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The mineral scarcity and rising prices of gold, copper and rare earth minerals is creating great interest among many nations for deep ocean mineral mining. The oceans, which cover seventy percent of our earth’s surface are believed to be able to satisfy our need of minerals like gold, copper, silver, zinc, cobalt and manganese for the next hundred years. There is enough gold on the seafloor to give every person alive nine pounds, scientists estimate. That would be worth about $150 trillion, or $21,000 a person.
Three kinds of platforms are generally used for mineral exploration the Remotely Operated Vehicles (ROV), Autonomous Underwater Vehicles (AUV) and manned submersibles. The manned submersible has advantage owing to the presence of the human in the loop when compared to the spatial limitations of tethered remotely operated vehicles (ROV) and requirement of autonomous technologies for underwater vehicles (AUV) which lacks human intervention. The primary advantage is that it permits the trained mind and eye to work in situ at greater depths in the ocean.
The mineral exploration requires submersibles to have capacity to teach deep underwater and with large endurance as the gas Hydrates in marine sediments are only found at more than 1000 m depth, hydrothermal Sulphides at greater than 2500m and Poly Metallic Nodules at more than 5500m depth.
Manned submersibles have long history, on 17 Mar, 1966 the US Navy’s deep-sea vehicle Alvin located a hydrogen bomb on the seafloor off the coast of Palomares, Spain. The new Alvin can reach the depth of 6500 m and endurance of 6-10 hours. Japanese manned submersible Shinkai 6500 which has 1 pilot and 2 observers has also carried out Hydrothermal Vent Exploration. Russian MIR 1 and 2 can also reach the depth of 6000 meters and have endurance of 17-20 hours. China launched JIAOLONG in 2010 can reach upto the depth of 7000 meters and have endurance of 12 hours.
OceanGate (Everett, Wash., U.S.) announced in November that it plans to build two new submersibles using its carbon fiber and titanium design, called Cyclops 3 and Cyclops 4, to meet increasing expeditionary, research and commercial demand for deep-sea manned submersibles. The company says it has begun construction planning for the two new submersibles, which are planned to be rated for up to 6,000 meters.
Operational deep-sea manned submersibles are important underwater vehicles that provide strong technical support for international deep-sea research. Deep sea reach is also important to Navies which can collect the information about enemy submarines as well as carry out their own operations undetected. China continues to make progress in deep sea exploration following the three-month mission of a new underwater glider in the South China Sea, which experts said will also help in maritime warfare.
China’s manned submersibles
China has completed the construction of a manned cabin for a new deep-sea manned submersible, which would be capable of carrying three persons deeper than 10,000 m. There are three observation windows on the spherical shell of the manned cabin. The one on front side is main driving window, while the remaining two on both sides are for general observations. After the crew enters the cabin from the top, the hatch cover gets closed, making the spherical shell completely enclosed. The shell will be the only activity space for crew members. With a diameter of less than two meters, the crew can only squat or sit in the cabin. Further work, including the installation and integration of devices in and outside the cabin is being progressed.
The cabin made of titanium alloy is the core component of the deep-sea manned submersible, and has reportedly passed through hydrostatic pressure-test and has received approval for the integration into the submersible unit.
The submersible was developed and built after a second-generation ‘Rainbow Fish’ vehicle reached a depth of more than 10,900 meters in 2018. When this submersible gets completed, it will be able to go deeper down into Mariana Trench in the Pacific Ocean, than the Chinese existing manned submersible ‘Jiaolong’ which achieved a diving depth of 7062 m in Jun 2012. It will enable China to carry out scientific research in the hithertofore unexplored deepest sea areas. With this breakthrough, China will be capable of exploring more than 99.8 percent of the ocean areas.
China another manned submersible, Shenhai Yongshi (Deep Sea Warrior), can reach a depth of 4,500 meters. Submersible finished the first ocean expedition of its operation stage, according to Science and Technology Daily. It returned to its mother vessel Tansuo-1 in May 2018 after over eight hours’ exploration in the South China Sea, carrying with it samples collected from a cold seep at a depth of about 1,400 meters.
The submersible conducting the third phase of science expedition in this sea area has completed three diving tasks within two days, including two successive night dives, which is quite extraordinary since other than China, there is only one country, Russia, that has mastered the night-dive technology
According to team leader Peng Xiaotong, night dive is challenging as it is hard to ensure the safety when launching and retrieving the submersible at night. Owing to an effective operation-and-maintenance procedure, Deep Sea Warrior can work full-time with enhanced efficiency and emergency response capability.
