How NASA trains astronauts 40 feet underwater

Before they get to the Space Station, astronauts spend hours at the Neutral Buoyancy Lab. CNET Road Trip 2014 dives in for a visit.

Daniel Terdiman Former Senior Writer / News
Daniel Terdiman is a senior writer at CNET News covering Twitter, Net culture, and everything in between.
Daniel Terdiman
7 min read

Astronaut Scott Kelly is lowered into the pool at the Neutral Buoyancy Lab in Houston. For the next six hours, he'll be underwater, practicing tasks he'll eventually be doing during spacewalks outside the International Space Station. Daniel Terdiman/CNET

HOUSTON -- When astronauts prepare for future missions to the International Space Station, the advance training for the specific tasks they'll carry out on the ISS is obviously crucial. But here on Earth, how do you mimic space's unique zero-gravity environment?

NASA answered that question in an ingenious way with a large-scale mockup of the ISS that the space agency built and placed in a huge swimming pool.

Training astronauts 40 feet deep (pictures)

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Welcome to the Neutral Buoyancy Lab (NBL), a NASA facility that's about 20 minutes away from the Johnson Space Center here. Since the mid-1960s, NASA has trained its astronauts in Houston to conduct extravehicular activities (EVAs), otherwise known as spacewalks, in underwater conditions. The agency has long considered working below the surface in neutrally buoyant conditions an ideal way to train for the zero-G environment of space.

In 1995, NASA broke ground on its existing facility, setting out to build a newer, larger lab. In late 1996, with construction complete and the pool filled, the space agency assumed ownership of the NBL.

As part of CNET Road Trip 2014, I've come to this southeast Texas city of 2.16 million people to visit Johnson Space Center, NASA's main astronaut training operation. Having visited JSC as part of Road Trip 2008, I was familiar with it, but I hadn't been able to see how NASA uses the NBL to train astronauts who will soon be doing real work on board, and outside of, the ISS. This is Part 1 of my JSC coverage. Tomorrow, see how NASA prepares food for astronauts' long missions into the harsh conditions of space, far away from the homes and restaurants in which they usually eat.

The ISS, underwater

When you first walk into the main pool area there, it's hard to be prepared for what you'll encounter. Forty feet below the pool's surface is the huge ISS mockup. Because the water is crystal clear and totally calm, you can see everything -- and it's bizarre. Your mind tells you something is not right about what you're looking at.


More adventures from Road Trip 2014

Check out the latest from Daniel's trip to the best tech spots in Texas, Oklahoma, Kansas, and more.

    But right it is. And it makes a lot of sense. If you've ever scuba dived, you know that when you're neutrally-buoyant -- weighted properly so that you're neither rising toward the surface nor sinking to the bottom -- you have great control in all three dimensions over where you are and how you move. It's a lot like flying, and it's a lot like what astronauts encounter in open space.

    During the Space Shuttle program, NASA astronauts had assigned missions they were responsible for when in space, and they would practice those missions underwater, taking advantage of the neutral buoyancy to prepare themselves for what it would be like high above the Earth. But with the Space Shuttle days over and astronauts getting ready for long missions aboard the ISS, they're doing much more general training. That's because, my NASA host Gayle Frere told me, astronauts going to the ISS are generalists. They have to be prepared to do any number of tasks. "They have to know how to do a little bit of everything," Frere said, "in case something goes wrong."

    That's where their regular NBL training comes into play. Almost every day, two astronauts come to the facility for six-hour underwater sessions -- the normal time for an EVA session. Over the course of their training, they'll spend between six and eight hours in the pool for every hour of actual EVA activity they expect to do in space.

    For scuba divers, getting ready to descend is fairly straightforward, and all you need is to be sure you've got the right equipment -- fins, snorkel, mask, buoyancy control device, tank, and regulator -- and a buddy. But for astronauts, things are a little more complex. For one thing, they submerge in full space suits that weigh in at more than 350 pounds, counting the astronauts' own weight. For another, each astronaut is supported during their time in the pool by rotating teams of four scuba divers -- one with a camera, one to help with tools, and two safety divers.

    The NBL pool is larger than your average public pool. It's 202 feet long, 102 feet wide, and 40 feet deep, and it holds 6.2 million gallons of water. Yet even at that size, the complete ISS, at 350-feet by 240-feet, won't fit inside the NBL, necessitating separate modules located in different areas of the pool.

