James Cameron is best known (to people of my *ahem* vintage) as the director of Titanic, or (to those slightly younger) as the director of Avatar. As a result of these multi-billion dollar grossing films, he has more leisure time than most of us. He has used this to excellent effect in recent years, and achieved something that very few others could have done.
Cameron’s interest in deep ocean exploration seems to have been born out of his interest in the Titanic, and he has used tethered ROVs to explore the Titanic as described in Ghosts of the Abyss. He partially funded and spearheaded a project to build a submersible capable of carrying one person down into deepest known part of the ocean, the Challenger Deep in the Mariana Trench, between Japan, Papua New Guinea and the Philippines.
Deepsea Challenger is that craft, and Cameron ultimately piloted it to nearly 11,000 metres underwater, and returned safely. James Cameron’s Deepsea Challenge is the story of the design, construction, and testing of Deepsea Challenger, and of her dive to Challenger Deep. Unlike Robert Ballard, who favours unmanned ROVs, James Cameron is a proponent of manned ocean exploration, and I can identify with his enthusiasm for putting human eyes on the seabed (in a figuratively literal sense).
Fewer people have seen the bottom of Challenger Deep than have been on the moon. The last (and first) manned voyage there was in 1960, when Jacques Piccard and US Navy Lieutenant Don Walsh piloted Trieste, a bathyscaphe, there and back. Trieste used gasoline for buoyancy, whereas a special, extremely buoyant foam was developed to do the same job for Deepsea Challenger. The challenges of descending to and ascending from such a depth meant that here and there, seemingly archaic pieces of technology were included in the craft. I was tickled by the release of steel ball bearings to establish initial neutral or slightly positive buoyancy at times.
An aspect of the documentary that I found particularly touching was the presence of Don Walsh on Cameron’s ship, to witness the dive to Challenger Deep. You can read a bit of a review of the documentary here. There is an excellent series of National Geographic articles that will give you a feel for the project: part one, part two, a photo gallery, details of the submersible, and a video.