Introduction: The Most Awesome Space Botany Instructables Ever Issue 02: PIGMats in Space
Astronauts on the ISS eat a varied diet, but miss the crunch of fresh vegetables. Lettuce is the crop chosen to fill this need, but it's a challenge to grow lettuce in a space-efficient way on the station. This Instructable endeavors to use a to create a modular growth environment that maximizes a tiny footprint. We are entering our design in the professional category of the Growing Beyond Earth Maker Challenge.
This design intersperses plants of different sizes in two plant grids. The conical nature of the plant cups allows for them to be cleverly fitted together, minimizing area for pots and maximizing the volume available for leaf growth. The grid of 36 cups is intended to be planted every-other cup so that young plants are growing interspersed with more mature plants. The shelf can be adjusted towards or away from lights on either side of it as plants grow, so that shorter plants could be grown on one side and taller plants on the other.
For the purposes of this contest, we intend to plant all of the lettuce cups within the first two weeks, but the design could be better utilized on ISS by planting 9 plants on either side, one week apart, to ensure a continuous harvest.
To date, we’ve found that this design interfaces best with a passive-wicking system, but we are working to optimize it for a more active watering system (see our Amazing Misters Instructable) to increase the re-usability of the grow cups.
Step 1: Preparing to Build the Grow Cube Frame
Since we had two design options we wanted to explore, we wanted a frame for our grow cube that would allow for easy reconfiguration. Our design was inspired in part by erector sets and in part by the threaded rods that allowed for adjustments on one of the maker-space 3D printers. The frame can be easily taken apart or folded up when not in use. The steel bars have lots of pre-formed holes for attaching various components, and the wing nut shelf brackets can be adjusted to shift the central shelf sideways as plants grow.
We tentatively plan to cover the frame with white woven polypropylene on the sides without lights and aluminum foil on the sides with lights and the bottom. We chose foil because we thought having a non-flammable material next to our homemade lights was the wisest course of action. On the bottom, foil serves to both reflect light and protect our counter from any leaks. The woven poly on the remaining sides provides water and humidity containment while still allowing for air infiltration and is a light-reflecting white (on the interior).
- Two (1 ⅜”) x (48”) Zinc-Plated Punched Steel Bars
- Two (1 ½”) x 14-Gauge x 36” Zinc-Plated Slotted Angle
- Four (3/8”) x (24”) Zinc-Plated Threaded Rod
- Sixteen ⅜” nuts
- Eight ⅜” wing nuts
- Eight ⅜ inch washers
- Hot glue (or epoxy)
- Powered cut-off saw, rotary cutter, or manual hack saw
- Bench grinder or file
- Measuring tape
- Two 9/16” box wrenches, or adjustable wrenches
1. Cut two 50 cm (19.7”) long pieces from each flat steel bar (4 total) and L steel bar (4 total). Cut one 50 cm (19.7”) long piece from each threaded rod (4 total). We used a powered cut-off saw for this, but many cutting options would work.
2. Grind or file all cut edges to remove metal burrs and rough spots. This step is especially important for the threaded rods, to ensure that the nuts will screw smoothly onto them.
3. Secure washers to wing nuts with hot glue. For longer term durability, you could glue with epoxy instead. We will likely do that if our design is accepted. Make sure you glue them so that the hole on the wing nut is unobstructed. These will be the adjustable supports for the shelves.
4. Screw two wing-nut supports onto each threaded rod. Exact spacing is not important at this time, but they need to be far enough away from the ends of the rods to attach the rest of the hardware. They can be adjusted as needed to support the cup shelves later.
Note: Unlike the photo above, one of the shelf brackets on each rod should be inverted so that the washers are facing each other. The flat faces of the washers will be tightened close together to hold the central shelf in place.
Step 2: Assembling the Grow Cube Frame
1. Form a square with two flat bars forming two parallel sides and, perpendicular to those, the two L-brackets forming the other two parallel sides. The flat bars should be installed outside of the L-brackets for simplicity of construction. See upper left picture.
