Distributed vector-drag drone swarm system for dynamic positioning
A hydrodynamic drag-modulation system for six-degrees-of-freedom (6-DoF) dynamic positioning (DP) of deep-sea payloads—including station-keeping and controlled translation of very large, submerged bodies—is introduced, wherein a distributed underwater swarm of vector-drag generating drones (tethered autonomous underwater vehicles or T-AUVs) leverages coordinated multi-agent control, independent of surface DP vessels and surface conditions. By commanding tether-retraction velocity and geometry of the drag-inducing elements, each drone agent functions as a virtual, relocatable bollard in three dimensions. Collectively, the swarm forms a virtual, dynamic dock around the payload, enabling both precision DP operations and long-range deep-sea transport missions. Furthermore, due to the non-propulsive, drag-modulation-based actuation principle, the system is inherently configurable for cavitation-free operation, thus suitable for industrial or scientific operations requiring low-acoustic-signature. By treating hydrodynamic drag as a programmable, distributed actuator, the system achieves surface-independent 6-DoF control, providing fault-tolerant, high-precision manipulation and transport under conditions where conventional DP systems fail.
1 . An underwater vector-drag dynamic positioning system for an underwater payload (“payload”), the system comprising:
(a) a plurality of dual-module, single-winch, coaxial alternating vector-drag drones (“drones”) spatially distributed around the payload and positioned such that respective tether lines-of-action are oriented to generate controllable forces and moments on the payload, each drone including:
(i) a first underwater module including a geometry-adaptive drag-inducing structure and one or more control surfaces, the geometry-adaptive structure and/or the control surfaces being configured to modulate hydrodynamic drag magnitude and direction, and an auxiliary intermittent repositioning subsystem operative during non-pull phases;
(ii) a second underwater module disposed coaxially with the first module including a geometry-adaptive drag-inducing structure and one or more control surfaces, the geometry-adaptive structure and/or the control surfaces being configured to modulate hydrodynamic drag magnitude and direction, and an auxiliary intermittent repositioning subsystem operative during non-pull phases;
(iii) a first tether coupled to the first module and a second tether coupled to the second module;
(iv) a local controller;
(b) a corresponding plurality of controllable dual-port winches mounted to the payload, each winch having a first port driving the first tether and a second port driving the second tether of a corresponding drone, each winch being dedicated to a single corresponding drone;
(c) for each drone, a coaxial routing in which at least one of the first and second modules defines an axial through-passage along a common longitudinal axis and the tether coupled to the other module passes through the axial through-passage such that the line-of-action of the tethers is maintained substantially collinear with the common longitudinal axis, thereby reducing yawing moments and tether interference during operation;
(d) a coordination controller, implemented centrally and/or distributed across the payload, the drones, and/or the winches, in communication with the local controllers and the winches and configured to command winch velocities, drag-geometry settings, and operation of auxiliary intermittent repositioning subsystems, including onboard propulsion where present, for the plurality of drones, and to control the spatial disposition of the drones relative to the payload;
(e) wherein, for each drone, the local controller, together with the corresponding winch, is configured to execute alternating phases in which, in a first phase, the winch retracts the first tether while releasing the second tether and, in a second phase, the winch retracts the second tether while releasing the first tether, the module undergoing release during each phase being positioned by its auxiliary intermittent repositioning subsystem, the local controller further being configured to command dynamic adjustment of the geometry-adaptive drag-inducing structures and the control surfaces to set the hydrodynamic drag vector, in both magnitude and direction, including, for at least one of the modules, independent of control surfaces, intentionally altering the deployed drag-inducing structure's geometry asymmetrically so as to produce a lateral component of hydrodynamic drag for attitude control, such that at least one of the modules remains in a drag-generating configuration throughout the alternating phases, thereby providing a substantially continuous vector-drag output for the corresponding drone; and, during each release phase, the local controller further being configured to steer the repositioning module to adjust its attitude in response to changes in the attitude of the module undergoing retraction, so that it remains substantially collinear with the common longitudinal axis of the module undergoing retraction, thereby suppressing yaw moments, minimizing tether interference, and maintaining the repositioning module's tether in tension along a line-of-action substantially collinear with the common longitudinal axis throughout operation, including during hand-off intervals;
(f) wherein modulation of pulling velocities in combination with adjustment of the geometry-adaptive drag-inducing structures and the control surfaces provides primary translational traction and attitude control via hydrodynamic counter-forces that increase approximately with the square of the magnitude of the component of the relative velocity of the respective drag-inducing structure with respect to the surrounding fluid along the retracted tether; and
(g) wherein the coordination controller includes a state-estimation module configured to fuse inertial data with at least one of acoustic, electromagnetic, or tether-based measurements and to command the winches and the drones' local controllers to maintain a six-degrees-of-freedom pose of the payload within a controller-specified tolerance band around a target setpoint or along a commanded trajectory.
