Patent Publication Number: US-8973860-B2

Title: Aerial recovery of small and micro air vehicles

Description:
RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 12/487,907, filed Jun. 19, 2009, which claims the benefit of U.S. Provisional Application No. 61/132,646, filed Jun. 20, 2008, which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to unmanned aerial vehicles. More specifically, the present disclosure relates to aerial recovery of small and micro unmanned aerial vehicles. 
     BACKGROUND 
     Due to recent directives from the Department of Defense, there is great pressure to develop the technology behind unmanned aerial vehicles (UAVs). UAVs are remotely piloted or autonomous aircraft that can carry cameras, sensors, communications equipment, or other payloads. 
     UAVs have proven their usefulness in military applications in recent years. Large UAVs have become an integral part of the U.S. arsenal. Large UAVs have executed surveillance and tactical missions in virtually every part of the world. For example, unmanned aircraft systems (“UAS”) have become an essential tool for warfighters. While high-altitude, long-endurance UAS like the Predator and the Global Hawk provide persistent intelligence, surveillance, and reconnaissance (“ISR”) capabilities, they are a scarce resource that cannot be given specific data-gathering tasks by individual troops. At the other end of the spectrum are backpackable small and micro air vehicles (“MAVs”), with wingspans less than 48 inches, which theoretically can be carried by every warfighter. 
     One drawback of MAVs is the recovery of the MAV after it has completed its mission. Although the relatively low cost of MAVs may suggest that they may be expendable (and thereby removing the need for recovery), MAVs still contain critical and often classified technology that needs to be kept out of enemy hands. Thus, innovative recovery techniques are critical to ubiquitous use of MAV technology. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow diagram illustrating an embodiment of a method of recovering an air vehicle. 
         FIG. 2  is a diagram illustrating an embodiment of a system that may be used to recover an air vehicle. 
         FIG. 3  is a diagram illustrating one embodiment of a drogue that may be used to recover an air vehicle. 
         FIG. 4  is a diagram illustrating another embodiment of a drogue that may be used to recover an air vehicle. 
         FIG. 5  is a diagram illustrating yet another embodiment of a drogue that may be used to recover an air vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. In addition, references to “an,” “one,” “other,” “another,” “the,” “this,” “alternative,” or “various” embodiments should not be construed as limiting since various aspects of the disclosed embodiments may be used interchangeably within other embodiments. 
     A method, apparatus, system, and computer system are disclosed to facilitate aerial recovery of an air vehicle (e.g., MAV). One embodiment of the method may include establishing a drogue in a drogue recovery orbit and recovering an air vehicle with the drogue. In various embodiments, one or more of the following may also be part of the method: establishing a mothership in a mothership recovery orbit; actuating one or more control surfaces of the drogue; maneuvering the drogue and the air vehicle in a cooperative manner to facilitate recovery of the air vehicle; utilizing a homing device on the drogue to guide the air vehicle; and compensating for wind. 
     One embodiment of the apparatus (e.g., drogue) may include an aerodynamic main body portion, at least one control surface located on the main body portion, a catch mechanism coupled to the main body portion, the catch mechanism to facilitate recovery of an air vehicle, and a homing device coupled to the main body portion to guide the air vehicle during recovery. The apparatus may also include an attachment mechanism to attach the main body portion to a mothership with a tow cable. In various embodiments, the catch mechanism may comprise at least one of an open cavity located within an interior of the main body portion, a closeable cavity located within the interior of the main body portion, and a dragnet coupled to the main body portion. In various embodiments, the homing device may comprise at least one of a color marker, an infrared marker, an acoustic beacon, and an electromagnetic beacon. 
     One embodiment of the system may include a mothership and a drogue coupled to the mothership by a tow cable, the drogue comprising an aerodynamic main body portion, at least one control surface located on the main body portion, a catch mechanism coupled to the main body portion, the catch mechanism to facilitate recovery of an air vehicle, and a homing device coupled to the main body portion to guide the air vehicle during recovery. In various embodiments, the catch mechanism may comprise at least one of an open cavity located within an interior of the main body portion, a closeable cavity located within the interior of the main body portion, and a dragnet coupled to the main body portion. In various embodiments, the homing device may comprise at least one of a color marker, an infrared marker, an acoustic beacon, and an electromagnetic beacon. 
     One embodiment of the computer system may include a processor, memory in electronic communication with the processor, and instructions stored in the memory, the instructions being executable to establish a drogue in a drogue recovery orbit and recover an air vehicle with the drogue. In various embodiments, the computer system may control one or more elements of the system (e.g., mothership, drogue, air vehicle). In various embodiments, the memory may further include instructions being executable to perform one or more of the following: establishing a mothership in a mothership recovery orbit; actuating one or more control surfaces of the drogue; maneuvering the drogue and the air vehicle in a cooperative manner to facilitate recovery of the air vehicle; and compensating for wind. 
