Celebrating Human Spaceflight: Sierra Space’s Contribution to the Plant Habitat-07 Experiment

On this International Day of Human Spaceflight, we celebrate the remarkable achievements in space exploration and look forward to the future of long-duration space missions. Amongst the challenges that must be overcome to enable regular, long-duration missions in the future; including survival systems, radiation protection, and constant communication is crucially, the health and wellbeing of crew. In maintaining a healthy crew, we must ensure a sustainable food supply for astronauts. Fresh produce is difficult to maintain in space given the lack of light and moisture, so we must innovate to find sustainable solutions. Growing fresh produce in space is particularly challenging due to the absence of natural sunlight and the difficulty in managing water distribution in microgravity. These conditions make it hard to cultivate plants that are essential for providing fresh food and necessary nutrients to astronauts.

Sierra Space, in collaboration with NASA, is addressing this challenge through the Plant Habitat-07 (PH-07) experiment, which focuses on understanding the impacts of substrate moisture on lettuce plants and microbiome development.

The Importance of Plant Habitat-07

The Plant Habitat-07 experiment is a critical step in advancing our knowledge of plant growth in microgravity. The ability to grow fresh food in space is essential for long-duration missions, such as those to Mars or extended stays on the Moon. Fresh produce not only provides essential nutrients but also contributes to the psychological well-being of astronauts by offering a sense of normalcy and crucial variety in their diet while in space.

Objectives of the Plant Habitat-07 Experiment

The primary objective of the PH-07 experiment is to study how different levels of substrate moisture affect the growth and development of lettuce plants and their associated microbiomes in a microgravity environment. By understanding how substrate moisture impacts plant growth in space, scientists can develop optimized watering strategies that ensure water availability to maintain plant health and productivity.

Challenges of Water and Oxygen Delivery in Microgravity

Delivering adequate water and oxygen to the root zones of crops growing in microgravity is highly challenging due to the complex behavior of fluids and gases during spaceflight. Chronic excess (flood) or insufficient (drought) water levels, or intermittent watering and wilting of plants, lead to alterations in plant growth and impacts on the nutritional and microbial composition of those plants. The PH-07 experiment will apply controlled water stress to assess and quantify changes in plant growth and the microbiome of a well-tested food crop, 'Outredgeous' red romaine lettuce, grown in the Advanced Plant Habitat (APH) on the ISS.

Preflight Definition and Verification Testing

Before the PH-07 experiment can be conducted on the International Space Station (ISS), extensive preflight definition and verification testing is necessary. These tests are designed to ensure that the experimental setup will function correctly in the unique conditions of space. Sierra Space plays a vital role in this phase, working closely with NASA to develop and test the hardware and procedures required for the experiment.

Ground testing was performed in strictly controlled environment chambers at Kennedy Space Center. Plants were grown for 28 days, and after several rounds of testing, moisture conditions were determined that would impose desired growth differences. Plant positions were defined to fall between porous tubes and sensors to allow for root extraction post-harvest. Root recovery is critical for understanding the microbiome in the root zone. Analog science carrier quadrants were constructed, and these were operated with standpipe irrigation control. Analog quadrants were run in chambers set to mimic desired APH settings. Germination domes were tested, but a simpler solution of increasing relative humidity (RH) and decreasing light during germination was determined for APH.

Verification Testing

Science Verification Testing (SVT) was conducted in the APH ground unit from 1/30/24 to 2/27/24. This test helped refine success criteria and better understand moisture control in the APH hardware. Flooded plants grew more than expected in SVT, and wilt plants grew less than expected based on definition testing. Moisture control settings were slightly modified to better manage these conditions to desired levels during EVT.

The Experiment Verification Testing (EVT) ran from 3/20/24 to 4/23/24 and was extended to 35 days to better understand abnormalities in plant growth. New substrate was obtained between SVT and EVT. During EVT, plants showed unexpected stress beginning at 9 days, with stress levels varying by treatment but present in all quadrants.

Astronauts Sunita Williams and Don Pettit harvested the PH-07 science aboard the ISS just before Crew-9 returned home. This concluded the flight experiment that started in late November 2024 and consisted of three different experiments each running for around a month. Sierra Space provided all the consumables for the APH facility and supported all flight operations during the experiments.

Next Steps

The next steps for the PH-07 experiment include:

• Three replicate 28-day growth tests on the ISS
• Ground controls offset by a 1-week delay
• Sample return (CRS-32) for post flight analysis
  • Plant chemistry
  • Food safety (cultural microbiology)
  • Microbiome analysis
  • Proteomics (Collaboration with the Australian Centre of Plants for Space (P4S))
• Image analysis (Collaboration with P4S)
• Recommendations for optimal failure modes for future space crop production water/nutrient delivery systems

Benefits for Long-Duration Space Missions

The insights gained from the PH-07 experiment will have significant implications for future space missions. Here are some of the key benefits:

• Optimized Watering Strategies: By understanding how substrate moisture affects plant growth in microgravity, scientists can develop optimized watering strategies that ensure healthy crops. This is particularly important for long-duration missions where water is a precious resource.
• Improved Crop Yields: Healthy plants are more productive, leading to higher crop yields. This is essential for providing a reliable food supply for astronauts on extended missions.
• Enhanced Nutritional Value: Fresh produce grown in space can provide essential nutrients that are difficult to obtain from pre-packaged food. This can help to prevent nutrient deficiencies and support the overall health of astronauts.
• Psychological Benefits: Growing and tending to plants can have positive psychological effects, providing astronauts with a sense of purpose and connection to Earth. This can help to mitigate the isolation and stress of long-duration space missions.
• Microbiome Research: The PH-07 experiment also includes studying the microbiomes associated with lettuce plants. Understanding how these microbial communities interact with plants in space can provide insights into maintaining plant health and preventing diseases.

Conclusion

As we celebrate the International Day of Human Spaceflight, we also recognize the contributions of commercial space companies such as Sierra Space in advancing our capabilities for future long-duration space missions. The Plant Habitat-07 experiment is a prime example of how collaboration between NASA and commercial industry can lead to groundbreaking research with far-reaching implications.

By studying the impacts of substrate moisture on lettuce plants and microbiome development, Sierra Space and NASA are paving the way for sustainable food production in space. This research will not only benefit future astronauts but also contribute to our understanding of plant biology and microbiomes in extreme environments.

As we look to the future, the knowledge gained from the PH-07 experiment will be instrumental in ensuring the success of long-duration space missions, ultimately bringing us closer to realizing humanity's dream of exploring and living on other planets.