Patent Publication Number: US-11639216-B2

Title: Propulsion system for a buoyant aerial vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 15/850,824, filed on Dec. 21, 2017, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Some buoyant aerial vehicles are capable of controlled flight. Such aerial vehicles rely on some form of thrusters to control lateral movement. However, such systems have substantial power requirements, whether in the form of batteries or fuel, to power the motors or engines. As such, simpler, more efficient propulsion systems for buoyant aerial vehicles could be beneficial in improving their maneuverability. 
     SUMMARY 
     According to one aspect of the present disclosure, a buoyant aerial vehicle includes: a balloon configured to store a gas; a payload coupled to the balloon; and a propulsion unit coupled to the payload by a tether. The propulsion unit includes: a fuselage having a substantially longitudinal shape, a first end, and a second end; a primary airfoil coupled to the fuselage; a secondary airfoil coupled to the fuselage at one of the first end or the second end; and a thrust generating device disposed at one of the first end or the second end and configured to move the propulsion unit relative to the payload along a propulsion flight path. The movement of the propulsion unit imparts movement of the buoyant aerial vehicle along a vehicle flight path. 
     In embodiments of the above aspect of the present disclosure, the tether is coupled to the primary airfoil. Tether is also coupled to a winch configured to adjust a length of the tether by which the propulsion unit extends from the payload. 
     In further embodiments of the above aspect of the present disclosure, at least one of the primary airfoil or the secondary airfoil includes at least one aileron. At least one of the primary airfoil or the secondary airfoil also includes at least one solar panel. 
     In other embodiments of the above aspect of the present disclosure, the propulsion unit includes a controller configured to actuate at least one the primary airfoil, the secondary airfoil, or the thrust generating device to move the propulsion unit relative to the payload along the propulsion flight path. The propulsion flight path may have a cyclical, reversible pattern. 
     In embodiments of the above aspect of the present disclosure, the thrust generating device includes an electrical motor and a propeller rotatable by the electrical motor. 
     In further embodiments of the above aspect of the present disclosure, a vehicle controller is included and configured to receive a movement command including at least one of a destination, direction, or speed for moving the buoyant aerial vehicle along the vehicle flight path. The propulsion unit further includes a propulsion controller configured to communicate with the vehicle controller. At least one of the vehicle controller or the propulsion controller is configured to determine the propulsion flight path that propels the buoyant aerial vehicle along the vehicle flight path. 
     The propulsion controller is further configured to control the primary airfoil, the secondary airfoil, and the thrust generating device. 
     In other embodiments of the above aspect of the present disclosure, the propulsion unit further includes a sensor configured to measure at least one flight property of the propulsion unit. The sensor is configured to transmit a measurement value corresponding to the at least one flight property to at least one of the vehicle controller or the propulsion controller. 
     According to another aspect of the present disclosure, a method for controlling an aerial vehicle includes: transmitting a movement command to a buoyant aerial vehicle having a propulsion unit attached thereto by a tether; determining, based on the movement command, a propulsion flight path for the propulsion unit to achieve a vehicle flight path corresponding to the movement command; and controlling at least one of a primary airfoil, a secondary airfoil, or a thrust generating device of the propulsion unit to move the propulsion unit along the propulsion flight path. 
     In embodiments of the above aspect of the present disclosure, the method includes: adjusting a length of a tether coupling the propulsion unit to the buoyant aerial vehicle. 
     In further embodiments of the above aspect of the present disclosure, the method further includes: measuring at least one flight property of the propulsion unit; and communicating a measurement of the at least one flight property to at least one of a vehicle controller of the buoyant aerial vehicle or a propulsion controller of the propulsion unit. 
     According to further aspect of the present disclosure, a non-transitory computer-readable storage medium storing instructions is disclosed, which, when executed by a processor, cause a computing device to: transmit a movement command to a buoyant aerial vehicle having a propulsion unit attached thereto by a tether; determine, based on the movement command, a propulsion flight path for the propulsion unit to achieve a vehicle flight path corresponding to the movement command; and control at least one of a primary airfoil, a secondary airfoil, or a thrust generating device of the propulsion unit to move the propulsion unit along the propulsion flight path. 
