Design considerations for a greenhouse on mars: Accounting for plant evapotranspiration

Increases in evapotranspiration of plants in low-pressure environments can lead to water stress. Plants will be an integral component of any long-term space mission, so it is important that design and management decisions consider effects on plant production. This paper discusses the ongoing development of an evapotranspiration model for low-pressure environments such as a greenhouse on Mars. The model is based on the Penman-Monteith model and accounts for the biological and physical interactions of plants and environment. A theoretical heat transfer model shows that boundary layer thickness increases significantly at low pressure, but external resistance becomes almost negligible. At low pressures, the leaf heat balance is dominated by evapotranspiration and radiation. In a preliminary study, the air-leaf temperature difference was 4-6°C for plants at 10 kPa and nearly 0°C at atmospheric pressure.