training for spacewalks at NASA’s giant pool

by Lee Hutchinson – Mar 4 2013, 8:30am EST

Though the day dawns cool, the deck of NASA’s Neutral Buoyancy Laboratory (NBL) remains warm—a side effect of keeping 6.2 million gallons of water at a constant 86°F. I stare down into the largest indoor body of water in the world and feel a surge of vertigo. Here, astronauts practice for spacewalk missions at the International Space Station (ISS), and today I’ll watch them do it.

The pool measures 202 feet long, 101 feet wide, and 40 feet deep, extending 20 feet down from the elevated deck and then an additional 20 feet below the floor level. Its wall and floor are white, though they’re smudged and darkened from years of repositioning model test stands. Spread throughout the water are life-sized component mock-ups of the ISS, looking exactly like some giant child’s Tinker Toy set. Refraction causes the perspective to bend sharply away until it’s obscured by the reflection of the ceilings and walls.

“Man, that is a deep looking pool,” I say, leaning over to stare at the bottom of the clear water. My brain tries and fails to conjure up eloquence. It’s busy, filled with thoughts of tumbling over the side.

The pool loses about 5,000 gallons per week in evaporation, and I can feel the moisture in the air. It’s nothing like the awful humid summers we typically have in Houston, where the NBL is located, but the transition into the pool area does feel like passing through an insubstantial curtain. The air in the high bay smells faintly of chlorine, and it hums with pumps and machine noises. Scratchy PA announcements occasionally echo down from speakers in the distant ceiling.

“What’s it like being underwater?” I ask my companion, safety diver Chris Peterman. The NBL has 28 full-time divers, all of whom work for Oceaneering, a company specializing in underwater engineering efforts.

“It’s incredible diving,” replies Peterman. “It takes a long time to sink in how large it is and how much stuff is in there.”

Even the largest pool in the world isn’t anywhere near large enough to hold the entire space station, though. The most recognizable feature of the space station is its backbone Integrated Truss Structure, which stretches longitudinally and holds the station’s radiators and solar arrays. Eleven individual segments make up the truss; the NBL pool can hold only three of them end-to-end. The ISS is really, really big.

Whether you regard it as humankind’s greatest laboratory or the costliest white elephant ever sold, the International Space Station remains an engineering marvel. Bolted together by men and women over more than a decade while skipping along at 17,500 miles per hour 200 miles up, the ISS is longer and wider than a football field, with a mass of almost 450 tons (though its precise mass varies depending on the amount of consumables currently on board). Its assembly required 37 space shuttle launches, and that’s not counting the additional components launched by Russia, or the Soyuz launches to keep the station crewed, or the Progress launches to keep it supplied.

A total of 155 spacewalks over ten years were needed to connect the components together—2.5 times as many spacewalks as had previously occurred in the entire history of manned space flight. Every second of every one of those of those spacewalks had to be planned and then rehearsed dozens of times. Unfortunately for the astronauts and engineers, assembling things in microgravity differs from assembling them on Earth—in addition to the obvious problem of your tools floating away, the human mind isn’t used to accounting for an object’s weight and mass as separate properties. Spacewalk rehearsals therefore have to happen in as close an environment to microgravity as possible.

How on earth do you simulate microgravity? Two ways. First, you can recreate it by flying parabolas in a plane. This works, but only for thirty seconds at a time. NASA does this with a Reduced Gravity Aircraft (popularly known as the “Vomit Comet”). It’s useful for microgravity acclimation and limited testing but not for rehearsing multi-hour spacewalks. So the second rehearsal strategy comes into play: build the largest pool in the world and go swimming—exactly what NASA did.

Read more: Swimming with spacemen: training for spacewalks at NASA’s giant pool | Ars Technica.

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