Environmental Control and Life Support System (ECLSS)

Context

The Environmental Control and Life Support System (ECLSS) is a technology that maintains Earth-like habitable conditions within a spacecraft. This system controls air, water, temperature, humidity, and waste management so that astronauts can safely survive in space for extended periods.
Essential supplies like food, water, and oxygen are transported from Earth during short-duration missions, and waste is safely stored. In longer missions, waste is recycled and converted into useful resources like clean water and breathable air.

On Earth, plants and oceans naturally absorb carbon dioxide from the atmosphere. However, this is not possible in a spacecraft. In the Indian Space Research Organization's Gaganyaan mission, carbon dioxide will continuously build up within the cabin due to astronauts' breathing, so artificial removal will be necessary.
If carbon dioxide levels become too high, a condition called hypercapnia can occur, which can cause headaches, dizziness, and impaired thinking. Normally, a healthy person exhales about 1 kilogram of carbon dioxide per day, while this amount can increase with increased physical activity.
The air resuscitation system provides fresh air, removes excess carbon dioxide, and filters out odors and fine pollutants that build up in the cabin. On short space missions, oxygen is supplied from high-pressure cylinders. On average, an astronaut requires about 0.84 kilograms of oxygen per day.
Lithium hydroxide-based canisters are used to remove carbon dioxide. They also contain activated charcoal, which absorbs odors. These canisters are typically replaced every 20 to 24 hours.
There is no natural air circulation in microgravity, so small fans maintain air circulation within the cabin. This prevents the formation of dangerous clumps of carbon dioxide or oxygen.

Gaganyaan's crew module is designed to maintain a temperature of approximately 20 to 26 degrees Celsius and a relative humidity of 30% to 70%. This provides a comfortable environment for the crew and protects electronic equipment.
Moisture in the cabin is primarily generated by astronauts' breath and perspiration. If the humidity drops too low, it can dry out the skin, irritate the eyes, and increase the risk of static electricity. Excessive humidity can lead to the growth of microorganisms, and condensation can cause corrosion or short circuits in equipment.
Heat within the spacecraft is primarily generated by the human body and electronic systems. Active cooling systems are used to control this. Excess heat is removed through heat exchangers.
The pressure is maintained at approximately 101.3 kilopascals, close to Earth's sea level. Sensors and safety valves regulate the balance of oxygen and air.

Water doesn't flow normally in space, but instead floats as tiny droplets. These droplets can be hazardous to electronic devices and pose a risk if inhaled.
For this reason, water is stored in special pressurized bags on spacecraft. In the Gaganyaan mission, astronauts will be able to drink water from these special bags, which will be pressurized to deliver water directly to their mouths.

Liquid and solid waste don't fall to the floor in microgravity, so suction-based airflow systems are used to control them. These systems draw waste away from the body and prevent it from floating in the cabin.
Gaganyaan will have special bags for collecting feces and a funnel-based system for collecting urine. Waste materials will be chemically treated to prevent odor and bacterial growth. They will then be stored in sealed containers for disposal upon return to Earth.

In the absence of gravity, a fire can spread in a circular fashion instead of the usual flames, making it more difficult to control. Smoke sensors on Gaganyaan will immediately alert the crew.
Special fire extinguishers will be used to extinguish fires, which emit a fine spray of water. This spray helps cool the fire and reduce toxic smoke particles. Some spacecraft, such as Soyuz, also have the option to depressurize the cabin in case of an emergency, although this is used as a last resort.