     In embodiments of the above aspect of the present disclosure, the computing device is further caused to: control a winch to adjust a length of a tether coupling the propulsion unit to the buoyant aerial vehicle. 
     In further embodiments of the above aspect of the present disclosure, the computing device is further caused to: determine at least one flight property of the propulsion unit; and communicate a measurement of the at least one flight property to at least one of a vehicle controller of the buoyant aerial vehicle or a propulsion controller of the propulsion unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects and features of the present systems and methods for controlling an aerial vehicle are described herein below with references to the drawings, wherein: 
         FIG.  1    is a schematic diagram of an illustrative aerial vehicle system, in accordance with an embodiment of the present disclosure; 
         FIG.  2    is a schematic diagram showing additional aspects of the aerial vehicle system of  FIG.  1   , in accordance with an embodiment of the present disclosure; 
         FIG.  3    is a schematic block diagram of an illustrative embodiment of a computing device that may be employed in various embodiments of the present system, for instance, as part of the system or components of  FIG.  1  or  2   , in accordance with an embodiment of the present disclosure; 
         FIG.  4 A  is a schematic diagram of the aerial vehicle system of  FIG.  1    illustrating a propulsion flight path of a propulsion unit in accordance with an embodiment of the present disclosure; 
         FIG.  4 B  is a schematic diagram of the aerial vehicle system of  FIG.  1    illustrating a propulsion flight path of a propulsion unit in accordance with another embodiment of the present disclosure; 
         FIG.  5    is a perspective view of a propulsion unit of the aerial vehicle system of  FIG.  1    in accordance with an embodiment of the present disclosure; and 
         FIG.  6    is a perspective view of a propulsion unit of the aerial vehicle system of  FIG.  1    in accordance with another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is directed to systems and methods for propelling a buoyant aerial vehicle. In embodiments, the buoyant aerial vehicle includes a wing-based propulsion unit that is attached to a payload of the aerial vehicle, such that the propulsion unit is suspended from the payload, e.g., by a tether. The propulsion unit is powered by a thrust generating device, such as an electrically powered propeller. The propulsion unit is configured to perform a cyclically reversing flight path, thereby generating movement along the swing line of the propulsion unit, which in turn generates lift. The lift vector of the propulsion unit is controlled by adjusting the direction and/or speed of the propulsion unit, which in turn allows for controlling steering and propulsion of the buoyant aerial vehicle. 
     Although the present disclosure makes particular reference to superpressure balloons, which are designed to float at an altitude in the atmosphere where the density of the balloon system is equal to the density of the atmosphere, this is being used for illustrative purposes only. The propulsion system according to the present disclosure may be used with any vehicles that maintain altitude at least in part by using buoyancy, such as other types of balloons, airships, and the like. 
     With reference to  FIG.  1   , an illustrative aerial vehicle system  100  includes an aerial vehicle  102 , one or more computing devices  104 , and one or more data sources  106 . The aerial vehicle  102  and the computing devices  104  are communicatively coupled to one another by way of a wireless communication link  108 , and the computing devices  104  and the data sources  106  are communicatively coupled to one another by way of wired and/or wireless communication link  110 . In some aspects, the aerial vehicle  102  is configured to be launched into and moved about the atmosphere, and the computing devices  104  cooperate as a ground-based distributed array to perform their functions described herein. The data sources  106  may include airborne data sources, such as airborne weather balloons, additional airborne aerial vehicles  102 , and/or the like, and/or ground-based data sources, such as publicly available and/or proprietary databases, examples of which are the Global Forecast System (GFS) operated by the National Oceanic and Atmospheric Administration (NOAA), as well as databases maintained by the European Center for Medium-range Weather Forecasts (ECMWF). Although the present disclosure is provided in the context of an embodiment where the system  100  includes multiple computing devices  104  and multiple data sources  106 , in other embodiments the system  100  may include a single computing device  104  and a single data source  106 . Further, although  FIG.  1    shows a single aerial vehicle  102 , in various embodiments the system  100  includes a fleet of multiple aerial vehicles  102  that are positioned at different locations throughout the atmosphere and that are configured to communicate with the computing devices  104 , the data sources  106 , and/or one another by way of the communication links  108  and/or  110 . 
