Feasibility of a Mars surface inflatable greenhouse: Availability of photosynthetic irradiance and the durability of transparent polymer films

Assessing the feasibility of an inflatable Mars surface greenhouse has been hampered by the lack of key information, primarily the availability of photosynthetic radiation and the durability of transparent polymer films from which greenhouses might be constructed. A more complete estimate of the available photosynthetically active radiation (PAR) has been developed, which combines the output from multispectral radiative transfer code developed for Mars with global dust measurements from NASA's Mars exploration probes. In contrast to previous Mars PAR estimates, this new approach captures the variation in spectral contribution to PAR levels as a result of diurnal variations in zenith angle and/or seasonal variations in dust loading and provides a global view of PAR availability as opposed to earlier estimates based on single landing site data. Further, transparent polymer films were evaluated for their suitability for use in a Mars surface greenhouse, which included exposure of several candidate materials to simulated Mars UV conditions. The observed degradation highlighted the need for UV protection if the materials are to survive for long durations in the Mars environment. Transparent, UV-resistant materials were evaluated as a potential external protective laminate to filter UV from the underlying structure. A review of earlier space environmental tests on these candidate films revealed these tests did not include the effect of simultaneous mechanical loading on material degradation. The most promising candidate film was tested for the affect of UV on the time to creep rupture of the filter material. The results indicate that the selected UV-resistant material would have difficulty meeting the proposed lifetime requirements of a greenhouse as an integrated laminate under loading. Therefore, it is proposed to remove the material as a laminate of the structural membrane and utilize it as a removable covering that can be replaced at intervals throughout the lifetime of the greenhouse. Finally, the results of this research will allow better estimates of the equivalent system mass of an inflatable Mars surface greenhouse, which improve mission analyses and trade studies.