2. Build the frame corners. Screw a nut down a few cm on the end of each threaded rod then put the rod through each corner where the bars and brackets overlap. Put another nut on top of the threaded rod to hold the bars in place. Tighten both nuts against the flat bars until secure, snugging the nuts so that the frame is square and the outer nut is within a few mm of the end of the rod. See upper center picture.
3. Repeat, forming a square and securing it to the threaded-rods for the other side of the cube.
Step 3: Covering the Grow Cube
- Woven polypropylene - We scavenged ours from three 50 lb chicken feed bags. Each bag provides a piece of material that is roughly 81 x 74 cm (32 x 29”). You could also use a white woven poly tarp.
- Aluminum foil - wide roll, heavy duty recommended
- Masking tape (optional)
- Adhesive hook-and-loop (Velcro)
Cover the frame with your selected materials using the above illustration as a guideline. Blue boxes indicate where holes should be cut. Fan holes should just fit the size of the fans and be sealed to the fans with tape or hook-and-loop. Intake holes should be slightly larger than the fans.
The aluminum foil can be secured in place with tape, and the woven poly can be secured with strips of hook-and-loop (Velcro) attaching the seams to allow for easy removal.
Step 4: Testing Growing Media and Wicks
Our grow cups are designed to work sideways with a low-power passive-wicking system. For the rooting area, we tested a variety of media:
- plastic beads
- wood fiber and peat grow plugs
- luffa gourd pieces
- rice hulls
- handknit wool swatches
Of these we found that composted wood-fiber grow plugs gave consistently the best results. We also tested a few different wicking materials: cotton knit, wool felt, and PIG Mat absorbent sheets. We found that PIG Mat works the best at wicking water, but stays too wet to be in prolonged contact with the plant stem or tender roots and leads to rot. Wool felt is better for areas in contact with plants.
We detail two options for the design of the cups; both have the same volume. We have an option that works well in 1 g, but we still are working to optimize a design that could potentially work in zero g, works in a sideways orientation in 1 g, and still gives the right air and water delivery to the roots. We also are working to adapt the mister system from our Amazing Mister design to work sideways in a cup.
The left-hand photo shows examples of two plants grown in different style wicking containers. The plant on the right was grown in a closed-wicking cup where the top was mostly covered in plastic. The plant on the left was grown in an open-wicking cup where the top had large openings to the air. The left plant is larger than the right, even though it was started a few days later. A similar trend was seen for plants in other protoypes. We are fairly sure this stunting is due to the enclosed cup not providing as much oxygen to the roots. Plants in both styles of cups seem otherwise healthy.
Nutrient delivery for all cups was by watering them with dilute complete fertilizer solution. We have gotten good results growing lettuce with 1 tsp Dyna Gro fertilizer per gallon of water.
Step 5: Making a Closed Grow Cup: Materials and Tools
This cup is more realistic for zero-g use, may need to be modified to improve air or water delivery to roots. We're confident we can grow lettuce in it, but it may not be the highest yielding option at 1-g.
- 9 oz squat plastic Solo cup and matching lid
- PIG Mat absorbent mat
- Wool felt
- Woven polypropylene - We cut ours from am old from chicken-feed bag - See Step 3 for other sourcing
- Rigid-plastic dollar-store placemat
- 2” hydroponic plastic mesh pot
- Hot glue or silicone sealant
- -9-5 complete liquid fertilizer (diluted at rate of 1 tsp/gal water) - We used Dyna Grow brand.
- Rapid Rooter composted wood-fiber grow plugs
- Measuring tape or ruler (a quilter’s ruler is recommended)
- Hot glue gun
- Exacto knife
- 50 mL syringe
- Cricut computer-guided cutter (optional)
Step 6: Making a Closed Grow Up: Constructing the Water Reservoir
1. Cut out the water reservoir divider insert from the rigid-plastic placemat. Since we wanted to make several, we used a Cricut computer guided cutter to do this, but you can also trace it out and cut it with scissors.
