracept*” OR “prenatal” OR “postpartum” OR “preconception” OR “women’s health” OR “miscarriage” OR “pregnancy loss” OR “menarche” OR “polycystic ovary syndrome” OR “menopause” OR “endometriosis” OR “stillbirth” OR “placental abruption” OR “low birth weight” OR “preterm birth” OR “in vitro fertilization” OR “irregular periods” OR “sperm” OR “testosterone” OR “semen quality” OR “oligospermia” OR “semen” OR “testis” OR “testes” OR “testicular” OR “offspring” OR “reproductive hormone” OR “asthenozoospermia” OR “oligozoospermia” OR “oligoasthenozoospermia” OR “oligoasthenoteratozoospermia” OR “teratozoospermia” OR “spermatogenesis” OR “varicocele” OR “erection” OR “libido” OR “erectile dysfunction” OR “sexual drive”) AND (“space travel” OR “astronaut*” OR “spaceflight” OR “space analogue” OR “cosmonaut*” OR “space simulation” OR “zero gravity” OR “microgravity” OR “hypogravity” OR “low gravity” OR “space radiation”) AND (“human” OR “participant*” OR “women” OR “men” OR “woman” OR “man”) NOT (“review”). The literature search did not exclude any studies published before certain data due to a limited number of scientific studies focused on the analyzed topic as proposed in Ahrari et al. 1 . Studies published until April 2023 were included in this study. Exclusion criteria included animal studies, non-English language, review articles, conference papers, books, and book chapters, and no full-text available. All studies identified in the search were imported into Rayyan systematic review software 62 to continue the selection process. Studies that did not meet the inclusion criteria (e.g., duplicates, non-English articles, reviews, conference papers, books and book chapters, and animal studies) were excluded by one researcher (MG). The title and abstract of the remaining studies were screened by two researchers (MG, ACP). Any disagreement between researchers was resolved by discussion. After that, the full texts of the included studies were screened to confirm their relevance to the current systematic review. The PRISMA flow diagram summarizes the study selection process (Fig. 1 ).

PRISMA flow diagram of the study selection process (template from 61 ).

Data collection process and assessment of study quality

Data extraction was performed by two researchers (MG, MB) using a pre-determined form consisting of (i) study characteristics (author, publication year and country, sample characteristics, study setting: Earth/space, and exposure: spaceflight/microgravity/ionizing radiation/bed rest/water submersion/dry immersion); and (ii) analyzed reproductive health parameters and results.

The methodological quality assessment of included studies was performed by one researcher (MG) using the Downs and Black Quality Assessment Checklist 63 . The original checklist consists of 27 questions assessing the quality of reporting, external and internal validity, and statistical power. For this review, 13 items were considered relevant. A similar approach was used in previous studies by Gimunová et al. 64 and Paludo et al. 65 . A binary score for each question: 0 = no/unable to determine, 1= yes was used. The final score (in %) was classified as follows: <45.4% “poor” methodological quality; 45.5–61.0% “fair” methodological quality”; and >61.0% “good” methodological quality 26 . The quality assessment was not used to exclude any study.

Additionally, as recommended in Space Biomedicine Systematic Review Methods, the Bed rest studies transferability was assessed by the recommended tool ( https://sites.google.com/view/sr-methods/guides/bed rest-transferability) used in a previous systematic review by Winnard et al. 66 . The methodological quality of bed rest studies was assessed by one researcher (MG) considering eight questions comparing the study design with “ideal design” resulting in a total score between 0 to 8 points.

Reporting summary

Further information on research design is available in the Nature Research Reporting Summary linked to this article.

Data availability

The original studies presented in the systematic review are included in the article; further inquiries can be directed to the corresponding author.

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Acknowledgements

This project was supported by the Rector’s Group for Space Research and Astronautics at Masaryk University, Brno, Czech Republic.

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M.G. and J.B.V.: conceptualization and search. A.C.P. and M.G.: data selection. M.B. and M.G.: data analysis. M.G., J.B.V., and A.C.P.: drafted manuscript. All authors critically revised the manuscript, contributed to the article, and approved the submitted version.

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Gimunová, M., Paludo, A.C., Bernaciková, M. et al. The effect of space travel on human reproductive health: a systematic review. npj Microgravity 10 , 10 (2024). https://doi.org/10.1038/s41526-024-00351-1

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Researchers detect a new molecule in space

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New research from the group of MIT Professor Brett McGuire has revealed the presence of a previously unknown molecule in space. The team's open-access paper, “ Rotational Spectrum and First Interstellar Detection of 2-Methoxyethanol Using ALMA Observations of NGC 6334I ,” appears in April 12 issue of The Astrophysical Journal Letters .

Zachary T.P. Fried , a graduate student in the McGuire group and the lead author of the publication, worked to assemble a puzzle comprised of pieces collected from across the globe, extending beyond MIT to France, Florida, Virginia, and Copenhagen, to achieve this exciting discovery. 

“Our group tries to understand what molecules are present in regions of space where stars and solar systems will eventually take shape,” explains Fried. “This allows us to piece together how chemistry evolves alongside the process of star and planet formation. We do this by looking at the rotational spectra of molecules, the unique patterns of light they give off as they tumble end-over-end in space. These patterns are fingerprints (barcodes) for molecules. To detect new molecules in space, we first must have an idea of what molecule we want to look for, then we can record its spectrum in the lab here on Earth, and then finally we look for that spectrum in space using telescopes.”

