49th International Conference on Environmental Systems ICES-2019-195 7-11 July 2019, Boston, Massachusetts

Astro GardenTM Aeroponic Plant Growth System Design Evolution

Sam A. Moffatti, Robert C. Morrowii, and John P. Wetzeliii Sierra Nevada Corporation, Madison, WI, 53717, USA

By providing dietary nutrients and unburdening physiochemical life support equipment, Hybrid Life Support Systems (HLSS) can be an attractive option for longer duration space exploration such as Mars transit missions. State of the art microgravity plant nutrient delivery utilizes a physical media in which the plant roots grow (e.g., clay-based arcillite). This added media increases the mass to orbit necessary for growing plants in space – limiting the appeal of large-scale plant growth systems in terms of Equivalent System Mass (ESM) when considering long duration mission architectures. Plants grown hydroponically or aeroponically represent a logistically favorable alternative for space-based plant growth systems, as nutrients are delivered without the added mass of a soil-like media. However, by removing the media material, controlling water delivery and recovery in a microgravity environment presents a challenge. Astro Garden is developed to provide a large- scale, space-based aeroponic plant growth system, leveraging modifications to current designs meant to operate within a gravitational environment. This paper details the design evolution of Astro Garden from the Phase 1 prototype through the upcoming ISS technology demonstration and future flight systems.

Nomenclature CEA = Controlled Environment Agriculture CFM = Cubic Feet per Minute DAQ = Data Acquisition System ECLS = Environmental Control and Life Support ESM = Equivalent System Mass HLSS = Hybrid Life Support Systems ISS = International Space Station LED = Light Emitting Diode LEO = Low-Earth Orbit NFT = Nutrient Film Technique NI = National Instruments PCB = Printed Circuit Board PPM = Parts Per Million SNC = Sierra Nevada Corporation TRL = Technology Readiness Level WCD = Water Capture Device WPM = Water Processing Module Zero-G = Zero Gravity Corporation

I. Introduction lants have been grown in space for over 40 years1. Research payloads such as Astroculture, Advanced P Astroculture, Biomass Production System, Veggie and Advanced Plant Habitat have provided valuable tools for plant physiology research in a microgravity environment. These systems have almost exclusively relied on nutrient delivery through a soil-analog medium such as arcillite. Scaling these research systems towards food production systems becomes problematic due to increased mass requirements2. To achieve plant growth on the scale necessary for significant astronaut dietary supplementation, as well as Environmental Control and Life Support (ECLS) system

i Mechanical Engineer, Sierra Nevada Corporation, and 1212 Fourier Dr. Madison, WI, 53717, USA ii Principal Scientist, Sierra Nevada Corporation, and 1212 Fourier Dr. Madison, WI, 53717, USA iii Program Manager, Sierra Nevada Corporation, and 1212 Fourier Dr. Madison, WI, 53717, USA

© 2019 Sierra Nevada Corporation hybridization, alternate methods for nutrient delivery and recovery are highly desirable. Systems that eliminate the need for a rooting media interface present opportunities for significant mass reduction of large-scale plant production systems. The Astro Garden system is being designed in a phased approach. The Phase 2 Astro Garden prototype builds upon the Phase 1 design and parabolic flight testing data to create a large-scale plant growth system capable of the level of production necessary to meet the NASA salad-diet architecture3. This level of plant production also has the added benefit of increased ECLS system hybridization (supplementing physiochemical processes with biological processes). The Astro Garden prototype relies on conditioned inlet gas (controlled humidity & temperature as well as enriched CO2 levels) to provide optimal conditions for peak plant growth. In terms of ECLS hybridization, the system provides a means for additional oxygen production to supplement the traditional physiochemical systems and can provide a near potable water source through the recovery of transpired water. The modular, scalable nature of the Astro Garden design allows for plant growth in a variety of environments and potential mission scenarios, enabling future low-Earth orbit (LEO), cislunar, lunar surface, Mars transit or martian surface plant food production.

