Astronaut Greens Need UV Beams

Canadian astronaut Jeremy Hansen, recently left on the first crewed mission outside of earth’s orbit in decades.  Prepackaged meals balance nutrition and safety with strict mass, volume and power limits dictated by the compact shared cabin.

Since Astronauts require 4 lbs of food per day, growing food for longer missions like Mars is necessary.  NASA currently uses Veggie to grow lettuce on the International Space Station, but along with the lettuce comes unwanted bacteria.  To clean the lettuce, they currently press a lettuce leaf between citric based wipes, but this method is impractical and uses up their valuable time and creates waste.

So, I created the DEMETER! Named after the Greek goddess of Agriculture, since NASA uses Greek entomology like Artemis 2 and Apollo when naming vessels.

An automatic, compact, low powered bacterial killing UVC LED based system to greatly reduce the likelihood of an astronaut getting sick from vegetables grown in space that could compromise the safety of other crew members and possible the mission.

The DEMETER allows astronauts also benefit from the social, mental and nutritional benefits of growing food for consumption while in space.

BACKGROUND:

I have always wondered about space, often staring at the solar system light mounted on my bedroom ceiling(Figure1).

Last summer after watching the movie “The Martian” (and reading the book), about an astronaut abandoned on Mars who needed to find a way to grow his own food to survive, I wondered if real life astronauts could grow food in space.

My investigation revealed that NASA was planning a mission to Mars, but with an optimal 24-month journey (Figure2) food supply was a critical issue. Unlike with shorter missions, astronauts couldn't pack enough prepackaged sterilized food (Figure3) with limited room on the spacecraft, so growing food would be necessary. (2,3)

Experiments on the International Space Station (ISS) reveal that lettuce (Figure4) is one of the easiest crops to grow.  Bacteria multiply faster in space while astronauts’ immune systems are weaker.  If one astronaut became sick from consuming contaminated food it could jeopardize the entire mission.

PURPOSE:

My device aims to effectively decontaminate leafy greens without compromising its integrity. Using UVC light (250-280 nm), investigated by NASA, as an effective method to kill bacteria on food (1).  To create a device that astronauts could use on the ISS and future missions (Figure5) to kill bacteria on food grown in space. Specifically to create a device for bacterial decontamination (Figure6) of leafy greens that was superior to the current NASA system of using citric acid wipes (pressing lettuce for 30 sec) (3) which is impractical and wasteful.

I created DEMETER (Figure 7,8) to kill bacteria on leafy greens grown, harvested and eaten by astronauts while in space.

At the heart of the system are 275nm UV LED strips selected for killing micro-organisms.  The small footprint, low powered, 2w strips are preferred considering the limited resources available on spacecraft.

An acrylic enclosure was selected for the DEMETER to block UVC from escaping and to allow monitoring during use. The size of the DEMETER was dictated by the dimensions of the LED strips strategically positioned at the top, bottom and sides of the enclosure. A meshed shelf was selected to secure leafy greens while in space and allow a complete UVC wash of the lettuce.

A FEP film is used to protect DEMETER components from organic contamination, since equipment is difficult to clean in space.  A programmable timer was also incorporated to allow for automatic operation.

I tested the Demeter performance by:

1.     Bacterial counts on lettuce treated with UV versus wipes (Figure 9,10)

Lettuce was left out for 48 hrs before processing to ensure bacterial growth.  Bacterial counts were recorded for lettuce treated with various UV treatment times compared to lettuce treated with citric acid-based wipes (lettuce leaf pressed between 2 wipes in a Ziploc bag as done by NASA) and control untreated lettuce.

2.     Colour analysis to ensure quality of lettuce was intact with UV treatment (Figure 11)

I used Image J software and colour analysis protocol developed by Dr.Oral(4).  The DeltaE or quantitative difference in colour of lettuce before and after UV light exposure was determined.  A DeltaE of less than 1 is imperceptible to the human eye whereas DeltaE of 5 would suggest completely different colours and that the DEMETER had significantly impacted the colour/quality of the lettuce after treatment.

Figure 12 confirms that the glow germ powder applied to a lettuce sample is completely lit up and covering all surfaces of the lettuce indicating that UVC light is reaching all areas of my samples during DEMETER treatment.

Initial results using the DEMETER showed similar bacterial killing efficacy when compared to controls.  This did not make sense. Ultimately, I discovered that the Ziploc bags I was using to house the lettuce during treatment with the DEMETER did not allow UVC light penetration, so I switched to FEP films which are fully UVC light transmissible and safe for use with food.

To better understand my test results and to ensure their validity, my mentor explained and helped me with some statistical analysis.

To statistically compare two sets of results a paired t-test was used, while to statistically compare 3 or more results an ANOVA test was used, where a p-values of less than 0.05 would mean that the difference was significant and not due to chance.

The Biosafety Cabinet (BSC) is a powerful UV lamp enclosure using 254 nm UVC located at my mentor’s lab. It was also used to test the lettuce samples.

