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'Trieste' as the convergence of the Piccards' scientific ambition and de Henriquez's vision of technology serving peace during the Cold War era. The pressure sphere was built separately and installed on the hull in the Cantiere navale di Castellammare di Stabia, near Naples.
The pressure sphere was attached to the underside of the hull and accommodated two crew who accessed it via a vertical shaft through the hull; this access shaft was not pressurized and flooded with seawater on descent. The sphere was completely self-contained, having a closed-circuit rebreather system with oxygen provided from cylinders while carbon dioxide was scrubbed from the air by being passed through canisters of soda-lime. Batteries provided electrical power.Piccard's original pressure sphere was built by Terni società per l'industria e l'elettricità spa of Terni/Italy, of steel forged in two hemispheres and joined to form a sphere 2.4 m in diameter and 89 mm thick. It was replaced in December 1958 with a sturdier sphere by the Krupp Steel Works of Essen, Germany, forged in three sections; an equatorial ring and two caps, which were finely machined and joined. The instrument rack for the sphere made by Krupp was separately manufactured by the Ateliers de Constructions Mécaniques de Vevey and subsequently brought to Germany to be integrated into the sphere. The new sphere was also steel, but smaller at 2.16 m diameter and with thicker walls, at 127 mm, calculated to withstand the 1250 kg/cm2 pressure at the bottom of Challenger Deep plus a substantial factor of safety. The new sphere weighed 14.25 MT in air and 8 MT in water giving it an average specific gravity 2.6 times (or 1.6 times greater than) that of seawater (13÷(13-8)).Outside observations by the crew were made through a porthole made from a single, tapered block of acrylic glass; the only transparent material available that could withstand the pressure. Outside illumination was by quartz arc-light bulbs, which could withstand the pressure without modification.The buoyancy tanks were filled with gasoline, which floats in water and is similarly incompressible. Changes in the volume of the gasoline caused by any slight compression or temperature changes were accommodated by the free flow of seawater into and out of the bottom of the tanks during a dive via valves, equalising the pressure and allowing them to be lightly built.
Ballast was held in two conical hoppers fore and aft of the crew sphere each containing 9 MT of iron shot. This shot ballast allowed the craft to sink, and its release caused it to ascend. The iron shot was locked in place at the throats of the hoppers by electromagnets thus was released either by switching the electromagnets off or automatically in the event of an electrical failure. Progressive release allowed buoyancy trim. Compressed-air-driven variable-buoyancy pressure vessels typically used in submarines are not feasible at extreme pressure.
Water tanks at each end of the hull were pumped out for flotation, lifting, and towing on the surface and fully flooded to allow sinking.
Following its acquisition by the United States Navy, Trieste was modified extensively by the Naval Electronics Laboratory, San Diego, California, tested in the Pacific Ocean over the next few years, and culminated in a dive to the bottom of Challenger Deep 23 January 1960.

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