2 . The system of claim 1 , further comprising one or more auxiliary Mono-Module Single-Winch Vector-Drag Drones (MMSVDDs), each MMSVDD including:
(i) a single underwater module including a geometry-adaptive drag-inducing structure and, when present, one or more control surfaces, the geometry-adaptive structure and/or the control surfaces being configured to modulate hydrodynamic drag magnitude and direction, and an auxiliary intermittent repositioning subsystem operative during non-pull phases;
(ii) a single tether coupled to the module;
(iii) a local controller; and
(iv) a corresponding controllable winch mounted to the payload;
wherein the coordination controller is configured to command the MMSVDDs to operate cooperatively with the plurality of drones; and
wherein the coordination controller is further configured to schedule the MMSVDDs in out-of-phase alternation of drag-generating and repositioning phases such that during operation, at least one MMSVDD supplies drag-based counter-force along a commanded axis, thereby ensuring continuity of net counter-force on the payload, and to utilize the MMSVDDs, in combination with the plurality of drones, to maintain a six-degrees-of-freedom pose of the payload within a controller-specified tolerance band.
3 . The system of claim 1 , wherein, for at least one of the drones, the corresponding winch includes an auxiliary retraction actuator configured, during hand-off intervals, to simultaneously retract the first and second tethers so as to eliminate a counter-force trough and provide continuous vector-drag output during the hand-off.
4 . The system of claim 3 , wherein the auxiliary retraction actuator comprises a piston-based linear mechanism arranged to pull both tethers via pulleys located proximate to respective winch ports, without interfering with primary winch operation.
5 . The system of claim 1 , wherein at least one of the drones comprises three or more underwater modules, and the local controller is configured to execute a multiphasic alternation cycle among the modules.
6 . The system of claim 1 , wherein, for at least one drone, the tether coupled to one module comprises a longitudinally openable containment-sleeve tether extending from a winch port to the module's axial through-passage, and the tether coupled to the other module is routed within the containment sleeve, the system further including a port-end opener/closer mechanism configured to selectively admit or release the other tether from the sleeve, thereby maintaining substantially collinear routing and preventing tether entanglement.
7 . The system of claim 1 , wherein, for at least one drone, the winch is configured to retract one tether and release the other at substantially equal magnitudes of linear speed during the alternating phases to maintain substantially constant tension.
8 . The system of claim 1 , wherein, for at least one drone, the winch includes an internal tether buffer configured to adjust a maximum separation between the modules while preserving synchronized retraction and release rates.
9 . The system of claim 1 , wherein, for at least one drone, at least one of the first and second modules includes a hollow-shaft motor having a through-bore that defines at least in part the axial through-passage.
10 . The system of claim 1 , wherein, for at least one drone, the first and second tethers are opposing runs of a continuous rope routed around a terminal pulley coupled to one of the modules, the dual-port winch driving the continuous rope to effect the alternating phases.
11 . The system of claim 1 , wherein the auxiliary intermittent repositioning subsystem of at least one module comprises a non-propeller repositioning mechanism operable in a non-cavitating regime.
12 . The system of claim 1 , wherein the coordination controller is distributed across the drones and/or the winches with peer-to-peer communication among drones via at least one of acoustic signaling, electromagnetic signaling, or tether-based signaling.
13 . The system of claim 12 , wherein, upon loss of a controller instance, the remaining instances reassign coordination tasks to maintain operation of the system.
14 . The system of claim 1 , wherein each module includes an inertial measurement unit and a tether-tension sensor, and the local controller for the drone uses said signals in closed-loop control of winch velocities and drag-geometry settings.
15 . The system of claim 1 , wherein at least one tether comprises a high-modulus polyethylene (HMPE) strength member, and the local controller enforces ramp-limit constraints and tension thresholds to maintain a working load limit.
16 . The system of claim 1 , wherein at least one tether is a hybrid electro-mechanical tether including integrated electrical conductors and/or optical fibers for power and/or telemetry.
17 . The system of claim 1 , wherein the drones are disposed around the payload along orthogonal axes to provide control authority in roll, pitch, yaw, surge, sway, and heave.