China’s deepsea manned submersible Jiaolong, which set a record by diving to a depth of 7,062 meters during tests in the Mariana Trench in June 2012, will officially begin operation in 2018. It finished a dive in “Challenger Deep” in the Mariana Trench, the world’s deepest known trench, in May 2017. By being able to dive to such depths, the vessel can conduct research and exploration on 99.8 per cent of the world’s seafloors.
The latest dive was the first of 10 dives planned for the third stage of China’s 38th oceanic expedition. The dive began at 7:09 a.m. local time. Nearly three hours later, the submersible reached the planned depth of 4,811 meters, where scientists worked for more than three hours. They conducted observation, sampling and surveying, and collected seawater, rocks and samples of marine life, including a sea cucumber, a sponge and two starfish.
China plans to develop two deepsea manned submersibles able to reach a depth of 11 kilometers (6.8 miles) by around 2020.
China will begin a global deep-sea scientific exploration mission with its Jiaolong manned deep-sea submersible starting in 2020, an official from the State Oceanic Administration said, as the vessel returned home last month. Sun Shuxian, deputy director of the administration, said the mission will begin around June 2020 and last about one year. It will cover the Pacific, Atlantic and Indian oceans.
The grand mission is intended to strengthen China’s capability in surveying and researching the deep-sea environment and resources, and will secure the nation a bigger say in this field, Mr Sun said, adding that no country has carried out such an extensive exploration mission. The mission will use a new mother ship for the submersible. Construction will begin on this vessel soon, and it will be put into service in 2019, he said.
India developing Deep Sea Manned Submersible
India’s National Institute of Ocean Technology (NIOT) is all set to design a new submersible vehicle, which will enable three persons to directly explore oil traps, gas hydrates under the ocean ground-level, said S Ramesh, scientist from the institute.
Ramesh said that an unmanned submersible vehicle is being used to explore the natural resources underneath the sea, and the new project would enable the vehicle to be operated by three people. “We are working on a new submersible vehicle design which could man three people for exploring the resources directly under the depth of 6,000 meters,” he added.
ISRO successfully developing a design for its crew module, a sphere shaped capsule. “The design for the manned submersible’s sphere has been successfully developed by ISRO. Now it has to be certified and then we will go ahead with the fabrication,” Secretary, Ministry of Earth Sciences, Madhavan Nair Rajeevan said. An MoU has already been signed between the ISRO and NIOT on development of the module.
A three member crew can be accommodated in the sphere, one of the key components of the manned submersible vehicle. “Work is already on for the deep ocean mission and scientific and technical work has started,” he said.
NIOT is tasked with aspects like electronics and navigation for the manned submersible. Also, multiple agencies, including the Goa based National Centre for Polar and Ocean Research, Centre for Marine Living Resources and Ecology at Kochi and Indian National Centre for Ocean Information Services (Hyderabad) are involved in the initiatives.
The submersible vehicle is expected to travel to a depth of approximately 6,000 metres under the sea for various studies, whereas submarines can reach only about 200 metres. This initiative is a part of the Deep Ocean Mission.
Deep Sea submerisble technologies
At an average depth of about 3,810m, with a maximum depth, at Challenger Deep in the Pacific, of 10,916m, the world’s oceans offer a formidable challenge to explorers. Scientists, marine biologists or oil and gas engineers and others who would dive to such depths require a vessel that can withstand deepsea water pressure that, at the 10,916m average, is a massive 5,551 psi or 378 atmospheres.
Such vessels, called submersibles, offer capacity for three to five occupants, can explore depths from 1,200m to 6,500m, provide a viewing porthole or portholes, and are equipped with lighting systems and cameras. Conventional submersibles feature steel, aluminum or titanium hulls. Metallic hulls, however, because they are not buoyant in designs for depths of more than 2,000m, present challenges when it comes to managing ballast for ascent and descent. In particular, metal-hulled craft require the use of syntactic foam attached to the outside of the craft to achieve neutral buoyancy.