II. Aeroponics in Space Aeroponics is a plant nutrient delivery mechanism that is characterized by spraying a nutrient solution directly on to plant roots, typically through use of pressurized nozzles. Aeroponics is a form of hydroponics where the roots are exposed directly to air (thus the aero-prefix) with the nutrient solution applied as a spray or mist. In more traditional hydroponic plant growth systems, the roots remain submerged in nutrient solution. Aeroponics has been used to grow and research plants on the ground dating back to the 1920s2. Commercialization and subsequent large-scale plant production through aeroponics took hold in the mid-1980s, beginning with systems such as GTI’s Genesis Machine4. Aeroponic plant growth offers a number of advantages over soil-based plant growth. From a research standpoint, aeroponics provides easy access to the plant roots, negating the need to remove soil for examination. Because of this access, roots are less likely to be damaged during the inspection process, allowing for quick, relatively undisturbed data collection throughout the growth cycle5. Aeroponics can also inherently isolate one plant from another, preventing the spread of disease through the soil medium. If disease does occur, the plant in question can be easily removed from the growth volume preventing further spread in the system. Aeroponically grown plants can also be grown faster. Because the roots are exposed directly to the nutrient solution, their absorption rate is typically higher than through a soil medium. When done in a recirculating mode, aeroponics is very efficient at regulating water delivery to the plants, decreasing the overall water needs for growth. Planting density can be increased through vertically stacked aeroponic nutrient delivery, requiring less overall volume. Because of the volume, water and nutrient absorption efficiencies, aeroponics is a highly desirable platform for urban plant growth, where space and water consumption are at a premium. Coupled with the reduction in mass through removing the soil medium, aeroponics presents an ideal solution for space- based agriculture. In addition to the benefits of using aeroponics on Earth, a number of space-focused attributes exist as well. Aeroponics can function the same in 1-g as it does in microgravity for nutrient delivery; because of the relative droplet size (~50 microns) and the velocity at which the droplet is discharged, the inherent momentum of the particle overcomes the effect of gravity acting on the particle mass. This has been demonstrated through numerous parabolic flight tests for various nozzle geometries and inlet pressures as noted in Section V. The nutrients are also typically delivered via a preset timed spray cycle. By determining the duration and frequency that a nozzle is effectively “on” and “off” a highly controllable quantity of nutrients can be delivered to plants roots without the use of additional sensors (such as pressure sensors used to control the level of negative pressure in porous media based systems). Nozzles can be easily replaced with the use of quick-disconnects, allowing fast on-orbit replacement when necessary. There are two primary concerns for using aeroponics in the absence of gravity: how to recover spray that does not impinge upon the roots, and how to prevent nutrient depleted water from adhering to the roots for extended periods. Removing depleted water from the roots is important to prevent blocking fresh nutrients from absorption sites and preventing oxygen uptake, resulting in a hypoxic condition. Without gravity acting upon the droplets, the solution will float as globules until coming into contact with a surface in the root zone. Depending on the wetting characteristics for that surface, and the capillary angle that the surfaces make with one another, the solution will adhere more or less strongly to that feature. Highly wetting materials and sharp angles will create regions that tend to collect more of the solution. Sealing becomes especially important as small, tight features can drive the solution to other regions over time through capillary action. Many of the challenges identified with microgravity aeroponics can be addressed through parabolic flight testing with Zero-G Corporation, but other challenges will need to be addressed through extended duration testing on the ISS.

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III. Phase 1 Astro Garden Design and Testing The Phase 1 Astro Garden program included design of a modular, open loop plant growth system prototype intended to demonstrate future flight system packaging. The module design relied on readily available parts and materials in an effort to reduce complexity, cost, and development-time. The system received inlet air from a controlled environment room via internal fans and rejected plant chamber air back to the room. Nutrients were delivered aeroponically to the roots through an internal pump and accumulator system used to control nozzle delivery pressure. Gravity was the primary means to drain the depleted nutrients from the roots to the root zones, and from the root zones back into a reservoir. Five modules were built into a rack fixture (Figure 1) to demonstrate the scalable nature of the system within a spacecraft structure.

