Space Motion Sickness and Deafness

Introduction

With the advent of commercial human spaceflight, there is a growing number of space travelers who weren't selected into the NASA astronaut training program, but who have experienced spaceflight. If the experiences of government astronauts are any indicator, the vast majority of these commercial astronauts will experience space motion sickness at some point. Over 700 people have been to space, but there remains a lack of data about how to stop motion sickness in that environment.

This post is about a research opportunity a deaf test subject might have to offer human spaceflight. If it pans out, it might result in new selection criteria or new treatments to reduce space motion sickness. This is based on my direct experience and that of a few others, as well as several more decades ago.

The Gallaudet Eleven

Not many know that deaf people played an important role in the development of human spaceflight, even though they didn't get to ride rockets. In the early days of the space race, NASA and the Naval School of Aviation Medicine recruited several test subjects from the Florida School for the Deaf and Blind. The first tests in Pensacola led to NASA selecting eleven men from Gallaudet College (now University), the world's only liberal-arts college for deaf people. NASA wanted to test various responses to unusual gravity scenarios. The Gallaudet Eleven were different from the norm in a way that NASA needed. Most of them had become deaf from spinal meningitis, which also affected their vestibular systems - the system responsible for balance.

In the inner ear, balance is detected with fine hairs (ciliae) that register fluid shifts in the cochlea, a corkscrew structure in the inner ear not unlike a snail shell. The most commonly accepted explanation for motion sickness is that it comes from conflicting inputs from the eyes and inner ears, which triggers nausea and other adverse reactions in the body.

These ciliae are not only responsible for balance; they also transform the eardrum response into auditory signals to be passed on to the brain. Someone with a nonfunctional connection between the ciliae and the auditory nerve, either by the ciliae not working or missing synapses, often turns out as deaf. Hence the study on the Gallaudet Eleven.

Most of what I'm about to summarize in this section is from the 25th volume of Quest, which is the only journal that chronicles the history of spaceflight. Nearly all of it consists of letters from Robert Greenmun. He was one of the original test subjects in Pensacola and he was the one who suggested additional test subjects from Gallaudet College. He remained with the project for the next decade, leaving an extensive record of what happened. I urge you to go through the whole document in its entirety - some of it is quite hilarious reading.

The Navy/NASA team of researchers, led by Captain Ashton Graybiel, set up several test apparatuses with multiple physiological experiments and put the Gallaudet Eleven through each. They did it all without sign-language interpreters, instead communicating with the test subjects by paper and pencil.

The first was the Slow-Rotation Room (SRR), which is exactly as it sounds. It was a fully-furnished room that could turn at a maximum constant speed of 20 revolutions per minute. Greenmun and a few Navy staff spent some time in that room, and it always ended with the hearing men suffering in silence while Greenmun adapted easily to the altered environment.

Some of the comment over the intercom was amusing. One fellow said that all he wanted was to “get out of here.” Going back to past runs I found Price had commented “Greenmun is happy because the rest of us are sick,” and the “three healthy ones are all sick, but Greenmun is feeling fine.” Now I ask you, was that a compliment or an insult?

-Actual quote, Robert Greenmun

Other apparatuses were the Human Disorientation Device (HDD), the Coriolis Acceleration Platform (CAP), and a few ad-hoc ones like using one of the express elevators in the Empire State Building.

In 1964, they put ten of the subjects on an Army tug in choppy seas off the Nova Scotia coast to induce seasickness. A joint NASA-NSAM report described the conditions as brutal:

Bizarre stimulation of the subjects’ vestibular organs was provided during early February by means of a 145-foot long tug (former U. S. Army transport) travelling the 200-mile distance between St. Pierre/Michelon [Miquelon], off the coast of Newfoundland, and North Sydney, Nova Scotia, over a twenty-eight-hour period during a storm. Sea conditions ranged from moderate to severe and were characterized during the first eight hours by 40-foot waves, 40-knot winds, and 80-knot gusts. The ship endured >40 degrees of roll, a roll rate of >10 degrees/second, and scend [surge] of >3G as indicated by acceleration recordings.

Not a single deaf subject got seasick, even though the test had to be cut short because the hearing researchers were suffering extreme seasickness!

The most relevant experiment was, I think, the one on a modified C-131 aircraft which simulated periods of microgravity by 1) accelerating upward on a 35-degree pitch, then 2) peaking at the apogee to cause 15 seconds of freefall, and plunging back to earth at a negative pitch until 3) bottoming out to start the cycle over again. The below figure is for a more modern aircraft doing a slightly different trajectory from that particular C-131.

By Greenmun's account, he and six other deaf men rode on that aircraft and experienced microgravity multiple times (the exact number is not given). They also rode on Navy dive bombers, some other aircraft, and on additional boats, with zero incidents of motion sickness.

By all accounts, the Gallaudet Eleven enjoyed their adventures in different gravity environments. They reported no adverse reactions. John Glenn, the first American to orbit the earth, was said to be jealous of their ability to resist motion sickness, while he was not able to during his own motion tests.

