It is one thing to understand that space alters the human body; it is another to see it happen before one’s eyes, on people and on plants, hundreds of miles above the ground. During more than seven months on the International Space Station, NASA’s SpaceX Crew-10 astronauts converted the orbiting laboratory into a testbed for the biology of exploration, exploring how microgravity and radiation transform living systems and how technology could help mitigate those effects ahead of humanity’s push to the Moon and Mars.
One of the most ambitious of these projects was a series of plant biology experiments that went well beyond basic growth tests. In the Rhodium Plant LIFE experiment, thale cress plants of both wild-type and genetically engineered varieties were grown to measure growth patterns in diverse orbital altitudes, following earlier work on the Polaris Dawn mission. These plants were not only food experiments; they were living sensors, demonstrating how the synergistic stresses of ionizing radiation and microgravity affect DNA. In companion research, the APEX-12 mission tested telomere function repeated DNA segments that protect chromosomes against space radiation. The telomeres are like a reporter for the physiological health of organisms and a biomarker for their ability to be healthy, said Dorothy Shippen, a principal investigator on plant telomeres in a space environment. Initial results from low Earth orbit indicated telomerase activity increasing greater than 150-fold, suggesting a protective function that would be essential for maintaining crops on Mars, where doses of radiation are 1–2 mSv per day.
Radiation’s danger to biology is not theoretical. In low Earth orbit, the astronauts are hit with galactic cosmic rays, solar particle events, and trapped protons and electrons, resulting in dose rates several hundred times greater than on the ground. Outside Earth’s magnetic field, shielding is a complicated engineering task: high-energy heavy ions are hard to stop without producing unwanted secondary particles. Research on the ISS, for example, JAXA’s PADLES dosimetry series, have been used to describe this environment in detail, guiding habitat design and biological countermeasures. Simulated galactic cosmic ray exposures on Earth in Crew-10’s plant trials showed dose-dependent activation of DNA repair genes such as RAD51 and BRCA1 and suppression of metabolic pathways associated with sulfur compound biosynthesis alterations which may influence nutritional quality as much as survivability.
Human physiology also came under scrutiny. Biomedical research on Crew-10 aimed at microgravity’s effects on vision, bone, muscle, and cellular function. Optical coherence tomography imaging monitored miniscule changes in retinal structure, part of a larger syndrome associated with fluid redistribution and, as recent findings indicate, mitochondrial oxidative damage in ocular tissues. In microgravity, mitochondrial function can bias towards augmented production of reactive oxygen species and impede ATP synthesis, leading to apoptosis in sensitive cells. These processes are now believed to underlie not just vision alterations but also vascular remodeling, immune suppression, and faster bone loss seen in long-duration crews.
Microgravity’s influence reaches down to the cellular level, where it causes disruption of cytoskeletal structure, modification of mechanotransduction pathways, and gene expression change in immune and cancer cells. On Earth, these phenomena are mimicked with rotating wall vessels and random positioning machines, instruments that average out gravitational vectors to near-zero. These simulators have demonstrated that T lymphocytes lose activation antigens such as CD25 and CD69 within hours, macrophage polarization tilts toward anti-inflammatory states, and endothelial cells lose stiffness and actin filament integrity phenomena also observed in spaceflight. It is important to understand these processes to develop countermeasures, from bespoke exercise programs to drugs that maintain mitochondrial and cytoskeletal well-being.
Not all of the work done by Crew-10 was biological in nature. The May 1 spacewalk Anne McClain’s third and Nichole Ayers’s inaugural was a mix of maintenance and technology demonstration. The duo also moved a communications antenna and started installing a roll-out solar array mounting bracket, a compact, high-output photovoltaic system that will add to the station’s power budget for science. These kinds of hardware improvements directly underpin energy-hungry experiments such as ELVIS, a holographic microscope that can record 3D motion of microscopic algae and bacteria. ELVIS’s capability to sense life signs in extreme environments would someday be applied to icy moons or Martian regolith.
Even the station’s microalgae cultures were multitasking. Crew-10 in the SOPHONSTER study evaluated how microgravity influences the yields of proteins in nutrient-rich species that might be used as sustainable alternatives to meat and dairy, or as the source of biofuels and medicines. Microalgae’s radiation tolerance and ability to recycle carbon dioxide make them top candidates for closed-loop life support systems, where each gram of biomass is precious.
The aggregate information from the Crew-10 mission directly inform future exploration system engineering. Radiation protection strategies can be a combination of material science breakthroughs and biological adaptation, choosing or bioengineering organisms human and plant that are tolerant of increased radiation loads. Microgravity countermeasures will probably include mechanical loading devices, custom exercise, and possibly artificial gravity habitats. And the biological findings that are derived from telomere dynamics, DNA repair mechanisms, and mitochondrial resistance will guide not just space agriculture and astronautal health, but also Earth medicine, from cancer treatment to regenerative therapy.
