Deep freeze

In 2012, during the fifth dive of the 7,000-meter sea trial in the Mariana Trench, the Jiaolong reached a maximum depth of 7,062 meters, marking the deepest dive the vehicle has ever completed.

The depth record, however, was only the most visible part of a far more demanding role. As the pilot ultimately responsible for the submersible and its crew, Tang had to ensure their safety, collect valuable scientific data and seafloor samples, and respond to the unknown challenges of the deep sea.

During a dive at a depth of 2-3 kilometers, Tang was observing the seafloor when several ropelike shapes appeared just 5 or 6 meters ahead. Such an obstacle could be catastrophic for a submersible because of the difficulty of escaping entanglement.

He immediately cut thrust and nudged the vehicle upward to investigate, only to discover a deep-sea octopus waving its arms in the darkness.

"If it had been a real cable, we might have been in serious danger," he said.

Another lesson came near a dormant volcanic vent. Pressure from the Jiaolong scraped the crust, triggering a sudden jet of hot hydrothermal fluid. The heat scorched a 20-cm black scar into the submersible's buoyancy block.

"Were the block to fail, it would detach and complicate the submersible's ascent," Tang said.

The incident prompted an immediate review and optimization of the Jiaolong's operating procedures in hydrothermal fields. It also reflected the latter part of Tang's career, which has been increasingly characterized by a pursuit of technical precision.

That pursuit proved vital when the Jiaolong headed north. In the Arctic, the risks were different but no less unforgiving. Water temperatures below zero threatened the submersible's batteries and hydraulic systems, while high-latitude geomagnetism could confuse navigation systems. Meanwhile, "rootless" ice floes could drift hundreds of meters a day, causing the planned exit hole to shift and shrink.

To counter these challenges, Tang's team reinforced the vehicle's cold-resistant systems, installed redundant under-ice positioning systems, and equipped it with ice-profiling sonar and a secondary ballast system. These enhancements laid a foundation for the record-breaking mission.

Behind Tang is a young but experienced team. "From research and development to sea trials and then to operational deployment, the Jiaolong was built through a relay of collective effort," Tang said, recalling how the team once worked until 3 am to secure the next day's dive. They slept where they dropped, still in oil-stained jackets, and rose two hours later to deploy the submersible.

Their drive, Tang explained, stems from a shared conviction to dedicate their youth to China's deep-sea endeavors.

"Today, the vehicle's navigation, observation, communication and environmental sensing have all improved, while the interior has become far more operator-friendly," Tang said. "We must carry forward the crewed deep-diving spirit, continue to explore, utilize and protect the ocean, and contribute more to building China into a strong maritime nation."

limenghan@chinadaily.com.cn