Overview:

The MDRS GreenHab "Salad Machine" is an automated portable hydroponics test bed to demonstrate the feasability for the growing fresh vegetables for future crews. The initial crops will consist of tomatoes and dwarf wheat from the Utah State University's Plant Physiology Lab, developed under contract by NASA for ET Agriculture use, primarily for use on ISS. An additional two units will containg off-the-shelf Lilly-Miller lettuce, (four varieties). The system consists of four individual plant growth modules, with a combined growing space of approximately one square meter. And additional stand-alone module is also being used to grow the wheat. The system makes use of a flood and drain system, known as "sub-surface irrigation," with the plants growing in an inert, grainy substrate of volcanic cinders.

How It Works:

Making use of the unique design of a common plastic drinking water filtration system, the Salad Machine's hydroponic growing trays sit inside the nutrient solution tank, which is slightly wider all around and about twice as deep. Removing the filter holder leaves a depressed socket just the right size for a 2" PVC straight junction pipe. This had a 1/2 hole drilled in the side to accomodate a 90 degree plastic pipe fitting, which is connected to a small submersable pump. The pipe fitting is attached to a long PVC tube with hole drilled evenly along the sides, for a controlled release of solution.

An initial layer of course gravel is laid down to cover the solution delivery system, and to make it easier for the solution to drain back when the pump cycles off. The finer-grained volcanic cinders fills out the tray. A sandwich of fine mesh screen between a pair of thin PVC pipe sections tops the unit off as an over-flow drain, to capture any stray chunks of cinders that might float up and accumulate.

Nutrient Delivery

Bottom Layer

Santiam Soil Sim

The Flooding Begins

Floating Fines

Four times during the day, a digital timer turns on the pump, which pumps the nutrient solution up, into the growing tray from below. This is known as "sub-surface irrigation." The pump runs for one minute, enough time to fill the spaces between the volcanic cinders with solution. The overflow drains off excess solution into the center opening back down to the holding tank. After one minute, the timer turns off the pump, and the liquid drains back by gravity into the storage tank. The times I set for use in the GreenHab were 1000, 1200, 1500 and 1800 hours. One timer runs all five of the units. Daily maintanence after the system was up and running consisted of brushing away chunks of cinders that floated up onto the drain screens, check the fluid level and add more when needed and to make sure that pumps did indeed come on, (evident from observing the screen area after a cycle for moisture).

The following pages linked above show details of the construction process, as well as a visual report of plant growth during Crew 28's rotation. The system initially setup to run off of solar power, partly in response to our shaky generator system that plagued us during our rotation. It was switched over to Hab power, and was left running after we left. Members of Crew 29 agreed to monitor the system and top the tanks with solution left behind. It is hoped that this test unit will inspire a more ambitous hydroponics system for GreenHab that could grow significant amouts of edible biomass for future crews, with minimum expenditure of crew time.