The G Machine

Riding an Atlas into space was a piece of cake compared to pulling 32 Gs on the Johnsville centrifuge.

Air & Space Magazine

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“I think it started when somebody spun a fish and didn’t notice anything irregular about the fish because of the high Gs,” says Stephen Cloak, a Navy research engineer and veteran centrifuge jockey. “So they postulated that if we put a human encased in water, it would dissipate the G forces and they could take high G.” The Maiden was an aluminum capsule designed by Gray, sculpted roughly in the shape of a seated human, that could be filled with water. Gray stayed alert throughout the 25-second run up to 32 Gs, suffering only mild sinus pain. “He was another one of these late ’50s, early ’60s guys that just kind of kicked the tires and went at it,” says Cloak. Gray wanted to go to the full 40-G capability of the centrifuge, but the Maiden was too big to fit inside the gondola and so had to be mounted farther inward along the arm, where 32 Gs was the maximum acceleration possible.

In the late 1950s, two scientists, Carl Clark and James Hardy, had a more daring idea. Physics dictated that if a spacecraft could be steadily accelerated at 2 Gs, it could reach the moon or Mars in days or even hours. But could a human being survive the constant acceleration? Clark used the centrifuge to find out.

“He essentially moved into the cab, brought his La-Z-Boy from home, and stayed in there at 2 G for 24 hours,” says Shender. Clark slept, ate, worked, and lived at two Gs for a full day under constant medical surveillance. He suffered nothing more than fatigue. Further marathon rides were planned, but more immediate space missions loomed and the idea was set aside.

One factor that eventually discouraged the sportier research projects was the mounting evidence of all that could happen to the body under acceleration. Under high Gs, Cloak explains, “you’re insulting the brain with a lack of oxygen in the blood. Each person’s brain is a little different, so you don’t know what’s going to happen.” Aside from G-LOC (for “G loss of consciousness”), possible effects included motion sickness, disorientation, anxiety, euphoria, and confusion. Cloak adds, “You get swelling of the feet and ankles, ruptured blood vessels in the groin area, blood clots, temporary change in blood-flow patterns in the lungs, possible collapsing of the lungs, fractured ribs, chest pain. For your heart it’s entirely possible to have arrhythmias, transient electrical changes, myocardial infarctions, interesting little things like that.”

Most of these effects were transient and fairly rare, but they were not to be dismissed. “We had to go through a battery of exams,” Cloak recalls, “because one of the major risks is sudden death. No matter how well they screen you, you just don’t know when you get in there if a 9-G ischemic insult to your system is gonna kill you or not.” Then there are the mild phenomena, such as petechial hemorrhaging. “You actually look like you’ve got measles—at high Gs, blood leaks through the blood vessels and you get little pinpoints all over. It’s kind of interesting, especially the first time you see it.”

Cloak rode the centrifuge routinely throughout his career at Warminster as an acceleration researcher. “I used to tell everybody it broke the week up,” he says with a laugh. He adapted quickly: “135 rides later, it was just like getting up and walking around. You get so used to it.” He became such an expert rider that he ended up teaching anti-G techniques to Navy fighter pilots.

Not everyone was a “G monster” like Cloak. For Barry Shender, one go-round was enough, a routine familiarization ride that didn’t exceed a mild 3 Gs. “I’m not the roller-coaster-ride type,” he admits. Centrifuge engineer Bill Daymon was another one-timer, although in his case the purpose of the ride wasn’t familiarization but basic troubleshooting. “People were hearing noises, and I took a 3-G ride to listen to it,” he recalls. “That was my only ride. The year before I had had bypass surgery, and they were rather reluctant to let me ride it again.”

Subjects generally rode the centrifuge in one of two modes: closed-loop, or dynamic flight simulation, in which the rider had full control over the movements of the centrifuge; and open-loop, or “meat in a seat,” in which the rider was essentially a lab rat at the mercy of the researchers. Riders were usually given various tasks to perform under the G stresses, such as flying simulated combat missions and other activities demanding certain cognitive or motor skills. Doctors monitored all test subjects at every moment, and both the subject and the doctors had the capability to immediately stop the ride. It’s a testament to the Johnsville researchers that no one was ever seriously injured riding the centrifuge.

Despite the discomfort and dangers, willing volunteers were never in short supply. “You have to give a lot of credit to the folks that volunteer to do it,” Shender says, “because basically we beat them up every day, and they come back.” So why did they clamber into the belly of the beast? “Motivations like I want to see what I can do physically. I want to do something that would make good stories. I want to do something that’ll get me out of the office today.” Subjects could also score a souvenir. “If they like, we give them a video of their experiences in the centrifuge so they can show their family and friends when they lose consciousness and how silly they looked.”

The centrifuge research has had a lasting impact on the training of military pilots, the development of anti-G suits and techniques, and the design of aircraft and spacecraft systems. Aside from the biomedical effects of high Gs, the Johnsville researchers investigated practical problems, including the disorientation of Navy pilots following night catapult launches from a carrier, and spin recovery techniques in fighter aircraft such as the F-4B Phantom and F-14 Tomcat. Such projects used the centrifuge’s flight simulation capabilities to full effect. Sometimes the centrifuge was used to re-create the conditions of puzzling crashes that might indicate aircraft design flaws.

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