Figure 1. Phase 1 Astro Garden Modules installed in rack structure to simulate spacecraft curvature.

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This system was used to grow a number of different plant species to highlight the system capabilities towards meeting the desired salad crop diet. These plants included potatoes (cv Norland), lettuce (cv Caesar), tomatoes (cv Red Robin) and Pak Choi (cv Green Fortune). The large growth area in the root and shoot zones allows multiple types of plants (vegetative and root) to be grown as shown in Figure 2. The Phase 1 system allowed a basis for beginning the Phase 2 design, as well as providing a means for producing aeroponically grown plant roots for use in parabolic flight tests.

Figure 2. Lettuce (left) and Potatoes (right) Grown in Astro Garden Phase 1 System.

IV. Phase 2 Astro Garden Design The Phase 2 Astro Garden leverages many design elements from the Phase 1 system such as aeroponic nutrient delivery, the general structure and envelope, LED lighting concepts and flexible bellows enclosed growth volumes. Each of these systems will be upgraded where necessary to increase the level of functionality required for a more “flight-like” design. General ease-of-use lessons-learned from the previous design were taken into account to help improve user friendliness for continuing plant growth research using the Astro Garden platform. Where the Phase 1 Astro Garden system operated with open loop functionality, the goal for the Phase 2 system is to close the loop and begin to recover or minimize the loss of valuable resources such as CO2, water, and plant nutrients. To accomplish this, an auxiliary module based on the same footprint as a deployed Astro Garden Module has been designed for incorporation into the larger system. For simplicity, many of the components in the Phase 2 system will operate with gravity driven processes (e.g., use of pressure sensors to determine reservoir levels, and open reservoirs instead of closed microgravity compatible bellows reservoirs). The aeroponics systems are also designed for use in gravity, as water is recovered through dripping from the roots and collected at the bottom of a reservoir. Though the prototype system is meant for use terrestrially, the end use for a representative flight system is planned for a microgravity environment. Because of this, the challenges for using aeroponics without the benefit of gravity must be weighed with the flight system goals. The Design for the Phase 2 Astro Garden Module is shown in Figure 3.

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Figure 3. Phase 2 Astro Garden Module design.

A. Module Structure The Astro Garden system consists of eight Astro Garden Modules, one Nursery Module, and one Water Processing Module (WPM). Each individual module is designed to fit within the Lunar Gateway ECLS pallet envelope (~63.5cm x 61 cm x 188 cm). The Astro Garden Module is designed for stowability such that two modules can fit within the pallet envelope for a launch configuration as shown in Figure 4. Once on-orbit installation is ready, the light cap assembly is easily deployed by lifting the armatures to raise, and lock it into place, as shown in Figure 5.

Figure 4. Astro Garden stowage configuration vs. pallet envelope (blue outline).

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Figure 5. Stowed and deployed Astro Garden configurations.

B. Shoot Zone The Phase 2 Astro Garden shoot zone is dimensionally similar to the Phase 1 system. Each module contains eight shoot zones with roughly 929 cm2 of growing area and 28 cm of shoot height potential per zone. Like the Veggie plant chamber on the ISS, the shoot zones in Astro Garden are designed for stowability and are comprised of folded Mylar bellows. Conditioned air is provided by blowers in the Astro Garden chassis and ducted to the inlet of each shoot zone. As the air mixes within the shoot zone, it captures humidity from plant transpiration and is rejected at the top of the zone into a central outlet manifold. The shoot zone is sealed and held in place with slide catches and magnet/steel plug pairs. It is easily removed for cleaning, and if necessary, can be replaced with a new enclosure. A single shoot zone is shown in Figure 6.

Bellows Enclosure

Bellows Interface

Figure 6. Astro Garden shoot zone bellows assembly.