     In various embodiments, the aerial vehicle  102  may be configured to perform a variety of functions or provide a variety of services, such as, for instance, telecommunication services (e.g., Long Term Evolution (LTE) service), hurricane monitoring services, ship tracking services, services relating to imaging, astronomy, radar, ecology, conservation, and/or other types of functions or services. Computing devices  104  control the position (also referred to as location) and/or movement of the aerial vehicles  102  throughout the atmosphere or beyond, to facilitate effective and efficient performance of their functions or provision of their services, as the case may be. As described in further detail herein, the computing devices  104  are configured to obtain a variety of types of data from a variety of sources and, based on the obtained data, communicate messages to the aerial vehicle  102  to control its position and/or movement during flight. 
     With continued reference to  FIG.  1   , the aerial vehicle  102  includes a lift gas balloon  112 , one or more ballonets  116 , and a payload or gondola  114 , which is suspended beneath the lift gas balloon  112  and/or the ballonets  116  while the aerial vehicle  102  is in flight. The ballonets  116  may be used to control the buoyancy, and thereby the altitude, of the aerial vehicle  102  during flight. In some aspects, the ballonets  116  include air and the lift gas balloon  112  includes a lifting gas that is lighter than air. As shown in  FIG.  1   , the ballonets  116  may be positioned inside the lift gas balloon  112  and/or outside the lift gas balloon  112 . An vehicle controller  126  controls a pump and a valve (neither of which are shown in  FIG.  1   ) to pump air into the ballonets  116  (from air outside the aerial vehicle  102 ) to increase the mass of the aerial vehicle  102  and lower its altitude, or to release air from the ballonets  116  (into the atmosphere outside the aerial vehicle  102 ) to decrease the mass of the aerial vehicle  102  and increase its altitude. The combination of the vehicle controller  126 , the lift gas balloon  112 , the ballonets  116 , and the valves and pumps (not shown in  FIG.  1   ) is referred to as an air-gas altitude control system (ACS). 
     The aerial vehicle  102  also includes one or more solar panels  134  affixed thereto. As shown in  FIG.  1   , the solar panels  134  may be affixed to an upper portion of the lift gas balloon  112  that absorbs sunlight, when available, and generate electrical energy from the absorbed sunlight. Alternatively, or in addition, the solar panels  134  may be affixed to the gondola  114  or elsewhere to aerial vehicle  102  (not shown in  FIG.  1   ). The solar panels  134  provide, by way of power paths such as power path  136 , the generated electrical energy to the various components of the aerial vehicle  102 , such as components housed within the gondola  114 , for utilization during flight. 
     The gondola  114  includes a variety of components, some of which may or may not be included, depending upon the application and/or needs of the aerial vehicle  102 . Although not expressly shown in  FIG.  1   , the various components of the aerial vehicle  102  in general, and/or of the gondola  114  in particular, may be coupled to one another for communication of power, data, and/or other signals. The exemplary gondola  114  shown in  FIG.  1    includes one or more sensors  128 , an energy storage module  124 , a power plant  122 , a vehicle controller  126 , a transceiver  132 , and other on-board equipment  130 . The transceiver  132  is configured to wirelessly communicate data between the aerial vehicle  102  and the computing devices  104  and/or data sources  106  by way of the wireless communication link  108  and/or the communication link  110 , respectively. 
     In some embodiments, the sensors  128  include a global positioning system (GPS) sensor that senses and outputs location data, such as latitude, longitude, and/or altitude data corresponding to a latitude, longitude, and/or altitude of the aerial vehicle  102  in the Earth&#39;s atmosphere. The sensors  128  are configured to provide the location data to the computing devices  104  by way of the wireless transceiver  132  and the wireless communication link  108  for use in controlling the aerial vehicle  102 , as described in further detail below. 
     The energy storage module  124  includes one or more batteries that store electrical energy provided by the solar panels  134  for use by the various components of the aerial vehicle  102 . The power plant  122  obtains electrical energy stored by the energy storage module  124  and converts and/or conditions the electrical energy to a form suitable for use by the various components of the aerial vehicle  102 . 