Deep-sea exploration — even in a well-designed, well-engineered, pressurized submersible — is not trivial and does carry with it substantial risk. The world record free-dive depth for a human is 214m (312 psi), and for most people the “safe” depth is probably half that. Thus, in the event of catastrophic failure of a submersible at any depth greater than even 250m, deepsea water pressure would instantly kill every passenger on board.
The biggest challenge, Spencer reports, was developing a manufacturable design that “would produce a consistent part with no wrinkles, voids or delaminations.” And without use of an autoclave. Spencer opted for a layup strategy that combines alternating placement of prepreg carbon fiber/epoxy unidirectional fabrics in the axial direction, with wet winding of carbon fiber/epoxy in the hoop direction, for a total of 480 plies.
The critical technologies of manned Submersible are Vehicle design which can withstand ; personnel sphere material selection, design, fabrication and certification ; Viewports design (PVHO) and realization, Life support systems, Underwater Communication, Power budget and Battery pods and Emergency recovery.
Navigation and positioning technologies are expected to facilitate the complete exploitation of the scientific value of samples and data collected by such submersibles, improve their underwater operation efficiency and enhance their safety.
World’s Largest Carbon Fiber Manned Submersible Hull Proven to 4000 Meters
OceanGate announces successful unmanned depth test of the manned submersible, Titan, to validate the hull to a depth of 4,000 meters (13,123 feet). Titan is the world’s first privately owned five-person manned submersible to reach this depth and opens over 50% of the ocean to manned exploration. Designed and engineered by OceanGate, Titan is constructed from carbon fiber and titanium and is the largest submersible of its type in the world.
Titan is constructed of carbon fiber and titanium, making it significantly lighter than other submersibles constructed from just steel or titanium. The vessel’s light weight coupled with an integrated launch and recovery platform significantly reduces transport and operating costs making it a more financially viable option for individuals interested in exploring the deep. The sub is scheduled to survey the wreck of the RMS Titanic in 2019.
OceanGate CEO Stockton Rush says the company had been evaluating the potential of using a carbon fiber composite hull since 2010, primarily because it permits creation of a pressure vessel that is naturally buoyant and, therefore, would enable OceanGate to forgo the use — and the significant expense — of syntactic foam on its exterior. So, for Cyclops 2 OceanGate decided to avoid the metallic hull altogether and began a search for a manufacturer that could help it develop a composite hull.
Stockton Rush, OceanGate’s CEO and Chief Pilot founded OceanGate in 2009 with the mission to make deep sea exploration accessible to the modern-day explorer. For decades, deep sea exploration has been limited by a severe lack of resources and government funding, and it is estimated that less than 95% of the world’s oceans have been explored to date. Titan is one of only five known manned submersibles in the world capable of reaching 4000 meters and it is the only one that is privately owned.
Cyclops 2 will consist of six primary structures:
A cylindrical composite hull with room for five adults (a pilot and four passengers).
Two titanium interface caps (one bonded to each open end of the hull).
Two separate titanium hemispherical domes, the front one featuring an integrated 380-mm-diameter acrylic viewport.
A glass fiber composite outer shell, bolted to flanges on the titanium interface caps.
A landing skid structure, also attached to the interface caps.
Cyclops 2 faces potential failure in any one of three structures: the composite hull, the titanium end caps and the acrylic viewport. OceanGate designed a real-time health monitoring system that will acoustically monitor the composite hull to detect the pings and pops that signal to the pilot the risk of potential failure. Strain gauges will measure the health of the titanium end caps, which will see a maximum axial end dome load of up to 22 million lb. The viewport, says Rush, because it is acrylic, fails optically long before it fails structurally — and in this case, catastrophically — thus the crew will detect a problem visually first. In any case, the goal is to alert the pilot of potential catastrophic failure in time to enable movement of the craft to shallower, safer water.
Titan is also the first, and only, manned submersible to implement real-time hull structural health monitoring by placing acoustic sensors and strain gauges throughout the hull. “The use of an acoustic emission monitoring is critical for human occupied pressure vessels” commented Allen Green, an expert in acoustic emissions monitoring. “This safety feature gives real time feedback and warns the pilot well in advance of any potential problem. It’s an early warning system that no other sub has.”
References and resources also include:
https://www.compositesworld.com/articles/composite-submersibles-under-pressure-in-deep-deep-waters
https://www.compositesworld.com/articles/composite-submersibles-under-pressure-in-deep-deep-waters
