James Cameron Plunges Off the Deep End

 

Watching the Deepsea Challenge project … James Cameron of movie-making fame intends to be the first man to return to Earth's deepest waters since the single two-man mission in 1960 by Trieste. Cameron's solo attempt could be any day now. He'll be riding the 13-ton submersible Deepsea Challenger to 36,000 feet below sea level. The goal now is plumb the Challenger Deep, but other deepwater destinations are likely to follow.

Here's a map of the big ditch, from Wiki page; it's a product of tectonic subduction.

The mother ship, Mermaid Sapphire, is in transit to the launch location, having left Guam. That follows a long delay for the weather to moderate. Technicians and engineers used the time to tune up the craft given lessons from previous dives. The bright-green submersible rides on the deck of Mermaid inside a climate-controlled hangar, bolted a rigid frame.

Some info and thoughts, in FAQ format:

Q. How much has the submersible been tested beforehand?

A. The pilot sphere was tested in a Penn State pressure chamber to a crushing force well in excess of the ocean depth of 36,000 feet, so that's pretty dependable. A point of particular interest is the penetration plate, where control and instrument cables must pass through the barrier. Other key components were also pressure tested individually.

The operational craft has not been so tested (the Penn State chamber wasn't big enough), but Cameron has safely taken it down to nearly 27,000 feet. Not surprisingly, some glitches needed attention. Some were minor and had no direct connection to the pilot's safety (difficulties with sampling, and closing a hatchway to store samples). Some were peripherally related to safety (problems with the cameras, one of the 12 thrusters going off line). 

A few of those gremlins had safety implications: an uncommanded dump of trim shot (due to low voltage), uncommanded intermittent operation of thrusters (following a change in programming), and the tripping of an electrical bus that cut off voice communications (possible seawater leakage into electronics). Some other problems were detected during inspections, prior to launch. All concerns have been addressed, we are told.

I haven't seen firm plans about an unmanned test to full depth first, but it's a possibility. Why? Testing and trials so far don't establish how it will perform as an all-up system at depth.

For those interested in technical stuff, there's much of interest in the expedition journal by Dr. Joe McInniss. As he writes: 

 “If something goes wrong, we have to fix it, and fix it quick. There’s no such thing as waiting for the rescue team. We deal with it, or else. And all of these 'or else’s' are not very appealing.”

The journal also includes an email that Cameron wrote to Don Walsh, narrating this month's successful plunge into the New Britain Trench (a record-setter for a solo mission).

Q. How does Deepsea Challenger differ from the bathyscaphe Trieste, the only vessel ever to make a successful dive to the bottom of the Mariana Trench?

A. The new sub's flotation is much more compact, it's got a great deal more equipment for science-gathering, and it's more maneuverable. And its pressure sphere is barely big enough for one man. But engineering is always about trade-offs. For one thing, the small size allows the mother ship to raise it via crane and carry it on board. 

Here's a size comparison, from Gizmag:

Trieste had to be towed to the site, which sometimes caused damage ... as happened before the 1960 expedition.

Here's a diagram of the new sub from the Deepsea Challenge website. What might be called the bow of the craft is on the left side.

Q. What do we know about plans for the manned deep dive?

A. Here's what I gather from the website: The sub starts out in horizontal fashion in its cradle on deck, braced by four steel arms, Cameron climbs in and the hatch is closed. After he finishes the checklist, a crane lifts the craft off the deck and puts it in the water. The craft is now oriented vertically with the pilot's sphere at the bottom end. 

With the aid of inflatable lift bags, it floats upright on the surface for a systems check. On command from Cameron, the divers release the bags and the sub drops at a speed of about 5 mph for about 90 minutes. Cameron slows its descent over the next half hour by dropping steel “trim shot” from a hopper. His goal is to arrive at the bottom with neutral buoyancy … almost. He'll probably aim to keep a little positive buoyancy, that is, a tendency to float upward, so that the craft's optimal depth can be maintained by pointing the six vertical thrusters to push downward, ever so slightly. That avoids stirring up silt, which blocks vision until it settles.

Here's the control panel:

He'll use the six horizontal thrusters to rotate the craft in the desired direction and then go forward. For visibility he depends on the bank of LED lights and the underwater 3D video cameras, rather than the viewport.

The craft is pretty maneuverable, according to the expedition journal. Cameron might roam a couple of miles from his starting point, over the next five or six hours. His trip into the New Britain Trench had him snapping photos of sea creatures, while maneuvering around cliffs he compared to the Grand Canyon.

