Marshall’s Neutral Buoyancy Simulator

We kidded about, we may have a dry workshop on orbit, but you’re going to
go through a wet workshop in training, that being underwater.

Jim Splawn

Joe Kerwin recalled: “From, I’d guess, 1968 onward, we traveled ever more frequently to Huntsville—for engineering tests and design reviews, but more and more to do eva training in the new, bigger, and better water tank. I remember going there with Paul Weitz. We’d fly up together in a T-38. You’d take off from Ellington, point the nose to a heading of just a lit­tle north of east, climb to 17,500 feet, and go direct. We could make it in an hour if all went well. When we landed at Redstone Arsenal [the Army base in Huntsville on which Marshall is located], there’d be a rental car wait­ing, and we’d hustle off to the Tourway Motel; $7.50 with black and white TV, $ 8.50 with color.

“Bright and early the next morning we’d go to the neutral-buoyancy tank. That was always a professionally run organization and always a pleas­ant experience. We’d suit up in the dressing room, brief the test, and make our way up to ‘poolside’ and into quite a crowd—with divers, suit techni­cians, mockup engineers, and test personnel. Hook up the suit to commu­nications, air, and cooling water. Down the steps into the water. Then float passively while the divers ‘weighted us out.’ They did this by placing lead weights into various pockets to counteract the buoyancy of the air-filled spacesuit, until we were neither floating to the surface nor sinking to the bottom. I recall gazing idly up through the bubble-filled water to the bright lights above and imagining that I was a medieval knight, being hoisted on to my charger before the tournament.

“Then the two of us, each accompanied by a safety diver (ready to assist us instantly in case we lost air or developed a leak) would move over to the Skylab mockup, laid out full size in the forty-foot-deep water and practice film retrieval from the atm. We’d evaluate handrails and footholds, open­ing mechanisms and locks, how to manage the umbilicals, which trailed out behind us as we worked. After two or three hours we’d quit, return to the locker room, and debrief. It was wonderful training. By the time we launched, each of us could don and zip his own suit unassisted and move around in it with the same familiarity as a football player in his helmet and pads.”

The idea of neutral-buoyancy simulation of the microgravity environ­ment had arisen at the Manned Spacecraft Center in Houston before it was developed at Marshall, though neither center would implement the concept until the mid-1960s. Mercury astronaut Scott Carpenter had proposed using a water tank for astronaut training early in the space program, but manage­ment did not pursue the idea at the time.

A water tank was constructed for astronaut training at msc, but not ini­tially for neutral-buoyancy work. Rather it was used to prepare astronauts for the end of their missions. Since Mercury, Gemini, and Apollo flights all con­cluded with water landings, the msc tank was used to rehearse the procedures that would be performed in recovery of the astronaut and spacecraft.

When Ed White made the first U. S. spacewalk in 1965 on the Gemini 4 mis­sion, his experience seemed to belie the need for intense training; for White, the worst part of the spacewalk was that it had to end. When Gene Cernan made the second American spacewalk the following year, however, his expe­rience was quite different. He found it difficult to maneuver, his faceplate

9- Astronauts practice for spacewalks in the neutral-buoyancy tank.

fogged up, his pulse rate soared, and he got overheated. It was obvious that changes were needed in spacewalking technology and procedures, and that included training. The idea of neutral-buoyancy training was revisited and implemented in time to prepare Buzz Aldrin for his Gemini 12 spacewalk, five months after Cernan’s. With the changes that had been made and the intervening experience, things went far more smoothly for Aldrin’s attempt on the final Gemini flight. Underwater training continued during the Apol­lo program; spacesuits weighted past the point of neutral buoyancy allowed astronauts to simulate the one-sixth gravity of the lunar surface.

At Marshall neutral buoyancy development came about from a grass­roots initiative, at first as almost a hobby among some of the center’s young engineers in the mid-1960s. “Some of us young guys got to talking about, we really are going to be in space, and if you’re in space, you’re going to need to do work,” said Jim Splawn, who was the manager of space simulation at the Process Engineering Laboratory at Marshall. “And if you do work, how do you keep up with your tools? How do you train? So that started the discussion about how are you going to practice. How are you going to simulate the weightlessness of space? And we talked and talked for weeks, I guess, about that.

