Extreme challenges
What is the Kessler Syndrome? 10 serious threats astronauts face in space
Published on January 26, 2025
Credit: NASA Hubble Space Telescope
Space is the final frontier, but that hasn’t stopped humans from pushing beyond its boundaries. Space exploration, however, is fraught with danger. On Earth, we’re shielded from the cosmic hazards and extreme conditions that dominate the universe, but beyond our atmosphere, astronauts face a multitude of threats. From handling microgravity’s impact on the body to navigating the deadly vacuum, survival in space requires precision and discipline. Here are 10 essential things astronauts must do to stay alive—and continue their quest to explore the cosmos.
Suiting Up
Credit: Benjamin Recinos
A space suit is essential for survival beyond Earth’s atmosphere, providing protection from various hazards such as extreme temperatures, radiation, vacuum, and even space debris. The suit contains several layers, including thermal control and micrometeoroid shields, ensuring astronauts don’t freeze in the shadow of space or burn in direct sunlight. It also prevents depressurization effects by maintaining a stable internal atmosphere.
The suit also contains communication systems and a supply of oxygen, allowing astronauts to breathe and stay connected with their team during spacewalks. Without a suit, exposure to space would cause an astronaut to lose consciousness within seconds due to the lack of atmospheric pressure and oxygen deprivation.
Maintaining Oxygen Levels
Credit: Joshua Chehov
As most people know, space lacks breathable oxygen. While oxygen is technically present beyond our atmosphere and elsewhere—ranking as the third most abundant element in the universe—its concentration in the vastness of space is so low that, for all practical purposes, it is equal to 0%. Thus, maintaining a sufficient oxygen supply is one of the greatest challenges astronauts face.
Fortunately, there are effective methods for generating oxygen to support long-duration missions. On the International Space Station (ISS), oxygen is produced through electrolysis, a process that splits water into oxygen and hydrogen. In the case of a system failure, astronauts can rely on emergency oxygen tanks, although these supplies are limited. Equally important is managing carbon dioxide levels. A process called carbon dioxide scrubbing is used to eliminate CO2, preventing suffocation.
Credit: NASA
Handling Zero Gravity
While there is no such thing as "zero gravity," the effects of Earth's gravity diminish the farther we travel from its sphere of influence. This near-weightless condition, known as microgravity, triggers immediate physiological changes in the human body. Without the gravitational pull that typically draws blood toward the legs, fluids shift upward, causing facial swelling and increased pressure behind the eyes. This can lead to a range of health issues, including impaired vision.
Over time, astronauts also face muscle atrophy and bone density loss, as their bodies no longer have to bear their own weight. To counteract this, astronauts must exercise daily with resistance machines, treadmills, and bikes. However, even with strict exercise regimens, muscle and bone recovery can take months once they return to Earth.
Protection from Radiation
Credit: NASA
While we may not always be aware of it, Earth's atmosphere and magnetic field provide essential protection against a range of invisible dangers found in deep space, with radiation being one of the most concerning. Even during a flight, passengers are exposed to elevated levels of radiation, roughly equivalent to a chest X-ray for every 10 hours spent in the air.
Astronauts, however, often operate beyond the protective layers of our planet, exposing them to even greater radiation levels. Spacecraft are equipped with radiation shields, but they can’t block all radiation. Astronauts can receive up to 10 times the radiation dosage they would on Earth, increasing their cancer risk in the long term. But the most dangerous radiation threat comes from solar flares. During these solar events, astronauts must take cover in specially shielded areas of their spacecraft.
Rationing Food
Credit: Kai Dahms
In space, every ounce of food and water must be carefully rationed. Thus, astronauts survive eating pre-packaged, freeze-dried meals that are both lightweight and rich in nutrients. They simply add water to rehydrate the meals before eating, ensuring they get enough calories to maintain energy levels. While it might not sound very appealing to live out of freeze-dried meals for months, astronauts also experience a noticeable reduction in taste due to the lack of gravity.
Drinking water presents its own set of challenges. Nothing can be wasted, so space stations designed for long-term habitation, like the International Space Station (ISS), often employ advanced filtration systems to recycle water from condensation, sweat, and even urine! Astronaut life isn’t all it’s cracked up to be, huh?
Monitoring Mental Health
Credit: NASA
Even with all their training, the deep isolation and confinement of space can significantly impact an astronaut’s mental health. Long missions far from Earth can lead to feelings of loneliness, anxiety, and depression. To deal with that, astronauts are encouraged to maintain a daily routine, exercise, and engage in team activities. Communication with loved ones back on Earth is also crucial for their emotional well-being.
Space agencies take mental health very seriously, conducting regular psychological assessments during missions. Studies have shown that astronauts on extended missions may experience a decline in cognitive abilities and an increase in stress levels—factors that can be critical in such a delicate environment, where mental clarity and emotional stability can be a matter of life or death.
Controlling Temperature
Credit: noe fornells
Despite the popular belief that it’s unforgivingly cold, space doesn’t have a temperature in the traditional sense—after all, it’s a vacuum. Instead, temperatures can shift dramatically, ranging from boiling hot to freezing cold, depending on exposure to the Sun. Astronauts rely on their suits and spacecraft systems to maintain a stable internal temperature. The suit’s liquid cooling garment, which contains a network of water-filled tubes, helps astronauts regulate their body temperature during spacewalks.
Inside the spacecraft, temperature control systems work to prevent the interior from becoming unbearably hot or cold. However, there have been instances where astronauts had to repair these systems themselves to avoid the dangers posed by extreme temperatures, which can fluctuate rapidly from 250°F to -250°F.
Preventing Muscle Loss
Credit: Muha Ajjan
Ever wondered why most astronauts struggle to walk by themselves after returning to Earth from long missions? As we pointed out before, without the constant pull of gravity, muscles weaken very rapidly. In fact, astronauts can lose up to 20% of their muscle mass in just two weeks without exercise.
While it would be technically possible to maintain proper muscle mass through rigorous exercise, doing so would require significantly more time than it does on Earth. Astronauts lead extremely busy lives—every minute counts up there—leaving little time for anything beyond essential tasks. So, if you were thinking about heading to space to hit the gym, you might want to reconsider and stick to your local fitness center instead!
Watching Out for Space Debris
Credit: NASA Hubble Space Telescope
Space debris, which includes everything from tiny meteoroids to fragments of defunct satellites and spent rocket parts, can travel at astonishing speeds of up to 17,500 mph! These high-speed projectiles can easily puncture spacecraft or damage equipment, putting astronauts' lives at serious risk.
The ISS is equipped with monitoring systems that detect nearby debris, allowing the station to perform evasive maneuvers when needed. However, this is far from a solved issue. Many scientists warn that if space pollution, much of which is produced by improper satellite disposal, is not addressed soon, it could lead to a cascading effect of collisions that would generate even more debris, and thus more collisions… you get the idea. This alarming scenario is known as Kessler Syndrome, and if left unchecked, it could threaten the safety and feasibility of future space exploration.
Weakened Immune System
Credit: National Cancer Institute
As if astronauts didn’t have enough going on already, space weakens the immune system, making astronauts more vulnerable to infections. This immunosuppression is caused by a mix of stress, microgravity, and increased radiation exposure. Studies have shown that astronauts’ white blood cells, which help fight infections, are less effective in space.
To make things worse, bacteria and viruses seem to behave differently out there, often becoming way more virulent than on Earth. Astronauts must be extra vigilant about hygiene, regularly disinfecting their living spaces and monitoring their health—not an easy task in the often cramped spaces where they must carry out their missions.