     The vehicle controller  126  is configured to control the ballonets  116  to adjust the buoyancy of the aerial vehicle  102  to assist in controlling its position and/or movement during flight. As described in further detail below, in various embodiments the vehicle controller  126  is configured to control the ballonets  116  based at least in part upon an altitude command that is generated by, and received from, the computing devices  104  by way of the wireless communication link  108  and the transceiver  132 . In some examples, the vehicle controller  126  is configured to implement the altitude command by causing the actuation of the ACS based on the altitude command. 
     The on-board equipment  130  may include a variety of types of equipment, depending upon the application or needs, as outlined above. For example, the on-board equipment  130  may include LTE transmitters and/or receivers, weather sensors, imaging equipment, and/or any other suitable type of equipment. 
     In addition to the aforementioned components, the gondola  114  is also coupled a propulsion unit  140 . The propulsion unit  140  is attached to the gondola  114  by a winch  120 , which allows for controlling the distance between the propulsion unit  140  and the aerial vehicle  102 . The winch  120  may be coupled to the gondola  114  as shown in  FIGS.  4 A and  4 B . In embodiments, the winch  120  may be coupled to the propulsion unit  140  as shown in  FIG.  6   . 
     The propulsion unit  140  includes one or more sensors  142 , a propulsion controller  144 , energy storage  146 , flight controls  148 , and a thruster  150 . The energy storage  146 , which may be any suitable electrical battery, is coupled to one or more solar panels  152  attached the propulsion unit  140 . 
     Having provided an overview of the aerial vehicle system  100  in the context of  FIG.  1   , reference is now made to  FIG.  2   , which shows certain operations of the aerial vehicle system  100 , in accordance with an embodiment of the present disclosure. In particular,  FIG.  2    illustrates an exemplary embodiment of corresponding components are allocated among the aerial vehicle  102 , the computing devices  104 , and/or the data sources  106 , to control a position and/or movement of the aerial vehicle  102  and how they function. The arrangement of components depicted in  FIG.  2    is provided by way of example and not limitation. Other arrangements of components and allocations of functionality are contemplated, for instance, with the aerial vehicle  102  including components that implement functionality shown in  FIG.  2    as being implemented by the computing devices  104 , or vice versa. However, in the example shown in  FIG.  2   , a majority of components and functionality are allocated to the computing devices  104  instead of to the aerial vehicle  102 , which decreases the amount of energy required to operate the components of the aerial vehicle  102  and thus enables the components of the aerial vehicle  102  to utilize a greater portion of the available energy than would be possible if more components and functionality were allocated to the aerial vehicle  102 . This increases the capabilities of the aerial vehicle  102  for implementing functionality and/or providing services for a given amount of available energy. 
     In addition to certain components that were introduced above in connection with  FIG.  1   ,  FIG.  2    shows a wind mixer module  202 , a navigation module  204 , and a maneuver automation module  206  that are included within the computing devices  104 . Once the aerial vehicle  102  is in flight in the atmosphere, the sensors  128  are configured to periodically transmit to the wind mixer module  202 , by way of the transceiver  132  and the wireless communication link  108 , location data, such as time stamped GPS positions and altitudes of the aerial vehicle  102  at corresponding times. The wind mixer module  202  utilizes the location data obtained from the sensors  128  and wind pattern data obtained from other data sources  106  (such as National Oceanic and Atmospheric Administration (NOAA) data sources, European Centre for Medium-Range Weather Forecasts (ECMWF) data sources, and/or the like) to infer or estimate the winds in which the aerial vehicle  102  is flying or is expected to be flying. In particular, wind points are stored in the wind mixer module  202 , which constructs a kernel function, such as a Gaussian Process kernel function that assists the navigation module  204  in determining how to navigate the aerial vehicle  102  based on the inferred or estimated winds, according to one or more predetermined navigation algorithms. Depending upon the navigation algorithm being implemented, the navigation module  204  generates a maneuver plan (e.g., navigation data), which is a set of locations (e.g., altitudes, latitude coordinates, and/or longitude coordinates) that the aerial vehicle  102  should attempt to attain at corresponding times. Additionally, the navigation module  204  receives weather data, including ambient temperature conditions and/or predictions, from the data sources  106  and/or from the sensors  128  via the transceiver  132 . Based on the temperature predictions, the navigation module  204  may determine adjustments to the maneuver plan including commands to the propulsion unit  140  to implement the maneuver plan, as further described below. The navigation module  204  then registers the maneuver plan with the maneuver automation module  206 . 