“And so one guy said, ‘Hey, have you ever watched your wife in the swim­ming pool?’ And we all giggled and said, ‘Yeah, you bet, we watch our wives and other wives too.’

“But he said, ‘No, no I’m serious. Have you ever looked at her hair while she’s underwater, how it floats?’ And that started a whole ’nother discussion, and so we said, ‘Well, why does it do that? It’s sort of neutrally buoyant—it doesn’t sink; it doesn’t necessarily float to the surface.’ So then we started talking about how we could do that. We started coming up with the idea then of going underwater. That was the first concept that we had, the first discussion about going underwater.”

The group thought the idea had potential and decided to use some of their free time to pursue it, and Marshall’s first neutral-buoyancy simula­tor was born. Of course official facilities and equipment require funding, so the first phases of their research relied on using whatever they had available. The first exercises were done in an abandoned explosive-forming pit. The pit had been used to create the rounded ends of Saturn I fuel tanks and was about six feet in diameter and about six feet deep. Initial dives were done in swimsuits until the group felt like they needed more duration underwater, at which point they began using scuba gear.

Their experiment was showing promise, and they were ready to graduate out of the six-foot-diameter tank. Once again, though, their almost non­existent budget forced them to make use of what was on hand, which was once again leftover Saturn hardware. The tank was based around an inter­stage for a Saturn rocket, the short, hollow cylinder that connects two boost­er stages together. “It was like a ring, probably twelve-feet vertical dimen­sion,” Splawn said. “So we had a backhoe, and dug a hole in the ground, and positioned the interstage and backfilled the dirt around it. And, guess what, we had a swimming pool now made out of excess Saturn hardware to become our next simulator for underwater work.”

The extra volume meant that they could take the next step in their under­water evaluation. Just as they had moved from swim trunks to scuba gear in the first tank, the second allowed them to move on to pressure suits, simu­lating the gear that astronauts would be wearing in orbital spacewalks.

“We had to go to Houston to try and get pressure suits,” Jim Splawn said. “Pressure suits in the mid – to late – 60s were few in number and of great demand and expensive and were very, very well protected by the Houston suit techs. So we took an alternate route; we contacted the Navy, and a cou­ple of us went to San Diego one Friday, worked with the Navy on Saturday, and they put us in high-altitude flying suits, and then they had huge over­size suitcases that they put these high-altitude pressure suits in, complete with gloves, helmet, everything, there. They trained us in a large swimming pool that they had; in fact, we had to jump off of diving boards into the water, and we took the helmets off, and we had to learn how to take a hoo­kah [breathing apparatus] for underwater diving, so they taught us how to get the helmet off and take the hookah and still survive. So anyway, they taught us how to do that, so then we flew home on Sunday afternoon; we brought back four pressure suits, just on commercial air. So that’s where we got our first pressure suits.”

The “hookah” is a rubber full-head covering that is used underwater, similar to scuba. Instead of coming from a tank, air is pumped down from the surface by a hose to maintain a certain airflow into the rubber “helmet,” regardless of the depth of the diver. It is particularly useful in tanks like Mar­shall’s neutral-buoyancy trainer because it allows voice communications to the surface. However, one must be careful to not turn upside down, as air goes out and water comes in.

Up until this point, Splawn said, Marshall and msc had not had any dis­cussions about the work each was doing on neutral buoyancy. “We had abso­lutely no interaction at all,” Splawn said. “We knew nothing at all about Houston and the type of simulations or training or anything else that they were doing. I really don’t know the timing between what Houston did and what we did. I just don’t have any data point there at all. Once it became known what we had and what we had done, there was competition, and some pretty heated discussions between Houston and us. But we ended up doing the crew training for Skylab.”

In fact the first astronauts came to check out the work when the team was still using the second tank. Alan Bean, at the time an unflown rookie, was one of the first astronauts to perform a pressure-suited dive in the interstage tank. It was also during the experimentation with the second tank that the team decided they could let the Marshall powers that be in on their work. Von Braun himself made a dive in a pressure suit to evaluate the potential of neutral-buoyancy simulation.

