A significant advantage of our AUV-based architecture is the flexibility to rapidly adapt to changes in surface vessel availability. Such changes can occur for various reasons, each with differing notification periods and durations. Below, we describe three scenarios outlining how our AUV fleet responds and provide details about the battery power capacity necessary to sustain operations underwater during these events.

As a larger system compared to Eureka III, Eureka IV features increased battery capacities, providing greater energy reserves that effectively mitigate delays in returning to the surface ship. The examples presented here specifically reflect Eureka III operations in the Clarion-Clipperton Zone (CCZ). Although exact figures may vary based on specific operational sites, the fundamental approach of subsea storage and battery usage remains consistent.

Battery Power Reserve

The Eureka III system is equipped with a battery pack that has a capacity of 142 kWh. The energy budget for key operational functions includes:

  • Buoyancy pump for travel: 22.0 KWh, 15.4%
  • Buoyancy pump for nodules: 38.2 KWh, 26.8%
  • Thrusters: 0.9 KWh, 0.6%
  • Arm operations: 15.9 KWh, 11.2%
  • Conveyor operations: 8.3 KWh, 5.8%
  • Reserve: 57.1 KWh, 40.1%

During an approximate three-hour mission, the vehicle initially utilizes half of its buoyancy pump travel energy to slow its descent and stabilize hovering over the seafloor. Subsequently, during nodule collection the buoyancy pumps (for nodules), thrusters, robotic arms, and conveyor consume energy. The remaining half of travel-energy is expended for ascent upon mission completion at the seafloor. Under standard conditions, the AUV uses about 59.9% of its battery capacity, leaving a substantial reserve.. To increase the working life of the battery and improve battery charging turnaround times, the AUV enters the water with a usable capacity of 114 kWh of energy because the batteries will be charged to an 80% state of charge..

Operational Scenarios

Battery consumption varies depending on the timing and nature of the surface vessel’s departure or operational interruption. The following scenarios illustrate specific responses:

Scenario 1: Planned Departure
A planned departure typically involves scenarios with advanced notice (4 hours or more, as this is the cycle time of the AUVs), such as scheduled ship replacement delays or anticipated adverse weather. In such cases, AUVs descend more slowly, reducing buoyancy requirements and energy usage. A slower descent requires only about 4% of battery capacity to reach the seafloor. Subsequent station-keeping to maintain position against subsea currents consumes approximately 0.76% every hour. Simply running the computers consumes approximately 200W, bringing the total bottom keeping energy consumption to 0.9% of the battery capacity every hour. Even during prolonged interruptions (e.g., a three-day weather event), some battery energy remains available for nodule collection before ascent. In a scenario when an AUV descends to the seafloor knowing that it needs to stay on station, conserving power, it can remain at the seafloor for over three days before surfacing.

Scenario 2: Delayed Recovery
Occasionally, recovery operations may experience consecutive delays. In such circumstances, adjustments in ascent/descent timings become necessary. Reducing ascent speed for a vehicle already in motion incurs minimal energy changes. However, slowing descent midway saves energy, as the vehicle expels water at lower pressures. Operational trade-offs can also be made by adjusting payload to optimize travel speeds, thus balancing production efficiency against energy management.

Scenario 3: Sudden Stop
Emergency events (e.g., a severe medical emergency) necessitate immediate operational cessation on the surface vessel. Vehicles ascending or already at the surface must promptly descend back to the seafloor. In the worst-case scenario, where an AUV is fully ascending and must reverse course, it will have already consumed approximately 60% of the battery. A slow, controlled descent consumes an additional 4% of battery capacity. A similar controlled ascent later requires another 4%, leaving roughly 12% of battery capacity available for precise station-keeping. Under these conditions, precise hovering near the seafloor can be maintained for approximately 12 hours while awaiting recovery signals. If communication with the surface ship is not restored before battery levels reach a critical threshold, the AUV will autonomously ascend to a predefined emergency resurfacing location away from the surface vessel. Once surfaced, the AUV communicates its position via satellite, powered by its remaining battery reserves and a dedicated emergency beacon backup power system, allowing it to remain locatable for weeks.

Additional Scenarios

In cases where the AUVs won’t be recovered for extended periods, there are various options to extend the AUV’s emergency bottom time. These options still need to be thoroughly thought through by the Impossible Metal’s team. Still, they may include: intelligent management of a drifting fleet to ensure the ability to locate the fleet once the ship returns to the harvesting location, having the vehicles set down onto the bottom to eliminate the battery usage from the thrusters as the vehicle station keeps and having the vehicle equipped with detachable anchoring gear, to again, eliminate thruster battery draw while station keeping. As the team develops these further ideas, we may incorporate elements into the response plans of the scenarios listed above.