Interaction between exercising humans and growing plants in a Closed Ecological Life Support System

Area of Science:

• Space life support systems
• Plant-human metabolic interactions
• Environmental control and life support systems (ECLSS)

Background:

• Closed Environmental Life Support Systems (CELSS) are crucial for long-duration spaceflight.
• Understanding gas exchange dynamics between humans and plants is vital for life support system design.
• Human metabolic activity, particularly during exercise, significantly impacts atmospheric composition.

Purpose of the Study:

• To quantify gas exchange between plants and humans in a CELSS.
• To determine buffer characteristics for carbon exchange in a closed-loop system.
• To assess plant-human metabolic balance under varying human physical activity levels.

Main Methods:

• Two human subjects exercised on a cycle ergometer at three work intensities (25%, 50%, 75% VO2max).
• Gas exchange (O2 consumption, CO2 production) was measured for both subjects and the CELSS plant module (potato).
• A 113 m3 CELSS chamber housing 20 m2 of potato plants was utilized.

Main Results:

• Human CO2 production and plant CO2 utilization balanced at approximately 50% of maximal aerobic capacity (VO2max).
• Average human O2 consumption rates were 0.88, 1.69, and 2.47 L/min.
• Average human CO2 production rates were 0.77, 1.47, and 2.21 L/min.
• The CELSS photosynthetic rate was 0.95 L/min.

Conclusions:

• A metabolic balance point between human CO2 output and plant uptake exists within CELSS.
• Plant selection and growth optimization are critical for matching human metabolic demands during spaceflight.
• Further research is needed to refine oxygen balance monitoring in CELSS.