Bob Schwinghamer, who was the head of the Marshall materials lab,

recalled a nerve-wracking incident that occurred during one of Bean’s ear­ly visits. “I was safety diving, and I was floating around in front of him. He was in there unscrewing those bolts off of that hatch cover. And all at once, it said, ‘poof,’ and a big bubble came out from under his right arm, a stream of bubbles. I thought, ‘Oh my god, I’m going to drown this astro­naut.’” Schwinghamer said he attempted to cover the hole in Bean’s suit, but he could see the suit collapsing—first near Bean’s feet, then up to his knees, then his thighs. Since he didn’t have a communications system at that time, Schwinghamer left Bean and surfaced, and told the operators to give him more air.

“He never lost his cool,” Schwinghamer recalled. “By then, he wasn’t neu­trally buoyant anymore; he was about sixty pounds too heavy. So he walked across [the tank], and he just climbed up the ladder and got out. That’s all there was. And I said, ‘Oh my goodness, what if we had drowned an astro­naut?’ But he was just cool.”

Working with pressure suits complicated the situation. The pressure suits, representing spacesuits, were basically balloons containing divers. That meant the air caused the suits to tend to float. In order to make the suits neutral­ly buoyant, weight had to be added to balance out the effect of the air. This had to be done very carefully. Putting too much weight in one area would cause that area to sink more than the rest of the body, invalidating the sim­ulation of weightlessness.

“After many, many stop-and-go kind of activities, we settled in on a low – profile harness of small pockets of lead strips, so that we could move the lead about depending on the mass of the human body that’s inside the suit and consequently what kind of volume of air you had inside that suit,” Splawn said. “We could move the lead weights around until we could put the test subject or flight crewman into any position underwater and turn him loose, and he would stay there.

“We started offjust in a room, so in order to get some data points, we put the guy in the pressure suit and then lay him flat on the floor and tried to get him to lift his arms—Is the weight distributed?—and lift his legs—Is the weight sort of distributed correctly?” Splawn said. “And so we said, ‘ok, get up,’ and he couldn’t get up, he had so much weight on him. That was in the very early days.” Typically, he said, about seventy to eighty pounds of lead weights were needed to achieve neutral buoyancy. To make sure the weighted,

pressured-suited divers didn’t encounter any problems, each one was accom­panied by two safety divers who could help out in an emergency.

Once the team had enough experience in the interstage tank, they were confident that neutral buoyancy could be used for weightlessness simula­tion. They were ready to move on to the next step. “From that we gradu­ated to what we called the big tank,” Splawn said. “The big tank is seven­ty-five feet diameter; it’s forty feet deep; 1.3 million gallons of water as best I remember. It was complete with underwater lighting, underwater audio system, umbilicals that would be very much like the flight crew would use to do an eva on orbit.”

This tank, Marshall’s Neutral Buoyancy Simulator, was designed to take the work to the next level. Unlike previous facilities, which were experiments designed to evaluate the efficacy of neutral buoyancy as a microgravity ana­log, the Neutral Buoyancy Simulator was a working facility. The theory had been proven and now was being put into practice. The facility was designed to be large enough to submerge mock-ups of spacecraft in order to test how easily they could be operated in a weightless environment.

“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,” Splawn said. “Because once we had the difficulty at the launch of the Skylab itself headed towards orbit, it really proved its worth because of all the hardware we had to assemble underwater.”

The origin of the “big tank” was rather unconventional. In order to has­ten the process of building the tank, Marshall leadership found a way to circumvent the bureaucratic requirements of creating a new facility. “The facility was not a ‘c of F,’ or construction of facilities type project,” Splawn explained. “There is a small tool tag that is on the side of the tank, and it has a number stamped on that tag, and so that designates the seventy-five – foot diameter tank as a portable tool. There were a lot of eyebrows raised at that.” While the tank was not technically secured into place, saying it was portable was somewhat of a stretch.

“I don’t really remember how that happened,” Splawn said. “I know there was great interest in having a facility, and we thought we had the right idea of how to simulate weightlessness and how to train. We needed a facility, and the schedule of when we needed it just could not be supported through the official construction of facilities kind of red tape that you had to go through to get a facility approved, and then all of that kind of business that occurs to acquire a facility. So that’s why we went this alternate route.”

As a result of the way the Neutral Buoyancy Simulator was built, many people elsewhere in the agency did not know what Marshall was doing until it had been done (as was the case with associate administrator George Muel­ler, who was not aware of the tank until his “wet workshop” dive).