     The maneuver automation module  206  sequentially transfers each item of location data (e.g., altitude, latitude, and/or longitude) to the vehicle controller  126  for implementation according to the corresponding times indicated in the maneuver plan. In particular, the maneuver automation module  206  transmits to the transceiver  132 , by way of the wireless communication link  108 , a movement command, which includes an altitude command (for example, which may be specified as a barometric pressure, which may be equivalent to pressure altitude, and which indicates a desired altitude for the aerial vehicle  102  to maintain within some tolerance band) and/or a speed and direction command. The vehicle controller  126  is configured to execute a loop whereby the vehicle controller  126  periodically receives the altitude command and/or a speed and direction command from the computing devices  104  and executes those commands to control the altitude as well as direction and speed of the aerial vehicle  102 . 
     With respect to the speed and direction command, the vehicle controller  126  transmits the command to the propulsion controller  144  of the propulsion unit  140 . The propulsion controller  144  then determines how to best implement the speed and direction command to move the aerial vehicle  102 . In particular, the propulsion unit  140  signals the flight controls  148  and the thruster  150  to move the propulsion unit  140  in a propulsion flight path  160 , which would result in propulsion of the aerial vehicle  102  along a vehicle flight path  162  ( FIGS.  4 A and  4 B ). In addition, the vehicle controller  126  and/or the propulsion controller  144  are coupled to the winch  120  and are configured to control the winch  120  to adjust the distance that the propulsion unit  140  extends from the aerial vehicle  102 . 
       FIG.  3    is a schematic block diagram of a computing device  300  that may be employed in accordance with various embodiments described herein. Although not explicitly shown in  FIG.  1    or  FIG.  2   , in some embodiments, the computing device  300 , or one or more of the components thereof, may further represent one or more components (e.g., the computing device  104 , components of the gondola  114 , the data sources  106 , the propulsion unit  140  and/or the like) of the system  100 . The computing device  300  may, in various embodiments, include one or more memories  302 , processors  304 , display devices  306 , network interfaces  308 , input devices  310 , and/or output modules  312 . The memory  302  includes non-transitory computer-readable storage media for storing data and/or software that is executable by the processor  304  and which controls the operation of the computing device  300 . In embodiments, the memory  302  may include one or more solid-state storage devices such as flash memory chips. Alternatively, or in addition to the one or more solid-state storage devices, the memory  302  may include one or more mass storage devices connected to the processor  304  through a mass storage controller (not shown in  FIG.  3   ) and a communications bus (not shown in  FIG.  3   ). Although the description of computer readable media included herein refers to a solid-state storage, it should be appreciated by those skilled in the art that computer-readable storage media may be any available media that can be accessed by the processor  304 . That is, computer readable storage media includes non-transitory, volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data. Examples of computer-readable storage media include RAM, ROM, EPROM, EEPROM, flash memory or other solid state memory technology, CD-ROM, DVD, Blu-Ray or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which may be used to store the desired information and which can be accessed by computing device  300 . 
     In some embodiments, the memory  302  stores data  314  and/or an application  316 . In some aspects the application  316  includes a user interface component  318  that, when executed by the processor  304 , causes the display device  306  to present a user interface, for example a graphical user interface (GUI) (not shown in  FIG.  3   ). The network interface  308 , in some embodiments, is configured to couple the computing device  300  and/or individual components thereof to a network, such as a wired network, a wireless network, a local area network (LAN), a wide area network (WAN), a wireless mobile network, a Bluetooth network, the Internet, and/or another type of network. The input device  310  may be any device by means of which a user may interact with the computing device  300 . Examples of the input device  310  include without limitation a mouse, a keyboard, a touch screen, a voice interface, and/or the like. The output module  312  may, in various embodiments, include any connectivity port or bus, such as, for example, a parallel port, a serial port, a universal serial bus (USB), or any other similar connectivity port known to those skilled in the art. 
