The Modular Dynamics Growth Testbed is a platform that leverages the dynamics of second order systems in microgravity, to grow plants efficiently and assess their growth in space.

About the author: Mohit Singhala, PhD Student, Johns Hopkins University

Step 1: Step 1: Establishing Design Criteria

Based on the prompt and constraints, design criteria were established and different objectives were given different priorities with the top two being the following:

1) Using the knowledge that plants grow towards the light

2) Effective Utilization of Space

Additional objective (nice to have): Based on prior experience from a Youtube SpaceLab entry, another objective was added of reducing the overall volume required to transport the testbed- such that the entire assembly could be packed in a smaller space while remaining easy to assemble once delivered.

Assumptions:

Key assumptions were made regarding some key aspects of the project:

1) The choice of soil, seed, irrigation method etc. were not included in this design. However, the design allows for the use of existing hardware to be integrated including space for seeds (in whatever form they are stored), soil, lines for irrigation etc.

2) Based on the prompt, the exact effect of different conditions and the magnitude of their impact on plant growth does not seem well-established. Therefore, the solution was designed as a testbed to allow for quantitative research and iterative design, while simultaneously meeting the core objectives of the challenge.

Step 2: Step 2: Working Principle

Controlling direction of light and Space efficiency

1) The key hypothesis behind this design is that using a dynamic source of light can enable a more uniform illumination of different areas of the growth tube, thus enabling the plant to grow more uniformly and thus, be efficient in how it occupies the available space.

To do this, a suspended mass (the Light source is designed to be the mass here)- spring system is proposed. Given that there is no appreciable source of damping in the environment where this platform will be placed, it is fair to assume that once disturbed, a mass-spring system will continue to oscillate for a long period of time, thus meeting the design objectives without the need for frequent human intervention or any electronic components and the associated control systems. The mass (light) is expected to stay near equilibrium due to the microgravity environment in its initial state.

The correct stiffness for the springs and the time period and how they affect plant growth will require some quantitative research and/or modeling and hence the system is designed as a testbed, with interchangeable components.

2) Another key element that enables uniform growth is the rotation. By allowing rotation of each tube, more uniform illumination of the plant can be ensured over its life.

Additional note: The 9 plant growth tubes can slide into each other in sets of three- allowing two 50cm cube systems to be packed in the space of one.
The suspended light and spring arrangement can also be extended to the corner, thereby allowing multiple systems of this kind to be placed next to each other- further increasing the efficiency of the system in terms of number of plants that are illuminated by a single light source.

Step 3: 3) Core Design Elements

1) Growth Tubes

The transparent/translucent tubes are the primary housing for plant matter in this design. It is assumed that any standard platforms for plant growth like trays that hold the seeds, nutrient content etc. can be either directly installed inside these tubes or can be easily modified to fit them.

In the current iteration there are 9 tubes of three different diameters (160 mm, 155 mm, 150 mm [inner diameters]), with 4 mm wall thickness and 400 mm height. The tubes are designed to slide into each other- thereby allowing 9 tubes to be packed in bundles of 3. This has been done intentionally to reduce the space occupied by the system when disassembled/sent as payload. However, the tubes are arranged in an equidistant manner along their z-axes to ensure modularity and ease of assembly.

2) Top Plate- (with SpurGears, Irrigation holes and Plunger holes)

The top plate (500mmx500mm) is the primary user interface for the device. It has spur gears with extensions that snap fit into the tubes and can then be locked. Out of the 9 gears, the gear in the center of the matrix has a handle that can be rotated to rotate all the gears and thus, rotate the tubes that they are fitted in.
In the current iteration this is manual, however it's 45mm high and has sufficient room for its operation to be motorized if needed.

3) Linear Springs and Suspended Light Mass
This is the core illumination system where the light source is expected to be similar to the existing sources- with intensity adjusted for size. Please note that the four springs and lights/mass are not inside the tubes, rather outside in the negative space between the tubes. They are hinged to the top and the base plates and can be independently changed/removed and rearranged.

4) Base plate
Base plate controls a seal to prevent any matter from leaking out while also acting as a rail for the growth tubes to rotate on.

5) Plunger
The plunger was added to allow for manual excitation of the suspended lights through the linear springs. Same plunger can be used for multiple testbeds of the same kind.

6) Irrigation Holes

Irrigation holes in the top plate allow for integration of exisitn girrigation systems to the testbed. However, by closing the entire testbed along its periphery, the water line can also be attached to the suspended light through the plunger through holes and the springs in order to have the irrigation system oscillate as well. However, some additional damping is to be expected as the irrigation tubes might bend. If hard tubes are used, the 50 cm cube criteria will not be met unless the core space is reduced which will not be efficient.