2.Mark a line down the middle of the cup and secure the insert to divide the cup in half. This will give you slightly over 100 mL volume for water. Attaching works best if you put the hot glue on the bottom half of the insert, smash it down hard, and then apply glue to the top part. We just used hot glue for prototyping purposes, but if you want this to be better sealed to keep the water down (in case the cup needs to tilt), we recommend sealing around the edges with silicone aquarium adhesive.
3. Feed a piece of aquarium tubing into the grow cup and through the hole on the reservoir insert.
Step 7: Making a Closed Grow Cup: Cutting Out Materials and Constructing Lid
1. Cut out PIG Mat, wool felt, and woven polypropylene as pictured above. In the image above, the large grey PIG Mat rectangle is 5” x 2.5”, the grey PIG Mat wick strip is 0.5” x 8.5”, the white wool felt square is 2.5” x 2.5”, the white wick strip is 0.5” x 4.5”, and the white woven-poly circle is 3.75” diameter (just trace the cup lid).
2. The woven poly blocks light from getting into the cup, but “breathes” slightly, which should allow for more air infiltration than the solid plastic used in earlier designs. Cut a strip and a hole out of the poly to allow for air exposure of the seed plug and a place for the water tube. Cut a semi circle out of the top half of the cup lid, but leave enough plastic on the side so that it still can snap firmly in place.
3. Hot glue the woven poly onto the lid. The holes go over the side with the semi-circle hole.
Step 8: Making a Closed Grow Cup: Assembling the Wicks
1. To make room for the wick. Cut away two of the spokes on the bottom of the mesh pot.
2. Insert the PIG Mat wick through the holes. Pull one end so that it is longer than the other.
3. Thread the wool wick under the top of the PIG Mat wick, and pull the PIG Mat wick tight to hold both in place.
Step 9: Making a Closed Grow Cup: Connecting the Wicking System
1. Thread the long side of the PIG Mat wick through the rectangular hole in the bottom of the reservoir insert. This bottom end will wick up water from the reservoir. Leave the other end on top of the reservoir insert. This top end will wick water into the wool felt mat. Keeping the wool mat wet provides an extra place for the roots of the mature lettuce to gain water.
2. Cut two one-inch slits, one inch apart, in the middle of the large PIG Mat rectangle.
3. Weave one end of the PIG Mat wick through these holes. This large PIG Mat piece is not necessary in 1 g, but would help to wick up water that floats around in the reservoir in zero g.
4. Sandwich the wool felt square below the black mesh cup but above the reservoir insert and the top PIG Mat wick piece.
5. Pull the plastic cup down so that its rim rests on the inner lip of the cup and the grove in the middle of the reservoir insert. Everything should fit nice and tight in place.
Step 10: Making a Closed Grow Cup: Planting and Watering
1. Put a grow plug in the mesh cup.
2. Thread the tubing through the hole on the lid and position the slit over the grow plug. Plant seeds into the little hole in the center of the plug.
3. Use a syringe to fill the cup by squirting water through the tubing. Use regular water until seeds germinate, then switch to fertilizer-water solution. The water level in the cups should be checked once daily, and water added if the reservoir is more than half empty.
The maximum the reservoir can hold is 100 mL. We recommend adding 20-50 mL at a time, then rechecking the water level before adding more. In the first two weeks of growth, the cups only need to be refilled once every few days. In the last two weeks of growth, checking daily is essential.
Step 11: Making an Open Grow Cup
This cup design is our back-up plan. We know we can grow really good lettuce in just grow plugs suspended over a cup with a wick to move water to it. This is basically a simplified version of the closed cup, and uses some of the same parts. It has a lower materials cost, and greater ease of assembly. It is only appropriate for places with gravity to hold the water in place.
1. Secure a piece of aquarium tubing to the bottom and side of the cup with a bit of hot glue, make sure the opening is unobstructed.
2. Cut out the top half of the plastic cup lid, leaving enough rim for the lid to lock into place.
3. Put one wick to hang out the bottom of the mesh cup, and loop the wool wick underneath it. (See Step 8.)
4. Secure the plastic mesh cup to the solo cup with a bit of hot glue.
5. Put a grow plug in the plastic mesh cup and put the lid on to hold it in place.
Whichever cup design you chose, repeat until you have 36 cups.