C. Root/Shoot Interface The root/shoot interface provides a physical barrier between the shoot zone and the root zone. It prevents shoot zone LED light from penetrating into the root zone. It also prevents sprayed nutrient solution in the root zone from penetrating into leafy region of the plants. The root/shoot interface provides a gasket to enclose the plant seed cartridges and is removable for replanting and subsequent reinstallation. Figure 7 shows an image of the root/shoot interface. The interface provides planting capability ranging between one and 16 plants depending on plant species. This represents a significant improvement over the single plant per zone capability of a Phase 1 growth chamber. The planting density is based on square foot gardening technique6 for the plants comprising the salad crop diet defined in the Baseline Values and Assumptions Document3.

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Gasket Material Seed Cartridge

Figure 7. Astro Garden Phase 2 root/shoot interface with seed cartridge design.

D. Root Zone Like many of the subsystems in Astro Garden, the Root zone is designed to be modular to allow for ease of replacement and cleaning. It also allows for evaluation of alternate designs and nutrient control techniques. The baseline design of the root zone utilizes aeroponic spray for nutrient delivery to the roots, and gravitational draining to collect the used nutrient solution prior to recovery to the WPM. Pressure is delivered to the nozzle manifold by activating a normally closed solenoid valve in the Astro Garden chassis. When the root zone fill level reaches capacity, a pump internal to the Astro Garden module activates to transport the used solution for recovery and recycle back into the nutrient mixing tank. The baseline root zone design is shown in Figure 8. This baseline can be removed and replaced with alternate designs for evaluating flight-like configurations that operate independent of gravity.

Root Spray Reservoir Nozzles

Drain Location

Figure 8. Astro Garden Phase 2 baseline root zone design cross-section with nozzles visible.

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E. Lighting To improve lighting performance, the multiple, single channel LED boards from Phase 1 have been replaced with a single, multi-channel design with predicted capability of up to 800 µmolm-2s-1 per shoot zone of photosynthetically active radiation. This overall intensity is distributed between red, white and blue LEDs. The individual light intensities are controllable to provide varied light spectra to specific plant species for research or productivity purposes. Four boards are linked together to cover an entire shoot row within an Astro Garden module. With two rows per module, there are eight total boards and two light bar assemblies. Cooling is provided by forced air convection through the light bar assembly as shown in Figure 9.

Cooling Fan

Light Boards

Figure 9. Astro Garden Phase 2 light bar design with cooling path noted.

F. Avionics and System Control The Phase 2 Astro Garden module replaces the previous NI DAQ control architecture with a dedicated Rabbit microprocessor and a custom control and power distribution interface PCB. Each module is assigned a unique IP address to create a modular and scalable system. Modules can be added, removed or replaced with no consequence to the control functionality. The Rabbit microprocessor architecture is based extensively on previous SNC program experience and has undergone prior space flight qualification testing. Application specific software has been written for the embedded program as well as the graphical user interface. A centralized panel PC provides a means for users to control and interface with Astro Garden. Various system set points can be monitored and modified to ensure optimum plant growth conditions. Remote monitoring and control capability reduces the need for an onsite operator. This architecture represents a step toward a flight-ready system for control and data collection.

G. Water Processing Module To help provide closure for resources used within the Astro Garden system, water and nutrients are mixed and recovered by the Water Processing Module (WPM). Nutrient depleted water from the root zone is pumped back into the nutrient mixing tank contained within the WPM. Humid air from the plant transpiration process is blown into the WPM from each Astro Garden module and the water content recovered from the stream using a regenerable desiccant system and a SNC-designed Water Capture Device (WCD). Both the desiccant and the WCD are operable regardless of gravitational environment. With the flow rates in the range of 8500 LPM (300 CFM), and relatively high water content (50L/day), this integrated water recovery system provides a minimal volume, minimal power, flight-like system for future spacecraft implementation.

