As an orbiting laboratory, the International Space Station (ISS) offers researchers around the world the unique opportunity to perform experiments in microgravity and under the rigors of the space environment. Scientists have used the station for everything from testing technology for future space exploration to studying human health. Sometimes their work involves some pretty unusual experiments. Here are 12 cool ones. 

1. Headless flatworms

On Earth, flatworms can regenerate their own cells, replacing them as they age or are damaged. Scientists cut the heads or tails off of flatworms and sent them to the station in September 2014 to study whether the cell signaling mechanisms behind this regeneration work the same way in space as they do on Earth.  The results should provide insight into how gravity affects tissue regeneration and the rebuilding of damaged organs and nerves, which is important for understanding how wounds heal—both in space and on the ground.

2. Space mice

For humans to explore deep space or live on other planets, we must learn how to deal with the effects of long-term exposure to potent space radiation, which can cause cancer and gene mutations, affecting subsequent generations. Lab mice are important tools for studying radiation effects, but currently, mice can’t go to the station. So instead, this investigation will send frozen mouse embryos for a ride in space and implant them into surrogate mothers on their return to Earth. Scientists will use these space mice to study longevity, cancer development, and gene mutations.

3. Talking Zucchini

In 2012, Astronaut Don Pettit wrote blog posts on behalf of a zucchini plant that was grown from a seed on the space station, one of many investigations on growing greenery in space. The ultimate goal is using plants to provide oxygen and fresh produce for crews on long-term space missions. Gravity plays an important role in normal plant growth and development, though, and not only is gravity nearly nonexistent in space, but plants also are affected by radiation, changes in light, and other factors of the space environment. The anthropomorphic Zucchini and its blog were a way to engage students with space-based research and encourage the next generation of space station scientists.

4. Putting out the fire

Fire behaves differently in space, thanks to complicated interactions of fuel vaporization, radiative heat loss, and chemical kinetics. Effectively extinguishing flames in space depends on understanding those interactions. This investigation, performed earlier this month, tested various fire suppressants in microgravity. Researchers found that flames in space burn with a lower temperature, at a slower rate, and with less oxygen than in normal gravity, meaning higher concentrations of materials must be used to put them out. The most surprising discovery was the way heptane droplets seemed to continue to burn under certain conditions even after the initial fire was extinguished. This phenomenon is called "cool-flame extinction." Those who understand conventional theories of droplet combustion say those theories don’t explain this behavior, making the cool flames a unique observation with significant theoretical and practical implications.

5. ISS, Robot

This two-armed humanoid robot torso mounted in the station can manipulate hardware and work in high risk environments to give crewmembers a break. Robonaut is operated via remote control and can be directed by ground operators through cabin video and telemetry. The half-a-mechanical astronaut also can be controlled by a crewmember wearing a vest, specialized gloves, and a 3D visor. Through this technology, Robonaut mimics the wearer’s movements in Wii-like fashion. In the future, the torso will be given legs and used to perform tasks both inside and outside the ISS.

6. Night lights—Lots of them

The publicly-accessible, online Gateway to Astronaut Photography of Earth contains photographs from space beginning with the early 1960s up to recent days. A million-plus of these images were taken from the space station, approximately 30 percent of them at night. These photographs are the highest-resolution night imagery available from orbit, thanks to a motorized tripod that compensates for the station’s speed—approximately 17,500 mph—and the motion of the Earth below. Scientists are asking for help cataloging the images through a crowd-source project called Cities at Night. It includes three components: Dark Skies of ISS, which asks people to sort images into cities, stars, and other categories (something computers aren’t good at); Night Cities, which relies on people to match the images to positions on maps; and Lost at Night, which seeks to identify cities within 310-mile-diameter images. Ultimately, the data generated could help save energy, contribute to better human health and safety, and improve our understanding of atmospheric chemistry.

