When you learn about the effects of spaceflight on human health, you usually hear about the dangers of radiation, loss of bone density, and changes in vision. While these long-term risks are important, a less frequently discussed concern is motion sickness.
As a child, one of us (Taylor) was very prone to motion sickness – sitting in the back seat of the car, sitting on the train or riding the bus. At the time, she thought it was a cruel twist of fate, but as an adult—and a scientist—Taylor can safely say it was entirely her fault.
You see, like most kids on long rides, Taylor would be bored. So, to overcome this boredom, she would read a book or play with her Gameboy. She would look down at whatever amusements were in her lap for the day until the familiar creeping nausea set in.
Sometimes a look out the side window would help, but mostly Taylor’s dad would have to take a break at another gas station or they’d all suffer the consequences.
Now she understands what happened on a fundamental level. As a child, you are taught about the five senses: sight, hearing, smell, taste, and touch. But there’s a hidden sixth sense that helps your body understand how you’re moving, the vestibular system. The brain takes information from all of these senses and compares it to what it would expect to be moving based on past experience.
Ideally, any discrepancy between your vestibular sensations and your brain’s expectations would be small. But when there are big, protracted conflicts, you get sick.
While reading in the car, Taylor stared at the still words on the page while her vestibular system told her brain that she was traveling on the road. This discrepancy messed with her brain, because normally when Taylor felt motion, she should see the world change around her in the same way – hence the motion sickness. If she had looked out the window and watched the world go by, she would have been fine. Even better, if she had been in the front seat, she would have been able to see the road ahead and predict how she would move in the future.
The sensory conflict between what you experience and what your brain expects causes more than illness. It’s also a prime suspect in cybersickness, seasickness on ships, and motion sickness caused by space flight from using virtual reality headsets. The latter is of particular interest to our team of aeronautical engineers.
Motion sickness during space flight
So far, all astronauts have grown up on Earth. Thus, their brains expect any motion signals to include the presence of Earth’s gravity. But once they’re in orbit in space, that’s gone.
When orbiting the Earth in microgravity, the vestibular system has no gravitational input. The conflict between the brain’s expectation of Earth’s gravity and the reality that there is no gravity causes space sickness.
Fortunately, the brain’s expectations can change over time with enough exposure to new environments. Often referred to as “sea legs” in the seafaring community, astronauts also eventually overcome space sickness in space. But after overcoming it, another problem arises when they return.
If an astronaut’s brain expects microgravity, what happens when they return to Earth? As you might expect, the process starts all over again, and the astronauts are now prone to terrestrial adaptation motion sickness. To make matters worse, the crew vehicles often launch into the water from the spacecraft’s exit, meaning the astronauts may have to deal with surging waves until their capsule is recovered. Seasickness can exacerbate terrestrial adaptation motion sickness.
These conditions are not uncommon. More than half of all astronauts experience some form of space sickness when they first enter space, and ground-adaptation motion sickness occurs at a similar rate when they return down.
Dangers to Astronauts
If you’ve ever experienced motion sickness, you know how hard it is to do anything but close your eyes and take deep breaths to ward off the creeping urge to throw up. As a passenger in a car, this can be good because you are not expected to be up and running instantly. But astronauts, isolated on water in a reentry capsule, must stay focused and clean. In the event of an emergency, they will need to respond quickly.
If astronauts have to exit the capsule before being picked up by a rescue team, any motion sickness can delay their reaction time and interfere with evacuation.
Possible solutions
Currently, most astronauts rely on drugs that disrupt the brain’s ability to use hormones to cause motion sickness. However, like many commercial products, these drugs can cause side effects such as drowsiness and may lose effectiveness over time.
Our research group completed two experiments to investigate how we could manipulate visual information to alleviate motion sickness in astronauts without relying on medication.
Our participants were exposed to motions designed to simulate the transition between a gravity environment and ocean wave-like motions. We investigated whether a “virtual window” could reduce the incidence of motion sickness during the hour of whale movement.
In a capsule on the ocean, astronauts are strapped to their seats and likely unable to see through small windows built into the capsule. Instead of windows, we used a virtual reality headset to create a full-view virtual window.
In our control group, subjects did not receive any visual cues of motion similar to Taylor’s ill-advised backseat reading. Meanwhile, one countermeasures group saw a visual scene that moved with natural movement, such as looking out the side window of a car at the world around them. Another response group saw a scene that was moving properly and was presented with an overlay that indicated future movement, such as looking out the front window and seeing the road ahead.
As expected, the no-exercise group got sick the most. Two-thirds of subjects had to stop before completing an hour of wave-like motion due to excessive nausea. Only about a fifth of the group given the side view had to stop early. Only one-tenth of the front window group that received present and future visual cues dropped out.
These results mean that by tracking the capsule’s motion and projecting it onto a headset for the astronauts inside, our team could cut debilitating motion sickness by about half. If we could figure out how to predict how the capsule would move, we could give them that front window experience and make the landing even better. They could always take the headphones off in case of an emergency.
This work shows promise for interventions for motion sickness that are independent of the drugs currently used to combat this effect. Our solutions do not have the same issues with shelf life, stability or side effects. In addition to benefiting astronauts, such techniques could help those prone to motion sickness here on Earth, especially in situations where it’s impossible to look out the front window at the road, such as on planes, trains, buses or high-speed transportation.
This article is republished from The Conversation, a not-for-profit independent news organization that provides facts and sound analysis to help make sense of our complex world. Written by: Taylor Lonner, University of Colorado Boulder and Torin Clarke, University of Colorado Boulder
Read more:
This work was supported by the National Aeronautics and Space Administration’s Human Research Program under grant no. 80NSSC21K0257.
Torin Clark receives funding from NASA, the Office of Naval Research, and the National Institutes of Health, and grants from the Charles Stark Draper Laboratory and the National Science Foundation.