18 . The system of claim 1 , wherein the coordination controller schedules inter-agent out-of-phase alternation among different drones to maintain multi-axis continuity of counter-forces.
19 . The system of claim 1 , wherein at least one geometry-adaptive drag-inducing structure comprises a variable-porosity canopy including panels configured to modify porosity during deployment and recovery.
20 . The system of claim 1 , wherein at least one geometry-adaptive drag-inducing structure includes independently adjustable telescopic arms enabling asymmetric area deployment to generate controllable moments.
21 . An underwater vector-drag dynamic positioning system for an underwater payload (“payload”), the system comprising:
(a) a plurality of dual-module, single-winch, coaxial alternating vector-drag drones (“drones”) spatially distributed around the payload and positioned such that respective tether lines-of-action are oriented to generate controllable forces and moments on the payload, each drone including:
(i) a first underwater module including a geometry-adaptive drag-inducing structure and one or more control surfaces, the geometry-adaptive structure and/or the control surfaces being configured to modulate hydrodynamic drag magnitude and direction, and an auxiliary intermittent repositioning subsystem operative during non-pull phases;
(ii) a second underwater module disposed coaxially with the first module including a geometry-adaptive drag-inducing structure and one or more control surfaces, the geometry-adaptive structure and/or the control surfaces being configured to modulate hydrodynamic drag magnitude and direction, and an auxiliary intermittent repositioning subsystem operative during non-pull phases;
(iii) a first tether coupled to the first module and a second tether coupled to the second module;
(iv) a local controller;
(b) a corresponding plurality of controllable dual-port winches mounted to the payload, each winch having a first port driving the first tether and a second port driving the second tether of a corresponding drone, each winch being dedicated to a single corresponding drone;
(c) for each drone, a coaxial routing in which at least one of the first and second modules defines an axial through-passage along a common longitudinal axis and the tether coupled to the other module passes through the axial through-passage such that the line-of-action of the tethers is maintained substantially collinear with the common longitudinal axis, thereby reducing yawing moments and tether interference during operation;
(d) a coordination controller, implemented centrally and/or distributed across the payload, the drones, and/or the winches, in communication with the local controllers and the winches and configured to command winch velocities, drag-geometry settings, and operation of auxiliary intermittent repositioning subsystems, including onboard propulsion where present, for the plurality of drones, and to control the spatial disposition of the drones relative to the payload;
(e) wherein, for each drone, the local controller, together with the corresponding winch, is configured to execute alternating phases in which, in a first phase, the winch retracts the first tether while releasing the second tether and, in a second phase, the winch retracts the second tether while releasing the first tether, the module undergoing release during each phase being positioned by its auxiliary intermittent repositioning subsystem, the local controller further being configured to command dynamic adjustment of the geometry-adaptive drag-inducing structures and the control surfaces to set the hydrodynamic drag vector, in both magnitude and direction, including, for at least one of the modules, independent of control surfaces, intentionally altering the deployed drag-inducing structure's geometry asymmetrically so as to produce a lateral component of hydrodynamic drag for attitude control, such that at least one of the modules remains in a drag-generating configuration throughout the alternating phases, thereby providing a substantially continuous vector-drag output for the corresponding drone; and, during each release phase, the local controller further being configured to steer the repositioning module to adjust its attitude in response to changes in the attitude of the module undergoing retraction, so that it remains substantially collinear with the common longitudinal axis of the module undergoing retraction, thereby suppressing yaw moments, minimizing tether interference, and maintaining the repositioning module's tether in tension along a line-of-action substantially collinear with the common longitudinal axis throughout operation, including during hand-off intervals;
(f) wherein modulation of pulling velocities in combination with adjustment of the geometry-adaptive drag-inducing structures and the control surfaces provides primary translational traction and attitude control via hydrodynamic counter-forces that increase approximately with the square of the magnitude of the component of the relative velocity of the respective drag-inducing structure with respect to the surrounding fluid along the retracted tether;
(g) wherein the coordination controller includes a state-estimation module configured to fuse inertial data with at least one of acoustic, electromagnetic, or tether-based measurements and to command the winches and the drones' local controllers to maintain a six-degrees-of-freedom pose of the payload within a controller-specified tolerance band around a target setpoint or along a commanded trajectory; and
(h) wherein, for at least one of the drones, the corresponding winch includes an auxiliary retraction actuator configured, during hand-off intervals, to simultaneously retract the first and second tethers to pull both of the modules, thereby eliminating a counter-force trough and providing continuous vector-drag output during the hand-off.