Step 12: Making the Grow Shelf: Materials
In this design, our cup shelf is positioned in the middle of the cube. Half the plants (18) face lights positioned on one side of the cube, and the other half of the plants (18) face lights positioned on the opposite side of the cube (36 plants total). This allows for vertical positioning of the shelf, with respect to the orientation of the users. The shelf was designed to “plug and play” with each grow-cup, so that each grow cup can be maintained, added, or removed separately, if needed. In other words, the “shelf” is made only of 9 oz solo cups and glue, in which each plant cup can be placed. Cups alternate “up, down, up, down, up, down” and are arranged into a 6x6 square.
- 9oz Solo cups
- Hot Glue Sticks and Glue Gun (Glue Gun with detail tip is very useful)
- Black Spray Paint
- Chrome Spray Paint
- Newspaper, or space where spray painting can occur
- Dual Lock
Step 13: Making the Cup Shelf: Assemble Cup Pairs
1. A Sharpie is used to delineate the approximate center of each cup.
2. Then, utilizing this midline, glue two cups together with hot glue. Importantly, the lip of one cup fits in the empty space of the opposite-facing cup, image below.
Note: Ridges of cups will fit together in this fashion, to construct the hardiest “shelf made of cups”.
3. Using hot glue, glue the drawn lines on the two cups together. Repeat until there are eighteen pairs of cups glued together in this fashion.
Step 14: Making the Cup Shelf: Gluing It All Together
Glue each of the eighteen pairs together, slowly and surely constructing the shelf. Make sure to glue the midpoints together, of any cups that are touching each other. This way there are no more than three places that cups are glued together at a time (important so that the hot glue does not dry too quickly). Take caution to note where glue is hot and fresh, so fingers are not burnt. Also, if glue gun has a low/high heat setting, make sure to use the lower heat, so as not to melt the plastic cups. The shelf is shown above right.
Step 15: Constructing the Cup Shelf: Painting
Finally, for finishing touches, spray paint all cups black first, to ensure that light does not reach the roots. The final spray paint layer should be reflective of light--so one could use white--but we used chrome for reflectivity, as the light does reflect well off the chrome.
Black Layer (Left) and Chrome Layer (Right). Both sides of the “shelf” were painted with both colors, first black, and then chrome.
Step 16: Putting the Cup Frame in the Cube
1. Insert the cup shelf into the frame like the picture below. We plan to build a frame around the cup array to hold it into place better, and to give an area to attach the ends of watering tubes.
2. Grow cups can be attached to the cup shelf with a piece of dual lock to hold the cup in place.
3. Tubing from grow cups can be extended to the front of the tube and secured with velcro for easy access to water. Imagine all these tubes in the lower part of the right picture were connected to grow cups.
Step 17: Grow Light Design and Materials
Our current design involves 16 3-W LEDs per level, which gives 3200-4000 lumens over a 0.25 square m area (12,800 - 16,000 LUX). We don't know the exact PAR, because those specs aren't given with the LEDs, but we've chosen a combination of blueish-white (6500K) and redish-white (3000K) to give us lots of blue and red light in the spectrum.
We've based our choice on a few things:
We've successfully grown lettuce to close to optimum size (~12 cm tall, 15 cm wide) in 28 days using a 4000 K white light that outputs 7000 lumens over a 0.38 m area (18,000 LUX). We estimate that a 4000K light should have slightly lower PAR than our combo of bluish- and reddish- white lights. We found a paper that reported excellent growth of lettuce under white light at 14,000-15,000 LUX, which is around what we have. We've opted for white light over red/blue based on the above paper and comments made during the NASA webinars that the folks there thought white light (with ample reds in the spectrum) might be a good route to go. We have room to add more lights to each panel, if needed, without significantly changing the volume needed in the grow cube.
