Although underwater training for extravehicular activity—spacewalks—is now the norm, NASA started out using aircraft to simulate weightlessness. Boeing KC-135 Stratotankers were used for this purpose, along with Convair C-131 Samaritans. The basic technique is the same today as it was then: The airplane makes a series of steep, roller-coaster-like climbs and dives, producing about 30 seconds of weightlessness at the top of each arc. These maneuvers frequently provoked airsickness, which led to the aircraft being nicknamed the “Vomit Comet.”
Ballet of Weightlessness
“Watching the Gemini 9 EVA from Mission Control convinced me that I’d better be well prepared for the space walks I was to perform on the Gemini 12,” Buzz Aldrin wrote in his 1989 memoir, Men From Earth. “I had a lot of respect for Gene [Cernan] and thought he could have done better had he had different training. In fact, after Gemini 9, Gene joined me in a series of underwater training sessions in a pool near Baltimore to prepare for the Gemini 12 mission. (He was on our backup crew.) I was an experienced scuba diver before beginning this ‘neutral buoyancy’ training. It seemed to me that practicing underwater was better preparation for an astronaut’s weightless EVA than with the wire-and-pulley training gadgets that came and went in Houston, but never really worked.
“Soon my underwater training became quite elaborate. I wore a carefully ballasted EVA suit to completely neutralize my buoyancy and closely approximate zero G. Eventually I mastered the intricate ballet of weightlessness.”
Here, astronaut Buzz Aldrin carries out underwater training in October 1966 at the McDonough School For Boys in Baltimore. The pool contained a full-size mockup of Gemini’s equipment section.
Gemini 9 EVA
During the Gemini 9 EVA in 1966, handrails, Velcro pads, and foot restraints failed to help astronaut Gene Cernan control his movements. In Walking to Olympus: An EVA Chronology, authors David S.F. Portree and Robert C. Trevino noted that Cernan spent half his time outside the capsule just maintaining his position. “As he struggled, he broke off an experimental antenna mounted on Gemini 9 and tore the outer layers of his suit…. After returning to Earth, Cernan conducted underwater neutral buoyancy simulations of his EVA in the Weightless Immersion Facility pool…. He reported that neutral buoyancy simulation nearly duplicated actual EVA conditions, helping to validate it as an EVA training tool.”
By the time Cernan returned to space, as the lunar module pilot of Apollo 10, underwater simulations were the norm. Nor was that the astronauts’ only water training. In this image from August 1968, he and crewmate John Young (in the raft) exit their Apollo Command Module trainer—practice for an ocean splashdown.
Skylab, a two-story, Earth-orbiting laboratory, was launched on May 14, 1973. For NASA’s first space station, Marshall Space Flight Center’s Neutral Buoyancy Simulator took underwater training to a new level. In Homesteading Space: The Skylab Story, authors David Hitt, Owen Garriott, and Joe Kerwin wrote, “The Neutral Buoyancy Simulator was a working facility. The theory had been proven and now was being put into practice.”
The NBL could fit spacecraft much larger than the capsules of the 1960s. The authors quoted tank manager Jim Splawn: “We sort of had the vision of building a facility large enough to accommodate some pretty large mock-ups of hardware, and it really proved out to be very, very beneficial.”
Shown here is astronaut Ed Gibson (a crewmember of the Skylab 4 mission), during EVA training at the Apollo Telescope Mount (ATM) mockup in November 1970. At that time, the ATM was the most powerful observatory put into orbit.
Underwater training in the space shuttle era: STS-5 astronauts William Lenoir and Joseph Allen stand on the Weightless Environment Training Facility platform at the Johnson Space Center in Houston, about to be lowered into the tank, in 1982. Once underwater, they will train inside a full-scale mockup of Columbia’s payload bay.
Just a few weeks before their launch date of April 24, 1990, STS-31 astronauts Bruce McCandless and Kathryn Sullivan practice space walking in the Weightless Environment Training Facility at the Johnson Space Center. McCandless (left) works with a mockup of the shuttle's remote manipulator arm, while Sullivan manipulates Hubble Space Telescope hardware on the support system module forward shell. The main purpose of the shuttle mission was to deploy the Hubble Space Telescope.
Astronaut Greg Harbaugh (here, with Steve Smith, training for a Hubble Space Telescope servicing mission in 1995) has logged 818 hours in space, including more than 18 hours of EVA. Of his underwater training experience, he said in a January 2009 interview, “The challenge is to strike a harmonious balance between what the suit wants to do, and what you need to do to get the job done. Sometimes you need to be upside down, head down, you need to be right side up, on your back, on your stomach—for somebody doing it right out of the starting gate, no experience doing that sort of thing before, it can be incredibly frustrating. You’re in this really ungainly, uncomfortable inflatable thing with these hard metal rings that can give you rubbing points. Your hands can get sore, your shoulders can get sore—overall, it’s not a very pleasant experience.
“But by the end of my training, when I got ready to do Hubble, by that time the suit fit like a second skin. You get so comfortable that you forget it’s there. After hundreds of hours in the water tanks, I really was very comfortable. And that, of course, is the whole goal, and makes you ready to do it on orbit, for real.”
In 2003, with his STS-116 shuttle flight still almost four years off, astronaut Robert Curbeam, Jr., practices space station assembly tasks underwater. The Johnson Space Center’s Neutral Buoyancy Laboratory pool is 202 feet long, 102 feet wide, and 40 feet deep. It holds more than 6 million gallons of water, and it took more than one month to fill the pool. Astronauts will spend seven hours in the water, training, for each hour they plan to spend in EVA.