Searching for molecules in space

The McGuire Group has recently begun to utilize machine learning to suggest good target molecules to search for. In 2023, one of these machine learning models suggested the researchers target a molecule known as 2-methoxyethanol. 

“There are a number of 'methoxy' molecules in space, like dimethyl ether, methoxymethanol, ethyl methyl ether, and methyl formate, but 2-methoxyethanol would be the largest and most complex ever seen,” says Fried. To detect this molecule using radiotelescope observations, the group first needed to measure and analyze its rotational spectrum on Earth. The researchers combined experiments from the University of Lille (Lille, France), the New College of Florida (Sarasota, Florida), and the McGuire lab at MIT to measure this spectrum over a broadband region of frequencies ranging from the microwave to sub-millimeter wave regimes (approximately 8 to 500 gigahertz). 

The data gleaned from these measurements permitted a search for the molecule using Atacama Large Millimeter/submillimeter Array (ALMA) observations toward two separate star-forming regions: NGC 6334I and IRAS 16293-2422B. Members of the McGuire group analyzed these telescope observations alongside researchers at the National Radio Astronomy Observatory (Charlottesville, Virginia) and the University of Copenhagen, Denmark. 

“Ultimately, we observed 25 rotational lines of 2-methoxyethanol that lined up with the molecular signal observed toward NGC 6334I (the barcode matched!), thus resulting in a secure detection of 2-methoxyethanol in this source,” says Fried. “This allowed us to then derive physical parameters of the molecule toward NGC 6334I, such as its abundance and excitation temperature. It also enabled an investigation of the possible chemical formation pathways from known interstellar precursors.”

Looking forward

Molecular discoveries like this one help the researchers to better understand the development of molecular complexity in space during the star formation process. 2-methoxyethanol, which contains 13 atoms, is quite large for interstellar standards — as of 2021, only six species larger than 13 atoms were detected outside the solar system , many by McGuire’s group, and all of them existing as ringed structures.  

“Continued observations of large molecules and subsequent derivations of their abundances allows us to advance our knowledge of how efficiently large molecules can form and by which specific reactions they may be produced,” says Fried. “Additionally, since we detected this molecule in NGC 6334I but not in IRAS 16293-2422B, we were presented with a unique opportunity to look into how the differing physical conditions of these two sources may be affecting the chemistry that can occur.”

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Paradox-Free Time Travel Is Theoretically Possible, Researchers Say

Matthew S. Schwartz

A dog dressed as Marty McFly from Back to the Future attends the Tompkins Square Halloween Dog Parade in 2015. New research says time travel might be possible without the problems McFly encountered. Timothy A. Clary/AFP via Getty Images hide caption

A dog dressed as Marty McFly from Back to the Future attends the Tompkins Square Halloween Dog Parade in 2015. New research says time travel might be possible without the problems McFly encountered.

"The past is obdurate," Stephen King wrote in his book about a man who goes back in time to prevent the Kennedy assassination. "It doesn't want to be changed."

Turns out, King might have been on to something.

Countless science fiction tales have explored the paradox of what would happen if you went back in time and did something in the past that endangered the future. Perhaps one of the most famous pop culture examples is in Back to the Future , when Marty McFly goes back in time and accidentally stops his parents from meeting, putting his own existence in jeopardy.

But maybe McFly wasn't in much danger after all. According a new paper from researchers at the University of Queensland, even if time travel were possible, the paradox couldn't actually exist.

Researchers ran the numbers and determined that even if you made a change in the past, the timeline would essentially self-correct, ensuring that whatever happened to send you back in time would still happen.

"Say you traveled in time in an attempt to stop COVID-19's patient zero from being exposed to the virus," University of Queensland scientist Fabio Costa told the university's news service .

"However, if you stopped that individual from becoming infected, that would eliminate the motivation for you to go back and stop the pandemic in the first place," said Costa, who co-authored the paper with honors undergraduate student Germain Tobar.

"This is a paradox — an inconsistency that often leads people to think that time travel cannot occur in our universe."

A variation is known as the "grandfather paradox" — in which a time traveler kills their own grandfather, in the process preventing the time traveler's birth.

The logical paradox has given researchers a headache, in part because according to Einstein's theory of general relativity, "closed timelike curves" are possible, theoretically allowing an observer to travel back in time and interact with their past self — potentially endangering their own existence.

But these researchers say that such a paradox wouldn't necessarily exist, because events would adjust themselves.

Take the coronavirus patient zero example. "You might try and stop patient zero from becoming infected, but in doing so, you would catch the virus and become patient zero, or someone else would," Tobar told the university's news service.

In other words, a time traveler could make changes, but the original outcome would still find a way to happen — maybe not the same way it happened in the first timeline but close enough so that the time traveler would still exist and would still be motivated to go back in time.

"No matter what you did, the salient events would just recalibrate around you," Tobar said.

The paper, "Reversible dynamics with closed time-like curves and freedom of choice," was published last week in the peer-reviewed journal Classical and Quantum Gravity . The findings seem consistent with another time travel study published this summer in the peer-reviewed journal Physical Review Letters. That study found that changes made in the past won't drastically alter the future.

Bestselling science fiction author Blake Crouch, who has written extensively about time travel, said the new study seems to support what certain time travel tropes have posited all along.