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The WPM also provides a means for nutrient composition control and distribution to the individual Astro Garden modules. A preset nutrient mixing schedule is delivered via peristaltic pumps to the nutrient mixing tank when the conductivity of the mixture changes as depleted solution returns to the tank. The system is scarred with allocated space to provide additional functionality for pH monitoring as a potential system upgrade. Nutrient solution is drawn from the mixing tank and into the delivery manifold through the manifold pressurization pump. An accumulator provides pressure stability to assist with nutrient flow delivery. The pump pressurizes the delivery manifold and maintains the necessary volumetric flow as nozzles activate and deactivate within their set delivery schedule. Double-shutoff fluid quick-disconnects allow Astro Garden modules to be disconnected from the pressurization system with no impact to the remaining modules, allowing for ease of servicing to an individual module.

H. Integrated Prototype Astro Garden System As previously noted, the Astro Garden system is comprised of eight Astro Garden modules, one nursery, and one WPM. The Astro Garden and nursery modules share the same structure, but the planting density within the nursery is increased to accommodate a microgreen production area space and efficient seed germination for producing transplants. For proper operation of the overall system, additional “ground-support” equipment is necessary. This equipment includes the piping and ducting required for interconnection, as well as the structure to physically mount the modules. For the ground prototype, chillers are used in place of a vehicle cooling loop, and inlet air is provided by an air conditioning unit within the duct system. Conditioned air consists of enriched CO2 levels (~450-5000ppm), controlled relative humidity (55-85%) and temperature (18-30C). Because of the size and complexity of the overall system, some dedicated vehicle infrastructure would likely be required for integration into future designs, taking the place of the ground-support equipment used for the prototype system. See Figure 10 for a proposed Astro Garden Phase 2 prototype system layout.

Astro Water Garden Processing Modules Module

Air Ducting

Nutrient Air Mixing Condition Tank Module

Figure 10. Proposed integrated Astro Garden system layout with support equipment.

V. Parabolic Flight Testing for Microgravity Aeroponics/Hydroponics Parabolic flight testing is being conducted to help demonstrate processes and component designs for use in microgravity, working to increase the Technology Readiness Level (TRL) of space-based aeroponics and hydroponics. For Astro Garden, three separate campaigns were planned to iteratively design and implement potential zero-g compatible aeroponic/hydroponic solutions. Each campaign consists of two flights with 25 microgravity parabolas each for a total of 150 microgravity parabolas. These flights take place aboard Zero G’s modified 727 G-Force One aircraft. A typical parabola provides ~10-15 seconds of ~1x10-2 microgravity. The end goal for the parabolic flight testing and incremental flight-to-flight component improvement is to aid in development of a design for implementation and evaluation on an ISS technology demonstration mission. Further testing and data analysis is still in progress, but a preliminary evaluation of parabolic flight testing conducted to date is discussed in the following sections. The various tests and key technologies are described below in Table V-1. 9 International Conference on Environmental Systems

Table V-1 Parabolic Flight Tested Technologies Technology Tested Application Parabolic Flight Set Aeroponic Spray Nozzles Nutrient Delivery 1, 2, 3* Aeroponic Foggers Nutrient Delivery 3* Nutrient Delivery/Recovery, Seed Porous Plates (NFT) 2, 3* Germination Nutrient Delivery/Recovery, Seed Porous Tubes (NFT) 1 Germination Forced Air Water Recovery Nutrient Recovery 1 Nutrient Delivery, Seed Wick Materials 2, 3* Germination Capillary Shapes (NFT) Nutrient Delivery/Recovery 2, 3* Membrane Gas Separators Gas/liquid Separation 3* *Testing planned for August 2019

A. Parabolic Flight Set 1 For the first set of parabolic flights conducted in March 2018, a modular flight experiment structure was designed to accommodate multiple experimental procedures. This structure consists of five experiment chambers plumbed into a centralized fluid management box according to the specific experiment needs. GoPro camera video data collection was used for experiment analysis post-flight. Control for the overall system was provided by a laptop computer with preloaded flight experiment profiles. This allowed for multiple experiments to run simultaneously with less flight crew interaction within a given parabola. The full system, as installed aboard the Zero-G aircraft for the first flight, is shown in Figure 11.

