I'm currently a Junior in High school (Entering into the High School category) and when I first heard about the Growing Beyond Earth contest, it seemed like a daunting task. Nonetheless, after drawing a few sketches and making a parts list, I had an idea for the project.

My design consists of multiple rows of PVC piping surrounding a central light source. Water is delivered throughout the pipes, which are filled with growing media. It's currently positioned vertically to prevent water from falling out from one side; in a micro gravity environment this is not an issue. Lighting, watering, monitoring, etc. are all automated by an Arduino Nano.

Step 1: Enclosure/Structure

The box is constructed with ~18.5 x 18.5 inch acrylic sheets (adheres to the size constraint). I later added a lid, which is attached with acrylic hinges and includes a latch to hold it in place.

The tubes in which the plants are situated are 1 1/2 inch PVC with 1 1/4 inch holes drilled in them. In order to fix the tubes to the enclosure, I first drilled small holes above and below the sides of the pipe; steel wires were then put through the holes, wrapping around the PVC pipe and being tied at the back. In total there are 8 wires holding each row/level.

Step 2: Water + Fertilizer

In order to water the plants, standard aquarium airline tubing is used, which travels throughout the PVC pipes. Small holes were made in the tubing where plants are; these are used to water the plants.

The reservoir, A 1.5L water bladder, is located on the opposite side of the door, and is secured with strips of Velcro. This specific bag has standard water bottle threads, allowing an adapter for the airline. A 12V peristaltic pump pumps water from this reservoir into the tubing, which distributes it to the plants. The pump is turned on and off at timed intervals to allow the roots to aerate while also preventing them from drying out.

The bladder can easily be disconnected by closing the valve and disconnecting the tubing. Once disconnected, it can be refilled and fertilizer can be added. I decided to use General Hydroponics's "Flora Series", which is directly added to the bladder.

Step 3: Lighting

A 12v RGB strip is used for lighting and is attached to a PVC pipe. It's currently set to turn on for 14 hours at a time. Individual colors are controlled by the Arduino nano via MOSFETs. The RGB value of the strip can be changed for optimal plant growth and experimentation.

Step 4: Electronics

Most of the electronics, with the exception of the pump, are attached with Velcro to one of the corners opposite of the lid's hinge. Humidity and temperature are monitored and displayed on a small OLED display. All electronics are controlled by the Arduino Nano.

The following electronics were used:

12v DC wall adapter
5v Relay for the water pump
DHT11 Temperature/Humidity Sensor
RGB strip
MOSFETs for the RGB strip
Small OLED display that displays basic info
DC to DC Buck Converter to step the 12v down to 5v (for the 5v electronics)
Arduino Nano + Terminal Adapter

Hydroponic_Grow_Box.ino
Download

Step 5: Plants

To prevent plants and the medium from coming out of the pipes, I cut small circles out of some pond liner scraps, cut an X in the center, and affixed them over the holes of the tube. The PVC pipes were filled with Expanded Clay Pebbles; Expanded Clay Pebbles were used as the growing medium because of their ability to retain large amounts of water, but still allow proper aeration of the roots. This is useful, because there is no air injected into the system.

Rockwool starter cubes can be used to grow plants from seeds; they can be placed in the middle of the cut-out, with the clay pebbles.

Step 6: Conclusion

This design allows for 36 individual plants, and can be made to support more if more rings are added or if more holes are made on each side. Its automation reduces the level of maintenance necessary. Given the size constraints, it should allow for a relatively high yield of crops. It gets quite humid in the box, so I may add a small fan in the future. Otherwise everything has been working well so far.