Astronauts use the world’s biggest pool as a proxy for weightlessness
My second grader’s swim classes have covered freestyle, backstroke, and butterfly, but they seem to have somehow overlooked extravehicular activity (EVA) training. Perhaps my kids would have washed out of those lessons when the specialized equipment of a Extravehicular Mobility Unit spacesuit didn’t fit perfectly, or perhaps this is due to the fact that our local pool couldn’t come close to holding life-size recreations of most of the International Space Station (ISS). For that, I’d need to start hauling the kids to the Neutral Buoyancy Laboratory (NBL) in Houston, which may be more than our Friday afternoons can accommodate.
The NBL is the largest swimming pool in the world, although as you may have guessed, very little actual swimming takes place there. The pool holds over 6.2 million gallons of water which can be completely recirculated in 19 hours, although for the most part the purity of the water is not the point of the facility. Instead, the pool and surrounding building are used to help astronauts prepare for working in microgravity, particularly in the bulky spacesuits used for EVAs, the spacewalks required to do repairs or assembly on the outside of the ISS. As such, the huge amount of water functions as a way to recreate the feeling of weightlessness while still on Earth.
Manageable option for faux-microgravity
Floating in water isn’t a perfect analog for floating in space, but it’s the best option available when the goal is a six-hour maintenance project 200 miles above the Earth. Flying in parabolic arcs on the Vomit Comet or even floating in especially dense water are other ways to “defy” gravity, but they don’t let astronauts practice and prepare the new set of movements they need to learn to maneuver in space. So the NBL offers a way for astronauts to get used to moving in a somewhat difficult spacesuit, learning how tools will or won’t float, getting used to their MAGs, and familiarizing themselves with the layout and topography of the ISS. It also allows for a team of four support divers to accompany each trainee, as well as pneumatic cranes to hoist astronauts in and out of the water (which may would probably beat even a diving board in the eyes of my four-year-old.)
At a minimum, astronauts have nine EVA training visits to the NBL. Even if that individual isn’t planning on a spacewalk in the near future, its better to be prepared in case more hands are needed outside the ISS. Even then, there will be some differences, such as the amount of drag on an object from the viscosity of the water, or the fact that water pressure changes about 0.5 PSI every foot deeper in the pool. Still, once weights are balanced, it’s a very effect way to practice general spacewalk activity, as well as rehearse very specific projects, like the installation of a specific piece of equipment. With a model ISS in the pool, mission commanders can also use it to experiment and try out protocols for new EVAs, even if the astronaut that will handle that mission is already in space, so that nobody has to figure out too much while actually in the vacuum of space.
Source: Swimming with spacemen: training for spacewalks at NASA’s giant pool by Lee Hutchinson, Ars Technica