Tools and Materials:
- 5 cm wide, 3 mm thick strip of aluminum, ~366 cm total length (to be cut into eight 45.7 cm lengths)
- 3.3 volt, 20 A power supply
- 32 high powered 3 watt LED chips with PCB - 16 warm white, 16 cool white
- 32 x 1Ω 1 watt resistors
- Thermal adhesive such as Arctic Silver Arctic alumina
- Red and black 18 gauge insulated wire
Electrical-grade silicone sealant
¼” drill bits Drill press or hand drill
Soldering iron and solder
Step 18: Preparing Aluminum Strips for Lights
1. Cut aluminum stripping into nine pieces 45.7 cm (18”) long using any method of your choice, this will function as the primary heat sink for the LEDs.
2. Place 4 LEDs on each of the eight pieces of aluminum stripping equidistant apart.
3. Mark the positions, then thoroughly clean the aluminum strips.
4. Drill a ¼” hole on either end of the LED strip ¾” from the end. Don’t be like us. Drill these holes before you glue and wire LEDs.
Step 19: Gluing the LEDs
Safety Note: Do this in a well ventilated area. Glue has fumes.
1. Place a 2-3mm bead of the thermal adhesive’s part A and equal sized portion of the thermal adhesive’s part B on a flat clean expendable surface. Mix the two together for 5 or 6 seconds until completely mixed.
2. Using a popsicle stick or similar device scrape the paste-like adhesive off the expendable surface and place it on the center of the back of an LED in large glob.
3. Then press the LED into its previously noted position on the strips and secure it tightly, preferably with clamps or screws. That’s not really necessary with LEDs of this power level though it will increase efficiency by a tiny margin. It’s important that you work quickly so that adhesive won’t set before the LED is secured in place.
Repeat until all LEDS are in place.
Step 20: Wiring It All Together
The LEDs on all panels are wired together in parallel.
1. Connect the positive terminals of each LED to the positive terminal of the unplugged 3.3 volt power supply in parallel, generally done using soldering and wire.
2. Connect each LED to the resistors on the LED’s negative terminals. It doesn’t matter how you orient the resistors. Then, connect the side of the resistor opposite of the LED to the negative terminal of the unplugged 3.3 volt power, also generally done using soldering and wire.
8. Plug power supply in to test whether or not the lights work.
9. To prevent corrosion and accidental shocks, cover exposed wires with electrical tape or coat exposed metal with electrical-grade silicone sealant.
Step 21: Attaching the Lights to the Grow Cube
We’ve arranged the lights vertically along both sides of the cube. In the example above, we just show one light loosely attached prototype attached, but there will be two in the final assembly. Our cable management of the wires will be better too.
- LED light array from previous step
- Wire or zip ties - We used pipe cleaners for prototyping, but our final design will be more sturdy.
Attach the LEDs to the wire frame in the orientation pictured below. Unlike our image, we recommend tucking your wires inside the cube and orient them downward, attached to the power supply.
Step 22: Ventilation System Design and Materials
Air movement is important for both plant growth and removing heat from the LEDs lights. Based on the rule of thumb that the CFM in a greenhouse should be roughly twice the footprint, we estimated our cube needed a minimum of 5.4 CFM of air movement in the cube (0.82 CFM airflow per cubic foot of cube volume). To see if this would be in the ballpark for a smaller container, we looked at growth chamber specs. We found a 17 cubic ft growth chamber with 20 CFM airflow (0.85 CFM airflow per foot of chamber volume), which is similar to our estimate.
For heat dissipation, we have read that 3-5 air exchanges per minute are ideal for warm enclosed grow rooms. (Note: We are a bit uncertain about linking to this statement, as we suspect it’s source is, er, less-than-reputable plant growers, but such growers are usually the ones trying to grow plants in small indoor spaces with homemade equipment.) Based on this exchange rate, we estimate that we need a maximum air exchange of 22 CFM.
In order to promote air movement in the corners and on either side of grow cup shelves, we are opting to use an array of smaller fans on either side of the box, instead of one big one. Our ventilation system consists of six 50-mm, 12-volt, 0.12-A fans, that provide ~ 9 CFM airflow each. Their combined 36 CFM should be more than sufficient for heat removal.