"The universe is deterministic and attempts to alter Past Event X are destined to be the forces which bring Past Event X into being," Crouch told NPR via email. "So the future can affect the past. Or maybe time is just an illusion. But I guess it's cool that the math checks out."

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• time travel

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The quest for greater knowledge and understanding— as well as Cold War rivalry between the United States and the Soviet Union—fueled the modern space race in both unmanned and manned spacecraft, but humans have acknowledged the powers of the solar system since prehistoric times. Advanced technologies, and an increasing spirit of private enterprise, open possibilities for new adventures and frontiers.

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Since the first people walked the Earth, the heavens have beckoned to the human spirit and inspired the human imagination. The drama of the sky has enthralled forty thousand generations of men and women. From prehistoric times, the sky and its celestial bodies have played key roles in mythology and religion throughout the world. Early American peoples, including the Aztecs of southern Mexico and the Anasazi of the North American Southwest, used the movements of the sun, planets, stars, and moon for calendrical and agricultural purposes and worshipped gods embodying the sun and moon. Similar religious trends emerged throughout the ancient world on every continent, and until the spread of monotheism, nearly every world culture worshipped some aspect of the sky. Hence, although the ancients had relatively little knowledge of the universe, they recognized the power of the heavens.

By medieval and early modern times, astrology, or the belief that the motion of the stars and planets shape the fates of individuals, kings, dynasties, and empires, was influencing the decisions of both political leaders and peasants. Not until the scientific revolution of the seventeenth century was the idea of the stars and planets as physical bodies obeying regular laws accepted by influential people. For human space travel to become a reality, the work of Kepler, Newton, and Galileo first had to predict the movements and characteristics of bodies in space.

Early Development of Space Travel and Rocketry

Space travel didn’t become feasible until the twentieth century. Rocket technology, which would become the basis of all space travel, began with the rocket development work of Konstantin Tsiolkovsky (1857–1935) in Russia and Robert Goddard (1882–1945) in the United States. The Chinese had invented a rocket weapon in 1232 using gunpowder, which was ultimately adopted in technologically sophisticated societies throughout the world. During the eighteenth and nineteenth centuries, various pioneers improved the rocket’s effectiveness as a weapon. It is Tsiolkovsky of Czarist Russia, however, who is remembered as the “father of astronautics.” Although he dealt with many aspects of the rocket as an instrument of interplanetary travel, his most important contributions concerned propellants and the rocket design needed to achieve flight into the Earth’s orbit and then farther into space. In particular, he discussed the possibility of powerful, controllable liquid propellants, such as hydrogen and oxygen, and multistage rockets. Although Tsiolkovsky accurately predicted many future developments, his writings were not widely read during his life.

The work of the U.S. physicist Robert Goddard also concerned multistage rockets and liquid propellants. In 1926 at a farm in Auburn, Massachusetts, Goddard used liquid oxygen and petrol to send the first liquid-propelled rocket into the air at a rate of 60 miles per hour. He continued his experiments, with a launch in 1935 ultimately achieving 1,000 feet and a speed of 700 mph. Despite his genius and some financial support from the U.S. government, the reticent and publicity-shy Goddard did not contribute directly to the American space program. However, his reticence paved the way for the Transylvanian and German rocket and space travel visionary, Hermann Oberth (1894–1989), who corresponded with Goddard. Like Tsiolkovsky, Oberth dealt with both detailed engineering and the broader issues regarding space exploration. He helped to spread popular awareness of the rocket and the possibilities of space travel throughout Germany. In the 1920s and 1930s, various rocket societies in Europe and the United States, which included engineers as well as visionaries, met to build rockets as well as to advance their general knowledge of space travel.

Military Rocketry and the Imaginative Vision

Meanwhile, leaders in the USSR, building on Tsiolkovsky’s ideas, formed a military organization in 1928 under young engineer Valentin Glushko (1908–1989). The laboratory, called the Gas Dynamics Laboratory (GDL), built solid-fuel war rockets. In 1931, Soviet leaders gained control of another key organization, the Group for the Study of Reaction Motion (known in the USSR as GIRD), which emphasized more powerful liquid-fuel rockets. GIRD had emerged from a core of Soviet engineers and space enthusiasts who dreamed of going to the moon and beyond. The Red Army funded this group as well as GDL. Sergei Korolev (1906–1966), the future mastermind behind the Soviet space program, was one of GIRD’s most enthusiastic members. During this era, Korolev focused on rocket aircraft and honed his organizational skills. Through the efforts of GIRD, the USSR launched its first liquid-fuel rocket in 1933. Its success caused Soviet leaders to take a greater interest in the use of rocket technology in weaponry. Ultimately, leaders consolidated GIRD and GDL into a single organization, RN-II, which made further contributions to rocket development. The tragic advent of Stalin’s purges in 1934 threatened the nascent Soviet rocket program. Many Soviet rocket pioneers and space visionaries perished in the purges. Stalin’s police imprisoned both Korolev and Glushko, but they managed to survive, working as state prisoners to advance rocketry.

In Germany, the state also harnessed space enthusiasts for military purposes. The most notable of these was Wernher von Braun (1912–1977), who would play a vital role in the United States space program as well as in the German rocket program. Born to a prominent family, von Braun was active in the VfR (Society for Space Ship Travel). He joined the German Army Ordnance Department in 1932 to work on a liquid-fuel rocket with a range greater than any preexisting artillery. In 1937, the group moved to Peenemunde, a new proving ground on the Baltic. Von Braun, who was talented as a manager as well as an engineer, led the rocket development program.

