The performance of an AUV (Autonomous Underwater Vehicle) is directly tied to how it manages its power budget. There are generally two classes of power consumption -- passive and active. The passive component is dominated by the “hotel” load -- the sum of all the onboard systems that continously consume electrical power. The active side generally is dominated by propulsion systems. It is generally understood that maximum vehicle range can be obtained in an actively propelled AUV by equating the power drop in the active and passive components. The picture becomes more complicated when the vehicle is expected to dive deep - deep enough to cause significant hydrostatic compression of both instrument and processor housings as well as vehicle flotation (syntactic or otherwise). The resulting loss of buoyancy can only be compensated by continuous thrusting, which squanders precious onboard power budget. To counteract this, it is common to equip the AUV (or ROV) with a “variable buoyancy engine” or VBE. Typically there are three architectures -- pneumatically driven (sometimes pump assisted; e.g. see the image at right - part of the DEPTHX VBE); pump driven (often with a “pressure intensifier” to deal with elevated hydrostatic pressure); and a piston-actuated displacement chamber. The use of such VBEs becomes required in more clever AUV designs such as Slocum gliders.

At Stone Aerospace we are familiar with all three design approaches and can build custom VBEs to customer performance specifications, including several levels of local intelligence -- the highest of which being a stand-alone VBE that is connected to the vehicle System Executive which passes the VBE a desired buoyancy level or buoyancy rate of change and the VBE locally will execute that command in closed loop control.

Contact us for further information.