    Going under

    Getting an astronaut ready for work is no small task. Just getting them fitted for their space suit is a big deal. According to NASA suit and tools engineer Robert Knight, astronauts get 36 measurements of their bodies and 46 measurements of their hands to ensure a perfect fit of the suit and gloves. "That's extremely important," Knight said. "They're not doing a space walk. They're doing a space translation. Everything's done by hand."

    Inside their suits is plenty of padding, and the key is to wedge them comfortably inside in such a way that they don't "fall inside the suit," Knight added.

    Once that's all worked out, and an astronaut has successfully -- with the help of several NBL technicians (see photo gallery, above) -- put on their suit, it's time to go to work.

    Astronaut Scott Kelly salutes just before he disappears below the surface of the NBL pool. Daniel Terdiman/CNET

    Before the astronauts even get in the water, a utility diver has set everything up -- preparing the tasks so that there's no wasted time underwater. And when it's time to submerge, the camera diver sticks with the astronaut, capturing everything that happens. So too do the two safety divers, who are there to deal with anything that might go wrong -- a loss of power to the suit, say, or even a loss of consciousness. In 115,000 dive hours of NBL exercises, there has never been an accident involving an astronaut, Knight said.

    The astronauts are connected to the NBL's various support systems (for air, power, and communications, for example) by two 85-foot-long tethers that snake off the suit. Underwater, they're breathing a special "nitrox" air that's 46 percent oxygen, compared with 21 percent in the normal air we all breathe every day. This reduces the risk of decompression sickness.

    The astronauts also have 6-foot "local tethers," Knight explained, that they use to lock themselves onto handrails at each place where they're practicing a task. "Everything they do today," Knight added, "is a simulation of what they do" on the ISS.


    It's 8:28 a.m. on a recent Tuesday, and there's tension in the air. The support teams are in place, and the safety divers are in their wet suits, though not yet zipped up. Almost everyone by the pool has on a headset. Everyone's waiting for the start of the show -- the arrival of astronauts Scott Kelly and Terry Virts.

    When they arrive, it's all business. But Kelly, the twin brother of astronaut Mark Kelly, took a moment to explain his EVA task today: practicing "routing a bunch of cables along the lab to the front of the ISS."

    Added Kelly, this is for "a docking assembly which will [eventually] allow commercial crew vehicles to dock. It's not technically complicated, but it's lots of cables."

    Scott and Mark Kelly are taking part in a special NASA experiment: studying the effects of space on identical twins. According to NASA, the work is about conducting "cleverly designed, but limited, short-term investigations for observational comparison between [the Kelly brothers]. These pilot demonstration projects, the first of their kind, will be unique investigations into the genetic aspects of spaceflight. They will provide insight into future genetic investigations that can build on this study, but with a larger study population of unrelated astronauts."

    But it's too early to tell how that study is going to go. For now, Scott Kelly and Virts are focused on the tasks at hand. And so, too, are the many NBL technicians supporting them today. They take their work extremely seriously, Knight said, and despite many people who would like to dive in the NBL pool -- after all, who wouldn't want to check out a mockup of the ISS underwater -- few will ever get such a chance.

    Technicians can monitor 21 different camera views of the astronauts' activity in the NBL pool. Daniel Terdiman/CNET

    Even a small number of oil-industry companies that pay to use the pool are segregated to a far corner, with no access to the space station mockup. "I don't care if you've dived all over the world, or you're the best scuba diver in the world," Knight said. "You're not diving here. To dive here, you either have to pay us a whole lot of money, or be directly related to EVA activities."

    Up in the control room, meanwhile, a large group of NBL technicians are monitoring Kelly's and Virts' every move via screens showing the views from dozens of cameras located both underwater and above the pool. This is a six-hour dive, so the monitoring is relaxed. Someone asks the astronauts if the audio being piped into their suits is too loud, and one answers, "No, that's good for me."

    But as "Spirit in the Sky" plays over the audio system, one of the astronauts adds sternly, "You're going to need a better song, though."

    Keep an eye out for more behind-the-scenes stories and photo galleries as I travel throughout Texas, Oklahoma, Arkansas, Tennessee, and Kansas during this year's Road Trip. I'll seek out most interesting technology, military, aviation, architecture, and other destinations our country has to offer. From U.S. Air Force basic training to NASA's Johnson Space Center and FedEx's massive package-sorting hub, and much more, Road Trip 2014 will take you along with me.