As the underwater robot travels through the mission, it adjusts the operating mode from having a desired depth while it travels down through the water, and then, as the acoustic sensors and optical sensors begin to observe the seafloor, the vehicle autonomously transitions to altitude control. Altitude control will be active while collecting nodules. The vertical thrusters adjust the force they exert to maintain the set altitude for the AUV over the seafloor. As nodules are collected, the buoyancy engines on board the AUV pump water out of the tanks to maintain the same small desired downward force from the vertical thrusters.
The seafloor’s typography, where we will collect nodules, gradually changes, and the vehicle travels relatively slowly. A forward-looking sonar provides feedback to the system for topography changes that are too much for the vertical thrusters to manage.