Aeroponic Testing

Air Flow Chamber Aeroponic Testing

NFT Chamber Porous Tube Hydroponics

Figure 11. Parabolic flight test modules and structure.

Two of the test chambers on the first flight were used to demonstrate the physics of aeroponic spray delivery in microgravity (freefall). A variety of nozzles and spray pressures were selected for evaluation during the flight. These nozzles were installed into the chambers contained within the larger flight test frame structure. The tests were meant to demonstrate differences (if any) between nozzle spray and subsequent fluid/surface interaction in a microgravity and a 1-g environment. Though nozzle size and pressure determine droplet size and flow rate, of the nozzles and

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pressures tested, there was no discernable difference in gravitational effect on spray application (all nozzles and pressure set points behaved the same in a microgravitational environment as they did in a 1-g environment). The microgravity behavior of aeroponic spray impinging on a root structure is shown in Figure 12. Note that the roots used for this testing were grown hydroponically, and are not completely representative for an aeroponically grown root structure. Observations from this testing indicate that the gravitational condition has little impact on the delivery mechanism; the spray velocity dominates the gravitational force exerted on the fluid mass, making the spray behave similarly regardless of gravitational condition. These test results demonstrate aeroponics as a viable nutrient delivery mechanism for a spacecraft environment.

Figure 12. Aeroponic spray in a microgravity environment.

Another objective for the first parabolic flight test was determining the effectiveness of forced air nutrient recovery from a representative root zone. In this test, fans mounted to the side of the test module forced air movement within the chamber. Similarly, fans mounted to the front of the box were intended to clear impinged water on the viewing surface. It was desired to show that air movement could be used as the primary method for removing unused nutrient solution for the root zone surfaces, free droplets within the root zone and depleted nutrient solution from the root mass. To remove free droplets, a fan pulled air cross-wise across the chamber, perpendicular to the root growth. Various fan speeds were tested with a maximum of 50 CFM. This testing demonstrated that forced air was a viable method for removing free droplets from the airstream at reasonable flow velocities (velocities that would not damage the root structure), but was not effective at removing nutrient solution adhered to the wall surfaces or the root structure. Design modifications would be necessary to prevent or remove solution on the surfaces within the root zone. Another test chamber within the parabolic flight structure was used to test wicking along the root structure from a hydroponic delivery mechanism. This test was meant to demonstrate that the nutrient solution fluid would move along the root structure through capillary wicking in the absence of gravity. This testing showed that wicking would occur along the root bundles, but it was not as aggressive as initially predicted. Because of the time limitations of freefall periods during the parabolic flight (~15 sec), it was difficult to observe the complete wicking nature of the solution. Given enough time it is likely that the solution would continue wicking within the inter-connecting voids created by the root strands of the bundle. Porous tubes were tested as a means to provide more control for nutrient delivery and recovery. This delivery and recovery mechanism could help prevent free nutrient solution from floating within the root zone and provide the capability for removal from the roots, whereas aeroponics can only provide delivery. Controlled nutrient solution movement was successfully demonstrated through this parabolic flight testing. Water from the tubes would begin to wet the roots and start moving into the adjacent root structure. The solution was then successfully withdrawn into the tubes and removed from the roots. Because porous media may have potential clogging issues with extended use, life testing with the porous tubes would be required to demonstrate a long-term spaceflight solution.

B. Parabolic Flight Set 2 A second set of parabolic flights conducted in November 2018 were used to further advance the microgravity nutrient delivery and recovery system design. This testing utilized the previous parabolic flight test platform, but exchanged various chambers within the structure for additional experiments. The fluid management components

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within the system were updated to align with new test objectives. This second set of flights focused on several research topics, including: continuing microgravity testing for aeroponic delivery methods, testing microgravity nutrient delivery in the germination phase, and testing various other nutrient delivery and recovery techniques. See Figure 13 for an in-flight image of the experiment structure and flight crew.