     With reference to  FIGS.  4 A and  4 B , the aerial vehicle  102  is shown with the propulsion unit  140  attached thereto by a tether  156  that is wound about the winch  120 . The tether  156  may be any rope or cable having suitable tensile properties for supporting the propulsion unit  140  that allows for the propulsion unit  140  to fly in any direction relative to the aerial vehicle  102 . The propulsion unit  140  is configured to move along the propulsion flight path  160  ( FIG.  4 A ) or a propulsion path  161  ( FIG.  4 B ) relative to the aerial vehicle  102 , since the propulsion unit  140  is tethered thereto. The propulsion flight path  160  may be any cyclical path and may have any suitable shape, such as circular, oval, obround, and combinations thereof. In embodiments, the propulsion flight path  160  may also be any cyclically reversible, e.g., ondulating, flight path that is substantially disposed along a swing plane  163 . 
     As the propulsion unit  140  moves along the propulsion flight path  160  ( FIG.  4 A ) or the propulsion path  161  ( FIG.  4 B ), the propulsion unit  140  generates lift. The lift vector of the propulsion unit  140  is controlled by adjusting the direction of propulsion unit  140 , which in turn allows for controlling steering and propulsion of the aerial vehicle along the vehicle flight path  162  at a set speed and direction. With respect to the embodiment of  FIG.  4 B , the lift vector of the propulsion unit  140  is substantially transverse to the swing plane  163  and is used to point, and thus, steer the aerial vehicle  102 . Thus, the flight path  162  is also substantially transverse with respect to the swing plane  163 . 
     With reference to  FIG.  5   , the propulsion unit  140  includes a fuselage  170 , a primary airfoil  172 , e.g., a pair of wings, a secondary airfoil  174 , e.g., a tail, and the thruster  150 . In embodiments, the secondary airfoil  174  may include a stabilizer. The primary airfoil  172  may be disposed at about the midpoint of the fuselage  170  and is attached to the tether  156 . The secondary airfoil  174  is disposed at a second, e.g., rear, end  182  of the fuselage  170 , which is opposite of a first, e.g., front, end  180 . 
     The thruster  150  may be a micro propeller powered by an electrical motor  176  and a propeller  178 , which is coupled to and rotatable by the electrical motor  176 . The electrical motor  176  and the propeller  178  are disposed at the first end  180  of the fuselage  170  and provide propulsion to the propulsion unit. In this configuration, the thruster  150  operates in a tractor configuration, such that the propulsion unit  140  is pulled through the air. The electrical motor  176  may be powered by the energy storage  146 , which stores electrical energy generated by the solar panels  152 . The solar panels  152  may be on any portion of propulsion unit  140 , e.g., on the primary airfoil  172  and/or the secondary airfoil  174 . In exemplary embodiments, the thruster  150  may be disposed at the second end  182 , and would be configured in a pusher configuration, such that the propulsion unit  140  is pushed through the air. 
     Each of the primary airfoil  172  and the secondary airfoil  174  may include one or more ailerons  184  that may be used to control direction of the propulsion unit  140 . As described above in  FIG.  2   , the propulsion controller  144  is configured to operate the flight controls  148 , which include the thruster  150  and the ailerons  184 , to control the flight of the propulsion unit  140 . This includes operating the flight controls  148  to guide to propulsion unit  140  along the propulsion flight path  160  to achieve a desired speed and/or direction of the propulsion unit  140 , to generate lift and by extension, propel the aerial vehicle  102  along the vehicle flight path  162 . 
     The sensors  142  of the propulsion unit  140  measure various flight data parameters, such as air pressure, wind velocity, etc. The sensors  142  transmit this data to the vehicle controller  126  and/or the propulsion controller  144 , which then make adjustments to the propulsion flight path  160  and/or the vehicle flight path  162 . 
     The propulsion unit  140  may move in any cyclical flight path having any suitable shape, e.g., obround, oval, circular, and combinations thereof etc., as shown in  FIG.  4 A . The pitch, roll, and yaw of the propulsion unit  140  may be varied during the propulsion flight path  160  by adjusting any or all of the ailerons  184  disposed on the primary and secondary airfoils  172  and  174  as well as the thruster  150 . In embodiments, the propulsion flight path  160  may be adjusted by controlling the direction as well as velocity of the propulsion unit  140 . In other words, the propulsion controller  144  would instruct the flight controls  148  of the propulsion unit  140  to execute half a loop at each end to generate a cyclical pattern. 
