astrogro

THE CHALLENGE
This challenge was based on 3D printing food. We took a different approach to resolving the same issues of the original challenge. Our solution is utilizing the current 3D printing capabilities in space to build an intelligent system to organically grow fresh foods.

Space travel and space colonization are not feasible without a renewable food supply that can adapt to the unpredictable conditions and needs, inside a shuttle and out. To build a system that both optimizes food growth in space and scales the food supply in a renewable manner means we help bring humanity one step closer to long-distance space travel. Additionally, it has immediate civilian applications here on Earth.

THE SOLUTION
AstroGro: a 3D printed pod that is integrated with artificial intelligence (AI) to organically grow fresh food, which will enable sustainable life.
- With 3D printed pods, the farming ecosphere is modular and food growth can be scaled.
- Using AI, conditions for plant growth is optimized to adapt to changing conditions, and multiple pods are managed under one system, or “brain.”
- Renewable and reusable: air is filtered by plants (http://en.wikipedia.org/wiki/NASA_Clean_Air_Study), waste is recycled for soil using greywater and night soil), and filament is reused for new pods.

Anyone – an astronaut, spouse, or child untrained in horticulture – can grow fresh crops.

THE TECHNOLOGY
The system uses a network of sensors and actuators to optimize plant growth.

Plant Growth Monitor
In order to optimize plant growth, variables such as temperature, lighting, and hydration must be tuned while successfully and reliably measuring plant growth. However, current image processing algorithms require computational overhead, camera elements, and suffer from limited perspective and depth-of-field problems. We propose a radiofrequency (RF) absorption measurement comprised of a small pair of transmit-and-receive antenna operating at 2.45 GHz, the absorption frequency of water molecules. The directional transmit (TX) antenna is directed through the plant's foliage to the receive (RX) antenna. The water content of the plant's foliage is proportional to the growth and water retention of the plant. A higher absorption implies a larger and healthier plant. This metric is used for evaluation of plant growth. The antenna would be pulsed on the time constant of plant growth (approximately once per day) and thus would have a minimal heating impact on the plant. The TX antenna can also be pulsed more frequently for more efficient heating of the plant.

Temperature Control
A feedback system of heating and cooling elements are combined with temperature sensors to maintain suitable plant temperature. The heating element is comprised of a microwave antenna operating at 2.45 GHz (the same one used as a plant growth monitor) and is used to directly heat the plant's water molecules through dielectric heating. This ensures energy is not wasted on convection heating. The antenna is temporally pulsed to optimize power amplifier efficiency rather than operating in backoff.

Light Cycling
Two modes of operation exist for the light cycling. In the autonomous control mode, the system provides correct intensity and spectral composition of lighting. The timing of light and dark cycles are optimized to improve yield. LED lighting at various bandwidths and center frequencies are applied at various levels.

In the energy-scavenging mode, ambient and environmental lighting is supplemented with artificial lighting to increase energy efficiency. An array of light sensors with various spectral filters is used to determine spectral composition of ambient lighting. The missing compositions are adjusted with varying levels of LED lighting.

Hydration
A soil hydration system ensures optimal hydration cycles for the plant. Impedance sensors are placed in the soil to determine hydration levels. A pump is actuated to sustain suitable wet and dry cycles. Additional pH sensors and hydrolysis units can be added to maintain a suitable pH level.

Gravity Adjustment
AstroGro pods can be modified for additional adjustment of gravity. In a weightless environment, gravity can be emulated through centrifugal force. Pods are arranged in a hexagonal "wheel" with plant growth directed towards the center. Rows of wheels are arranged in a coaxial position and additional wheels are added to either end. Pairs of adjacent wheels undergo contra-rotation to reduce torquing. A weightless environment decreases frictional losses in rotation. Rotational velocity is adjusted to modify gravitational forces.

Growth Optimization
Plants on Earth behave differently from plants in a weightless or reduced weight environment such as the Mars surface. In addition to different gravity conditions, plants can have additional environmental constraints not present on Earth. For example, ethylene from spacecraft mold and plastic outgasing inhibits plant growth. This necessitates extensive controlled testing of various plant species in space environments.

The inputs of the system are light cycle timing, light spectrum levels, hydration, temperature, and in some cases, gravity. The outputs of the system are nutrition density and produce yield. An exhaustive search of the input space is unfeasible. Therefore, a coarse optimization using the inputs and plant RF absorption will first be used to optimize growth. Further fine optimizations to analyze produced nutrition will be required. Plant soil supplements can be used to enhance yield.

Waste Reclamation
Greywater and night soil can be used to hydrate and fertilize crops. In addition to reusing waste materials, the filtration requirements on water are reduced because plants naturally filter their water supply.

Air Filtration
In addition to providing supplemental oxygen to the crew, plants serve as air filtration for the crew. A recent study found that various species may reduce levels of toxic agents such as formaldehyde, benzene, trichloroethylene, xylene, toluene, and ammonia.
Reference: BC Wolverton, WL Douglas, K Bounds (July 1989). A study of interior landscape plants for indoor air pollution abatement (Report). NASA. NASA-TM-108061.

Filament Reclamation and Pod Construction
The advantage of a completely 3D printed chassis is the ability to print, reclaim, and reprint filament. Old pods can be broken down and heated into new filament. This filament can be stored, used for additional parts and tools, or reprinted into new pods.

Multi-pod Optimization
A variety of constraints are placed on the entire system. The system can adapt to external factors of the crew and living space. Predictive algorithms can adjust pod composition depending on changing conditions:
- Is there a higher caloric requirement because of unforeseen physical exertion? Additional pods can be printed or the composition of crops can be modified for calorie maximization.
- Is there a decrease in available growing space for pods? Does the crew require additional filament for printing other parts and tools? The filament from lower priority/yield pods can be salvaged through filament reclamation.
- Does a hardware update increase the effectiveness of existing pods? Instead of shipping entirely new pods, a software update will be transmitted to 3D printers, and new pods can be constructed.
- Are there changing nutritional needs in response to the changing health of the crew? Crop composition can be modified to incorporate produce that provides those nutritional needs.

OTHER BENEFITS
AstroGro alleviates the psychological stress attributed to long-term missions because the astronaut now has the ability to customize her meal from a variety of fresh vegetables.
- Fresh foods are already being brought to ISS for their psychological wellbeing, but can only be supplied for a few days at a time.
- Fresh foods can be available daily, even in transit, with AstroGro.
- AstroGro can empower the astronaut by restoring her dietary choice.

RESEARCH APPLICATIONS
We are just scratching the surface of zero-gravity plant biology, and AstroGro can be used as a research tool to discover optimal growing conditions and further explore the ideal “superfood” plants. AstroGro allows for carefully controlled experimentation on Earth and in space.

APPLICATIONS ON EARTH
Ever diminishing fresh water supplies on Earth means that we have to be more efficient with our farming techniques. Moreover, transportation of produce contributes to negative externalities such as pollution, fuel consumption, and lack of freshness. A terrestrial version of AstroGro is also proposed.

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