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Getting sick at home, where you can rest in bed, is bad enough, but getting sick in space does not sound like fun. So space agencies have been monitoring their astronauts' health before, during, and after missions to try to prevent people from getting sick in space.

And researchers are coming up with technology to keep them healthy during missions. Here's Reid to explain why it can be easier to get sick in space.

[Reid] If you set out to design the perfect method of disease transmission, you probably couldn't do much better than a spaceship. You're crammed together in a small space with a bunch of other people. Every bit of air breathed out by one person is going to get breathed in by someone else. As if that wasn't bad enough, actually getting sick in space is way worse than getting sick here on Earth.

It's harder for your immune system to fight off the infection, and microbes can actually get stronger in space. So with NASA and companies like SpaceX finally thinking seriously about how to get humans to Mars, making sure people don't get sick is pretty high on the list of priorities. One problem is that weight and power are incredibly limited for anything that gets sent into space.

That lack of power makes it pretty much impossible to use the kind of high-quality air filters found in places like hospitals. There's another kind of filter that's also not available on spacecraft: the pull of gravity. Particles in the air generally drift downward, which is how that layer of dust on the top of your bookshelf keeps reforming.

It's not just dust, though. Imagine what happens when you sneeze in space. Instead of falling to the ground, everything you sneezed out just floats around, waiting to be breathed in again.  Gross. 

To make matters worse, places like the International Space Station don't really have separate rooms for different tasks. For example, one section contains the main control computers, a greenhouse, a treadmill, a stationary bike, two crew quarters, and the main cooking area. That's a recipe for a lot of germ exchange.  All this is just the setup, though, for what happens when those germs get inside the astronauts.

For reasons researchers are only beginning to understand, simple organisms like bacteria get stronger in space, while complex ones like us get weaker. After just days in orbit, astronauts start losing muscle mass and bone density. And most critically, their immune systems start to weaken.

That means cuts and bruises take longer to heal, and bone marrow doesn't regenerate as easily. The terrifyingly named "natural killer cells" that help fight off infection, well, they kill less.

These symptoms aren't unique to space travel: submarine crews and antarctic explorers can end up with weakened immune systems too. It's what's trying to kill you that makes space so much scarier.

While humans are suffering, microbes seem downright thrilled to be up there. Bacteria cultivated on the ISS, for example, grow thicker cell walls than their siblings back on Earth. Which makes things like anti-bacterial soap less effective at killing them. And not only do individual cells get stronger, the large-scale communities they create do too.

Some kinds of microbes build slimy, 3D structures called biofilm. Bacteria on the old Russian space station, Mir, formed biofilm so effectively that eventually nearly every available surface was covered in one. Again, gross.

Things like bacteria tend to get stronger in space because of the weightlessness. On Earth, things tend to settle out of a fluid in layers based on their density, which can separate microbes from their food. But in microgravity, everything will stay more evenly mixed, which gives microbes easier access to nutrients.

Everything in space is also exposed to a lot more DNA-altering radiation, which can make simple organisms mutate faster.   In one study carried out on Mir, after just 40 days in orbit, bacteria more than doubled their mutation rate. That leads to a lot more variety for our immune systems to deal with.

NASA and the other space agencies take these threats seriously. Astronauts are quarantined before they leave Earth, and almost everything they touch is sterilized before being sent to orbit. The crews themselves are also composed of some of the healthiest human beings in the prime of their lives. Despite that, in a study of more than a hundred space shuttle flights, researchers identified twenty-nine cases of infectious disease transmission between members of the crew.

For missions lasting no more than about a week, this wasn't that big of a deal, and astronauts on the ISS always have capsules available to get them home if there's an emergency. But imagine finding out one week into year-long mission that you've got a serious infection and no chance to return to Earth. Once we figure out how to deal with that, we'll be ready for our first long term trip out into to solar system.

[Hank] That video was from 2017 before we were all intimately familiar with the whole close-quarters, droplets flying around thing. And since space seems to be a pressure cooker for sickness ,it is no surprise that astronauts have had health problems crop up during missions. Here's one example of a health scare during the Apollo 16 mission.

