Nearly 250 miles above the earth, there is a satellite the size of a football field orbiting the Earth at around 17,000 miles per hour—the International Space Station. Since the launch of its first crewed mission in 2000, the ISS has been home to up to six astronauts at a given time, surpassing the Russian Mir station as the longest continuously occupied space station in low-Earth orbit.
Although the space station has hosted innumerable experiments, ranging from controllers for robotic Legos on Earth to growing lettuce, its most valuable use has been helping scientists learn about how long-duration spaceflight affects the human body—a crucial variable as our species begins plotting the details for our first sojourn on the Red Planet.
Generally speaking, astronauts who travel to the ISS tend to stay in orbit for a period of 4-6 months, which is enough time to learn quite a bit about human physiology in microgravity.
Perhaps the most seriously impacted organ in spaceflight is the brain.
Based on data from astronauts returned from the ISS, one of the most pressing problems for astronauts in orbit is the deterioration of their muscles and their skeleton. Since microgravity doesn't require astronauts to use many of the muscles they regularly use on Earth, such as the back muscles or leg muscles used when standing, these can decay rapidly. Indeed, NASA has documented up to 20 percent muscle mass loss in astronauts within just 11 days of arriving at the ISS. To combat muscle and bone atrophy in space, NASA launched the Digital Astronaut Project, which uses computer simulations to improve astronauts' already rigorous exercise routines.
Moreover, astronauts living in low gravity environments will also significantly affect bodily fluids. The human body is about two-thirds water and as anyone who has seen those videos where astronauts mess around with floating droplets of water in space will know, water acts really weird in zero G. While playing with the surface tension and cohesion of water makes for an entertaining video, it can also have serious effects on the body's ability to regulate crucial internal processes while in space. When an astronaut first arrives at the ISS, they will begin to have symptoms similar to that of a common cold (swelling of the face and nasal congestion) as their body fluids are redistributed to the upper portion of their body.
As the astronaut's body adjusts to weightlessness, their body fluids become more evenly distributed and the body doesn't have to work as hard to regulate blood pressure. While this may sound like a boon, it turns out it can have some pretty negative side effects, like a 20 percent reduction in blood volume, which in turn can cause the heart to atrophy because it has less blood to pump.
Although there are a number of other interesting physiological effects that have been discovered through living on the ISS (take for example, an astronaut's inability to shed tears because they stick together in a ball when the astronaut cries, or the loss of taste), perhaps the most seriously impacted organ in spaceflight is the brain. Although some of the psychological effects of going to space are positive (such as the so-called "overview effect," or the sense of peace and inner calm that results from seeing the Earth from above), generally speaking, astronauts are constantly under a lot of stress.
While doing somersaults in zero G might not sound stressful, one has to consider that these astronauts are living in an extremely hostile, high-risk environment—the smallest mistake could be the difference between life and death. Even with the best of preparations, there have been a number of close calls on the space station.
Take, for instance, the case of the Italian astronaut Luca Parmitano, who in 2013 had to terminate a spacewalk early after water from his space suit started leaking into his helmet and risked drowning him. As Parmitano would later describe the experience, he said he felt like "a goldfish inside a fishbowl" as water started leaking into his helmet.
Since liquid doesn't act the same way in microgravity (it balls up and floats around), keeping the liter of water that was floating around in his helmet out of his eyes, nose and mouth while he was trying to breathe in a space helmet was a tall order. Although Parmitano made it safely back to the ISS, the same suit he used was the culprit behind a similar malfunction last year, which resulted in a spacewalk being terminated early to save a NASA astronaut from the possibility of drowning.
During the early days of the space station, an astronaut on a spacewalk became coated in an inch of toxic frozen ammonia and had to remain outside the space station for a full orbit until the ammonia could evaporate from his suit. During what would have otherwise been a routine spacewalk, NASA astronaut Robert Curbeam was working on the cooling system of the brand new ISS, which uses ammonia due to its low-freezing point. Yet when the system sprung a leak and ammonia flakes started leaking from the piping, everyone on board knew there was a problem. After three minutes, Curbeam managed to close the leaking valve, but at this point his entire suit was covered in frozen ammonia, making him look like "Frosty the Snowman," according to another astronaut who was with Curbeam on the space walk.