My Microgravity Experiences

I am the first deaf person to fly in microgravity since the Gallaudet Eleven. I led a student flight experiment with NASA in 2011, on the Boeing 727 G-Force One aircraft chartered from Zero-G Corporation, nicknamed the "Vomit Comet". In 2021 and 2022, AstroAccess selected me to fly on the very same aircraft. AstroAccess is a nonprofit organization founded in March 2021 to further the inclusion of disabled people in spaceflight. Our goal on these flights were to see how well people with various disabilities (deafness, blindness, paralysis, amputations) could perform tasks in microgravity. The results were more than stellar. Several people from SpaceX, Blue Origin, Virgin Galactic, and NASA have flown with us, including actual astronauts. The knowledge we generated from our flights is being evaluated in the space industry to create guidelines and accommodations for future spaceflights.

But let me back up to the 2011 flight with NASA. During the on-site work period leading up to that flight, we were in an open hangar for 10 hours a day for a week, in Houston in June. A Houston summer is no joke. I soon got nauseous from constantly being in 100 degrees F and 100% humidity, and it seemed like I was the only one in my team of four and in the larger cohort of about fifty student researchers, which was pretty demoralizing. So when the NASA staff offered us anti-nausea pills for our flight, I took them just to stop the misery I was experiencing right on the ground. I wasn't thinking about motion sickness in the air... because I had never suffered it, not even on turbulent flights.

I remember my nausea receding before we boarded the aircraft. The interior of G-Force One was air-conditioned, and when it reached altitude, it was somewhat cold. That and the pills killed off my nausea, and I found myself energized for the parabolas to follow. The NASA flight had experiments padded in pool foam and bolted to the floor so we weren't allowed some physical movements, such as turning upside down, for safety reasons. As the flight progressed, I watched four researchers (out of 20) retreat to the seats at the back of the plane so they could throw up into bags with the help of staff. Some more people did throw up into their issued barf bags, but not severely enough to move to the rear. For my part, I was thrilled and carefree. We completed our experiment without issue except for a technical difficulty that wasn't obvious until we returned to the ground and the other half of my team re-flew it a day later.

I thought it very strange that I suffered nausea on the ground, but not in freefall while some of the other student researchers did. I believe that the vast majority of us took the pills. Yet it seemed to affect each person differently. Some people still got nausea even after taking the pills. These observations led to a lingering suspicion that I had some kind of advantage in freefall. When I found out years later about the Gallaudet Eleven, that confirmed it.

Fast-forward 10 years to 2021. After I was selected to each AstroAccess flight, I consulted with their physicians and decided to skip the pills entirely. With the Gallaudet Eleven in mind, I wanted to see if I really had an immunity to motion sickness without any medication to mask it. The other deaf flyers took them just to be safe. The AstroAccess flights differed from NASA's in that each were shorter, with 15-18 parabolas to NASA's 32. The 2021 flight was from Long Beach, California in October and the 2022 flight from Houston in December, so the ground environment was much more pleasant. This time, we were allowed to go inverted. I gleefully took advantage of that opportunity by spending half of AstroAccess Flight 2 upside down while doing ASL comprehension tests with my partner Sheila Xu, keeping my head on a swivel the whole time. I mention this to give you an idea of how little I was affected by motion sickness (read: none at all). After each flight, we (me, Apurva, Sheila, Vicky, Renee) agreed that we could have easily withstood more parabolas.

As of December 2022, 9 deaf men (including me) and 3 deaf/hard of hearing women have flown in microgravity. None of us suffered motion sickness. In both AstroAccess Flights 1 and 2, the rate was definitely higher in the non-deaf group, even with the pills.

Deafness and the Vestibular System

In 2012, I took a genetic test from the now-bankrupt company 23andMe. It revealed that my deafness was caused by a mutation in the GJB2 gene, called 35delG. This is a common mutation, occuring in >60% of deaf people. The GJB2 gene encodes a protein called connexin-26 which mediates the signals between ciliae and the auditory nerve. I didn't understand the connection to balance until I came across this paper about the prevalence of vestibular dysfunction in my type of deafness (DFNB1). Apparently, DFNB1 is also associated with physical abnormalities in the vestibular system. Some people with it experience vertigo and motion sickness in mundane situations, while others have no vestibular response at all.

Balance problems have been reported as well in survivors of meningitis who became deaf from the disease, although the Gallaudet Eleven didn't suffer from these. We can take away from these studies that damage to the vestibular system is very common among deaf people, but it seems to affect each individual differently. Maybe your vestibular system needs to be affected in "just the right way" for you to be immune to motion sickness.

Personally, I've always had good balance. Anecdotally, most of the deaf people I know don't have issues with balance or motion sickness. If we have dysfunctional vestibular systems, our brains must have adapted to compensate for it. Our 100% success rate in freefall was probably due to the fact that we knew about our lack of sensitivity to motion sickness before applying to AstroAccess. We have flown in aircraft, ridden roller coasters, and scuba dived without feeling nauseous.

But does that translate to motion sickness in space?

