Is There a Limit to How Long Humans Can Survive in Space?

Space is hard, particularly connected our bones and muscles, our hearts, our eyes, and fundamentally astir each quality organ. And yet, we can’t enactment distant from it. Nearly 700 radical person been to abstraction truthful far, and that fig is lone going to summation arsenic backstage spaceflight begins to instrumentality off. But erstwhile it comes to enduring agelong duration stays successful space, however overmuch tin the quality assemblage truly take?

Earlier this year, two Russian cosmonauts broke the grounds for the longest duration stay connected committee the International Space Station (ISS), spending 374 consecutive days successful the microgravity environment. Astronauts connected committee the ISS assistance scientists larn astir the effects spaceflight has connected the quality body. Spoiler alert: they’re not great.

The weightless situation causes nonaccomplishment of bony density, muscular atrophy, reduced measurement of blood, decreased bosom musculus functions, blurred vision, and disorientation. NASA and different abstraction agencies are hoping to larn much astir these effects successful bid to assistance mitigate the risks connected astronauts traveling connected long-duration journeys done space.

A quality ngo to Mars would instrumentality astir 3 years, according to NASA. But what would that benignant of journey—and adjacent longer durations successful space—do to the quality body? For this Giz Asks, we spoke with experts to recognize the challenges of surviving successful a weightless situation for extended periods. How agelong could a idiosyncratic endure beingness during a deep-space voyage? And successful the worst-case scenario, what would hap if idiosyncratic were stranded indefinitely connected the ISS? Here’s what they had to say.

Mark Shelhamer

Professor astatine Johns Hopkins University School of Medicine, vice president of the Human Research Program for Civilians successful Space and Chief Scientist astatine the NASA Human Research Program from 2013 to 2016.

The elemental answer: it depends. Several nonrecreational authorities astronauts person spent astatine slightest 1 continuous twelvemonth successful space, with small to nary superior adverse effects. We cognize that this tin beryllium done, astatine slightest for those who are successful fantabulous wellness to commencement with and who adhere to rigorous countermeasure protocols (mostly exercise). How agelong tin this beryllium extended? It depends connected what is expected of the radical successful space, what countermeasures are disposable to them, and whether oregon not they volition instrumentality to Earth.

If their lone occupation is to enactment alive, careless of their quality to execute immoderate meaningful work, past it is conscionable a substance of survival. In this case, radical could past successful abstraction for rather a agelong time. Without countermeasures specified arsenic exercise, their clip would beryllium leisurely and enjoyable. Their lone extremity would beryllium to bask the experience, which could beryllium rather pleasant. For a time. Eventually, the deficiency of adjacent minimal carnal exertion (which we get connected Earth conscionable by moving against gravity to enactment upright) would origin terrible degradation of the bones, muscles, and heart. These changes mightiness not beryllium atrocious if these radical enactment successful the benign weightlessness of space, but this physiological de-conditioning would precise apt preclude their quality to instrumentality to the Earth’s gravity environment.

Even if these physiological changes are not debilitating oregon fatal, determination are different stressors that could instrumentality a toll implicit time. The intelligence challenges of surviving successful a tiny abstraction with a tiny fig of radical tin beryllium significant—especially without an overarching extremity to marque the trouble worthwhile. If extracurricular the comparative information of low-Earth orbit, deep-space radiation mightiness person important effects. Some of these effects would beryllium cumulative: an expanding hazard of crab with expanding clip successful space. Other aspects would beryllium connected sporadic events similar star flares for which extortion mightiness beryllium inadequate, and which could nutrient acute effects precise quickly.

In parallel with these issues is the little-understood interaction of weightlessness connected the organisation of fluids successful the body. Without gravity, these fluids (blood, cerebrospinal fluid, lymphatic fluid, and others) disperse much evenly, alternatively than being drawn to the legs. It is thought that immoderate effects of this fluid shift—seen already successful spaceflights of respective months—are changes successful the operation of the eye, an upward displacement of the encephalon successful the skull, and flimsy changes successful encephalon function. These mightiness beryllium harbingers of existent neural harm from extended clip successful space. It’s imaginable that radical could enactment successful abstraction for precise agelong times yet acquisition gradual deterioration of neural function—things specified arsenic cognition and centrifugal control. If others onboard are disposable to assist, these radical mightiness past for a agelong time. But to what end? These are among the large risks of which we are aware. There volition apt beryllium others that originate arsenic radical walk longer times successful space. It is these chartless unknowns that could beryllium the limiting factors, but of people we don’t cognize what they are.

I would hazard a conjecture astatine 5 years, possibly more, for endurance successful abstraction nether the conditions conscionable described. But these radical would dice successful space, having done small of worth but found biologic boundaries connected the quality to past successful specified a harsh environment. Countermeasures would assistance to mitigate immoderate of the aesculapian issues, successful which lawsuit the viable duration mightiness widen to possibly 10 years, and possibly adjacent let instrumentality to Earth if workout is sufficiently vigorous.

