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ABE User Manual


How ABE Works

ABE operates autonomously from the support research vessel. It has no tether, and is controlled in real-time by onboard computers using its own rechargeable batteries for all power. Upon launch, ABE descends to the seafloor with the help of a descent weight that is released after safe arrival at depth. On most dives ABE uses acoustic long-baseline transponder navigation with (when close enough to the seafloor) bottom-lock acoustic Doppler measurements to determine its position and velocity over the seabed. ABE descends at 15-20 m/minute following a controlled spiral trajectory to ensure that it reaches the desired starting point while consuming minimal energy.

After reaching the seafloor and performing a series of checks, ABE releases its descent weight to become neutrally buoyant and begins its pre-programmed survey. A dive can consist of any mix of water column investigations (e.g. hydrothermal plume surveys) at constant water depths, seafloor geophysical investigations at fixed heights above the seafloor (anywhere from 50-200 m off depending on the application: e.g. magnetics, high-resolution bathymetric mapping) and digital photography at a height of just 5 meters above the seafloor. ABE usually surveys until either it reaches the end of its program or its batteries are depleted (typically between 20-30 km along track and 15-30 hours of survey time, depending on sensor payload, survey type, and terrain). At the end of its dive, ABE releases two ascent weights to become positively buoyant and return to the surface at 15-20 m/minute.

ABE Vehicle Characteristics

ABE is a three-body, open frame vehicle that utilizes glass balls as flotation in two free-flooded upper pods while the single, lower housing is host to the batteries that power the vehicle and all of its electronics. This separation of buoyancy and payload gives a large righting moment that simplifies control and allows the vertical and lateral thrust propellers to be located inside the protected space between the three faired bodies. ABE has five thrusters allowing it to move in any direction. It can travel forward at a cruising speed of 0.6m/sec, but one of ABE’s most unique characteristics is that it can also hover and reverse - characteristics that are particularly valuable in the rugged terrain routinely encountered when investigating the deep seafloor.

The navigation system onboard ABE consists of two proven and complementary navigation systems. For general use, ABE uses long “baseline” transponders identical to those used by Alvin and ROV Jason, and these allow deep seafloor surveys over distances of ~5km to be carried out. In addition, ABE also carries an acoustic Doppler velocity log (DVL) which provides short-range, high-precision navigation. With these navigation systems, ABE has the ability to follow tracklines with a repeatability of order 10m or better.

ABE Support Vessel Requirements

Because ABE is a free-swimming vehicle that navigates from its own long-baseline navigation array, it is mobilized worldwide from a single 20-foot container. It can be deployed from a range of non-specialized research ships (e.g. ships without a dynamic positioning system), facilitating rapid response efforts and exploratory research in new areas. Consequently, the support vessel requirements are simply 1) deck space for a 20-foot container aboard ship, 2) deck area for the vehicle in its cradle (3 m long, 2 m wide), and 3) a shipboard crane able to lift the vehicle (550 kg) into and out of the water at launch and recovery.

ABE At-Sea Personnel Requirements

The ABE vehicle requires a 3-person support team at sea: a mechanical engineer who also oversees all shipboard launch and recovery operations and coordinates with the ship’s crew and officers; an electrical engineer to maintain the health of the vehicle systems and batteries and a software engineer to over-see mission programming, vehicle navigation and data manipulation/delivery to science.