     Alternatively, the propulsion unit  140  may move along a cyclically reversible undulating propulsion flight path  161 . The propulsion flight path  161  may be adjusted by controlling the thruster  150  such that the propulsion unit  140  undulates along the propulsion flight path  161 . It is envisioned that ailerons  184  may also be adjusted to ensure that the propulsion unit  140  stays within the swing plane  163 . The thruster  150  may be operated in a cyclical manner such that the thruster  150  switches between tractor and pusher configurations. In order to propel the propulsion unit  140  along the propulsion flight path  161 , the thruster  150  is operated at a variable speed to ensure that the velocity and acceleration vectors of the propulsion unit  140  correspond to the undulating trajectory of the propulsion flight path  161 . Thus, as the propulsion unit  140  is approaching either end of the propulsion flight path  161 , the velocity of the propulsion unit  140  approaches zero. At these points, the thruster  150  reverses the direction of the thrust (e.g., switches between the tractor and pusher configurations) to propel the propulsion unit  140  in a reverse direction. 
     With reference to  FIG.  6   , another embodiment of a propulsion unit  240  is shown. The propulsion units  140  and  240  may be used interchangeably with respect to the flight paths  160  and  161  of  FIGS.  4 A and  4 B , or any other desired flight paths. Since the propulsion unit  240  is suspended from the aerial vehicle  102 , aerodynamic demands on the propulsion unit  240  are different from a conventional aircraft that needs to maintain flight without the aid of another aerial vehicle, e.g., aerial vehicle  102 . Accordingly, the propulsion unit  240  may include any number or airfoils having any suitable shape or size designed to achieve directional control and drag reduction of the propulsion unit  140  to achieve flight control of the aerial vehicle  102  rather than of the propulsion unit  140 . 
     The propulsion unit  240  is substantially similar to the propulsion unit  140  of  FIG.  5   , and only the differences are described below. In particular, the propulsion unit  240  may include a primary airfoil  272  having a single a wing extending from the fuselage  170 . In addition, the propulsion unit  240  may include the winch  120  that is coupled to the primary airfoil  272 . In exemplary embodiments, the winch  120  may also be coupled to the primary airfoil  172  of the propulsion unit  140 . 
     Various operational parameters of the propulsion unit  140  or  240 , such as tether extension, direction and speed of the propulsion flight path  160  may be controlled remotely in order to move the aerial vehicle  102  to a desired destination. Commands to the propulsion unit  140  may be sent from the computing devices  104  through the vehicle controller  102  or directly to the propulsion controller  144 . Commands may include GPS coordinates to instruct the aerial vehicle  102  to move to a desired location. The vehicle controller  126  would then communicate with the propulsion controller  144  to achieve the desired positioning of the aerial vehicle  102  by moving the propulsion unit  140  or  240  along the propulsion flight path  160  to generate movement, e.g., desired speed and direction, along the vehicle flight path  162 . Thus, the vehicle controller  126 , upon receiving movement commands from the computing devices  104 , is configured to generate propulsion commands for the propulsion unit  140  or  240  to move the aerial vehicle  102  along the vehicle flight path  162 . In embodiments, the vehicle controller  126  and/or the propulsion controller  144  may control the winch  120  to adjust the distance of the tether  156  to make additional adjustments to the propulsion flight path  160  since the length of the tether  156  directly affects the length of the propulsion flight path  160 . 
     In embodiments, in addition to being used to generate desired movement, the propulsion unit  140  or  240  may be also used as a sail to guide the aerial vehicle  102  using wind currents. In further embodiments, the propulsion unit  140  or  240  may be used as an anchor to counteract any movement of the aerial vehicle  102  due to atmospheric conditions, e.g., currents. In these embodiments, the propulsion unit  140  or  240  is lowered into lower reaches of the atmosphere and the flight controls  148  are used to maintain the position and orientation of the propulsion unit  140  or  240  relative to the wind current depending on the desired effects of the winds (e.g., to minimize or maximize the surface area of the primary airfoil  272  or the primary and secondary airfoils  172  and  174  exposed to the wind). 
