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Bathyscaphe Trieste

Trieste was a Swiss-designed deep-diving research bathyscaphe ("deep boat") with a crew of two people, which reached a record-breaking depth of about , in the deepest part of any ocean on earth, the Challenger Deep in the Mariana Trench, in 1960. The dive has never been repeated, and currently no crewed or uncrewed craft exists capable of reaching such depth.

Design

Trieste was designed by the Swiss scientist Auguste Piccard and built in Italy. The pressure sphere, composed of two sections, was built by Acciaierie Terni, and the upper part was manufactured by Cantieri Riuniti dell' Adriatico, Trieste; thus the name of the vessel. The installation of the sphere was done in Cantiere navale di Castellammare di Stabia, near Naples. The Trieste was finally launched in 26 August 1953 in the Mediterranean near the Isle of Capri. The design was based on previous experience with the FNRS-2, also designed by Piccard and built in Belgium and operated by the French Navy. After several years of operation in the Mediterranean the Trieste was purchased by the U.S. Navy in 1958 for $250,000.

The Trieste consisted of a float chamber filled with gasoline for buoyancy, and a separate pressure sphere. This configuration (dubbed a "bathyscaphe" by Piccard), allowed for a free dive, rather than the previous bathysphere designs in which a sphere was lowered to depth and raised from a ship by cable.

At the time of Project Nekton, Trieste was over 15 m (50 ft) long, the majority of this was a series of floats filled with 85 m³ (22,500 US gallons) of gasoline, and water ballast tanks at either end of the vessel as well as releasable iron ballast in two containers along the bottom, fore and aft of the crew compartment sphere. The crew occupied the 2.16 m (6.5 ft) pressure sphere, attached to the underside of the floats and accessed from the deck of the vessel by a vertical shaft which penetrated the float and ran down to the sphere hatch.

In the Trieste the pressure sphere provided just enough room for two persons. It provided completely independent life support, with a closed-circuit rebreather system similar to that used in modern spacecraft and spacesuits: oxygen was provided from pressure cylinders, and carbon dioxide was scrubbed from breathing air by being passed through canisters of soda-lime. Power was provided by batteries.

Trieste was fitted with a new pressure sphere, manufactured by the Krupp Steel Works of Essen, Germany, in three finely-machined sections (an equatorial ring and two caps). To withstand the high pressure of 1.25 metric tons per cm² (110 MPa) at the bottom of Challenger Deep, the sphere's walls were thick (it was overdesigned to withstand considerably more than the rated pressure). The sphere weighed 13 metric tons in air and 8 metric tons in water (giving it an average specific gravity of 13/(13-8) = 2.6 times that of sea water). The float was necessary because the sphere was dense: it was not possible to design a sphere large enough to hold a person which would withstand the necessary pressures, yet also have metal walls thin enough for the sphere to be neutrally-buoyant. Gasoline was chosen as the float fluid because it was lighter than water, yet relatively incompressible even at extreme pressure, thus retaining its buoyant properties.

Observation of the sea outside the craft was conducted directly by eye, via a single highly-tapered cone-shaped block of Lucite (Plexiglas) plastic, the only transparent substance identified which would withstand the needed pressure, at the design hull thickness. Outside illumination for the craft was provided by quartz arc-light bulbs, which proved able to withstand the over-1000 atmosphere pressure without any modification.

Nine tons of iron pellet shot were taken on the craft as ballast, both to speed the descent and allow ascent, since the extreme pressures would not have permitted air-ballast tanks to be refilled with gas at depth. This additional weight was held actively in place at the throats of two hopper-like ballast silos by electromagnets, so that in case of an electric failure the craft would immediately rise to the surface.

Transported to the Naval Electronics Laboratory's facility in San Diego, the craft was extensively modified and then used in a series of deep-submergence tests in the Pacific Ocean during the next few years, including a dive to the Mariana Trench, the deepest known part of the ocean, in January 1960.

The Mariana Trench dives

Trieste departed San Diego on October 5, 1959 on the way to Guam by the freighter Santa Maria to participate in Project Nekton — a series of very deep dives in the Mariana Trench.

On January 23, 1960, Trieste reached the ocean floor in the Challenger Deep (the deepest southern part of the Mariana Trench), carrying Jacques Piccard (son of Auguste) and Lieutenant Don Walsh, USN. This was the first time a vessel, manned or unmanned, had reached the deepest point in the Earth's oceans. The onboard systems indicated a depth of , although this was later revised to , and more accurate measurements made in 1995 have found the Challenger Deep to be slightly shallower, at .

The descent took 4 hours and 48 minutes before reaching the ocean floor. After passing 9,000 meters one of the outer Plexiglas window panes cracked, shaking the entire vessel. The two men spent barely twenty minutes at the ocean floor, eating chocolate bars to keep their strength. The temperature in the cabin was a mere 7°C (45°F) at the time. While on the bottom at maximum depth, Piccard and Walsh (unexpectedly) regained the ability to communicate with the surface ship, USS Wandank II (ATA-204), using a sonar/hydrophone voice communications system. At a speed of almost a mile per second (about five times the speed of sound in air), it took about 7 seconds for a voice message to travel from the craft to the surface ship, and another 7 seconds for answers to return.

While on the bottom, Piccard and Walsh observed small soles and flounders swimming away, proving that certain vertebrate life can withstand all existing extremes of pressure in earth's oceans. They noted that the floor of the Challenger Deep consisted of "diatomaceous ooze".

After leaving the bottom, they undertook their ascent, which required 3 hours, 15 minutes. Since then, no manned craft has ever returned to the Challenger Deep. A Japanese robotic craft Kaiko reached the bottom of the Challenger Deep in 1995. This craft was lost at sea in 2003, leaving no craft in existence capable of reaching these most extreme ocean depths.

Other deep dives by Trieste

In April 1963, Trieste was modified and used in the Atlantic Ocean to search for the missing submarine . In August 1963, Trieste found the wreck off New England, 8,400 feet (2.56 km) below the surface. The bathyscaphe was then retired and dismantled. The Krupp pressure sphere is now on display at the Naval Historical Center, Washington D.C.

Her original Terni pressure sphere was incorporated into the Trieste II, which also conducted some dives to the Thresher site in 1964.

In 1966, the pressure sphere of the Trieste II was replaced by a new sphere designed for work at depth.