James Clawson

Microgravity Root Zone Hydration Systems

Accurate root zone moisture control in microgravity plant growth systems is problematic. With gravity, excess water drains along a vertical gradient, and water recovery is easily accomplished. In microgravity, the distribution of water is less predictable and can easily lead to flooding, as well as anoxia. Microgravity water delivery systems range from solidified agar, water-saturated foams, soils and hydroponics soil surrogates including matrix-free porous tube delivery systems. Surface tension and wetting along the root substrate provides the means for adequate and uniform water distribution. Reliable active soil moisture sensors for an automated microgravity water delivery system currently do not exist. Surrogate parameters such as water delivery pressure have been less successful.

Mass Transport in a Spaceflight Plant Growth Chamber

The Plant Generic BioProcessing Apparatus (PGBA), a plant growth facility developed for commercial space biotechnology research, has flown successfully on 3 spaceflight missions for 4, 10 and 16 days. The environmental control systems of this plant growth chamber (28 liter/0.075 m2) provide atmospheric, thermal, and humidity control, as well as lighting and nutrient supply. Typical performance profiles of water transpiration and dehumidification, carbon dioxide absorption (photosynthesis) and respiration rates in the PGBA unit (on orbit and ground) are presented. Data were collected on single and mixed crops. Design options and considerations for the different sub-systems are compared with those of similar hardware.

Design, Testing and Operation of Porous Media for Dehumidification and Nutrient Delivery in Microgravity Plant Growth Systems

Porous plate dehumidifiers (PPD) and porous tube nutrient delivery systems (PTNDS) are designed to provide a means for accurate environmental control, and also allow for two-phase flow separation in microgravity through surface tension. The technological challenges associated with these systems arise from the requirement to accurately measure and control the very small pressures that typically occur within and across the porous media. On-orbit automated priming or filling of the system in the absence of gravity may be necessary. Several porous plate dehumidifiers and porous tube nutrient delivery systems have been tested and evaluated, and experimental results for engineering design are presented.

Inflatable Transparent Structures for Mars Greenhouse Applications

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.

AG-Pod - The Integration of Existing Technologies for Efficient, Affordable Space Flight Agriculture

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 offthe-shelf inflatable technology. AG-Pod will support low Earth orbit as well as planetary missions, including transit and surface operations.

Microbial Detection Array (MDA), a Novel Instrument for Unambiguous Detection of Microbial Metabolic Activity in Astrobiology Applications

MDA is designed as a test bed for an astrobiology field instrument to detect microbial metabolic activity in terrestrial or extraterrestrial geological soil samples. MDA employs electrochemical sensors in a unique differential chamber configuration, able to detect minute changes in the chemical composition between the two otherwise identical chambers. Both chambers are filled with identical autoclave-sterilized, sample-water mixtures. Only one of the chambers receives an additional minute, non-sterilized inoculation sample. Under the minimal assumptions that the geological sample contained nutrients (energy), organisms, and required water to initiate growth, the differential electrochemical measurements would now allow detection of metabolic activity, in addition to the electrochemical characterization of the soil samples in both chambers.

Global Estimates of the Photosynthetically Active Radiation at the Mars Surface

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.

Atmosphere Composition Control of Spaceflight Plant Growth Growth Chambers

Spaceflight plant growth chambers require an atmosphere control system to maintain adequate levels of carbon dioxide and oxygen, as well as to limit trace gas components, for optimum or reproducible scientific performance. Recent atmosphere control anomalies of a spaceflight plant chamber, resulting in unstable CO2 control, have been analyzed. An activated carbon filter, designed to absorb trace gas contaminants, has proven detrimental to the atmosphere control system due to its large buffer capacity for CO2. The latest plant chamber redesign addresses the control anomalies and introduces a new approach to atmosphere control (low leakage rate chamber, regenerative control of CO2, O2, and ethylene).