Bathyscaphe Trieste - Design

Design

The Trieste was designed by the Swiss scientist Auguste Piccard and built originally in Italy. His pressure sphere, composed of two sections, was built by the company Acciaierie Terni, and the upper part was manufactured by the company Cantieri Riuniti dell'Adriatico, in the Free Territory of Trieste (on the border between Italy and Yugoslavia); hence that name was chosen for the bathyscaphe. The installation of the pressure sphere was done in the Cantiere navale di Castellammare di Stabia, near Naples. The Trieste was launched on 26 August 1953 into the Mediterranean Sea near the Isle of Capri. The design was based on previous experience with the bathyscaphe FNRS-2, also designed by the Piccards. (It was built in Belgium). Trieste was operated by the French Navy. After several years of operation in the Mediterranean Sea, the Trieste was purchased by the United States Navy in 1958 for $250,000.

The Trieste consisted of a float chamber filled with gasoline for buoyancy, with a separate pressure sphere. This configuration (dubbed a bathyscaphe by the Piccards) 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, the Trieste was more than 15 m (50 ft) long. The majority of this was a series of floats filled with 85,000 litres (22,000 US gal) of gasoline, and water ballast tanks were included at either end of the vessel, as well as releasable iron ballast in two conical hoppers along the bottom, fore and aft of the crew sphere. The crew occupied the 2.16 m (7.09 ft) pressure sphere, attached to the underside of the float and accessed from the deck of the vessel by a vertical shaft that penetrated the float and continued down to the sphere hatch.

In the Trieste the pressure sphere provided just enough room for two people. 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.

The Trieste was later 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 great pressure of 1.25 metric tons per cm² (110 MPa) at the bottom of Challenger Deep, the sphere's walls were 12.7 centimetres (5.0 in) thick (it was overdesigned to withstand considerably more than the rated pressure). The sphere weighed 13 metric tons in air and eight 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 of the sphere's density: it was not possible to design a sphere large enough to hold a person that would withstand the necessary pressures, yet also have metal walls thin enough for the sphere to be neutrally buoyant. Gasoline (petrol) was chosen as the float fluid because it is less dense than water, incompressible even at extreme pressure, thus retaining its buoyant properties and negating the need for thick, heavy walls for the float chamber.

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

Nine tons of magnetic iron pellets were placed on the craft as ballast, both to speed the descent and allow ascent, since the extreme water pressures would not have permitted compressed air ballast-expulsion tanks to be used at great depths. This additional weight was held in place at the throats of two hopper-like ballast silos by electromagnets, so that in case of an electrical failure the bathyscaphe would automatically rise to the surface.

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