[Reid] Stories about human space flight are usually full of heroism, math, and the triumph of human ingenuity over incredible odds. The story of how an astronaut got the farts on Apollo 16 is no exception. It all started on the Apollo 15 mission, which landed on the moon in 1971. The mission was successful, but while they were in space the astronauts experienced some arrhythmia, or irregular beating of the heart.

Arrhythmia can signal all kinds of serious cardiovascular problems, like heart attack and stroke. So even though the astronauts made it back just fine, NASA very much wanted to make sure that astronauts on future missions avoided arrhythmia while they were in space, where humans have yet to establish any solid healthcare infrastructure. So NASA physicians did some blood work on the Apollo 15 crew when they returned to Earth and found that they had too little potassium in their systems, a condition called hypokalemia.

Potassium is super important for your heart, because it's a major part of nerve cell function and your nervous system is what controls your heartbeat. Specifically, potassium is used in the sodium-potassium pump, which is found in all kinds of cells, including those in every part of the nervous system. An enzyme separates out the sodium and potassium on either side of a nerve cell's membrane, building up voltage across the cell surface. For carefully timed bursts of cellular activity, you usually want the cell's membrane to reach a particular voltage before firing, called the action potential.

Once you hit that voltage, the cell fires. Otherwise it just waits for the voltage to build up again. A network of nerve cells throughout the heart rely on the sodium-potassium pump, among other cell-signaling pathways, to time your heartbeat. If components of that system fall out of whack--like, if you aren't getting enough potassium--your heartbeat can get off-kilter.

So, be sure to eat your bananas, friends. But back to our astronauts. To keep the Apollo 16 astronauts safe from the arrhythmia experienced by the Apollo 15 crew, NASA prescribed a ton of potassium. Not enough to mess up the sodium-potassium pump in the other direction, but still a whole bunch. Potassium is typically very bitter, so, it needs to be dissolved into something with a lot of flavor.

NASA decided to use lots of citrus drinks. The crew had various citrus-flavored rehydratable drinks that they had to drink every day, multiple times a day. As you can probably imagine, the astronauts got really tired of this.

And the diet had some physical downsides, which we know because NASA records all its communication with astronauts and makes the transcripts publicly available. At one point, the mission commander John Young was unaware that he had a hot mic, and well, I'll just let you listen to what he said to fellow astronaut Charles Duke. 

"I've got the farts again, I got 'em again Charlie. I don't know what gives 'em to me... I think it's acid stomach, I really do. I haven't eaten this much citrus fruit in 20 years! I'll tell you one thing, in another 12 days I ain't never eatin' any more."

So, of course, the press reported this, and because farts are always funny, everyone had a good laugh about it. That is, everyone except for Florida Citrus Mutual, the organization representing Florida's citrus industry. They issued some official statements saying that the astronauts were using artificial citrus drinks, and not wholesome Floridian O.J. (part of this complete balanced breakfast). So, citrus is not to blame, and they would like you to please continue to buy their products. And that was true; the flatulence wasn't caused by fruit, it was the potassium.

See, potassium is used in another enzyme pump in the digestive system. It's the hydrogen-potassium pump. Your stomach acid is kept nice and acidic by an enzyme that pumps potassium in, and hydronium ions out. The hydronium quickly dissociates to regular water and free hydrogen ions. Having free hydrogen ions in a solution is what makes it acidic. In fact, pH stands for "power of hydrogen". So, all the extra potassium the astronauts were taking in caused the hydrogen-potassium pump to overwork, which gave them... the farts. But their heartbeats were good and steady, so at least they solved that problem.

There has actually been a great deal of research into space farts by NASA, because they pose a safety hazard. Methane is a flammable gas, so having a container of people emitting flammable gas on top of a rocket could conceivably pose some problems. But the amount of methane the Apollo 16 astronauts produced didn't cause a fire, and the astronauts didn't experience an arrhythmia. So, unfortunately for the Apollo 17 crew, NASA physicians required the potassium diet for them too.

[Hank] Luckily, all of these astronauts were able to complete their missions; but some health problems cannot be fixed with preventative care, so here is how we could treat space sickness in real time, one day soon.

[Hank] We've known for quite some time that space travel can do a number on human health. In addition to the common injuries and illnesses that people always face, space exploration adds new risks: from radiation exposure to bone density changes. Plus, the immune system can struggle to do its job under the challenging conditions of microgravity, while some viruses get even stronger. No thank you, space shingles!

