Sea Pole-class bathyscaphe

The Sea Pole (Hai Ji, or 海极) class bathyscaphe is a class of little known bathyscaphe of the People's Republic of China (PRC), capable of diving up to 7,000 metres, covering 99.8% of the oceanic floor of the world. Two units of this class in planned, with derivatives to follow, and they all are used by both the civilian and military establishments in China.

Design
Sea Pole class bathyscaphe is designed by the 702nd Research Institute of China Shipbuilding Industry Corporation. The general designer is Mr. Xu Huangnan (徐芑南), a professor of School of Naval Architecture, Ocean and Civil Engineering(船舶与海洋工程学院) of Shanghai Jiao Tong University (SHJTU), who also designed many other Chinese submersibles and unmanned underwater vehicles. The first deputy general designer is Mr. Cui Weicheng (崔维成), and the deputy general designer was Mr. Zhu Weiqing (朱维庆), all of the three are academician of Chinese Academy of Sciences. There are two mechanical arms with associating tools that enable the bathyscaphe to perform a various tasks at its maximum operational depth, and this pair of mechanical arms with 7 degrees of freedom (7-DOF) are mounted on the right and left sides of the vehicle, which is powered by 110 kWh (110 V, 800AH) silver oxide – zinc batteries.

Sea Pole bathyscaphe is equipped with a various communication systems, but the data transfer rate remains a bottleneck, with the transmission rate only being 80kbit/s, compared to 100Mbit/s in the usual internet transmissions. As a result, the transmission of an ordinary color image requires approximately half a minute.

The pressure hull is built of titanium alloy, and the manufacturing method for the pressure hull involves producing two hemispherical parts by tungsten inert gas welding (TIGW) six-side plates to a top plate, followed by heat treatments and polishing by machining; the two halves are then joined by TIGW to form a complete sphere. The plate thickness is 76 – 78 mm, with deviations of ±4mm in the completed radius, and sphericity is 0.4% or less. Pressure tests of the pressure hull was performed in Russia, and included a one-hour test at a water pressure equivalent to 7,700 metres, or a 10% greater depth than the vessel's, 7000 metre maximum operational depth, a continuous either hour test at water pressure equivalent to 7000m, and a test simulating 0 to 7,000 metre ascent/descent of the submersible, which was repeated six times. There was not any problem reported in any of these tests, and the pressure hull passed with flying colours.

All viewports of Sea Pole class bathyscaphe have a circular truncated cone shape. There is a large viewport with diameter of 20 cm mounted in the bow, and this central view port is the same type of that of Russian Mir class bathyscaphe. The two additional smaller side viewports of 12 cm diameter are mounted on portside and starboard side, closer to the front than other bathyscaphes. The advantage of this arrangement is that it enables navigation while both the pilot and the scientists simultaneously observe an objective in front of the vehicle. However, the side views have limited field of vision. There are two onboard life supporting system based on that of Shenzhou 6 spacecraft, and additionally, there are two onboard oxygen generating systems independent of life supporting system for additional safety. The pressure hull is built of titanium.

Sea Pole class bathyscaphe has a teardrop shape tapering toward the stern and four tail fins which form an X shape. The main thruster system is based on the same design principle as that of the Russian Mir class bathyscaphe. Four main thrusters inclined in a narrowing shape are mounted in the spaces between the four fins. One horizontal thruster is mounted on the top of the bow, and thrusters for vertical / horizontal turning and auxiliary propulsion are provided on the two sides of the hull. Parallel movement in the horizontal direction is achieved by using a combination of the horizontal thruster on the bow and the right and left stern thrusters, while vertical movement uses a combination of the bow side thrusters and the top and bottom stern thrusters.

Sea Pole 1
Sea Pole 1 (Hai Ji Yi Hao, 海极一号) or Sea Pole #1, is the first unit of Sea Pole class bathyscaphe. Due to the high standard of design requirement, the Chinese industrial capability is not adequate enough to meet the requirement, and as a result, the titanium pressure hull is built in Russia, the mechanical arms are built in USA, and the buoyancy system is built in UK. Sea Pole 1 begins trial at the sea in October 2008, and reportedly entered service in 2009. Trials were mostly conducted with a mother ship named (Da Yang Yi Hao, 大洋一号), a modified research ship. Although Sea Pole class bathyscaphe is designed to carry an operator with two scientists, Chinese authorities have announced that in the near future, Sea Pole 1 will carry three operators and no scientists for test and evaluation purposes. The unit price of Sea Pole 1 is around 180 million ¥, or roughly 25 million US dollars.