Space Motion Sickness

Space motion sickness (SMS) is a subset of Space Adaptation Syndrome (SAS) that astronauts experience as their bodies acclimate to microgravity. It is distinct from the motion sickness that is experienced in cars and aircraft. Terrestrial motion sickness is experienced when one's surroundings are perceived to be motionless while the body is in motion. In space, it's the opposite. That's why the first astronauts did not experience much motion sickness - because their capsules were tiny and did not provide much room to move around in. When crew habitats grew in size, from Apollo to Skylab to Shuttle and finally the ISS, we saw the occurence of SMS skyrocket.

It's not just nausea. It's also increased body warmth, sweating, vertigo, vomiting, fatigue, loss of appetite, and anorexia, all things that impact astronaut effectiveness. The research literature shows there to be some energy directed towards minimizing SMS and its symptoms. This isn't surprising since each crewed space mission represents a serious investment of time and money.

To date, there is no way to predict who will get space-sick. Even experienced fighter pilots who routinely executed high-G maneuvers during their combat missions aren't immune to it. Senator Jake Garn of Utah was a highly accomplished fighter pilot with more flight hours than any NASA astronaut. When he went up on STS-51D in 1985, he quickly developed SMS so severe he couldn't do anything for the duration of the mission (about a week). Another Shuttle astronaut, Steven Smith, had this to say in an interview (paywalled):

Your body just isn't built to deal with zero-gravity. But there's no way of predicting how someone will handle it. Someone who gets car-sick all the time can be fine in space - or the opposite. I'm fine in cars and on rollercoasters, but space is a different matter.

Steven Smith, NASA astronaut

About 70% of astronauts get some degree of SMS within the first 72 hours after entering microgravity and returning to gravity, as described in this review article. That's with medication. That's notable because 53% of NASA astronauts were selected from military pilot service, where sensitivity to motion sickness should have been weeded out early in training.

It matters because SMS is not just unpredictable; it can be debilitating if not deadly. It is disruptive of operations to the point where NASA Mission Control has to avoid scheduling any spacewalks for the first few days of a mission, until the crew's SMS symptoms disappear. A survey of pharmaceological countermeasures discovered that while they can help mitigate SMS symptoms, they are associated with side effects that can be detrimental to mission success.

Even artificial gravity isn't a solution. A person prone to motion sickness would be affected by the Coriolis force inside a rotating habitat. Minimizing the Coriolis force would require a larger spin radius and slower revolutions, increasing the mass and complexity of the spacecraft. It seems plausible that rotating habitats would be mostly relegated to space stations and not spaceships, because the increased mass will reduce acceleration from thrust and rotating sections cause gyroscopic forces which add stress on a spacecraft as it changes orientation.

Implications

The sensory-conflict hypothesis of motion sickness implies that space motion sickness is the opposite of terrestrial motion sickness. The variety of responses seen in astronauts shows that vestibular systems vary in their responses to different types of relative motion. To date, there has not been an astronaut launched to space who had a known vestibular dysfunction.

It has been established that some deaf people do not suffer from motion sickness on Earth, but we do not know for certain if that translates to space motion sickness, where the triggers are different. I hypothesize that because some deaf people do not experience motion sickness on parabolic aircraft where freefall lasts 20-30 seconds, they would experience no motion sickness in prolonged microgravity. Suborbital flights will not be sufficient to investigate this because their timeframes are too short. A flight on Blue Origin's New Shepard is only 11 minutes long, with about 3 minutes of weightlessness. On an orbital mission, SMS symptoms start developing within the first hour. Based on that, I would argue this investigation is worth a few slots on an orbital crew. The benefits of finding an effective and predictable countermeasure to SMS are obvious.

What would a complete theory of motion sickness do for us in space?

Knowing the cost of crew time, and the complications of pharmaceological countermeasures, it makes sense to select crew who are known to be (or can be made) immune to SMS. The benefits would be more pronounced on short missions than longer ones, where there's less time to adapt, but there is still a case for choosing SMS-immune crew for interplanetary missions. Again, SMS affects the return to a gravitational field as well as the speed of adaptation to microgravity.

The journey to Mars takes 7-9 months with chemical rocket propulsion. A realistic near-term nuclear propulsion option would reduce this flight time to 3-4 months. This much time in freefall will cause problems upon landing, as evidenced by the medical attention returning astronauts undergo.

Would vestibular-compromised astronauts, deaf or hearing, be less affected upon entering and leaving microgravity? If so, is there a relationship between hearing and vestibular status and immunity to space motion sickness?

I intend for you to take away the following from this post:

• Space motion sickness is not the same as terrestrial motion sickness
• That said, the triggers for each seem to be the opposite, and so can be investigated with test subjects who do not have functioning vestibular systems.
• Some deaf people do not suffer from motion sickness due to different vestibular systems, and these results could be generalized to space motion sickness
• Space motion sickness is a crucial issue to address for future space missions, and so a complete theory is required

If it wasn't obvious before, I would volunteer for such an opportunity. I have no doubt my AstroAccess peers would too.

'Til next time!