Although the Nazi leadership supported the program only erratically, von Braun and his associates made progress as they dreamed of future trips to the moon and Mars. The V-2/A-4 rocket, or “vengeance weapon,” first flew in late 1942. It was much more powerful than any preceding rocket, standing almost fifty feet high, weighing 28,000 pounds, reaching a height of sixty miles, and carrying a heavy bomb. It burned liquid oxygen and ethyl alcohol and had sophisticated guidance and control systems. This rocket was an ancestor to many American rockets, including the powerful Saturn V which would take the first humans to the moon. Workers enslaved by Hitler built most of the V-2 rockets used in World War II. Although the weapons were not accurate, their victims had few defenses against them. In September of 1944, Hitler launched a V-2 bombardment against targets in southern England and liberated Europe. While powerful, these weapons made little difference to the war’s final outcome.

Space Exploration and the Cold War

As the Cold War between the United States and the Soviet Union intensified after World War II, both the Americans and the Soviets utilized the survivors of Nazi Germany’s military rocket teams. Stalin’s rocket program, approved in 1947, was intended to culminate in the production of an Intercontinental Ballistic Missile (ICBM). The Soviet army recreated the V-2 rocket through the SS-I and SS-II rockets, but the Soviet aviation industry avoided rocket technology. The first Soviet ICBM, the SS-6/R-7, was built to carry the heavy Soviet nuclear warhead. However, its most significant flight occurred on 4 October 1957, when it launched the first human-made satellite, Sputnik I, into Earth orbit. As euphoria overtook the Soviet Union, the American public reeled in shock. If the Soviets were capable of launching a satellite to fly over American soil, were they not also capable of launching a nuclear weapon to the United States? And why hadn’t the United States launched a successful satellite first? Nikita Khrushchev (1894–1971), who succeeded Stalin as Soviet premier in 1958, recognized the symbolic importance of Sputnik. The worldwide perception was that the USSR had overtaken the United States in science and technology; this implied military superiority.

As Americans panicked, President Dwight D. Eisenhower (1890–1969) remained secure in his knowledge of America’s military superiority in the areas of intermediate-range missiles, miniaturized nuclear weapons, bases near the Soviet Union, and spy planes. Just a year after Sputnik, von Braun’s Army rocket team managed to launch the first American satellite, Explorer 1, with a modified Redstone rocket, the Jupiter- C. On 1 October 1958, Eisenhower announced the creation of the National Aeronautics and Space Administration (NASA), which would be based on the modest National Advisory Committee for Aeronautics (NACA). Although the military branches wished to carve out a place for themselves in the arena of spaceflight, they would not hold responsibility for the high-profile manned space programs of the 1960s.

NASA’s first mission, now that the Soviets had beat it into space, was to put a man in space first. NASA called the program Project Mercury. On 9 April 1959, NASA administrator T. Keith Glennan announced the names of the first seven American astronauts who would fly in Project Mercury. The American media and public went into a frenzy over the “Mercury 7,” one of whom they believed would be the first man in history to orbit the Earth. Americans viewed the photogenic military test pilots as space warriors who, through their bravery, would save the United States from the spreading “red tide” of communism. In the USSR, however, Khrushchev and Sergei Korolev, the Soviet space program’s chief designer, had likewise determined that a Russian should be the first man into space. Indeed, the Soviets won this particular race as well. On 12 April 1961, the cosmonaut Yuri Gagarin, in a Vostok spacecraft atop a new A-1 rocket, was launched into Earth orbit. The United States reacted strongly to the news, and NASA administrators and engineers accelerated the pace of Project Mercury.

The first American astronaut was Alan B. Shepard Jr. His fifteen-minute suborbital flight, launched on 5 May 1961, by the von Braun-designed Army Redstone rocket, did not match the Soviet achievement but it did put America back into the space race. However, the Redstone launcher, with a thrust of 75,000 pounds, did not have the power to place a manned spacecraft into the Earth’s orbit. For this objective, NASA used the U.S. Air Force’s Atlas ICBM, with a total thrust of 360,000 pounds.

The Race to the Moon

Following on the heels of Shepard’s flight, President John F. Kennedy (1917–1963) made a dramatic announcement to Congress on 25 May 1961. He called for the achievement of landing a man on the moon and returning him safely to the Earth before the end of the decade. Kennedy’s announcement accelerated the space race because it gave an increased sense of national importance and urgency to NASA. The agency continued with Project Mercury, but it accelerated development of its lunar landing program, Project Apollo. In December of 1961, NASA announced Project Gemini, which would place two men into Earth orbit for extended periods. Gemini would practice many of the techniques used on Apollo, including the rendezvous of two spacecraft, the docking of two spacecraft, and spacewalking.

NASA successfully launched astronaut John H. Glenn Jr. into orbit on 20 February 1962, in the Mercury spacecraft, Friendship 7. This flight required much more effort on the part of the astronaut, the flight controllers, and the spacecraft, which had to perform critical maneuvers and keep the astronaut alive for several hours. The Mercury program continued with three more flights, concluding with Gordon Cooper’s successful 22-orbit flight on 15 May 1963. Mercury had achieved its major objectives of placing a man into Earth orbit and recovering him successfully.

