In 2020, NASA put seeds from 11 crops aboard an experimental spaceplane; after months in orbit, scientists brought them back to test whether they could still grow

In 2020, NASA put seeds from 11 crops aboard an experimental spaceplane; after months in orbit, scientists brought them back to test whether they could still grow. The experiment was designed to study what happens to plant seeds when they remain in the space environment for a long period. Researchers wanted to examine the effects of microgravity and space radiation on seed viability, germination, plant development and molecular changes. The research was carried out through two experiments called RAD-SEED 1 and RAD-SEED 2. The experiments used the X-37B Orbital Test Vehicle-6, or OTV-6. The reusable vehicle is operated by the United States Space Force. It launched on May 17, 2020.

The research involved NASA Kennedy Space Center scientists and collaborators. The team included principal investigator Ye Zhang, Ph.D., along with Howard G. Levine, Ph.D., both from NASA Kennedy Space Center. Jeffrey T. Richards from LASSO Contract, Amentum, at NASA Kennedy Space Center, was also part of the team.

What the X-37B seed experiment studied?

The study focused on a question linked to future human missions beyond Earth. If astronauts travel to Mars or other destinations, they could need fresh food during missions that last for long periods.

Processed food can provide nutrition, but growing plants could add fresh food to the diet. Plant production could also provide benefits for astronauts during isolation and confinement. Before seeds can be used as part of such a food system, researchers need to understand how long-term storage in space affects them.

The study examined three main objectives:

• Measure how long-term exposure to the space environment affects seed viability and quality.
• Study how seeds respond to the space environment and why different species may respond in different ways.
• Test the OTV passive sample exposure platform for possible future missions involving biological samples.

The research hypothesis was that long-duration exposure to space could reduce seed viability and quality. Researchers expected that some seeds could show changes in germination and plant development when compared with seeds kept on Earth.

The 11 crops and two model plants

Researchers selected two model plant organisms and 11 crop species or cultivars for the experiments. The model plants were Arabidopsis thaliana and Brachypodium species. Both have been grown on the International Space Station.

The crop seeds included plants that have been or will be grown on the International Space Station. These were:

• Mizuna
• Lettuce
• Tomato
• Pak Choi
• Radish
• Hatch chile pepper
• Dwarf wheat

The research also included crops selected because they have different seed shapes and characteristics. These were:

• Chard
• Onion
• Rice
• Cucumber

Several of these crops have been grown under conditions that resemble spaceflight conditions in ground facilities at Kennedy Space Center. Some have also been grown on the International Space Station, including for possible crew consumption.

How researchers compared space and Earth samples?

The researchers did not rely only on the seeds that travelled on the X-37B. The project included ground-based control experiments so scientists could compare the results. Some ground control seeds were exposed to a modified GCRsim radiation environment at the NASA Space Radiation Laboratory, or NSRL, at Brookhaven National Laboratory.

The purpose was to simulate aspects of the radiation conditions experienced during the flight. Radiation dose and dose-rate measurements from the flight were used when developing the comparison scenarios.

The researchers also planned to compare the results with data from Kennedy Space Center ground controls, NSRL radiation experiments, the MISSE project and an HRP-funded Seed Radiation project. Published research would also be included in the comparisons. These comparisons were intended to create a database covering seed storage and crop production for future deep space missions.

What happened after the seeds returned?

After the flight, the researchers planned to grow the seeds under controlled conditions at Kennedy Space Center. The growing environment was designed to be comparable to conditions used for Veggie plant experiments on the International Space Station.

The conditions included:

• Temperature of 22°C
• Relative humidity of 40–45%
• Carbon dioxide level of 3000 ppm
• Light level of 300 μmol·m⁻²·s⁻¹
• A 16-hour light and 8-hour dark cycle

Seeds from each model plant and crop species would be planted and examined after six to 10 days, depending on the species. Researchers would measure germination rates and examine plant form and tissue structure. Images would be collected to identify signs of stress, developmental abnormalities and differences in root length.

At different stages of growth, seedlings would be preserved in RNAlater. This material could be used for transcriptomic and mutation analysis. The molecular work could help researchers understand why different plant species or variants respond differently to long-term space exposure.

How crop production was tested?

Researchers also planned to examine edible plant material from selected crops. The crops would be grown under the same controlled conditions and harvested between 28 and 90 days after planting, depending on the species.

The researchers would then examine features such as:

• Plant appearance
• Size
• Weight
• Other morphological characteristics
• Fresh produce characteristics

Fresh produce could also be examined for minerals and vitamins that are relevant to human nutrition. This part of the experiment connects seed storage with the question of whether plants grown from stored seeds could eventually contribute food during deep space missions.

Why seed storage matters for Mars missions?

Long-duration missions create a need for systems that can operate without frequent resupply from Earth. A mission to Mars would require food supplies for the journey and the time spent at the destination.

Seeds could provide one option because they can be stored and planted when needed. However, researchers first need to know whether seeds remain usable after spending long periods in a space environment.

Space radiation is one of the main concerns. Unlike Earth, deep space does not provide the same level of protection from radiation. Microgravity and other spaceflight conditions may also affect biological material. The RAD-SEED research therefore addresses a knowledge gap related to space radiation, seed storage and plant growth.

What the research could mean for future space agriculture?

The response of each crop species or variant could help researchers identify traits linked to plant growth in space. Such information could help select crops for future spacecraft and planetary habitats. It could also help researchers develop ways to protect seeds and crops from radiation exposure.

The X-37B provided a way to expose samples to the space environment and return them to Earth for examination. This capability allowed researchers to study the same seeds after their period in orbit. The data could contribute to plans for producing crops during deep space exploration and for establishing permanently inhabited planetary surface bases.

Possible uses for agriculture on Earth

The research also has applications beyond space exploration. Different crop species and variants may respond differently to environmental stress. Understanding these responses could help researchers identify plant traits associated with growth in harsh or extreme environments.

The findings could therefore contribute to agricultural research on Earth. The researchers' aim was not limited to determining whether seeds could germinate after space exposure. They also wanted to understand the biological mechanisms behind the responses.

The combined results from flight samples, ground controls and simulated radiation experiments could provide information for future research into seed storage, plant growth and radiation protection.