We put six matching holes for air intake on the front of the box. On the space station, these could be enlarged slightly and covered with absorbent mesh to reduce the escape of any leaks and debris. The negative pressure sucking things away from the “front” of the box (i.e.facing the cabin area) would also help contain any leaks or debris. On a space station, the exhaust fans could be hooked up to the ISS Express Rack ventilation system.
- Six 50 mm wide x 10 mm thick, 12 V, 0.12 A fans similar to these
- Six three-pin fan Y-splitters
- One switching power supplies with output of 12V, 1A
- 2 jumper wires
- 1 female barrel jack
- Thin wire for attaching fans to structure - We used pipe-cleaners for prototyping, and will use 12 gauge-wire (aka coat hanger) for the final design.
- Small screwdriver
- Needle-nosed pliers (if working with heavier gauge wire)
Step 23: Building the Ventilation System
1. Connect fan splitters and fans as pictured above. Fans should all be connected in parallel. Fortunately, the y-splitters allow you to attach the fans only in the correct configuration.
2. Use the Jumper cables to attach the female barrel jack to the positive and negative pins holes on the first y-splitter. If you follow the line of wire to a fan, the positive wire is the red, the negative is black, and the yellow one is for controlling the fan (and doesn’t matter here).
3. Using wires, attach three fans on either side near the rear of the growth chamber. Evenly space three fans in between the 3rd and 4th rack of lights.
4. Feed the cables along the bottom of the cube and repeat on the other side. Fans should be positioned so that they blow air outward.
5. Secure fans to the outtake holes in the outer cover. We will likely use velcro for this for easy disassembly.
Step 24: Giving Credit Where It Is Due:
About the team
We are competing in the professional category. However, we have dubbed our team “The Amateur Professionals,” due to the fact that none of us are designing things based on our actual profession. We’ve had engineers doing horticulture, biochemists doing lighting design, and entomologists experimenting with metal working tools and Arduinos. We’ve enjoyed the chance to learn new skills.
Jessica Frega - Jessica works in public health, but has never lost her teenage love of space. When not chasing after a 3-year old, she loves to garden, craft, and precisely design things to be cut with computer-guided cutting machines.
Austin Marty- Austin is a recently graduated biochemist, member of Splatspace makerspace, and botany enthusiast. He is our lighting designer, as he has ample experience building grow lights for his ever-growing collection of epiphytes and aquatic plants.
Sandra Paa - Sandra is an entomologist turned agronomist who works to develop better fertilizers for plants. She is interested in automation in plant growth systems and is always up for tinkering. Sandra is both a fount of creative ideas, and a useful critic when our ideas become too impractical. She’s had a hand in building many of the grow cube systems from the supports, to the lights, to the cup shelves.
Aurora Toennisson - Aurora is an entomologist, gardener, and wannabe space biologist. She originally instigated the formation of the team, and helped organize meetings for the build team. She worked on testing different growing media and pot sizes, tinkered with water delivery systems, designed the ventilation system, and designed the support structure for the grow cube.
Dawn Trembath - Dawn is a member of Splatspace makerspace, Triangle DIY Biology, and Durham’s Community Lab. Dawn's background is in engineering, though she's spent recent years doing policy work. Dawn designed the mister system, and contributed a ton to group design brainstorming. She plans to use the knowledge from this project to build an automated system to keep her plants alive so she can continue to ignore them while working on automated plant systems.
Julie Hoover - Julie is a former professor and leader of a community college high-altitude ballooning team, and now NASA employee. She recruited several of the team members and has project managed our progress from afar. She is a wealth of knowledge of inexpensive supply sources, strategies for problem solving, and creative uses of dollar store items.
Jimmy Acevedo - Jimmy got his start as a high-altitude balloon team member. He enjoys tinkering at home and uses every excuse to fold Maker culture into his day job. Jimmy is also the graphic designer of the group.
Peter Reintjes - Peter claims he's too busy to be on the team, as he is heavily involved with other projects at Splatspace (and his work designing continuous evolution protein engineering equipment). However, he's given us a lot of advice about tiny fluid delivery systems, so we're counting him as an unofficial advisor.
Participated in the
Growing Beyond Earth Maker Contest