“The tank was built in-house,” Splawn said. “We used the construction crew out of a test lab because they were equipped and they were accustomed to doing construction work. So the steel segments of the tank, of course, were rolled steel. They were shipped in, and then the government employ­ees welded the tanks together, and we installed all the systems, electronic, mechanical, filtration, all of that was worked internally.”

The tank attracted some unusual visitors, Splawn recalled: “It was very interesting to have some of the caliber people come through our area that came through. Of course, starting with von Braun—back when we had just first started the thinking and the dream of going underwater to do evaluations in a weightless environment, we found out that von Braun was a scuba diver. So once we had been through the early stages and thought we could sort of reveal our thoughts a little bit, we contacted his secretary, Bonnie, and told her we’d like to have Dr. von Braun come and see what we were doing.

“I guess the first time he ever knew anything about it, we were on the twenty-foot tank. He didn’t know about it up until about then. Because us bunch of young guys, what we would do is work our regular kind of work through the day, and then we would go out in the late evenings and play, and I say ‘play’ in quotes. But we would try to figure out just exactly what we were trying to do. We didn’t know if we had a cat in the bag or not. But we finally revealed the cat to Dr. von Braun and got him to come down, and he thought it was wonderful. He said, ‘Ja, ja, keep going, keep going.’

“I remember one day that von Braun had been to the Cape for a launch, and we got a call from his secretary again. Bonnie said, ‘Dr. von Braun has just called me from the Cape, and he is bringing a guest on the NASA air­craft back with him from the Cape to Huntsville, and they want to go to the neutral-buoyancy facility this afternoon, and this guy’s name is Jacques Cousteau, and can you accommodate him?’ And I said, ‘Yes, ma’am, we sure can.’

“So von Braun dressed out in swim trunks, and Jacques Cousteau dressed

out in swim trunks, and they went for a dive in scuba gear, and von Braun showed Jacques Cousteau some of the things that we were doing underwater, put him through a few paces with some of the hardware that we had mount­ed in the tank at that point in time. So it was sort of interesting.”

As an additional safety precaution, the Marshall facility also included a decompression chamber, which could be used if a diver surfaced too quick­ly. The medical term is “dysbarism”—Greek for “pressure sickness” — but to divers it’s simply the “bends.” Bends has affected divers since humans began to dive for pearls centuries ago. It doesn’t just happen underwater; workers building the foundations of the Brooklyn Bridge a hundred feet beneath the surface of the East River developed the strange pains and dis­orientation of “caisson disease.” The doctor hired by the company to look into the problem noted with interest that the pains often went away when the men went back down to the diggings. But it was another twenty years before other doctors figured out what was happening.

When a diver descends in water, the water’s weight increases the pres­sure against the body; at thirty-three feet it’s double the pressure at the sur­face. In order to breathe, the pressure of the air the diver breathes also must increase. And that pressure drives nitrogen into the lungs, blood, and tis­sues. That’s not normally a problem; nitrogen is inert except at very high pressures, when it exerts a narcotic effect.

But if a diver ascends rapidly to the surface, the pressure suddenly dimin­ishes. Then the absorbed nitrogen reverses course and comes out of the tis­sues. The diver is able to breathe some of it out, but if the pressure was high, some of it forms bubbles in the blood and tissues, and these can have dan­gerous effects—bubbles compressing nerves in the joints cause bends, bub­bles blocking capillaries in the lungs cause chokes, bubbles in the blood ves­sels of the brain can mimic a stroke. To prevent these things, it’s essential to reduce the pressure on the body slowly enough to allow for “breathing out” the nitrogen without letting bubbles form.

The dives in Marshall’s tank never caused the astronauts to have any prob­lems. However, the recompression chamber was used once, Splawn said, for a Tennessee Valley Authority utility diver in the area who had been doing work underwater and surfaced too quickly and was rushed to Marshall. Splawn said that, while it was too late to prevent lasting harm, the cham­ber may have saved his life.

Concerns over rapid decompression did affect the crews training in the tank in one way, though. “In our dives, we never went deep enough for long enough that we couldn’t safely return to the surface of the tank in a hurry,” Kerwin said. “But climbing into the cockpit of a T-38 and flying home at reduced cabin pressure was another story. Flying after diving sets pilots up for bends. So we did a study, and came up with rules for how long a diver had to loiter on the surface before launching for home. It varied from a few hours after one dive to an overnight stay after two days’ work underwater.”