Sea Pole 2
Sea Pole 2 (Hai Ji Er Hao, 海极二号) or Sea Pole #2, is the 2nd unit of the Sea Pole class bathyscaphe, and possibly the last unit of this class. Unconfirmed Chinese reports (mostly on the internet) have suggested that previous deals China signed with foreign contractors for Sea Pole 1 included technological transfer, and Sea Pole 2 would utilize more domestically produced components once Chinese manufacturers mastered the technologies transferred, but such claims have yet to be confirmed by independent or official sources. One of the most important upgrade of Sea Pole 2 is to increase its communication capability by boosting the data transmission rate via fiber optics. Based on the experience of sea trials of Sea Pole 1, it was recommended that a class of dedicated mother ship of to be built, with the first one being Great Ocean II (Da Yang Er Hao, or 大洋二号).

Specifications
The specification for Sea Pole 2 bathyscaphe is not yet publicized, but it is reportedly differs from that of Sea Pole 1 slightly. The specification of Sea Pole 1 is listed here.
 * Length: 8.2 metre
 * Width: 3 metre
 * Height: 3.4 metre
 * Inner diameter of the pressure hull: 2.1 metre
 * Mass: 24 tons in air
 * Payload: 220 kg
 * Maximum speed: 2.5 kt
 * Cruise speed: 1 kt
 * Worst weather condition for deployment: Sea state 4
 * Crew: 3
 * Endurance: 12 hr
 * Maximum operating depth: 7,000 metres
 * Never to exceed depth: 7,100 metres
 * Crash depth: 7,700 meter
 * Life support: 3 x 12 hr

Dragon class bathyscaphe
Dragon (Jiao Long, 蛟龙) class bathyscaphe is developed from Sea Pole class bathyscaphe, claimed to be a indigenous design by the Chinese government. Designed by the 702nd Research Institute of the China Shipbuilding Industry Corporation, Dragon class bathyscaphe is slightly smaller than its predecessor, with overall length slightly reduced to 8 metre from the original 8.2 metre of Sea Pole class. Other external difference included the reconfiguration of the support skid: instead of a single large skid on each side totalling a pair in the Sea Pole class, the support skid system of the Dragon class is consisted of two smaller ones on each side, totalling four. The propulsion system of the Dragon class is also different than that of the Sea Pole class: while the propulsion system at the stern remain unchanged, the smaller thrusters at port side and starboard side on board Sea Pole class is replaced by a pair of much larger thrusters on the Dragon class, with one on each side. Furthermore, these two larger thrusters are protected by frames that are not present on the Sea Pole class. Other dimensional and performance parameters remain the same.

Harmony class bathyscaphe
Harmony (He Xie 和谐) class bathyscaphe is a further development of the original Sea Pole class, and looks very similar to the Dragon class bathyscaphe. The main external difference between the Dragon class and the Harmony class is in the number of search lights: instead of three on the port and starboard sides as on the Sea Pole and Dragon classes, there are four on the Harmony class, and instead of four above the main observation window on the Sea Pole and Dragon classes, there are five on the Harmony class.

Deployment
Sea pole class bathyscaphes are deployed on the mothership, Chinese research ship Xiangyanghong (向阳红) No. 9, the only ship right now capable of handling these bathyscaphes. More ships need to be built or converted if every bathyscaphe is to have its own mothership. At least one specially built mothership is requested by the scientific research establishment in China, designated as Great Ocean No. 2 (Da Yang Er Hao, 大洋2号). However, in an interview in March, 2009, the general engineer of the 702nd Institute, Mr. Yan Kai (颜开) revealed that there was not sufficient funding and the program was significantly slowed down, with the work on the follow-on units postponed. Meanwhile, the first unit completed 300 metre dive test after 18 dives on Sept 20, 2009. In early Oct 2009, it reached 1109 metre depth during test dives. On May 31, 2010, 3000 meter dive tests begun, concluded on Jul 18, 2010, with test dive reaching 3757 metre on Jul 9, 2010. More test to follow up on the availability of funding. Should enough funding is provided for all units planned, only one unit would be operating at any given time, while the second unit is in transit, the third is being maintained, and the fourth being used for training.