The Indian Space Research Organisation (ISRO) has achieved a significant milestone in its Deep Ocean Mission with the successful development of the personnel sphere for the MATSYA-6000 submersible. This submersible is designed to carry a crew of three humans to depths of 6,000 meters. The project, named 'Samudrayaan,' is overseen by the Ministry of Earth Sciences (MoES) and aims to enhance India's capabilities in deep-sea exploration.
The personnel sphere, a critical component of the submersible, measures 2.26 meters in diameter and has a wall thickness of 80 millimeters. It is constructed from a titanium alloy known for its high strength and corrosion resistance. This pressure hull is engineered to withstand extreme pressures of up to 600 bar and temperatures as low as -3°C, ensuring the safety of the crew at great ocean depths.
One of the most significant technical challenges was developing a reliable Electron Beam Welding (EBW) process capable of fusing the thick titanium plates. The Liquid Propulsion Systems Centre (LPSC) in Bengaluru took on this task, augmenting its welding facility from a 15kW to a 40kW EBW capacity. Over 700 weld trials were conducted to optimize the process parameters, ensuring high quality and structural integrity.
To ensure the quality of the welds, ISRO enhanced its X-ray radiography capability, creating one of the highest energy levels used in India. This allowed for detailed non-destructive evaluation (NDE) of the welded joints. Techniques such as Time of Flight Diffraction (TOFD) and Phased Array Ultrasonic Testing (PAUT) were employed to detect microscopic defects, guaranteeing safety and reliability. Artificial defects were also introduced in test samples to validate and calibrate the inspection techniques.
The first welding on the actual hardware was completed after the extensive process development and optimization. This involved high penetration welding of 80mm thickness over a 7100mm length, achieved in a continuous 32-minute operation, which ISRO called "a national first in scale and precision". Third-party certification agencies are currently reviewing and approving the welding procedures, qualification protocols, and NDE processes.
The successful welding and rigorous testing of the full-scale personnel sphere marks a significant achievement for India. This accomplishment places India among a select few nations with the technological expertise to construct deep-sea human habitats. Once complete, the MATSYA-6000 vehicle will be among the few human submersibles in the world capable of reaching such depths, opening new opportunities for deep-sea science, resource exploration, and technology development.
