Creating a renewable food source in space is essential for a sustainable human presence in space. Plants will likely be an important component of such a sustainable space life support ecosystem for the same reasons they are valuable on Earth. Plants provide both a food source and aesthetic value on Earth. They are also a valuable source of raw materials for products, such as cotton for clothing. In space, they provide the added benefits of recycling exhaled carbon dioxide as well as offering the ability to recycle other human waste. There is also the hope that growing plants in thematic environments of space will lead to new botanical discoveries that will be beneficial to Earth agriculture.
For over fifty years, scientists have been researching whether plants can grow in space and how they react to the space environment. That effort continues. This article will identify and discuss recent space research and its significance.
Plant research must occur in a suitable place in space. That space must be capable of providing a suitable pressure and temperature, radiation protection, and communications capabilities. Although it is possible to construct such an environment in a standalone satellite, locating plant experiments in a location that already possesses those characteristics, such as space stations, tends to be much more convenient. There are presently two such stations: the International Space Station (ISS) and the Chinese Tiangong space station. Most contemporary plant research in space is conducted in these two locations. There are two recent exceptions. First was the Chinese Chang’e 4 lunar spacecraft (2018–2019) on which cotton plants were grown for a short time. The other was the European Eu:CROPIS satellite (2018–2019) which made it to space, but then experienced a malfunction.
This article focuses on research conducted on the ISS. There are currently two chief facilities for plant experiments there. The Advanced Plant Habitat (APH) is suitable for more rigorous plant experiments that require considerable environmental control and sensing. The VEGGIE chamber is suitable for a range of experiments, and is especially well suited for growing. There are sometimes other facilities which will be covered in a future story.
Advanced Plant Habitat (APH) Experiments
Plant Habitat-03—Epigenetic Adaptation
The Epigenetic Adaptation to the Spaceflight Environment – Accumulated Genomic Change Induced by Generations in Space (Plant Habitat-03) is an important experiment from the perspective to developing plant species to improve specific traits. Anna-Lisa Paul, Ph.D. (University of Florida Space Plants Lab) is the principle investigator. The experiment arrived at the ISS on the Northrup Grumman Commercial Resupply Services Mission 18 on 9 November 2022. Results are expected some time in 2024.
In this experiment, Arabidopsis thaliana leaves from plants were grown across several generations of exposure to spaceflight conditions to discover epigenetic modification patterns over multiple generations. Arabidopsis thaliana is a plant species that is used as a benchmark species for plant research due to its relatively short DNA. Epigenetics refers to the way that genes express themselves. This is different than genetic modification such as DNA manipulation.
This experiment will help answer the question to what extent do epigenetic changes endure and evolve among generations in space. According to NASA, “results could demonstrate whether epigenetic changes transfer from the first generation of plants to the second and then continue to accumulate or stabilize. This could provide insight into how to grow repeated generations of crops to provide food and other services on future space missions.” (NASA, 2023).
This experiment builds upon the earlier experiment Epigenetic change in Arabidopsis thaliana in response to spaceflight – differential cytosine DNA methylation of plants on the ISS (APEX04) grown in 2017 in the VEGGIE chamber.
Microgravity Growth of New Mexico Hatch Green Chile as a Technical Display of Advanced Plant Habitat’s Capabilities (Plant Habitat-04) involved the cultivation of peppers aboard the ISS for the first time. Matthew W. Romeyn, M.S. (NASA Kennedy Space Center) is the principle investigator. Some differences were noted concerning growing peppers in space versus on Earth. For example, pepper production is delayed by about two weeks on the space station, possibly due to a delay in germination (possibly related to fluid challenges in microgravity, but slowed plant metabolism has been noted in at least one past experiment in space).
VEG 4A & 4B—Pick-and-eat Salad
In the 28-day VEG-04A Pick-and-eat Salad-crop Productivity, Nutritional Value, and Acceptability to Supplement the ISS Food System, experiment, Mizuna mustard plants, a leafy green crop, were grown for 28 days under two different light quality treatments in space, and the impact on crop growth is analyzed in terms of the differences observed in plant yield, nutritional composition and microbial levels. Gioia Massa, Ph.D. (NASA Kennedy Space Center) is the principle investigator. The VEG-04B experiment featured a 56-day grow-out (twice that of VEG-4A).
VEG 5—Pick-and-eat Salad
The Veg-05 Pick-and-eat Salad-crop Productivity, Nutritional Value, and Acceptability to Supplement the ISS Food System experiment, grew dwarf tomatoes to study the impact of light quality and fertilizer on fruit production, microbial food safety, nutritional value, taste acceptability by the crew, and the overall behavioral health benefits of having plants and fresh food in space. Gioia Massa, Ph.D. (NASA Kennedy Space Center) is the principle investigator. Tomatoes are a more challenging plant to grow for food purposes than the previous leafy vegetables grown on VEG-04, since tomatoes need to be pollenated to bear fruit (i.e. the tomatoes). Several tomatoes were successfully grown. However, tomatoes in space can sometimes be a challenge to harvest, as some of the tomatoes from that experiment went missing for several months (CNN: Tomato lost in space by history-making astronaut has been found, December 8, 2023).
Summary of Trends
We see two chief trends in the selection of plant experiments for space research. First, is an expansion of growing plants as crops for consumption in space, especially in terms of species. Recent experiments involving salad greens, tomatoes and peppers are beginning to make the ISS sound like a backyard garden. This is a major breakthrough in the progress of astroculture and has been a half-century in the making. Second, is an increase in longer lifespans and series of lifecycles. It has been difficult and resource-intensive to grow plants in space beyond more seedlings, but the capabilities to do so have become more established, as shown by the Space Habitat 03 epigenetic experiment, as well as the ability to grow multiple species such as tomatoes and peppers to fruition. There has also been a third trend, oriented towards growing plants on the Moon, such as growing cotton on the Moon by the Chang’e 4 mission, and the recent growth of plants in real lunar regolith by the University of Florida scientists, that will likely increase as the Artemis missions proceed.
- Epigenetic Adaptation to the Spaceflight Environment – Accumulated Genomic Change Induced by Generations in Space (Plant Habitat-03) (NASA, 2023).
- Other sources linked in the article.