Tony Robinson's Titanic Adventure
The Mir Submersibles
The alien environment in which Titanic lies is almost as hostile as outer space. Here, the pressure due to the weight of water is over 400 times that of the atmospheric pressure at sea level – it's more than enough to crush a human instantly. Equally hostile is the temperature, which hovers just above freezing point. The water is so deep that no light and heat from the Sun can ever penetrate this world of icy perpetual darkness.
To explore such a harsh environment requires a special type of submarine – the Mir submersible. Jointly designed and built by scientists at the Russian Academy of Sciences and the Finnish company Rauma Raepola Oy, the two Mir submersibles, Mir 1 and Mir 2, represent the cutting edge of underwater exploration. They are capable of diving to a depth of almost 6000 metres (equivalent to two thirds the height of Everest), allowing them to explore 98% of the ocean floor.
A Mir submersible weighs in at a little over 18 tonnes and has a total length of 7.8 metres. The 2.1-metre diameter cabin sphere is constructed of specially strengthened nickel steel and at 5 centimetres thick is designed to withstand enormous pressure. Inside, the air pressure is kept at a comfortable one atmosphere.
Mir can accommodate a maximum crew of three – the pilot and two others. After squeezing through the top hatch, each crewmember can be sustained by the submersible's life support system for approximately three and a half days.
The air the crew breathe is recycled in a similar way to that onboard the space shuttle – using lithium hydroxide scrubbers to remove what would be a deadly build-up of carbon dioxide. There are, incidentally, no toilet facilities on board!
Diving in the sub is a slow process. The descent rate is typically 35-40 metres per minute, and diving to Titanic takes well over an hour. Once at the seabed, Mir may travel around by means of large manoeuvrable propellers, at a top speed of 5 knots. Mounted on the side of the submersible are smaller propellers used to steer the craft.
At the seabed, Mir gets to work, documenting objects of interest with a sophisticated package of lighting and camera equipment, customised to suit individual requirements. When filming James Cameron's blockbuster Titanic, for example, six 5000-watt lights were adapted and fixed externally, along with high-definition cameras. With both Mirs at their disposal, a film or science crew have the advantage of using one submersible as a lighting platform, whilst the other is concentrated on filming.
Real-time images are relayed to a suite of monitors inside the submersible. Mir does have three portholes, but owing to the enormous pressures encountered they have to be small to reduce the risk of structural failure (the largest is only 20 centimetres in diameter).
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