Exposed! The International Space Station tests organisms and materials in space

Space may look empty, but it contains extreme temperatures, high background radiation, micrometeoroids, and the sun’s unfiltered glare. In addition, materials and equipment on the outside of the International Space Station are exposed to atomic oxygen (AO) and other charged particles as it orbits the Earth at the very edge of our atmosphere. Only the toughest materials, devices, and organisms can withstand this harsh environment, and scientists working in the orbital laboratory have identified some of them with a variety of potential uses.

“There are ways to test the various components of space exposure individually on the ground, but the only way to get the combined effect of all of them at once is in orbit,” says Mark Shumbera of Aegis Aerospace, which owns and operates the MISSE Flight Facility ( MISSE-FF), a platform for space exposure studies on the station. “This is important because combined effects can be very different from individual ones.”

Missions to MISSE-FF, sponsored by the ISS National Lab, launch approximately every six months. Experiments began with the platform’s installation in 2018 and will continue for the life of the space station, Shumbera says. A previous MISSE facility, operating from 2001 to 2016, housed the first station-based exposure experiments.

Some of these missions help researchers understand how new technologies respond to the space environment. “Before you deploy a technology on an operational satellite or vehicle, you want to be sure that it will work in the space environment as you envision it,” he says.

MISSE-FF has high-resolution cameras that regularly take photos of all items on its exposure decks and sensors to record environmental conditions such as temperature, radiation, and UV and AO exposure. All test items are also returned to the ground for post-flight analysis.

NASA scientists have flown multiple missions on the MISSE-FF to analyze the effects of atomic oxygen and radiation on hundreds of samples and devices.

For example, MISSE-9 assessed how polymers, composites and coatings coped with exposure to space. For this and other MISSE missions, Kim de Groh, senior materials research engineer at NASA’s Glenn Research Center in Cleveland, is testing two primary environmental degradation effects. The first is how fast a material erodes due to the AO interaction. It measures mass loss in space-exposed materials and uses this information to calculate AO erosion yield values. These values ​​help spacecraft designers determine whether certain materials are appropriate for use and how thick those materials need to be.

Materials used as spacecraft insulation can become brittle in space due to radiation and temperature changes in orbit. This embrittlement can create cracks and cause problems such as B. overheating of a spacecraft component. De Groh also tests the durability of different materials to find those that won’t become brittle.

“The ideal situation is to actually expose samples to space to experience all of the harsh environmental conditions at the same time,” says de Groh.

The ESA (European Space Agency) EXPOSE-R-2 facility is another platform that offers scientists the opportunity to test samples in space. ESA studies that have used the facility include BOSS and BIOMEX, which exposed biofilms, biomolecules and extremophiles to space- and Mars-like conditions. Extremophiles are organisms that can live in conditions that are unbearable or even deadly for most life forms.

Increasing autonomy is crucial for future missions that are farther from Earth and cannot rely on resupply missions. Microorganisms that tolerate extreme conditions could be used in life support systems for such missions, according to Daniela Billi, professor in the Department of Biology at Tor Vergata University in Rome and researcher for BOSS and BIOMEX. For example, cyanobacteria can use available resources to fix carbon (convert atmospheric carbon dioxide into carbohydrates) and produce oxygen.

During exposure on the space station, dried Chroococcidiopsis cells received a dose of ionizing radiation equivalent to a trip to Mars. Their answer suggests the bacteria could be transported to the planet and rehydrated if needed. The dried cells were also mixed with a simulant of Martian regolith or dust and given a UV dose equivalent to approximately 4 hours of exposure to the Martian surface.

“The aim of this study was to verify whether this cyanobacterium can repair DNA damage accumulated during travel to Mars and exposure to unmitigated Martian conditions,” says Billi.

Recently published results suggest it can: DNA sequencing of cells rehydrated after exposure showed no increase in mutation rate compared to controls grown under soil conditions. This result increases the potential for using this organism to utilize locally available resources to support human settlements.

Another study using the EXPOSE-R-2 facility found signs of life in melanin-containing fungi after 16 months of exposure in space. Fungal melanin pigment appears to play a role in cellular resilience to extreme conditions, including radiation, and may have the potential to be used as radiation shields in future space missions. In the experiment, a thin layer of a melanized fungal strain reduced radiation levels by almost 2% and possibly up to 5%.

In addition to fungi, researchers used ESA’s platform to expose the dormant stages of around 40 species of multicellular animals and plants to space for the EXPOSE-R-IBMP study. The results showed that many of these organisms remained viable and even completed life cycles and reproduction over several generations, suggesting future voyages to other planets could take terrestrial life forms with them for use in ecological life support systems and to create artificial ecosystems.

As humans advance farther into space and stay there longer, tests conducted on the space station’s exposure platforms help ensure the materials and systems they take with them are appropriate for the journey.