To get the toxic chemical off his suit, Curbeam had to stay outside the space station for a full rotation around the Earth (about 90 minutes), so the sun could melt the ammonia crystals. Once safely back inside the airlock, he and the rest of the crew had to wear oxygen masks for about half an hour while the ISS filtered the toxins from the air inside the station.
Curbeam's ordeal outside the space station also calls to mind the luckless case of consider two Soviet cosmonauts in 1990, who were trapped outside the Mir space station when the airlock failed and they had to use an emergency entry procedure as their oxygen levels ran dangerously low. The two cosmonauts had been spacewalking to repair the thermal blankets on their transport craft, which had torn loose and jeopardized their safe return to Earth. After a five hour spacewalk and a successful repair of the craft, it came to light that the airlock door would not properly close and that the chamber was unpressurized. Running dangerously low on oxygen, the cosmonauts had to execute an emergency entrance procedure to get back inside the pressurized craft, although the Soviet account of how this was accomplished remains a mystery.
The Soviet account of how this was accomplished remains a mystery.
The Mir station also had a few other close calls in 1997. In February of that year, a canister of lithium perchlorate that was used to generate oxygen on board sprung a leak and caused a fire on board the space station, although the crew was able to extinguish the fire after about a minute and a half. But just a few months later, the Russian cargo freighter Progress collided with one of the Mir modules and punctured a hole in the space station, causing it to begin depressurizing. What could have easily been a deadly incident was resolved thanks to the quick thinking of the cosmonauts on board and the visiting NASA astronaut, who were able to seal the leaking module from the rest of the space station by cutting a number of cables that were preventing the hatch connecting the module to the rest of the space station from closing.
These are just a few of the numerous mishaps which have occurred while humans have lived in space aboard a handful of space stations, a good reminder that even with the best of planning, human error will always be a factor. All things considered, it's hard to blame astronauts for being a little stressed out, especially considering that many of them suffer chronic sleep deprivation in space as well (when you see the sunrise 15 times a day on the ISS, it can be hard to catch some shuteye).
Yet despite everything we know about the tolls that spaceflight can take on the human body, this was all based on data collected over a maximum period of six months, not nearly enough to understand the toll a journey to Mars (which will last upwards of a year and a half) will take on the human body. To rectify this, NASA began an unprecedented experiment last year, appropriately called 'The Twin Study.' This study sent Scott Kelly to the ISS for a full year while his twin brother, Mark, stayed on the Earth in order to study the effects of truly long duration spaceflight on the human body.
Although the first results of this year-long study are just beginning to roll in, NASA has already seen some interesting results. In the first place, a study on space flight and aging found that Scott's telomeres (a region of DNA that decreases with age) actually increased during spaceflight, something which the researchers attributed to increased exercise and a reduced-calorie diet. Moreover, another study found that Scott's stopover in space had no discernable effect on his mental abilities once he returned to Earth.
Another study, which is ongoing, involved complete genome sequencing of each twin. While each twin was found to have hundreds of unique mutations in their genomes, which was expected, the study also found that some 200,000 RNA molecules had expressed differently between the twins. Whether or not this is indicative of some sort of "space gene" that was activated during Scott's time at the ISS remains to be seen.
With human missions to the Moon and Mars on the books for the first time in decades, understanding how to live in the final frontier has become more pressing than ever. Thanks to the pioneering work of dozens of astronauts over as many years, who basically turned themselves into orbital lab rats, we now have a pretty good idea of how to not die in microgravity. A mission to Mars will bring its own set of physiological challenges (like the threat of radiation exposure), but without these preliminary experiments would be impossible. Staying alive in a microgravity environment will always be a challenge, but improved technology and lessons learned on Earth and in orbit have made the prospects of turning humans into a multi-planetary species more realistic than ever.
Subscribe to pluspluspodcast, Motherboard's new show about the people and machines that are building our future.