When Cameron is ready to head up, he'll alert the Mermaid and jettison the two steel ascent weights, which are stowed in slots at the bottom. He has a switch to do this, but there are several backup systems that can dump the ballast as well. One is a corrodable "galvanic timed release," now used in the fishing industry to avoid killing fish in ghost traps. If Cameron were rendered unconscious, the timed release would drop the ascent weights within 13 hours.

Why such redundancy? The mission is a free dive; the sub has no tether or cable that the Mermaid could use to haul it back to the surface. So once stabilized on the bottom, the sub can't come back up until it drops a half-ton of ballast. Nor is it an option to somehow separate the pilot's capsule from the rest of the craft and have it float free. The pressure capsule is so heavy with thick-walled steel to resist the 16,500-psi pressure that it won't float by itself.

The buoyancy that the pilot depends on to get him to the surface is syntactic foam, in this case a patented form of it called Iso-Float, that serves as the green-painted upper body of the craft. (Trieste didn't use it; it depended on thousands of gallons of gasoline for its buoyancy, held in big tanks above the pressure capsule.)

I don't know the unique details of Iso-Float, but in general, syntactic foam is a composite of very small glass or ceramic spheres, bonded into a shape with tough resin. It's also very expensive, per cubic foot. Iso-Float is said to be an improvement on conventional syntactic foam because it's strong enough to serve as girder that connects top to bottom. Tensile strength is no small matter when raising the craft by crane, given that the bottom of the craft is heavy with ballast and the pilot sphere, but the crane lifts from the top. To have the craft break in half at the surface, letting the lower half fall free, could be catastrophic. I haven't seen the safety margin but presume that it's substantial.

Okay, now it's time to go up. Dropping the two 550-lb ascent weights gives the craft enough positive buoyancy to get to the surface in about an hour, depending on how much trim shot Cameron retains in the ballast hopper. It makes a spectacular arrival on the surface; Cameron calls this moment splash-up, as opposed to the space program's splash-down.) 

Good communication with the mother ship avoids a collision with the hull. If standard communications go out, say, due to a power failure, the mother ship will be able to track the craft's rise passively.

Q. What was Cameron referring to during interviews about the mission risks, when he said that two men had once died in a submersible accident?

A. Cameron most likely was referring to the deaths of two men in Johnson Sea Link off Florida in June 1973. At a depth was 360 feet, JSL fouled a cable while at the wreck of Fred T. Berry, a Navy destroyer sunk as an artificial reef. A rescue team pulled the craft up but by that time the two men in the diver's compartment had died from carbon dioxide poisoning. The other two men survived because they were in a separate compartment forward, with different equipment. Here's the NTSB report.

Perhaps reassuring to Deepsea Challenger's crew is that a common cause of submersible mishaps and near-misses has been entanglement, and we can presume there won't be tangling hazards in the Mariana Trench. 

But past lessons are worth reading, and anyone planning to build or board a submersible today would be well advised to read section II of this 1974 safety panel report on submersibles, which summarizes submersible incidents and near-misses during the boom years.

A flip through that report and other articles indicates that one risk is seawater intrusion -- conductive water getting into powered gear such as an electrical bus, sensor, or battery pack. 

Clearly Deepsea Challenger's 67 lithium-ion battery packs are thoroughly engineered for depth -- filled with oil to resist pressure, and having compensation bladders to allow for fluid compression. I asked Robert Wernli Sr. what he thought about the pressure-compensated approach. (Wernli is a long-time submersible engineer, co-author of the ROV Manual, and author of the submersible techno-thriller Second Sunrise. I interviewed him two years ago for my article on the history of ROVs.) Says Wernli:

Lithium ion batteries are common in undersea vehicles today. The ROV/AUV Nereus, that visited the bottom of the Mariana Trench last year, had lithium ion batteries, although they were housed in ceramic pressure housings at one atmosphere. The pressure compensated (PC) housings for the batteries are common in undersea vehicles to save weight by eliminating pressure housings. With proper design, PC systems will survive extreme pressures.

The Cameron deep-dive team knows all about batteries. Among its many experiences was a close-call event in 2001, while descending in a pair of Mir submersibles to the Titanic wreck. One of the two Mirs was carrying a small ROV in a basket when a battery in the ROV violently overheated, belching out superheated bubbles inches from the Mir and raising concern among the three occupants that thermal stress might crack the Mir's viewport. Fortunately they headed for the surface and managed the situation without having to dump the ROV, and the danger passed.  

Fire is also a concern in tight quarters that are jammed with electronics, but there are extinguishers and a closed-circuit breathing system to cope with that contingency.

And means to cope with many others. Given that Deepsea Challenger has multiple and independent methods to jettison its ascent weights, pilot Cameron should be able to get back to sea level in good shape, toting lots of interesting data.

So from all of us, to one of you, bon voyage!