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U.S. Navy history of submersibles

U.S. Navy tests the "hard suit" (video)

Apart from space, deep water is perhaps one of the most hazardous environments human beings work in. And just like space exploration, working there requires special equipment, extensive training, and careful preparation.

One way to protect divers from high pressures at great depths is to put them in atmospheric diving suits (ADS) that function like person-shaped submarines.

Nuytco Research Ltd., North Vancouver, B.C., is on the cutting edge of ADS development with its Exosuit Swimmable ADS, due for beta testing later this year.

Dr. R. T. “Phil” Nuytten, the company’s founder and chief researcher, has been involved in deep-water diving since the 1960s. In 1987, for example, he developed the “Newtsuit,” an ADS which permits dives of 8 hr down to 1,000 ft.

In the past 20 years, Nuytten has been improving the Newtsuit and putting those innovations toward the Exosuit. The new product is more flexible, capable of longer dives, and applicable to more industries.

Like all ADS, the suit’s rigid structure withstands immense water pressure. More importantly, it lets occupants breathe air with the same pressure and content as the air at the water’s surface.

Saturation dives, in which divers acclimate to underwater environments, change the way gases dissolve in the divers’ blood. Higher pressures below the surface force breathing gases into solution with the blood and body tissues. That’s why deep divers need to surface slowly. As they ascend and pressure around them drops, dissolved gas comes out of solution. If the ascent is slow enough, reformed gas bubbles leave through the lungs. But ascending too fast traps these bubbles in body tissues, causing itching, joint pain, neurologic effects, shortness of breath, and even death.

According to Nuytten, a conventional saturation diver would need to undergo “a slow, finely controlled decompression lasting 8 to 10 days” after he had acclimated to pressures equivalent to 1,000 ft below the surface. Atmospheric dives, like those in Nuytten’s Exosuit, only require 3 to 5-min recovery independent of dive depth and duration.

In the Exosuit, divers are surrounded by air, 80% nitrogen, 20% oxygen, at atmospheric pressure; they don’t need mouthpieces or oral-nasal masks to breathe.

“Oxygen is fed in to match the exact amount metabolized by the diver. Nitrogen acts merely as a diluent,” Nuytten says. Since the atmosphere inside the suit is at 1 atm, divers aren’t susceptible to the bends or nitrogen narcosis. (The latter is impaired perception and judgment a diver can experience as nitrogen or other gases become more soluble in fatty tissue.)

A soda-lime chemical absorbent scrubber removes exhaled carbon dioxide from inside the suit. The scrubber and oxygen circulator are battery powered, but carbon-dioxide removal can be done by passive scrubbing if the battery fails.

To be classified as an A1 submersible, the lifesupport systems have to last at least 72 hr. Nuytco has timed the Exosuit’s duration at over 85 hr.

The suit keeps pressure from getting to its occupant with a combination of rigidity and flexibility. The Exosuit is covered in an A356-T6 aluminium alloy skin cast to an average thickness of 0.375 in. Thicker ribs support high-stress areas of the suit. The suit is cast into molds that can also accommodate titanium alloys that withstand greater working depths.

The standard Exosuit is rated to 1,000 ft or 445 psi. Its crush depth is over 2,000 ft (890 psi). Nuytco intends to test each suit to 623 psi, equivalent to 1,400 ft. This lets the suit be certified as an A1 Submersible.

The core of the suit encases the diver’s torso and head. Rotary jointed arms and legs permit easy movement. The joints are machined from 6061-T aluminium stock and use silicon nitride bearings and PTFE seals. On some models, specially designed seals preserve joint integrity when pressure switches from being greater outside the suit to being greater inside or back the other way.

Joints let divers move the suit’s limbs simply by moving their own limbs. Although the suit’s arms and legs are heavy in air — the suit weighs 260 lb on land — in the water, the force required to move them is similar to that an astronaut needs to operate in a space suit. The confined volume of air, combined with a foam flotation coating, makes the limbs neu- trally buoyant in water. “It’s the syntactic foam which gives the limbs a distinctive scalloped look,” Nuytten says.

Limb mobility lets divers propel themselves by walking or swimming using the suit’s swim-fin boots. Nuytten is working on a thruster pack that would allow the diver to “fly” through the water.

The arms are just as functional. Instead of ending in gloves like space suits, the Exosuit’s uses an artificial hand Nuytco calls the Prehensor. The Prehensor has three fingers that mimic human hand movements, letting users retain 90 to 95% of their usual dexterity. Previous manipulators had two jaws that worked like pliers when divers squeezed handles inside the suit.

Although the Prehensor is still in prototype testing, the finished version will replicate the motions of the diver’s hand inside the suit, including the thumb position, angle and rotation, which make stable grips possible. The final version may also provide proportional sensory feedback that will let users sense and control pressure put on gripped items.

According to Nuytco, the Prehensor lets users perform tasks that require coordination and dexterity such as starting a nut on a bolt thread and tightening it. This capability has attracted the attention of NASA, as well as the Canadian Space Agency, as a possible alternative to conventional spacesuit gloves.

In addition to protecting divers for up to three days, the Exosuit is also less costly to operate. Divers working at saturation depths often let themselves acclimate to higher underwater pressures. To save time, they will continue living at that pressure, either below the surface or in pressurized quarters on a support vessel, until their underwater job is complete.

“Saturation divers require a support crew of 12 to 18,” says Nuytten. “Saturation living chambers and the diving bell that transports saturated workers between living chambers and worksite eat up 1,000 to 1,500 sq ft of critical deck space. With gas storage, the full system can weigh upwards of 100 tons and cost $4 to 6 million.”

Saturation diving also requires special breathing-gas mixtures, like oxy-helium. Helium as a diluent does not impair divers the way nitrogen does. According to Nuytten, oxy-helium for a 1000-ft dive costs about $125,000.

In contrast, the Exosuit needs only a four-person crew. All its components weigh less than 1 ton and take up only 150 sq ft of deck space. Gas for the diver costs about $35/dive, and the suit itself costs less than $250,000.

Better diver safety and lower cost makes the Exosuit attractive for a variety of applications. And Nuytco is making different versions of the suit for different uses.

“The basic suit will be totally autonomous,” Nuytten says. The diver will move by walking or swimming with flippers, and he will have life support for three full days.”

A commercial version is more bare-bones. The diver would be tethered to the surface with lines to supply air and take away carbon dioxide. This simplifies the design and lets Nuytco beef up the suit for industrial applications. Supplying air and exhausting gas to the surface while keeping the suit at 1 atm does present challenges, but Nuytten says his company has a proprietary method of handling the pressure differentials.

A third version is specifically designed to let submarine crews escape disabled vessels. When a sub loses power, it also loses the ability to keep its internal atmosphere at surface conditions, and occupants can start to go into saturation. In that case, crewmembers could wear suits inside the sub to keep their tissues from getting saturated with atmospheric gases while they repair the sub or wait for rescue.

“Alternatively, they could allow themselves to gas-saturate. Then as they ascended, the suit could maintain the pressure they had experienced on the sea floor. Once on the surface, the suit could serve as a personal decompression chamber for each crewmember,” Nuytten says.

The submarine-escape version has joints that tolerate both external and internal pressure. According to Nuytten, no previous or current atmospheric suits are able to do that. The joints give crewmembers enough flexibility to climb up into a stricken sub’s escape lock, operate valves, and perform other tasks.

At the moment, the Exosuit is a prototype; Nuytten hopes beta testing will begin later this year. Nuytco has completed patterns for the torso and limbs and made test castings. It has also tested individual subsystems, like swim-testing the rigid lower torso and flexible legs.