7. Channeling Captain Kirk

Famous explorers kept journals that give us insight into what it took to survive extreme missions, such as reaching the South Pole. Spending months confined in cramped quarters orbiting the earth is one of today’s extreme missions, and for this study, researchers asked 10 crew members aboard the station to keep journals. Crew members wrote on a laptop at least three times a week, and investigators identified 24 major categories of entries with behavioral implications. Ten of those categories accounted for 88 percent of the text: work, outside communications, adjustment, group interaction, recreation/leisure, equipment, events, organization/management, sleep, and food. Men and women from various specialties such as science and engineering and both military and civilians participated. Studying small groups living and working in isolation and confinement is like studying social issues with a microscope, scientists say.

8. The Force is strong here

This project evaluated funky footwear designed to measure exercise load. NASA developed the Advanced Resistive Exercise Device, which supplies resistance through the power of vacuum cylinders, to give crew members the ability to do weight-bearing exercise in space. Weight-bearing exercise is critical to helping reduce the loss of bone density and skeletal muscle strength that astronauts experience during spaceflight. Four crew members exercised while wearing the high-tech, spring-bottomed sandals, which, like a kind of enhanced bathroom scale, measured the loads and the torque, or twisting force, they applied. The data will help determine the best exercise regimens for safe and effective bone and muscle strength maintenance during spaceflight.

9. Squids in space.

Hawaiian bobtail squids and their symbiotic luminescent bacterium take a ride to the space station. Rather than the start of a joke, this was part of an experiment, performed in September, to look at the effect of microgravity on microbe-dependent animal development and its implications for human health. The squid were inoculated with their symbiotic bacteria once in orbit on the space station and allowed to develop for approximately 24 hours. Researchers closely examined them and found that the bacteria were able to colonize squid tissue in microgravity conditions. The experiment also illustrated the feasibility of using these animals as subjects for microgravity research, so expect to see more squid in space in the future.

10. My microbes grow better than your microbes

For this project, people collected swabs of micro-organisms from museums, historical monuments, football stadiums, and weird places like Sue the T. Rex at Chicago’s Field Museum, the set of the Today Show, and the Liberty Bell. Scientists at University of California - Davis transferred those samples to Petri dishes, incubated them to see which grew into colonies, and identified 48 to send to the space station. Scientists need to know how various microbes behave in space before we seal up people and their microbes in a spacecraft for a long trip together to Mars. The 48 samples and identical cultures on Earth will be analyzed to see how their growth differs between microgravity and the ground. Each microbe has an online trading card that tells where it was collected, how well it grows, and some interesting facts about it.

11. Sloshing around the station

In space, liquids move differently than they do on earth, but the physics of this motion are not well understood. Researchers at the Florida Institute of Technology, Massachusetts Institute of Technology and NASA’s Kennedy Space Center performed a series of experiments on slosh dynamics in the station using robotic, free-floating satellites that can independently navigate and re-orient themselves. Researchers hope to design an externally mounted fuel tank that is driven from inside the station by two of these devices to simulate a launch vehicle upper-stage propellant tank and the maneuvers of real vehicles. The experiments will improve computer models of how liquid fuel behaves to make rockets safer.

12. Ant Farm

This investigation compared the behavior of groups of ants in normal gravity and in microgravity and measured how interactions among ants depend on the number of ants in a given area. Eight ant habitats with approximately 100 residents each launched to the space station, where scientists used cameras and software to analyze their movement patterns and interaction rates. Ant colony behavior is a combination of responses by individual ants to local cues, and previous studies suggest ants use the rate at which an individual meets other ants to determine how many of them are in the area. This estimation of group density is needed in many different situations, such as searching for food. When there are many ants in a small space, each ant moves round and round in roughly the same place, but when density is low, each ant walks a straighter path to cover more ground. Data on the ant colony’s adaptations can be used to build various algorithms, or sets of steps followed in order to solve a mathematical problem. For example, ant-based algorithms could help scientists develop cheaper, more efficient strategies for robot-based searching and exploration.