Does the International Space Station (ISS) Need Water Resupply or Can It Be Recycled Forever?
The International Space Station (ISS) is a unique environment where recycling water is crucial for the survival of its crew. This article explores the extent to which the water on board can be recycled and how often water resupply is necessary. We will also discuss the limitations of the recycling system and how it impacts the longevity of the ISS.
Water Recycling Systems on the ISS
Water management on the ISS is a critical aspect of mission success. Unlike on Earth, water is a precious resource that needs to be conserved and reused. The station has a highly efficient water recycling system that has evolved over time, with improvements made as technology advanced.
Back in the days of the Space Shuttle era, water was delivered to the ISS in the form of water bags. However, the complexity and frequency of deliveries were a logistical challenge for the crew. In 2010, the situation changed with the introduction of water reclaimer machines. The Water Recovery System (WRS) has proven to be highly effective, able to recycle up to 96% of the water on board.
Efficiency of the Water Recycling System
The Water Recovery System is among the most sophisticated and reliable in the world. The system not only recycles water but also ensures its safety for consumption. Let’s break down the process briefly:
Initial Collection: Urine, sweat, condensation, and recycled water are collected and stored.
Processing: The recovered liquid undergoes a series of purification processes, including ion exchange, distillation, and microfiltration to remove impurities.
Final Treatment: The purified water is treated with UV light and hydrogen peroxide to ensure it is safe for drinking.
While the system is highly efficient, no recycling system is perfect. A small residue of about 4% remains as a salty, unusable substance. This means that despite the advanced recycling capabilities, the station still needs to account for this small percentage of unrecyclable water.
Water Loss and Consumption
Water loss and consumption on the ISS are also significant factors that affect how long the station can operate without resupply. Every system on the station consumes water, including:
CO2 removal systems, where some water is electrolysed to produce oxygen.
Uneaten food, which decomposes and can release moisture.
The harsh living conditions, leading to increased sweat and condensation.
On average, each crew member consumes between 2-3 liters of water daily. Therefore, the total water consumption per crew member is approximately 730-1095 liters per month. Considering the ISS typically hosts a crew of six, this amounts to a minimum of 4,380 liters and a maximum of 6,570 liters of water per month.
Longevity of the ISS with Recycling Only
The question remains: can the ISS operate solely on recycled water? The answer lies in the balance between consumption and recycling.
Assuming no additional water was delivered to the station since 2010, the crew would need to rely on the existing water supply and the recycling system. The ISS has roughly 54,000 liters of water storage capacity. Given that 96% of the water can be recycled, the station can sustain itself for a considerable amount of time.
Robust calculations show that with a crew of six and assuming no further water resupply, the station can survive for about 2-3 months before needing another supply. However, this timeframe can be extended with more efficient use of water and additional recycling processes.
Conclusion
The International Space Station has made significant strides in water management and recycling. The 96% recycling rate is a testament to the station's advanced life support systems. However, even with the best recycling systems, a small percentage of unusable water remains, necessitating periodic resupply to ensure the missions' success.
For more information on the ISS and its ongoing technological advancements, visit the official NASA website: NASA's ISS Research and Technology.