Survival in space poses significant challenges, especially without external support.

Existing extravehicular mobility units (EMUs) offer astronauts a certain level of protection, enabling them to work and explore in the harsh environment of space.

Each EMU is equipped with two oxygen tanks and an emergency oxygen supply system, which typically provides between 6.5 and 8 hours of breathable oxygen.

This duration is crucial for astronauts performing extravehicular activities, allowing them to complete short-term missions or respond to emergencies. However, this timeframe does not imply that astronauts can survive indefinitely in space; it merely ensures they can manage specific tasks within a limited period.

Human exploration of the universe, evolving from early geocentric theories to contemporary advancements such as black hole imaging, space elevator concepts, and commercial manned orbital flights, highlights the rapid progress in science and technology.

Despite these remarkable achievements in astronomy and space technology, the issue of long-term survival in space remains a complex challenge.

The question of whether humans can survive in space for extended periods is intricate. Even with the protection offered by space suits, astronauts' survival time in space is subject to numerous constraints.

The environment in outer space is exceptionally harsh, and the absence of breathable oxygen presents a primary threat. In the vacuum of space, the body's oxygen reserves last only about 15 seconds. Once the oxygen supply is depleted, the brain quickly becomes hypoxic, leading to a loss of consciousness.

Nevertheless, if astronauts can return to an oxygen-rich environment within 1 to 2 minutes, survival is still possible. Timely rescue and rapid return to a breathable atmosphere are critical for ensuring life safety.

Additionally, the lack of atmospheric pressure in space presents other severe threats. When an astronaut holds their breath in space, the absence of external atmospheric pressure causes the air inside the body to expand gradually, ultimately leading to the rupture of the lungs.

This phenomenon can result in gas embolism, further endangering life. Therefore, maintaining normal breathing, even in emergencies, is crucial to prevent the expansion of air within the body.

Another significant threat is the boiling of body fluids. In the vacuum of space, the boiling point of bodily fluids, such as saliva, sweat, and tears, is greatly reduced, causing them to evaporate almost immediately.

Although blood does not boil because the circulatory system maintains normal blood pressure, nitrogen dissolved in the blood can vaporize, leading to the expansion of body tissues and, in severe cases, organ damage.

Fortunately, the skin's elasticity helps prevent the body from expanding to life-threatening levels, but once the astronaut returns to a normal pressure environment, the body will revert to its usual state.

Astronauts also face the dangers of unshielded cosmic radiation and solar wind. Cosmic radiation can cause severe sunburns and damage to human tissues, resulting in DNA mutations that increase the risk of cancer, cataracts, and potential infertility.

Additionally, fast-moving micrometeorites and space debris pose significant risks, potentially penetrating the body like bullets.

Contrary to the dramatic depictions often seen in films and television, the extremely low temperatures of space do not cause immediate freezing. Cooling in space occurs through radiation rather than conduction or convection. Because radiation is a slower cooling process, the human body will gradually freeze over a period of 12 to 20 hours.

To address these challenges, modern extravehicular space suits (EMUs) are designed with multi-layered protective structures. EMUs consist of two main components: the pressure suit and the life support system.

The pressure suit comprises the upper torso, lower torso, cooling suit, and helmet. It is constructed from multiple layers of materials to regulate temperature, maintain pressure, and protect against radiation.

The cooling suit contains micro-tubes through which water circulates to dissipate heat, while the hard outer layer provides essential physical protection. The helmet’s ventilation system supplies oxygen to the astronaut and is equipped with cameras and communication devices to facilitate extravehicular activities.

The life support system, a core element of the space suit, includes oxygen tanks, carbon dioxide filters, batteries, and pressure regulators. These components ensure that astronauts receive the necessary oxygen and that carbon dioxide produced by their bodies is removed during extravehicular activities. Additionally, emergency oxygen packs offer supplementary oxygen supplies in case of emergencies.

The survival time of humans in space is constrained by various factors. While modern technology has provided effective protection, long-term survival in space remains fraught with challenges.

Scientists continue to explore and refine technologies to overcome these challenges and enable longer durations of space exploration.