22 . An underwater vector-drag dynamic positioning system for an underwater payload (“payload”), the system comprising:
(a) a plurality of dual-module, single-winch, coaxial alternating vector-drag drones (“drones”) spatially distributed around the payload and positioned such that respective tether lines-of-action are oriented to generate controllable forces and moments on the payload, each drone including:
(i) a first underwater module including a geometry-adaptive drag-inducing structure and one or more control surfaces, the geometry-adaptive structure and/or the control surfaces being configured to modulate hydrodynamic drag magnitude and direction, and an auxiliary intermittent repositioning subsystem operative during non-pull phases;
(ii) a second underwater module disposed coaxially with the first module including a geometry-adaptive drag-inducing structure and one or more control surfaces, the geometry-adaptive structure and/or the control surfaces being configured to modulate hydrodynamic drag magnitude and direction, and an auxiliary intermittent repositioning subsystem operative during non-pull phases;
(iii) a first tether coupled to the first module and a second tether coupled to the second module;
(iv) a local controller;
(b) a corresponding plurality of controllable dual-port winches mounted to the payload, each winch having a first port driving the first tether and a second port driving the second tether of a corresponding drone, each winch being dedicated to a single corresponding drone;
(c) for each drone, a coaxial routing in which at least one of the first and second modules defines an axial through-passage along a common longitudinal axis and the tether coupled to the other module passes through the axial through-passage such that the line-of-action of the tethers is maintained substantially collinear with the common longitudinal axis, thereby reducing yawing moments and tether interference during operation;
(d) a coordination controller, implemented centrally and/or distributed across the payload, the drones, and/or the winches, in communication with the local controllers and the winches and configured to command winch velocities, drag-geometry settings, and operation of auxiliary intermittent repositioning subsystems, including onboard propulsion where present, for the plurality of drones, and to control the spatial disposition of the drones relative to the payload;
(e) wherein, for each drone, the local controller, together with the corresponding winch, is configured to execute alternating phases in which, in a first phase, the winch retracts the first tether while releasing the second tether and, in a second phase, the winch retracts the second tether while releasing the first tether, the module undergoing release during each phase being positioned by its auxiliary intermittent repositioning subsystem, the local controller further being configured to command dynamic adjustment of the geometry-adaptive drag-inducing structures and the control surfaces to set the hydrodynamic drag vector, in both magnitude and direction, including, for at least one of the modules, independent of control surfaces, intentionally altering the deployed drag-inducing structure's geometry asymmetrically so as to produce a lateral component of hydrodynamic drag for attitude control, such that at least one of the modules remains in a drag-generating configuration throughout the alternating phases, thereby providing a substantially continuous vector-drag output for the corresponding drone; and, during each release phase, the local controller further being configured to steer the repositioning module to adjust its attitude in response to changes in the attitude of the module undergoing retraction, so that it remains substantially collinear with the common longitudinal axis of the module undergoing retraction, thereby suppressing yaw moments, minimizing tether interference, and maintaining the repositioning module's tether in tension along a line-of-action substantially collinear with the common longitudinal axis throughout operation, including during hand-off intervals;
(f) wherein modulation of pulling velocities in combination with adjustment of the geometry-adaptive drag-inducing structures and the control surfaces provides primary translational traction and attitude control via hydrodynamic counter-forces that increase approximately with the square of the magnitude of the component of the relative velocity of the respective drag-inducing structure with respect to the surrounding fluid along the retracted tether;
(g) wherein the coordination controller includes a state-estimation module configured to fuse inertial data with at least one of acoustic, electromagnetic, or tether-based measurements and to command the winches and the drones' local controllers to maintain a six-degrees-of-freedom pose of the payload within a controller-specified tolerance band around a target setpoint or along a commanded trajectory;
(h) wherein, for at least one of the drones, the corresponding winch includes an auxiliary retraction actuator configured, during hand-off intervals, to simultaneously retract the first and second tethers to pull both of the modules, thereby eliminating a counter-force trough and providing continuous vector-drag output during the hand-off; and
(i) wherein, for at least one drone, the tether coupled to one module comprises a longitudinally openable containment-sleeve tether extending from a winch port to the module's axial through-passage, and the tether coupled to the other module is routed within the containment sleeve, the system further including a port-end opener/closer mechanism configured to selectively admit or release the other tether from the sleeve, thereby maintaining substantially collinear routing and preventing tether entanglement.