ISRO successfully conducted the Second Integrated Air Drop Test (IADT-02) for Gaganyaan, India’s first human spaceflight mission, on April 15, 2026.
| Photo Credit: PTI
The Environmental Control and Life Support System (ECLSS) replicates the earth’s atmosphere in earth orbit by managing air, water, temperature, and waste. In short-term space missions, all supplies are carried from the earth and waste is stored for disposal later. Long-duration missions recycle the waste back into useful resources like breathable air and clean water.
What is air revitalisation?
Carbon dioxide is removed from the earth’s atmosphere by photosynthesis and by dissolving in the oceans. In Gaganyaan (the Indian Space Research Organisation mission to place a small crew of Indian astronauts in a 400 km orbit around the earth), astronauts’ exhalation will increase the cabin’s carbon dioxide content and has to be artificially removed. Elevated levels of carbon dioxide can lead to hypercapnia, causing symptoms such as headaches, dizziness, and impaired cognitive function.
A healthy adult normally exhales around 1 kg of carbon dioxide per day, though this amount increases significantly with physical exertion. The air revitalisation system (ARS) provides fresh air, removes carbon dioxide, and filters trace contaminants or odours that would otherwise accumulate in the cabin. For short missions, oxygen is supplied from high-pressure gas bottles. According to standards, a healthy crew member needs 0.84 kg of oxygen per day to support metabolic functions.
Carbon dioxide is removed using lithium hydroxide canisters. Each canister has activated charcoal that absorbs any odours in the cabin air. A spent canister is replaced by the crew with a fresh one typically every 20-24 hours. In a microgravity environment lacking natural convection, small fans in the ECLSS are the circulatory system that prevents lethal carbon dioxide and hazardous oxygen pockets from lingering.
How are pressure, temperature and humidity controlled?
The Gaganyaan crew module is designed to maintain a comfortable environment with a temperature of 20-26°C and relative humidity between 30% and 70% to ensure crew comfort and equipment safety. The moisture released through the crews’ breath and sweat are the main sources of humidity in the cabin.
Low humidity in the crew cabin can lead to dry skin, irritated eyes, and higher risk of static electricity discharge that could damage electronics. High humidity promotes microbial growth and causes condensation that may lead to short-circuits or corrosion.
Heat in the crew module is primarily generated by the metabolic body heat of the astronauts (100 to 150 W per crew) and continuously operating onboard electronics and avionics. An active cooling system is used to regulate temperature. Heat is removed by circulating the air through heat exchangers, which will expel the heat into space. The humidity is managed by condensing units that collect water to prevent fogging and short-circuits.
The pressure is held at 101.3 kPa. To mimic the earth’s sea-level conditions, the pressure control system uses electronic sensors and safety valves to balance the air and oxygen levels.
Where does water come from?
The primary challenge in space is water doesn’t ‘pour’ but forms floating globules that can cause short-circuits in electronics or pose a hazard if inhaled accidentally. So water must be mechanically forced from storage using pressurised bladders to avoid gas-liquid mixing.
In Gaganyaan, the crew relies on supply of potable water stored in specially designed pouches. They can be pressed to force water directly into the mouth.
How is waste managed?
In microgravity, liquid and solid waste do not “fall”, requiring suction-based airflow systems to pull waste away from the body and prevent it from floating around. These systems must also separate and stabilise waste to avoid microbial contamination and the buildup of toxic gases like ammonia.
In Gaganyaan, specialised faecal collection bags will be used and urine will be sucked through funnels. All waste will be chemically treated to neutralise odours and inhibit bacterial growth, then stored in sealed containers for disposal after return.
How are fires suppressed?
The lack of gravity allows fires to expand into a sphere that is harder to reach with traditional suppressants. In Gaganyaan, smoke detectors will sound an alarm to alert the crew. Fire extinguishers that create fine water mists can be used to put the fire out. A water mist effectively cools the fire and also scrubs toxic smoke particles.
Russia’s Soyuz has the option to depressurise the cabin as a last resort to extinguish the fire after the crew has worn a pressure suit.
(Unnikrishnan Nair S. is Former Director, VSSC and IIST; Founding Director, HSFC; and an expert in launch vehicle systems, orbital re-entry and human spaceflight technologies. He is currently working as Dr Sarabhai Professor at VSSC)
Published – May 22, 2026 08:00 am IST