NASA announced Lunar Orbit Rendezvous (LOR) as the Apollo mission mode in June of 1962. With LOR, von Braun’s Saturn V rocket, with a thrust of 7,500,000 pounds, would propel a crewed spacecraft, a service module with supplies, and a lunar module toward the moon. Once in orbit around the moon, the lunar module would separate from the command and service modules, carrying two astronauts to the moon’s surface while the command module pilot stayed in lunar orbit. The lunar module itself would have two stages, an ascent stage and a descent stage. When the astronauts finished their exploration of the moon’s surface, they would return to lunar orbit in the ascent stage, leaving the descent stage on the moon, and dock with the command module. On approach to Earth, both the ascent stage and the service module would be jettisoned. Only the command module would return to Earth. Although NASA originally thought this method too risky, its weight-saving advantages and the fact that each component could be engineered independently for a particular purpose ultimately made it the most practical of the modes considered. The LOR mission mode determined nearly every aspect of Apollo development, from crew training to spacecraft design to spacecraft maneuvering systems.

Mercury astronaut Gus Grissom and “New Nine” astronaut John Young piloted the first flight of Project Gemini, on 23 March 1965. The Gemini spacecraft, while based on the Mercury spacecraft, was larger and had a number of more sophisticated systems to allow performance in maneuvering, rendezvous, and docking. Later Gemini flights would dock with the Agena target vehicle, which was really the hollowed-out upper stage of an Atlas rocket fitted with docking adapters. But on 18 March 1965, Korolev dealt the United States another blow when Aleksei Leonov made the first spacewalk, lasting twelve minutes and nine seconds. Leonov and fellow cosmonaut Pavel Belyayev orbited the Earth in Voshkod 2, an updated version of Gagarin’s Vostok spacecraft. Edward H. White III of Gemini IV performed the first American spacewalk on 3 June 1965. However, from this point on, American performance in manned spaceflight would consistently outstrip Soviet performance up to the lunar landings.

Between March 1965 and November 1966, ten Gemini flights took place. While the United States set one space record after another, no cosmonauts orbited the Earth. In October of 1965, Gemini VI rendezvoused with Gemini VII, with the crew of Gemini VII spending two weeks in Earth orbit. The first successful docking of two spacecraft occurred during Gemini VIII, which was crewed by Neil Armstrong and David Scott. The final flight of the program, Gemini XII, solved many problems inherent to spacewalking and helped to refine flying techniques as well as spacesuit technology. With the conclusion of Project Gemini, spaceflight had become operational if not routine, and many of the skills needed for Apollo had been honed to sharp accuracy.

Although Project Gemini had seen some close calls in space, NASA’s first major catastrophe occurred on the ground. On 27 January 1967, during a routine ground test at the Kennedy Space Center, the Apollo One command module burst into flames and the three crew members, Gus Grissom, Ed White, and Roger Chaffee, perished through asphyxiation. Investigations showed that while faulty wiring was the immediate cause of the fire, neither NASA nor the contractor North American Aviation had fully understood the need for all components to work together in a complex system. Many at NASA and at North American Aviation believed that the fire gave them a new awareness of possible problems and actually facilitated the success of Apollo. The tragedy shook public confidence in Apollo, but, inspired by the memory of John F. Kennedy, Americans continued to support the program.

With many changes now built into the Apollo spacecraft, Apollo 7, a test of the command and service module in Earth orbit was launched on 11 October 1968. Apollo 8, launched on a Saturn V on 21 December of the same year, successfully circumnavigated the moon with the command and service modules, albeit after the USSR had managed to orbit the moon with an unmanned spacecraft, Zond 5. Satellite photos revealed that the Soviet moon rocket, the N-1, might soon be ready to take men to the moon. Project Apollo culminated in the Apollo 11 mission, launched on 16 July 1969, with commander Neil Armstrong, lunar module pilot Buzz Aldrin, and command module pilot Michael Collins. Two weeks before the launch, a Soviet N-1 moon rocket blew up on its launch pad, effectively ending the moon race. Armstrong and Aldrin touched down on the moon on 20 July1969, with a television audience of approximately a billion people. Backed by many thousands of workers, managers, and engineering specialists, Armstrong, Aldrin, and Collins met Kennedy’s goal and fulfilled the age-old dream.

With Apollo now fully operational, the focus of the program shifted to scientific lunar exploration. With the exception of Apollo 13, subsequent missions made significant discoveries regarding the geological composition and history of the moon using new equipment, such as the lunar rover. The final Apollo mission, Apollo 17, splashed down on 19 December 1972. The crew had taken the first photograph of the full Earth from space, underscoring the planet’s fragility and interconnectedness.

In retrospect, it is not surprising that the Americans reached the moon before the Soviets, despite early Soviet success. The death of Sergei Korolev in 1966 sealed the fate of a Soviet moon program that was under funded and subject to corruption, with resources spread too thinly over many design bureaus. The result was less equipment, fewer tests, and weaker technology. The American space program had the benefit of a thriving economy, largely due to its position after World War II, which was much stronger than that of the Soviet Union. Government and private enterprise formed strong partnerships in the United States that benefited the space program through NASA’s practice of awarding contracts to aerospace companies who would then build space hardware. Ironically, the democratic-capitalist United States government had better command of its space resources than the totalitarian USSR.

