The Space Salad System Blog 6 - Plant Pot System + Assembly

rockcacti

1 Jan 2021

Previous Blog Posts

Blog 1 - Challenge Overview + Plant Growth Factors

Blog 2 - Plant Growth Chamber Design

Blog 3 - The Project Plan + Prototype Materials

Blog 4 - Automation Using The Challenger Kit

Blog 5 - Enclosure Prototype + Light/Air/Temperature

In this blog, I'll describe my plant pot system and explain how it satisfies the relevant plant growth factors. I'll also demonstrate how my plant pot system innovates upon existing methods.

Plant Pot System

According to the experimental results outlined by "VEG-01: Veggie Hardware Validation Testing on the International Space Station," watering malfunction was the cause of death for the plants that withered. NASA's Veggie plant pillows require watering daily through injecting water via an injection port. Failure to water daily or failure of the injection port, makes this process unreliable. To insulate my system from watering malfunction, I innovated upon NASA's plant pillows and designed a passive, self-watering plant pot system that can sustain up to one week without watering. This saves valuable astronaut time and energy. (PDFs of NASA's research attached)

My passive, self-watering plant pot system uses a wick to pull water via capillary action from a reservoir into the substrate where the roots are found. When the reservoir is empty, it can be replenished.

Supplies

Metal cans
Plastic pots
- I found pots that fit perfectly into the metal cans!
Wicks
Seeds
- Outredgeous Red Romaine Lettuce | Vegetable | deep red leaves with a nutty/sweet flavor

- Special thanks to organic gardening consumer products startup Back to the Roots for providing me with some seeds!
  - Cherry Tomato | Fruit | bite-size tomatoes - bright red, sweet, and juicy
  - Walla Walla Onion | Bulb | large onions with mild, juicy, sweet flesh
  - Cilantro | Herb | aromatic, zesty leaves

Roots require water and oxygen, so I chose an absorbent yet porous soil substrate: calcined clay. I chose solid growth media because liquid growth media cannot easily retain a homogenous mixture of both water and oxygen in microgravity; I avoided traditional soil because it may harbor harmful microbes and it can decompose/compress to a point where no oxygen can reach the roots. This rules out hydroponics and traditional soil in favor of calcined clay. Moreover, calcined clay's use as a soil substrate has been validated on the ISS.

To ensure a steady supply of nutrients, I use slow-release fertilizer as our method of nutrient delivery. For experimentation purposes, I grow only one plant per pot so that confounding variables such as competition and cross-contamination are eliminated. For food production, it is more efficient to merge rows of pots into a large pot that is shared by many plants.

Sowing millimeter-sized seeds at a precise germination depth under microgravity conditions is difficult; thus seeds must be secured on Earth so that they maintain the desired depth while in space.

Assembly

Each pot can hold up to 300cm³ substrate and each metal can reservoir can hold up to 175mL water.
Cut rectangular wicks and insert wicks through the holes in the pot. Cover up all remaining holes with tape to prevent substrate from falling out.
Mix 2.25g of slow-release fertilizer with 300cm³ calcined clay substrate to achieve ratio of 7.5g fertilizer to 1000cm³ dry substrate as suggested by NASA research.
Pour fertilizer-substrate combination in the pot without burying the wick and place the pot in the reservoir.
Glue the seed to the wick with guar gum to ensure it maintains the desired germination depth.
Initiate growth by pouring 225mL over the substrate. 50mL will be absorbed by the substrate and 175mL will trickle into the reservoir.

Results

I grew radish successfully! (Although radish is not one of the four plants I selected back in Blog 1, it was the best choice for rapid prototyping because it has the fastest seed to harvest time.)