Design Journey

Define the box we had to build inside

NASA HUNCH gave us the brief: a modular 2U nanolab (20×10×10 cm) with no more than 50 mL of water. The problem was bigger than "grow a plant in space": study how fluids and plant substrates behave in microgravity, to help feed long-distance spaceflight. Water had to move freely — ideally passively, though pumps were allowed — and every sensor, camera, light, and electronic part had to sit inside the sealed system, away from condensation. We added a web interface on top so astronauts could run it easily.

Read everything that came before

We reviewed NASA Veggie, the Advanced Plant Habitat, U-Michigan's 3D-printed PLA substrate, MIT 2020 payloads, Astrobeat, and four patents. The gap was consistent: too big, not modular, water sources that drew power, not user-friendly. We pulled literature on capillary fluidics and soil-moisture sensors, and started logging everything in individual design notebooks (our "D.A.A.N.s").

Test everything, even the ramen

Before committing to a design we ran preliminary tests on tons of random materials — sponge, ramen noodles, Spanish moss, bonsai rock, pine bark and more — and mold grew in all of them. Only pine bark produced substantial growth.

An idea from Wild Kratts

In November, Nate was watching Wild Kratts with his brother and saw the thorny devil lizard (Moloch horridus), whose grooved skin moves water by capillary action with no pump. He realized it might be useful, modeled the channel system in SolidWorks, and it became the core of the project: the TDC — Thorny Devil Capillary.

Preliminary Design Review

We presented to NASA HUNCH mentors, including Nancy Hall (NASA Glenn) and Glenn Johnson (NASA Johnson): the thorny-devil hex pattern holding water upside down, our October substrate tests, our sensor choices, and the first web UI. The feedback that shaped what came next:

• Glenn Johnson called the hexagonal shape and our upside-down demo "really smart" and "a terrific method," and suggested short drops at school — from 10 ft or off a building — to catch a brief moment of zero-g on camera.
• Use dyed water, and aim the camera at the fluid movement rather than plant growth, since the drop test is so short.
• Nancy Hall told us to focus on one plant with a backup; for the drop, the experiment should already be running when it falls.
• Lighting matters: the camera needs light, position it to avoid reflections, and consider a second light on the opposite side to shine through.

Watch our PDR on YouTube (23:47–46:16) ↗

Developing the whole design

December was for developing the whole design and getting our early CAD models and schematics finalized. Physical prototyping came after.

Seven shells and a removable reservoir

We iterated the enclosure seven times: wire holes 5 mm→8 mm, walls 4 mm→2 mm, half-slotted modules that kept falling off the rails until we added supports. The reservoir became removable to stop moisture contaminating the electronics — a heat-sealed pouch in a friction-fit pocket.

Drop, measure, repeat — nine times

We dropped the bare TDC — the original "brick" — from 14 feet, nine times, with dyed water, measuring the water radius before and after each drop — about 0.9 seconds of free-fall per drop, a local stand-in for NASA Glenn's 2.2-second drop tower. Mean capillary movement reached 14.7 mm.

The vision model closes the loop

By Critical Design Review the system was whole: TDC capillary channels, dual pumps (1 mL/min for the long term, 150 mL/min for the drop test), a Raspberry Pi Zero 2W running an AI vision model, aeroponics plus rockwool and clay pebbles, and a modular shelf enclosure. The vision model came out of extensive brainstorming on how to pump water through the system in a loop — until Aidan realized a vision model could watch the roots and pump only the amount the plant actually needed. The main critique at CDR: more water. Our design held about 10 mL, and it needed to handle 50 mL.

Retiring "the brick"

Internally, we thought the original TDC — "the brick" — was comically heavy to ship anywhere, and we wanted the cameras on the inside. That gave birth to the TDC V2.