Beyond the Moon

Mars exploration has been prominent in the space programs of the Soviet Union (and later Russia), the United States, Europe, and Japan, with numerous missions and robotic spacecraft having been launched toward or directly at Mars since the 1960s. Mercury has been visited by the Mariner 10 and MESSENGER missions, the former in 1975, while the latter made a flyby in January 2008. A third mission is due to arrive in 2020. Similar to Mars, Venus has had many missions sent to it; the first was the American Mariner 2 craft in 1962, but most have been from Soviet Venera craft. Exploration of Jupiter has been undertaken since 1973 by a series of NASA’s automated spacecraft, most of them, apart form the orbiting Galileo craft, have been flybys. Saturn too has been explored only through unmanned NASA visits, including flybys by Pioneer 11 (1979), Voyager 1 (1980), Voyager 2 (1982), and the Cassini mission which entered orbit in 2004 and is likely to run into 2010. Uranus has only been explored through Voyager 2, with the closest approach coming in January 1986. Similarly, the sole visit to Neptune was the flyby of Voyager 2 in 1989.

After the Space Race

With the winning of the space race and the advent of detente, America’s political will to support large-scale space initiatives dissolved. The Skylab temporary space station project of the 1970s utilized leftover Saturn V rockets and increased knowledge of living and working in space. The Apollo-Soyuz test project of 1975, in which Apollo and Soviet Soyuz spacecraft rendezvoused and docked in the Earth’s orbit, marked the first major cooperative venture in space.

During the late 1970s, NASA completed the development of the space shuttle program. Originally intended to serve as a taxi with routine flights to and from a permanent orbital space station, the shuttle instead stood on its own because of NASA’s reduced budget. A private company built the shuttle fleet, which had its maiden voyage with the shuttle Columbia launching on 12 April 1981. During nearly three decades in service, space shuttles have deployed military satellites, housed numerous science experiments, carried the Hubble space telescope into space, and helped build the International Space Station (ISS). Yet the two major disasters of the Shuttle program, the Challenger explosion on 28 January 1986, and the disintegration of Columbia during reentry on 1 February 2003, underscored the problems of constant, routine access to space that had plagued the shuttle program since its inception. In both cases, experts blamed the nature of NASA bureaucracy, which had become increasingly inflexible since the days of Apollo.

The Soviet policy of glasnost (openness) initiated under Premier Mikhail Gorbachev (b. 1931) meant that the successes and failures of the Soviet space program could be discussed openly. This policy certainly helped the success of the Mir space station (1986– 2001), the world’s first long-term orbital structure for living and working in space. Assembled with updated versions of the Soyuz spacecraft, the station proved the feasibility of long-term space habitation, hosting several American crews during its tenure. The fall of the USSR in 1989, although difficult on the Russian program, opened up new commercial opportunities for spaceflight in Russia.

International Cooperation in Space

Since the end of the superpower space race, many other nations have begun to participate in the arena of space exploration. Major European nations joined the European Space Agency in 1980. The agency has contributed key satellites and scientific instruments to Russian, American, and joint endeavors. Additionally, the agency has produced many launchers for commercial use. Groups in Japan, including the National Space Development Agency (NASDA) have also begun to make strides into space with sophisticated technology. The Chinese space program, while younger than and not as versatile as the European and Japanese programs did succeed in putting a man into space on 15 October 2003.

The construction of the International Space Station (ISS) began in 1994. Although NASA has overall responsibility for the project, major components have been built by Russia, ESA, and NASDA. The station has been widely criticized for cost overruns and delays that have consumed much of the NASA budget. However, the station has hosted important research, particularly in the area of pharmaceuticals, and has provided humans with a permanent place to live and work in space.

The Future of Space Exploration

Two major themes currently dominate much of the discourse surrounding space exploration: the possibility of a manned mission to Mars and the widespread privatization and democratization of space travel. For years space enthusiasts of many stripes have been lobbying for a manned mission to Mars. However, without major political impetus, such as the need to upstage the Russians in the Cold War, American leaders have seen little reason to fund such an expedition, and countries other than the United States do not have the resources for such a mission in the near future. President George W. Bush (b. 1946, in office 2001–2009) announced plans for a permanent lunar base with a Mars landing in the next twenty years, but even with careful budgeting, this will be difficult to complete without a strong national commitment. In 2010, at the beginning of the second year of President Barak Obama’s administration, rumors that U.S. plans for future human spaceflights would abandoned were met with harsh criticisms (especially from NASA) until he renewed the goals, which included a Mars landing by 2030.

The flight of the first privately funded spacecraft, SpaceShipOne, designed by the U.S. aerospace engineer Burt Rutan (b. 1943), on 21 June 2004, inspired many entrepreneurs who wish to expand the opportunities for human spaceflight. Using SpaceShipTwo, a reusable sub-orbital spaceplane, Virgin Galactic aims to be taking tourists into space by 2010. Other privateers include Bigelow Aerospace, which has launched two space station modules—Genesis I and II—and plans to build an orbiting hotel in space. SpaceX’s Falcon 1, a liquid-propelled orbital launch vehicle has undertaken two successful flights; Falcon 9 is scheduled to launch in May 2010. To a certain extent the Google Lunar X-Prize has served to hasten private space exploration through the announcement of a $20 million prize for the first privately funded mission to the moon. But so has the general desire for space exploration and the need to be the first.

