Management of water and oxygen supply to plant root zones is critical to the development of healthy plants and will be necessary as more sophisticated plant growth systems are developed for use in reduced gravity. Because the microgravity substrate environment operates in a force balance between surface tension and capillary forces, it cannot readily be simulated on Earth (1g). Maintaining proper oxygen levels in microgravity requires flight systems to be able to monitor and manage for both optimum substrate water and oxygen concentrations inside the substrate itself. The MOCSS was developed to provide the necessary feedback to manage both moisture and oxygen in the root zone of space-based plant growth systems. The MOCSS sensors provide the information needed to minimize moisture and oxygen stress to plants and provide a tool for studying and understanding the mechanisms of water transfer and oxygen diffusion in microgravity root zone environments.

Figure 1a. Single TMAS Sensor Box
With 8 Soil Moisture Probes

Figure 1b. Full Array of 16 Sensor Boxes With 8 Soil Moisture Sensors Per Sensor Box (The sensor boxes are linked together serially.)

The integrated MOCSS system is composed of three elements that can stand alone or be used as an integrated system. These elements include the soil moisture sensor, the soil oxygen sensor, and a substrate gas and liquid distribution model.

The soil moisture system developed during the MOCSS project is shown in figures 1a and 1b. The system can be used in three modes – soil moisture and soil temperature monitoring mode, soil moisture measurement mode (more rapid cycling between readings), and a “front detection” mode that allows tracking of water movement into a dry matrix (figure 2).

Figure 2. MOCSS Soil Moisture Sensors in Root Module Planted With Dwarf Wheat Plants

The oxygen sensor was modified for use in space-based nutrient delivery systems, including integration of Teflon barriers for use in wet environments, miniaturization of the sensor (figure 3), use of flight-approved materials, development of temperature compensation circuits, and testing to select electrolytes not toxic to plants

Figure 3. Oxygen Sensor Size Reductions Under the MOCSS Program

The BlueBurst software program was developed to simulate transport of liquids (e.g., water), gas species (e.g., oxygen and carbon dioxide), and solutes in a 2-dimensional vegetated porous medium. Unlike any other program, BlueBurst was designed to handle multiple domains (atmospheric, vegetative, porous medium) and coupled processes under variable gravity force settings. The user-friendly graphical user interface (GUI) facilitates input and provides a variety of graphical and textual output options. In the near term, this model will allow optimization of space-based nutrient delivery systems and provide a tool for visualization of the root environment based on sensor inputs.

Key accomplishments:

Key milestones:

Contact: Dr. J.C. Sager (John.Sager-1@ksc.nasa.gov), YA-E4, (321) 476-4270
Participating Organizations: Orbital Technologies Corporation (Dr. R.C. Morrow) and Space Dynamics Laboratory (Dr. G.E. Bingham)