     As can be appreciated in view of the present disclosure, the systems and methods described herein provide advancements in aerial vehicle propulsion. The disclosed system minimizes the need for multiple thrust generating devices by using a single thruster to move the aerial vehicle in any desired direction. The present disclosure also provides for a low cost and low weight propulsion system that can be integrated within the existing framework of any buoyant aerial vehicle system by being suspended from the payload. In addition, the disclosed propulsion unit has minimal power requirements for generating propulsion, which leverages atmospheric conditions, e.g., wind, and/or momentum to move the balloon. Furthermore, the configuration of the propulsion unit provides for additional surface area for mounting solar panels. 
     The embodiments disclosed herein are examples of the present systems and methods and may be embodied in various forms. For instance, although certain embodiments herein are described as separate embodiments, each of the embodiments herein may be combined with one or more of the other embodiments herein. Specific structural and functional details disclosed herein are not to be interpreted as limiting, but as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present information systems in virtually any appropriately detailed structure. Like reference numerals may refer to similar or identical elements throughout the description of the figures. 
     The phrases “in an embodiment,” “in embodiments,” “in some embodiments,” or “in other embodiments” may each refer to one or more of the same or different embodiments in accordance with the present disclosure. A phrase in the form “A or B” means “(A), (B), or (A and B).” A phrase in the form “at least one of A, B, or C” means “(A); (B); (C); (A and B); (A and C); (B and C); or (A, B, and C).” 
     The systems and/or methods described herein may utilize one or more controllers to receive various data and transform the received data to generate an output. The controller may include any type of computing device, computational circuit, or any type of processor or processing circuit capable of executing a series of instructions that are stored in a memory. The controller may include multiple processors and/or multicore central processing units (CPUs) and may include any type of processor, such as a microprocessor, digital signal processor, microcontroller, programmable logic device (PLD), field programmable gate array (FPGA), or the like. The controller may also include a memory to store data and/or instructions that, when executed by the one or more processors, causes the one or more processors to perform one or more methods and/or algorithms. In exemplary embodiments that employ a combination of multiple controllers and/or multiple memories, each function of the systems and/or methods described herein can be allocated to and executed by any combination of the controllers and memories. 
     Any of the herein described methods, programs, algorithms or codes may be converted to, or expressed in, a programming language or computer program. The terms “programming language” and “computer program,” as used herein, each include any language used to specify instructions to a computer, and include (but is not limited to) the following languages and their derivatives: Assembler, Basic, Batch files, BCPL, C, C+, C++, Delphi, Fortran, Java, JavaScript, machine code, operating system command languages, Pascal, Perl, PL1, scripting languages, Visual Basic, metalanguages which themselves specify programs, and all first, second, third, fourth, fifth, or further generation computer languages. Also included are database and other data schemas, and any other meta-languages. No distinction is made between languages which are interpreted, compiled, or use both compiled and interpreted approaches. No distinction is made between compiled and source versions of a program. Thus, reference to a program, where the programming language could exist in more than one state (such as source, compiled, object, or linked) is a reference to any and all such states. Reference to a program may encompass the actual instructions and/or the intent of those instructions. 
     Any of the herein described methods, programs, algorithms or codes may be contained on one or more non-transitory computer-readable or machine-readable media or memory. The term “memory” may include a mechanism that provides (in an example, stores and/or transmits) information in a form readable by a machine such a processor, computer, or a digital processing device. For example, a memory may include a read only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, or any other volatile or non-volatile memory storage device. Code or instructions contained thereon can be represented by carrier wave signals, infrared signals, digital signals, and by other like signals. 
     The foregoing description is only illustrative of the present systems and methods. Various alternatives and modifications can be devised by those skilled in the art without departing from the disclosure. Accordingly, the present disclosure is intended to embrace all such alternatives, modifications and variances. The embodiments described with reference to the attached drawing figures are presented only to demonstrate certain examples of the disclosure. Other elements, steps, methods, and techniques that are insubstantially different from those described above and/or in the appended claims are also intended to be within the scope of the disclosure.