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Thin films continue to play an ever-increasing role in high performance structures for space exploration. Membrane structures have been developed or envisioned for such applications as scientific balloons, deep space antennas, Earth radiometers, radars, concentrators, telescopes, sun shields, solar sails, solar arrays, spacecraft booms, and planetary surface habitats. Inflatable membrane structures can have very high packaging efficiencies, are easy to construct at remote locations and are lightweight because pressure differences provide structural stabilization without the need for rigid supports or internal framework. Recent proposals have suggested construction of an inflatable greenhouse from transparent polymer films for Mars surface operations. This paper reports on the progress to examine the effects of mechanical loading on the rates of photodegradation in transparent polymer films exposed to simulated Mars ultraviolet radiation.

This paper reports on the approach and progress to refine the estimates of the Mars surface photosynthetically active radiation (PAR) on a global scale that is averaged over a longer time period. While the PAR on Mars has been evaluated previously, the results have been limited in scope either temporally or spatially, such as only at a particular landing site or only over the time span of a few months. Understanding the availability of PAR is important in evaluating the practicality of using greenhouses and/or solar irradiance collectors for growing crops during manned missions to the Martian surface. Until surface investigations can be performed, computational modeling of the surface PAR can help to refine site selection and evaluation of engineering approaches and indicate the most favorable location at which to operate a greenhouse. The proposed approach is to combine multispectral irradiance models with global atmospheric opacity models developed from multiyear observations.

It is proposed to employ a greenhouse for life support on the Martian surface to reduce the equivalent system mass (ESM) penalties encountered with electrical crop lighting. The ESM of a naturally lit plant growth system compares favorably to an electrically lit system when corrections for area are made based on available light levels. A transparent structure should be more efficient at collecting insolation than collectors due to the diffusivity of the Mars atmosphere and inherent transmission losses encountered with fiber optics. The need to provide a pressurized environment for the plants indicates the use of an inflatable structure. Materials and design concepts are reviewed for their applicability to an inflatable greenhouse.

Technology for microgravity plant growth has matured to a level which allows detailed gravitational plant biology and commercial plant biotechnology studies. Consequently, plants have been shown to adapt to the space flight environment, which validates their use in advanced life support applications. However, the volume available for plant growth inside pressurized modules is severely constrained, both in present and future spacecraft. Furthermore, the required power and heat rejection associated with the artificial lighting on existing systems, and the resulting weight and volume increases, affect the viability of these systems for life support. The Autonomous Garden Pod (AG-Pod), an inflatable module specifically for plants, resides outside the habitable modules and uses passive solar illumination. It’s based on existing technologies including flight-proven plant growth subsystems, commercial satellite thermal systems, and off-the-shelf inflatable technology.

PGBA, a plant growth facility developed for commercial space biotechnology research, successfully grew a total of 50 plants (6 species) during 10 days aboard the Space Shuttle Endeavor (STS-77), and has reflown aboard the Space Shuttle Columbia (STS-83 for 4 days and STS-94 for 16 days) with 55 plants and 10 species. The PGBA life support system provides atmospheric, thermal, and humidity control as well as lighting and nutrient supply in a 33 liter microgravity plant growth chamber. The atmosphere treatment system removes ethylene and other hydrocarbons, actively controls CO2 replenishment, and provides passive O2 control. Temperature and humidity are actively controlled.