Why are space agencies considering higher oxygen levels in spacecraft?

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Space Agencies Are Considering Higher Oxygen Levels to Reduce Launch Costs

Space agencies are considering increasing oxygen levels in new spacecraft and space stations to 35 per cent primarily to reduce operational costs. This proposal stems from the understanding that higher oxygen concentrations permit lower internal pressure within the spacecraft. A lower internal pressure allows for a lighter structural design, which in turn requires smaller and less expensive rockets for launch.
Reduced Structural Weight and Launch Expenses

The core economic driver behind the proposal to increase oxygen levels relates directly to the physics of spacecraft design and launch. By maintaining a higher percentage of oxygen, approximately 35 per cent compared to the current 21 per cent, the internal pressure of the spacecraft can be significantly reduced. This reduction in pressure means the vehicle's hull does not need to be as robust to withstand the internal forces, leading to a lighter overall structure. Consequently, launching a lighter payload into orbit necessitates less powerful, and therefore more economical, launch vehicles.
The Apollo 1 Disaster and Oxygen Levels

Historically, the risks associated with oxygen levels in spacecraft were highlighted by the tragic Apollo 1 fire in January 1967. During a ground training exercise, a fire erupted within the command module, killing all three crew members. At the time, the capsule was filled with 100 per cent pure oxygen at a reduced pressure. This incident led to a subsequent reduction in oxygen levels to 21 per cent for subsequent missions, matching Earth's atmospheric composition, to mitigate fire risks.
Fire Behaviour in Low Gravity

Understanding fire behaviour in space is critical, especially with potential increases in oxygen. In the microgravity environment of space, flames do not behave as they do on Earth. Instead of rising due to convection, heat from a flame remains localised, causing the fire to form a spherical shape. This "ball of flame" radiates heat in all directions, potentially leading to rapid and unpredictable fire spread, a phenomenon being actively researched by scientists like Serge Bourbigot and his colleagues.
Ongoing Research into Space Fire Safety

The potential increase in fire risk associated with higher oxygen levels is being addressed through dedicated research programmes. Scientists are investigating various methods for fire detection and suppression in space. This includes exploring the use of acoustic waves to smother flames, developing advanced sensors to monitor temperatures and fire spread, and creating digital simulations of flame behaviour in low gravity. These efforts are crucial for ensuring the safety of future long-duration space missions, such as those planned for Mars.

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Why are space agencies considering higher oxygen levels in spacecraft?

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