Figure 13 shows the following:

a) No significant difference in bacterial killing between treatment groups on the x axis with or without FEP film, indicating that UV light can effectively pass through the film and reach the lettuce to kill bacteria.

b) The Demeter had similar bacterial counts compared to control at UV times 5-15 minutes, indicating that it was ineffective to kill bacteria at these time intervals.

c) The Demeter achieved approximately 1 log reduction in bacterial counts compared to the controls at UV time 20 and 30 min.

d) The Demeter achieved 2.5 log reduction in bacterial counts at 45 minutes which was the same as the BSC result at 10 minutes.

Figure 14 shows no significant difference in bacterial counts with or without citric acid-based wipes treatment (NASA’s method).  This shows that the NASA’s method of pressing the lettuce between 2 wipes is ineffective at killing bacteria.

The DeltaE colour analysis Figure 15 shows that from 5-30 min UV exposure the lettuce colour was not altered (imperceptible to eye) and at 45 min there was only a perceptible difference under very close observation.

Colour is the first thing people notice when they look at food(4). DEMETER treatment did not affect the quality of lettuce as confirmed by the colour analysis results.  Comparing before and after UV treatment results (Figure 17) showed no perceptible colour difference.  Figure 18 interestingly shows a gradation of colour change with increase UV time.

The FEP film did not impact bacterial killing at any UV treatment interval proving it a good solution to housing the lettuce.  FEP film used in the DEMETER device is important to prevent contamination of the parts and allow for anchoring to the mesh shelf while in space.

DEMETER is effective at killing bacteria on lettuce with 1-2.5 log reduction in bacterial counts compared to NASA’s approach which yielded no difference in bacterial counts using citric acid-based wipes. The 2.5 log reduction at 45 min of DEMETER UVC exposure, although encouraging, is too long for practicality in space.  The BSC showed 2.5 log reduction in bacterial counts at only 10 min of UVC exposure using a more powerful UV light source and 254nm UVC.  This suggests that 254nm UVC and increased intensity provided better bacterial killing than DEMETER’s 275nm UVC LED strips.

My results suggest that NASA's wipes method to decontaminate lettuce in space is ineffective, impractical and wasteful.  The DEMETER has shown promise in solving this important problem (Figure16) with more effective bacterial killing, time savings from not having to physically press lettuce with wipes and significantly reducing waste.

Iterations of DEMETER will add synergistic UVC wavelengths to improve bacterial killing efficacy.  Combining all DEMETER components into one optimized polycarbonate design for protection and streamlining.  A new tray design will expand testing to accommodate additional vegetables.

Future experiments could be conducted in a microgravity chamber to better simulate conditions in space, while a more detailed sensory analysis evaluating texture and nutritional content could further demonstrate that DEMETER treated lettuce remains unchanged.

Using a human gut model (5) comparing the effects of DEMETER-treated to untreated lettuce on gut bacteria could also provide insights into potential impacts on human health.

I would like to thank my parents and grandfather for fostering in me a love of science.   My parents helped purchase equipment and supplies in addition to showing me how to use power tools during my construction phase.  I would also like to thank the CBSN for its support and particularly Dr. Lawrence Goodridge for his mentorship and helping me to understand that good and bad results are both useful.    I am grateful to Dharamdeo Singh from the Goodridge Lab for helping me with Statistical Analysis and Dr. M. Onur Oral for developing the ImageJ protocol I followed for colour analysis.   I would also like to thank my science teacher, Ms. Yee at Holy Trinity School for showing me how operate lab equipment safely and always making science fun.

1.    National Aeronautics and Space Administration. 2018. Food Sanitation Device for Use in Microgravity. eXploration and Habitation Challenge 2018.

2.    National Aeronautics and Space Administration. 2014. Human Integration Design Handbook.

3.    BEC Crew. 2015. Science Alert: NASA Astronauts Will Eat Space Lettuce For The First Time Today.

4.    Department of Food Science, University of Guelph. (2026). Digital image analysis of food product surfaces using ImageJ (M. Onur Oral, Prep.; M. G. Corradini, Revised).

5.    Pakroo, S., Soltani, S., Tarrah, A., & LaPointe, G. (2025). The effect of dietary transition on infant microbiota composition and metabolic activity captured with the simulator of the human intestinal microbial ecosystem (SHIME). Gut Microbiome, 6, e9. https://doi.org/10.1017/gmb.2025.10007

6.    ChatGPT. (2026). NASA Astronaut in space suit eating lettuce  [AI-generated image]. OpenAI.

7.    ChatGPT. (2026). Combination of UVC wavelengths to improve bacterial kill [AI-generated image]. OpenAI.

8.        National Aeronautics and Space Administration. (2021). Selection factors for space crops (Document ID 20210023343) [Conference presentation]. American Society for Gravitational and Space Research Annual Conference, Baltimore, MD, United States. https://ntrs.nasa.gov/citations/20210023343

9. Douglas, G., Zwart, S., Smith, S. (2020) Space Food for Thought: Challenges and Considerations for Food and Nutrition on Exploration Missions. https://www.sciencedirect.com/science/article/pii/S0022316622023100?via%3Dihub

10.    Wood, A. (2015, October 20). A closer look at NASA’s journey to Mars road map. Refractor. https://refractor.io/space/a-closer-look-at-nasas-journey-to-mars-road-map/