Act 2.6 Study Guide - Space Life Support Systems

Atmospheric Requirements and Baseline Physiological Needs

Human survival in space environments necessitates specific atmospheric conditions that mirror Earth's natural environment. Regarding oxygen consumption, an individual in space requires exactly $0.84\,kg$ of Oxygen ($O_2$) daily, which is the same amount required for someone on Earth. The broader atmospheric composition consists primarily of two critical gases: Nitrogen and Oxygen. These gases exist in specific proportions, with Nitrogen accounting for $78\%$ of the atmosphere and Oxygen accounting for $21\%$.

Resource Allocation and the Logistics of Water in Space

There is a significant disparity between the water requirements of individuals on Earth compared to those in a space environment. On Earth, a person requires a total of $7\,L$ of water per day, with $3\,L$ used for drinking and the remaining $4\,L$ dedicated to food preparation and growing produce. In contrast, astronauts in space have a total daily requirement of $2.4\,L$. This is broken down into $1.6\,L$ for direct consumption (drinking) and $0.8\,L$ for the purposes of growing produce or rehydrating food.

The logistics of providing water to space are governed by extreme costs. It costs approximately $42,720$ to send just $1\,Liter$ of water to space. To calculate the total water requirement for a mission involving $4$ astronauts on an $180$-day trip, the daily requirement per astronaut ($2.4\,L$) is multiplied by the number of crew members ($4$), resulting in a daily total of $9.6\,L$. Over the course of the $180$-day mission, the calculation is $9.6 \times 180 = 1,728\,L$. Based on the provided data, the cost to send this volume ($1,728\,L$) to the International Space Station (ISS) is calculated as $1,728 \times 42720 = \$4,700,160$.

Wastewater Reclamation and Recyclable Sources

Water management on the ISS relies heavily on recycling processes to maintain sustainability. Approximately $30\%$ of the water on the ISS is recycled, while the remaining portion is allocated for the oxygen generation system. Once this water is recycled, it is utilized for essential daily activities including drinking, the rehydration of food, and general hygiene.

The recycled water is collected from a wide variety of sources within the cabin, including moisture from brushing teeth, hand washing, urine (pee), breathing, showering, and sweat. Once collected, the water undergoes a rigorous purification process where it is cleansed with chemicals and filtered. Following this treatment, it is reused in various shapes and forms to support the crew.

The Oxygen Generation System: Chemical Conversion via Electrolysis

The primary purpose of the Oxygen Generation System is to produce breathable air for the crew by converting water ($H_2O$) into its component elements. This system uses a specific electrochemical process known as electrolysis to break down water into Oxygen ($O_2$) and Hydrogen ($H$).

Each product of electrolysis serves a specific role in the ship's life support cycle. The Oxygen ($O_2$) produced is released back into the cabin environment to ensure the astronauts have access to clean, filtered air for respiration. The Hydrogen ($H$) produced is not wasted; instead, it is fed directly into the Sabatier system to aid in further chemical processing and carbon dioxide removal.

The Sabatier System: Carbon Dioxide Reduction and Environmental Control

The Sabatier System is the primary mechanism used to remove Carbon Dioxide ($CO_2$) from the cabin of the ISS, which is exhaled by the astronauts. The system functions by taking the $CO_2$ from the cabin and adding the Hydrogen ($H_2$) produced by the oxygen generation system. This chemical interaction occurs under pressure (indicated as $400$) to produce methane gas ($CH_4$) and water ($H_2O$). The chemical reaction for this process is defined as:

$CO_2 + 4H_2 \rightarrow CH_4 + 2H_2O$

The outputs of the Sabatier System are managed differently: the methane gas ($CH_4$) is vented out into space, while the water ($H_2O$) is processed and cleansed to be used for drinking. This recovery of water from waste gases is essential for mission efficiency.

Integrated Mission Sustainability and Waste Classification

The Sabatier System and the Oxygen Generation System are critically important because they work in tandem to ensure that every space mission aboard the ISS is as safe and efficient as possible. These systems minimize the need for external resupply by reclaiming essential life-support elements. In addition to gaseous recycling, the station must manage various forms of waste produced during operations. These are categorized into four types: Human waste, Wastewater, solid waste, and Gaseous waste.