Once the space-farers commencement doing work, the accidental of wounded increases, but truthful does the request to support a higher level of carnal fitness. This is simply a challenge. If they spell with enactment to beryllium done and the volition of returning to Earth, the reply changes. In this case, specified endurance is not enough: the quality to execute meaningful enactment and to clasp bone, muscle, and cardiovascular information is necessary. Even with the existent champion workout and nutrition countermeasures, radiation and isolation volition instrumentality their toll. With small supporting evidence, I would spot this bounds astatine astir 4 years. With artificial gravity it whitethorn beryllium overmuch longer. In this lawsuit the limitations whitethorn beryllium predominantly owed to science and radiation. If artificial gravity is decently implemented, with radiation shielding and attraction to intelligence concerns, determination mightiness successful information beryllium nary bounds to the clip that tin beryllium spent successful space.

Not lone does the last reply beryllium connected the factors conscionable described, it besides depends connected the circumstantial idiosyncratic – his oregon her familial predisposition, lifestyle, and quality to header with stress. The numbers present transportation a immense magnitude of uncertainty, but they supply a starting point, bespeak the factors to beryllium considered, and amusement however antithetic ngo scenarios person an impact.

Francis Cucinotta

Professor for the section of wellness physics and diagnostic sciences wrong the School of Integrated Health Sciences astatine the University of Nevada, Las Vegas.

ISS has received a [radiation] dose-rate astir 3 times little than heavy abstraction due to the fact that of the Earth’s shadiness blocking astir one-third and Earth’s magnetic tract an further one-third. The aboveground of Mars is astir one-third of heavy abstraction owed to Mars’ assemblage and atmosphere.

The shielding of the ISS is capable to trim the doses from adjacent ample star particle events truthful determination are nary important risks of acute radiation sickness. Therefore the main hazard is alleged precocious effects (cancer, bosom disease, cataracts) and a imaginable hazard of changes to cognition and memory, which is observed successful mice and rats but not firmly established successful humans.

So 1 mode to reply is to inquire however overmuch hazard a idiosyncratic is consenting to accept? If unlimited hazard is acceptable past the reply has to bash with probabilities of occurrence of the assorted diseases.

Radiation causes DNA harm and creates radicals owed to ionizations successful insubstantial starring to accrued oxidative stress. This tin pb to cistron mutations, chromosomal aberrations, insubstantial situation alteration specified arsenic perturbation of the immune strategy and aberrant biochemical signaling. These are precursor changes to assorted wellness diseases.

With shielding specified arsenic connected the ISS, a idiosyncratic tin past but has a precocious probability of fatal diseases oregon morbidity exceeding 10% probability aft a fewer years successful heavy space.

I deliberation the main constituent to inquire is if the endeavor to walk a fewer years successful abstraction is invaluable capable to instrumentality the risks, and should abstraction agencies marque ample investments to trim risks. Late effects instrumentality immoderate clip to look babelike connected which type. Minimum times aft vulnerability see imaginativeness impairing cataracts (a small implicit 5 years), leukemia (two years), coagulated cancers (about 5 years), bosom illness (about 10 years), changes to cognition is little known. So possibly different question would be, however agelong tin a idiosyncratic enactment successful abstraction if attraction [to those diseases] is not possible.

Eneko Axpe

A physicist astatine Stanford University who’s worked with NASA connected processing biomaterials to forestall and dainty bony nonaccomplishment successful astronauts during spaceflight.

As of 2024, the grounds for the longest continuous enactment successful abstraction is held by Russian cosmonaut Valeri Polyakov, who spent 437 days and 18 hours aboard the Mir abstraction presumption from January 1994 to March 1995. This shows that a idiosyncratic tin stay successful abstraction for implicit 1.2 years. Could idiosyncratic enactment longer? Absolutely. However, the wellness risks go progressively severe.

Let’s see a 1,000-day ngo to Mars, which would beryllium the expected duration with our existent technology. In microgravity, muscles and bones weaken owed to the deficiency of regular weight-bearing activity.

In a survey we conducted, a collaboration betwixt NASA and Stanford University, we developed a predictive mathematical model. This exemplary shows that connected a Mars mission, 100% of astronauts are apt to make osteopenia [when bony density is little than normal], with 33% astatine hazard for osteoporosis, depending connected factors similar age, gender, and ethnicity. Even much concerning is the radiation exposure. For heavy abstraction missions similar a Mars journey, the crab hazard rises importantly owed to higher vulnerability to galactic cosmic rays (GCRs) and star radiation. A Mars ngo could exposure astronauts to 0.7 to 1 sievert (Sv) of radiation, with 1 Sv expanding crab hazard by astir 5%. This is overmuch higher than the emblematic radiation dose connected the International Space Station (ISS), which is astir 0.3 Sv for a six-month stay.

In addition, abstraction travelers look different superior wellness challenges: Spaceflight-Associated Neuro-Ocular Syndrome (SANS), cardiovascular disease, and imaginable tense strategy damage. Vision problems caused by fluid shifts successful microgravity whitethorn persist adjacent aft returning to Earth. Mental wellness is besides a concern, arsenic extended isolation, confinement, and the region from Earth tin pb to stress, anxiety, depression, and cognitive decline. The altered immune strategy effect during long-duration missions besides raises concerns astir warring disconnected infections oregon handling aesculapian emergencies.

In my opinion, a three-year ngo to Mars is feasible, though astronauts would apt instrumentality with important wellness issues, immoderate of which could beryllium severe. Missions longer than this would propulsion the limits of quality endurance.