Getting to the nearest hospital from orbit is no easy feat either, and, on a future mission to Mars, it might be downright impossible. So as our species prepares for longer, farther journeys into space, we need to up our space medicine game as well. The good news is that medical science has already made amazing advances in diagnosing and treating conditions that pop up in space.

Even so, the options for medical equipment are still quite limited, due to storage issues and the high cost of getting them into space in the first place. Instead, the focus is on preventing and controlling any hazardous situations. That way, doctors can catch health issues early before someone gets to the point of being unstable or critically ill—because, if it got to that point, that could make a trip home impossible, even from low orbit.

Knowing an astronaut's white blood cell count could help determine how severe their illness or infection is and track how they're responding to treatments during long-haul missions. The trouble is, getting that count requires drawing and analyzing a patient's blood. Historically, that simply hasn't been possible in space.

In part, we can blame microgravity for this, because it changes how fluids behave. Traditional analysis techniques don't work in space because they were designed to count and identify cells in a way that requires blood samples to flow as you would expect under normal gravity conditions. On top of that, analysis equipment is too bulky to be easily taken on a spacecraft.

Astronauts today draw their blood and freeze it until they return to Earth; that's helpful for long-term research but useless for an in-the-moment diagnosis. But all that may be about to change thanks to an innovative blood analysis technology called Hemocue.

Hemocue is the first machine to successfully analyze white blood cells in space, using only the tiny prick of a finger. It requires less than a milliliter of blood for the test, which saves a lot of time and effort compared to dealing with tubes full of blood. Better still, the approach doesn't require any added liquid substances, like those typically used for terrestrial blood analysis. Plus, the device is small, about the size of a toaster, and the small sample size gets around a lot of the hassles that microgravity creates for traditional techniques.

That's a significant contrast from most blood analysis machines which require large quantities of added compounds and generate a lot more biohazardous waste from larger blood samples. The Hemocue technology was tested on the International Space Station in 2021 with promising results, opening the door to identifying and monitoring a variety of health conditions on future space flights. Diagnosis is not the only medical realm scientists are trying to improve on in space.

Say an astronaut does end up discovering a health problem through a blood test. They'll probably want to treat it as soon as possible, so it doesn't become a bigger issue. For many ailments, that treatment comes in the form of medication.

The ISS stocks nearly 200 different medications on board, which, yes, is a lot, but it is not an exhaustive list, and there can only be so many of any given pill. In 2017, NASA tracked the drug consumption of six space station crew members: on average, each used four different medications per week. That amounted to around 450 medication uses per crew member over the five to six month-long missions.

The longer the mission, the larger the pharmacy you would need on hand. Just the volume of medication needed for a years-long mission to Mars would present serious storage challenges. So to plan around this, NASA is funding research focused on the manufacture of medicine in space!

One possibility is to genetically modify a plant, like lettuce, to turn it into a drug factory. In 2020, researchers at the University of California began developing a lettuce that produces a drug used to treat osteoporosis. Now, this work is in the early stages and, even if the medicinal lettuce successfully produces the desired drugs consistently, there's still the problem of how to get it into the astronauts.

The researchers are still unsure how the drug might be extracted from the lettuce—though it would certainly be nice if it were as simple as just having a salad. And if that isn't sci-fi enough for you, one of the more wild ideas is to implant each astronaut with their own little tiny drug factory. A special device that's inserted inside the stomach, known as a gastric resident system, is already being developed to help manage the daily doses required for tuberculosis infections here on Earth.

This device could be taken one step further for use in space, not only releasing but creating necessary medicines right inside the guts of those who need them. The core of this system would be a bacterium, like E. coli, which is already used to produce drugs in other contexts. The embedded bacteria could produce and then slowly release melatonin, acetaminophen, or even caffeine.

While overcoming some of these challenges, like dealing with microgravity, are unique to spaceflight, others might have more earthly applications. Sure, outer space might be about the hardest place to make a delivery, but getting medicines to remote communities in far-flung areas isn't a picnic either.

With luck, breakthroughs made to enable the exploration of the solar system will translate to increased access and better equity here on Earth. And if, one day, taking a life-saving drug involves nothing more than snacking on a tasty salad, sign me up.

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