Credit: ZeroG Corporation

Figure 13. Parabolic flight testing November 2018.

The aeroponic nozzle testing from the first set of parabolic flights was continued into the second set of flights. This testing utilized roots grown aeroponically rather than hydroponically. These root structures tend to be more distributed rather than the clumped structure of the hydroponic roots. Additional visual data through the use of GoPro cameras were collected to increase the understanding for how microgravity affects the aeroponic delivery mechanism. The data from the second flight set closely matched that of the first, with the primary takeaway that microgravity does not significantly affect the aeroponic delivery of nutrients to the root bundle. The more distributed nature of the aeroponic roots tended to collect less bulk water than that of the hydroponic roots, but capillary wicking is still visible within nodes between root strands. Nutrient delivery to seed cartridges was also tested. Primary objectives for this testing were to ensure that the nutrient solution could be delivered in a controlled and metered process and that the seeds did not become flooded. Nutrient delivery to the seeds was accomplished through capillary delivery along a wick structure and through porous plates with a felt backing. It was demonstrated over the course of four parabolas that seed water contact could be accurately controlled with backpressure on the porous material. This was accomplished by metering water injection with a manually controlled syringe and visually observing water and seed interaction. Intentionally overfilling the tray resulted in loss of fluid stability and would need to be avoided in a flight system. Additional hydroponic techniques using Nutrient Film Technique (NFT) were tested for effectiveness at fluid control. These techniques included delivery and recovery through porous walled materials, and engineered capillary shapes to control fluid location among others. Evaluation for these technologies is scheduled to continue with the third set of parabolic flights.

VI. ISS Technology Demonstration for Astro Garden To evaluate solutions for the technical challenges posed by aeroponics application in space-based plant growth systems, an ISS technology demonstration is planned to validate the media-less nutrient delivery and recovery systems. This technology demonstration will build upon the design and process experience from the Phase 1 Astro Garden, the Phase 2 Astro Garden and the parabolic flight test campaigns for use in evaluating extended duration aeroponics/hydroponics in a microgravity environment. This extended microgravity testing aboard ISS will provide valuable data that cannot be gathered through drop-tower or parabolic flight testing. Many capillary driven fluid 12 International Conference on Environmental Systems

movements, as well as plant growth and development, operate on timescales far exceeding the short durations available on parabolic or sub-orbital flight tests. The extended microgravity time aboard ISS will allow detailed assessment of the nutrient delivery and recovery techniques throughout the plant root growth life cycle.

VII. Conclusion The multi-phased approach to Astro Garden’s design targets incremental development of the core technologies to produce a space-flight pedigree system. The Phase 2 design provides a framework for what that system will resemble, and the parabolic flights and ISS technology demonstrations will help definitize the Astro Garden core technologies. Astro Garden provides the transition from small plant growth research payloads into larger food production installations. By leveraging the mass reduction benefits provided by aeroponics at the scale necessary for dietary food production, and coupled with the partial ECLS system closure, Astro Garden represents a logistically favorable architecture for long duration space missions. The design versatility allows space habitat designers the option to incorporate Astro Garden into their future vehicle architectures. By decreasing the need for resupply, Astro Garden extends the current boundaries for long-duration, manned space missions, working towards the goal for eventual life support system closure. Ultimately, the Astro Garden platform is intended as a versatile, large-scale plant production system for a variety of gravitational and microgravitational environments. The modular, scalable nature of the system allows for stowage and deployment to transition between mission phases, i.e. growing plants in transit to Mars, then transitioning all or part of the system for use on the Martian surface. Targets for system incorporation include: the Lunar Gateway, lunar base infrastructure, and Martian transit and surface excursion missions.

Acknowledgments This work is supported by NASA Advanced Exploration Systems, Human Exploration and Operations Mission Directorate, with special thanks to Dr. Jitendra Joshi, Dr. Daniel Barta, and Dr. Raymond Wheeler for their continued collaboration throughout the Astro Garden system design process.

References

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