Existing space technology is extremely expensive and space travel is dangerous. These factors currently inhibit space exploration from being immediately profitable and accessible to all. Yet, if you have enough money the Russian space program has been willing to take paying passengers into space. But if dedicated scientists and engineers continue to pursue solutions to the problems of propulsion, spacecraft control, and long-term human survival in space, the possibility of space exploration for all—both in the Earth’s orbit and in interplanetary space—will come closer to our grasp.

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April 23, 2024

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Researchers detect a new molecule in space

by Danielle Randall Doughty, Massachusetts Institute of Technology

New research from the group of MIT Professor Brett McGuire has revealed the presence of a previously unknown molecule in space. The team's open-access paper, "Rotational Spectrum and First Interstellar Detection of 2-Methoxyethanol Using ALMA Observations of NGC 6334I," was published in the April 12 issue of The Astrophysical Journal Letters .

Zachary T.P. Fried, a graduate student in the McGuire group and the lead author of the publication, worked to assemble a puzzle comprised of pieces collected from across the globe, extending beyond MIT to France, Florida, Virginia, and Copenhagen, to achieve this exciting discovery.

"Our group tries to understand what molecules are present in regions of space where stars and solar systems will eventually take shape," explains Fried. "This allows us to piece together how chemistry evolves alongside the process of star and planet formation. We do this by looking at the rotational spectra of molecules, the unique patterns of light they give off as they tumble end-over-end in space.

"These patterns are fingerprints (barcodes) for molecules. To detect new molecules in space, we first must have an idea of what molecule we want to look for, then we can record its spectrum in the lab here on Earth, and then finally we look for that spectrum in space using telescopes."

Searching for molecules in space

The McGuire Group has recently begun to utilize machine learning to suggest good target molecules to search for. In 2023, one of these machine learning models suggested the researchers target a molecule known as 2-methoxyethanol.

"There are a number of 'methoxy' molecules in space, like dimethyl ether, methoxymethanol, ethyl methyl ether, and methyl formate, but 2-methoxyethanol would be the largest and most complex ever seen," says Fried.

To detect this molecule using radio telescope observations, the group first needed to measure and analyze its rotational spectrum on Earth. The researchers combined experiments from the University of Lille (Lille, France), the New College of Florida (Sarasota, Florida), and the McGuire lab at MIT to measure this spectrum over a broadband region of frequencies ranging from the microwave to sub-millimeter wave regimes (approximately 8 to 500 gigahertz).

The data gleaned from these measurements permitted a search for the molecule using Atacama Large Millimeter/submillimeter Array (ALMA) observations toward two separate star-forming regions: NGC 6334I and IRAS 16293-2422B. Members of the McGuire group analyzed these telescope observations alongside researchers at the National Radio Astronomy Observatory (Charlottesville, Virginia) and the University of Copenhagen, Denmark.

"Ultimately, we observed 25 rotational lines of 2-methoxyethanol that lined up with the molecular signal observed toward NGC 6334I (the barcode matched), thus resulting in a secure detection of 2-methoxyethanol in this source," says Fried. "This allowed us to then derive physical parameters of the molecule toward NGC 6334I, such as its abundance and excitation temperature. It also enabled an investigation of the possible chemical formation pathways from known interstellar precursors."

Looking forward

Molecular discoveries like this one help the researchers to better understand the development of molecular complexity in space during the star formation process. 2-methoxyethanol, which contains 13 atoms, is quite large for interstellar standards—as of 2021, only six species larger than 13 atoms were detected outside the solar system, many by McGuire's group, and all of them existing as ringed structures.

"Continued observations of large molecules and subsequent derivations of their abundances allows us to advance our knowledge of how efficiently large molecules can form and by which specific reactions they may be produced," says Fried.

"Additionally, since we detected this molecule in NGC 6334I but not in IRAS 16293-2422B, we were presented with a unique opportunity to look into how the differing physical conditions of these two sources may be affecting the chemistry that can occur."

Journal information: Astrophysical Journal Letters

Provided by Massachusetts Institute of Technology

This story is republished courtesy of MIT News ( web.mit.edu/newsoffice/ ), a popular site that covers news about MIT research, innovation and teaching.

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Facility for Rare Isotope Beams

At michigan state university, frib researchers lead team to merge nuclear physics experiments and astronomical observations to advance equation-of-state research, world-class particle-accelerator facilities and recent advances in neutron-star observation give physicists a new toolkit for describing nuclear interactions at a wide range of densities..

For most stars, neutron stars and black holes are their final resting places. When a supergiant star runs out of fuel, it expands and then rapidly collapses on itself. This act creates a neutron star—an object denser than our sun crammed into a space 13 to  18 miles wide. In such a heavily condensed stellar environment, most electrons combine with protons to make neutrons, resulting in a dense ball of matter consisting mainly of neutrons. Researchers try to understand the forces that control this process by creating dense matter in the laboratory through colliding neutron-rich nuclei and taking detailed measurements.

A research team—led by William Lynch and Betty Tsang at FRIB—is focused on learning about neutrons in dense environments. Lynch, Tsang, and their collaborators used 20 years of experimental data from accelerator facilities and neutron-star observations to understand how particles interact in nuclear matter under a wide range of densities and pressures. The team wanted to determine how the ratio of neutrons to protons influences nuclear forces in a system. The team recently published its findings in Nature Astronomy .

