The level of CO2 in our atmosphere is increasing at alarming levels, affecting all life on Earth either directly or indirectly. For instance, it is related to global warming risks, reducing the quantity of ice in the polar regions, which in turn changes the level of seas all around as the ice melts. This has significant consequences on several human activities such as fishing. It also affects the submarine environment adversely, together with the associated biological sphere. For long, scientists have been monitoring the marine environment and studying the status of the seas.
However, the harshness of the marine environment and/or the remoteness of the location preclude many explorations under the sear by vehicles driven by the mother ship. Scientists are of the view robots could effectively contribute to such challenging explorations. This view has led to the development of Autonomous Underwater Vehicles or AUVs.
One such AUV is the Semi-Autonomous Underwater Vehicle for Intervention Mission or SAUVIM, and is expected to address challenging tasks as above. The specialty of SAUVIM is its capability of autonomous manipulation underwater. As it has no human occupants and no physical links with its controller, SAUVIM can venture into dangerous regions such as classified areas, or retrieve hazardous objects from deep within the oceans.
This milestone is a technological challenge, as it gives the robotic system the capability to perform intervention tasks such as physical contact with unstructured environment but without a human supervisor constantly guiding it.
SAUVIM, being a semi-autonomous vehicle, integrates electronic circuitry capable of withstanding the enormous pressure deep ocean waters generate. In general, it can operate in the harsh environmental conditions—low temperatures of the deep oceans—in a reliable and safe manner. Ensuring the effectiveness of such robots requires a high level of design and accurate choice of components.
As SAUVIM operates semi-autonomously, it needs huge energy autonomy. For this, Steatite, Worcestershire, UK, has introduced a new solution in the form of long-life batteries, ones capable of operating in submarine environment. These Lithium-Sulfur (Li-S) battery packs, a result of the first phase of a 24-month project, improves the endurance and speed of autonomous underwater vehicles when deep diving.
Primary advantages that Li-S batteries offer are enhanced energy storage capability to provide improvements in operational duration, despite being constructed from low-cost building materials.
The National Oceanography Center in Southampton, UK, completed the first phase of the Li-S battery project, after repeatedly testing the cells at pressure and temperatures prevailing in undersea depths of 6 Kms. According to the tests, Li-S cells can deliver performances similar to those at ambient conditions, while their effective Neutral Buoyancy Energy Density or NBED is almost double that offered by Li-ion cells used as reference. Life tests, performed on a number of Li-S cells demonstrate they can reach over 60 cycles with slow discharge, and 80 cycles with fast discharges.
The energy within an AUV is limited, which also limits its endurance. Therefore, to conserve the available energy, speeds of AUV are usually kept low at 2-4 knots. Therefore, to enhance or expand this operational envelope, it is necessary to increase the energy available within the vehicle, and the Li-S batteries do just that to increase the vehicles range and speed.