Posey's Moonshot

Why Astronauts Train for Spacewalks Underwater

To replicate true zero gravity conditions without actually going to space, would-be astronauts usually have to take parabolic flight. But sometimes, as Brien explains, they have to go in the opposite direction.

When I was a kid, I heard people say that being underwater while scuba diving was almost exactly like being weightless. Of course, the fact that none of those people had ever been weightless before was lost on me.

However, I had seen pictures of astronauts training in a large swimming pool (NASA's Neutral Buoyancy Lab in Texas), so I assumed that scuba diving and zero gravity were a lot alike. For a long time, I was completely obsessed with the idea. I wanted to learn to dive in the worst kind of way so I could experience weightlessness for myself. As soon as I was old enough, I learned how to scuba dive and have been an avid diver ever since.

As much as I might love diving, though, scuba diving has little in common with zero gravity. After all, gravity doesn't just go away because you are underwater. If you do a head-first decent, for example, you can feel the blood rushing to your head just as it would if you were upside-down on dry land. Zero gravity isn't like that at all. When you are weightless, being upside-down feels exactly like being right-side-up.

Zero gravity is kind of an odd sensation, at least until you get used to it. When you are weightless, some of the blood that is normally in your lower extremities tends to go upward. It makes you feel a bit stuffy, as though you have a mild cold. Another unfortunate side effect is that zero gravity causes your face and torso to appear a bit fuller. I once sent a video of some of my zero gravity work to a family member who responded by saying they couldn't believe how much weight I had gained. In reality, I hadn't gained any weight, but zero gravity often creates the illusion of weight gain.

So if scuba diving feels nothing like real weightlessness, why do astronauts train underwater? The only way to create true weightlessness without actually going to space is through parabolic flight. A parabolic flight involves putting an airplane into a dive. The airplane plunges toward the ground at the same speed as gravity, effectively canceling out the effects of gravity. Although parabolic flights give you exactly the same experience as being in space, the periods of zero gravity don't last very long. There are a number of factors that determine how long the weightlessness can last, but it is usually somewhere between 20 and 30 seconds.

Even though an underwater environment does not truly recreate the space environment the way that a parabolic flight does, it still serves as a decent analog. Spacesuits can be weighted in a way that makes them neutrally buoyant, giving the astronaut the illusion of floating weightless, but with a few differences. For example, when I wear a spacesuit in zero gravity, I am actually floating inside of the suit. That doesn't happen underwater.

Of course, the tradeoff is that an underwater environment doesn't limit you to experiencing just a few seconds of weightlessness at a time the way that parabolic flight does. Parabolic flights also have a tendency to cause severe motion sickness, but that doesn't happen when you are working underwater.

Long before I ever applied to become a commercial astronaut candidate, I wanted to try an underwater extravehicular activity, or EVA -- essentially, a spacewalk. After all these years of training to go to space, though, I still haven't had the chance. That may be about to change, however. As the world slowly begins to reopen, the hands-on portion of my spaceflight training will eventually resume. Right now, I am tentatively scheduled to do an underwater EVA at the end of May, assuming that there are no more lockdowns.

To say that I am super excited about doing an underwater EVA would be an understatement. Even so, there is a lot more to an underwater EVA than just putting on a spacesuit and getting into a swimming pool. Next week, I begin a 12-week online instruction to prepare for the underwater EVA. Keep in mind that I already know how to use a spacesuit, so the online instruction has nothing to do with spacesuit familiarization (although it's possible that I would be using a different type of EVA suit than I am used to, or possibly even an analog EVA suit). Instead, it focuses on risk mitigation, protocols, airlock operations and things like that. There is also going to be discussion about the tools I will be using while underwater and the tasks I will be completing.

Anything could change by the time I actually do the underwater EVA. As it stands right now, however, I am told that I will be working through three tasks and may also be working through a simulated emergency, such as a suit leak.

The EVA is currently scripted to begin in an airlock that is similar to the one used on the International Space Station. After opening the airlock, I am to open a toolbox and retrieve a wrench, then make my way along a series of handholds to a specific location. In doing so, I will be using tethers to avoid floating away, just as I would if I were in space. Once I arrive at the designated spot, I am supposed to use the wrench to open a panel, connect some electrical connectors, then close the panel.

I don't have much information about the second or third tasks yet. I have been told that the second task will involve some sort of payload installation requiring the use of tools and foot restraints, but that's all I know. I haven't been given any information yet about the third task.

If past experience is any indication, I'm sure that my underwater EVA will be technically complex, physically demanding and probably a little stressful with people scrutinizing my every move. Even so, I am thrilled to be getting the opportunity to experience something so unique.

About the Author

Brien Posey is a 22-time Microsoft MVP with decades of IT experience. As a freelance writer, Posey has written thousands of articles and contributed to several dozen books on a wide variety of IT topics. Prior to going freelance, Posey was a CIO for a national chain of hospitals and health care facilities. He has also served as a network administrator for some of the country's largest insurance companies and for the Department of Defense at Fort Knox. In addition to his continued work in IT, Posey has spent the last several years actively training as a commercial scientist-astronaut candidate in preparation to fly on a mission to study polar mesospheric clouds from space. You can follow his spaceflight training on his Web site.


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