“In nuclear physics, we are often confined to studying small systems, but we know exactly what particles are in our nuclear systems. Stars provide us an unbelievable opportunity, because they are large systems where nuclear physics plays a vital role, but we do not know for sure what particles are in their interiors,” said Lynch, professor of nuclear physics at FRIB and in the Michigan State University (MSU) Department of Physics and Astronomy. “They are interesting because the density varies greatly within such large systems.  Nuclear forces play a dominant role within them, yet we know comparatively little about that role.” 

When a star with a mass that is 20-30 times that of the sun exhausts its fuel, it cools, collapses, and explodes in a supernova. After this explosion, only the matter in the deepest part of the star’s interior coalesces to form a neutron star. This neutron star has no fuel to burn and over time, it radiates its remaining heat into the surrounding space. Scientists expect that matter in the outer core of a cold neutron star is roughly similar to the matter in atomic nuclei but with three differences: neutron stars are much larger, they are denser in their interiors, and a larger fraction of their nucleons are neutrons. Deep within the inner core of a neutron star, the composition of neutron star matter remains a mystery. 

  “If experiments could provide more guidance about the forces that act in their interiors, we could make better predictions of their interior composition and of phase transitions within them. Neutron stars present a great research opportunity to combine these disciplines,” said Lynch.

Accelerator facilities like FRIB help physicists study how subatomic particles interact under exotic conditions that are more common in neutron stars. When researchers compare these experiments to neutron-star observations, they can calculate the equation of state (EOS) of particles interacting in low-temperature, dense environments. The EOS describes matter in specific conditions, and how its properties change with density. Solving EOS for a wide range of settings helps researchers understand the strong nuclear force’s effects within dense objects, like neutron stars, in the cosmos. It also helps us learn more about neutron stars as they cool.

“This is the first time that we pulled together such a wealth of experimental data to explain the equation of state under these conditions, and this is important,” said Tsang, professor of nuclear science at FRIB. “Previous efforts have used theory to explain the low-density and low-energy end of nuclear matter. We wanted to use all the data we had available to us from our previous experiences with accelerators to obtain a comprehensive equation of state.”   

Researchers seeking the EOS often calculate it at higher temperatures or lower densities. They then draw conclusions for the system across a wider range of conditions. However, physicists have come to understand in recent years that an EOS obtained from an experiment is only relevant for a specific range of densities. As a result, the team needed to pull together data from a variety of accelerator experiments that used different measurements of colliding nuclei to replace those assumptions with data. “In this work, we asked two questions,” said Lynch. “For a given measurement, what density does that measurement probe? After that, we asked what that measurement tells us about the equation of state at that density.”   

In its recent paper, the team combined its own experiments from accelerator facilities in the United States and Japan. It pulled together data from 12 different experimental constraints and three neutron-star observations. The researchers focused on determining the EOS for nuclear matter ranging from half to three times a nuclei’s saturation density—the density found at the core of all stable nuclei. By producing this comprehensive EOS, the team provided new benchmarks for the larger nuclear physics and astrophysics communities to more accurately model interactions of nuclear matter.

The team improved its measurements at intermediate densities that neutron star observations do not provide through experiments at the GSI Helmholtz Centre for Heavy Ion Research in Germany, the RIKEN Nishina Center for Accelerator-Based Science in Japan, and the National Superconducting Cyclotron Laboratory (FRIB’s predecessor). To enable key measurements discussed in this article, their experiments helped fund technical advances in data acquisition for active targets and time projection chambers that are being employed in many other experiments world-wide.   

In running these experiments at FRIB, Tsang and Lynch can continue to interact with MSU students who help advance the research with their own input and innovation. MSU operates FRIB as a scientific user facility for the U.S. Department of Energy Office of Science (DOE-SC), supporting the mission of the DOE-SC Office of Nuclear Physics. FRIB is the only accelerator-based user facility on a university campus as one of 28 DOE-SC user facilities .  Chun Yen Tsang, the first author on the Nature Astronomy  paper, was a graduate student under Betty Tsang during this research and is now a researcher working jointly at Brookhaven National Laboratory and Kent State University. 

“Projects like this one are essential for attracting the brightest students, which ultimately makes these discoveries possible, and provides a steady pipeline to the U.S. workforce in nuclear science,” Tsang said.

The proposed FRIB energy upgrade ( FRIB400 ), supported by the scientific user community in the 2023 Nuclear Science Advisory Committee Long Range Plan , will allow the team to probe at even higher densities in the years to come. FRIB400 will double the reach of FRIB along the neutron dripline into a region relevant for neutron-star crusts and to allow study of extreme, neutron-rich nuclei such as calcium-68. 

Eric Gedenk is a freelance science writer.

Michigan State University operates the Facility for Rare Isotope Beams (FRIB) as a user facility for the U.S. Department of Energy Office of Science (DOE-SC), supporting the mission of the DOE-SC Office of Nuclear Physics. Hosting what is designed to be the most powerful heavy-ion accelerator, FRIB enables scientists to make discoveries about the properties of rare isotopes in order to better understand the physics of nuclei, nuclear astrophysics, fundamental interactions, and applications for society, including in medicine, homeland security, and industry.

The U.S. Department of Energy Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of today’s most pressing challenges. For more information, visit energy.gov/science.