The Biology of Low Atmospheric Pressure – Implications for Exploration Mission Design and Advanced Life Support

Atmospheric pressure is a variable that has been often manipulated in the trade space surrounding the design and engineering of space exploration vehicles and extraterrestrial habitats. Low pressures were used to reduce structural engineering and launch mass throughout the early human space program; moreover, low pressures will certainly be considered in future concepts for the same reasons. Fundamental understanding of the biological impact of low pressure environments is therefore critical for the successful consideration of this variable, being particularly important when considering future, potentially complex bioregenerative life support systems. However, low pressure biological effects are also critical considerations that should be incorporated into near term vehicle designs, designs that may set hardware and operations criteria that would carry over into far-term future designs. In order to begin to define the fundamental biological responses to low atmospheric pressure, we have identified the molecular genetic responses central to the initial exposure of the model plant Arabidopsis to hypobaric stress. Less than half of the genes induced by hypobaria are induced by hypoxia, establishing that response to hypobaria is a unique biological response and is more complex than just an adaptation to low partial pressures of oxygen. In addition, the suites of genes induced by hypobaria confirm that water movement is a paramount issue in plants. Current experiments examine gene expression profiles in response to a wide variety of pressures, ranging from slight to extreme hypobaria. Results indicate that even small changes in atmospheric pressure have attendant biological consequences deserving consideration during the concept and design of vehicles and habitats. Moreover, the range of pressures to which plants can adapt suggests that very low pressures can be considered for plant-specific habitats. The choices of atmospheric pressure within spaceflight and extraterrestrial habitats are not merely engineering considerations but are biological considerations of the highest order, and modern molecular tools can be employed to increase understanding of the biological consequences of pressure engineering decisions.