     Backpackable MAVs enable warfighters on the ground to gather time-critical, over-the-hill ISR information. However, retrieving the MAV is problematic because landing the vehicle near the soldier could disclose his/her location to an enemy. Another potential application of MAVs is collecting battle damage information. For example, the MAV could piggyback on munitions until several seconds before impact, when it is deployed so that it can circle the target to assess the damage caused by the munitions. Again for this application, retrieval of the MAV after it has performed its mission is difficult because target locations are often deep in enemy territory, and the MAV may not have enough fuel to return home. 
     A third potential application of MAV technology is to assist gunship operators to track and prosecute multiple targets. For example, enemy combatants may separate and flee in multiple directions when there is a threat of attack by a gunship. The gunship could potentially deploy multiple MAVs to assist in tracking the combatants as they flee. Yet again, it is difficult to retrieve the MAV after it has completed its mission, primarily because the airspeed of the gunship, which may be approximately 200 knots, is so much greater than the airspeed of the MAV, which may be approximately 30-40 knots. There are numerous other applications where MAVs could be used to safely gather high resolution ISR data but for which retrieval of the asset is problematic. 
     The primary difficulty with aerial recovery is the relative size and speed of the mothership compared to the MAV. Aerial recovery is much like aerial refueling where the goal is to extend the operational lifetime of the asset. However, in aerial refueling, the fighter jet and the tanker can match their airspeeds, which is not possible with MAVs and larger aircraft. The embodiments disclosed herein may facilitate aerial recovery of existing MAVs using a much larger fixed wing mothership. The mothership could either be unmanned (e.g., Predator) or manned (e.g., AC-130). 
     Referring now to  FIG. 1 , an embodiment of a method is shown. The method begins by establishing a drogue in a drogue recovery orbit at block  100 . As used herein, a “drogue” refers to a device to be towed by an aircraft (e.g., mothership) to facilitate the recovery of an air vehicle (e.g., a small or micro air vehicle). In various embodiments, recovery of the air vehicle is conducted in the air (e.g., an aerial recovery). As used herein, a “drogue recovery orbit” refers to an orbit in which the drogue is established to facilitate recovery of an air vehicle. 
     In various embodiments, the drogue recovery orbit may be an orbit in which the drogue maintains substantially the same altitude while flying in a generally circular pattern. In other embodiments, the drogue recovery orbit may have patterns that are not circular. Thus, any shape orbit may be utilized to facilitate recovery of an air vehicle. Furthermore, a particular orbit shape may be utilized to compensate for one or more environmental factors (e.g., wind, avoiding detection, evading enemy attacks) while attempting to recover an air vehicle. For example, the drogue recovery orbit may be generally elliptical. In other embodiments, the altitude of the drogue may be intentionally varied while in the drogue recovery orbit to facilitate recovery of an air vehicle. 
     Establishment of the drogue in a drogue recovery orbit may be achieved in various embodiments by establishing a mothership, which is towing the drogue, in a mothership recovery orbit. As used herein, a “mothership recovery orbit” refers to an orbit in which the mothership is established to facilitate recovery of an air vehicle. Similar to the drogue recovery orbit discussed above, the mothership recovery orbit may be an orbit in which the mothership maintains substantially the same altitude while flying in a generally circular pattern. In other embodiments, the mothership recovery orbit may have patterns that are not circular. Thus, any shape orbit may be utilized to facilitate recovery of an air vehicle. Furthermore, a particular orbit shape may be utilized to compensate for one or more environmental factors (e.g., wind, avoiding detection, evading enemy attacks) while attempting to recover an air vehicle. For example, the mothership recovery orbit may be generally elliptical. In other embodiments, the altitude of the mothership may be intentionally varied while in the mothership recovery orbit to facilitate recovery of an air vehicle. 
     In other embodiments, establishment of the drogue in a drogue recovery orbit may be achieved by actuating one or more control surfaces of the drogue. These control surfaces may be any type of control surface used in aviation to control the flight path and characteristics of an air vehicle. Examples of control surfaces that may be actuated to establish the drogue in a drogue recovery orbit can be seen below in connection with the discussion of  FIGS. 3-5 . 
     In various embodiments, the drogue recovery orbit may have a radius greater than a minimum turning radius of the air vehicle to be recovered. During recovery, the drogue may be controlled to have an airspeed that is less than the airspeed of the air vehicle to be recovered. In various embodiments, the airspeed of the air vehicle is a nominal airspeed, and the airspeed of the drogue is less than the nominal airspeed of the air vehicle to be recovered. 
     At block  102 , an air vehicle is recovered with the drogue. In various embodiments, recovery of the air vehicle includes maneuvering the drogue and the air vehicle in a cooperative manner to facilitate recovery of the air vehicle. This maneuvering in a cooperative manner may include, for example, controlling both the drogue and air vehicle to move towards a common point or to reduce the relative distance between the drogue and the air vehicle to facilitate recovery. 
     In various embodiments, recovery of the air vehicle includes utilizing a homing device on the drogue to guide the air vehicle. The homing device may be active, passive, or have components that are both active and passive. Examples of passive homing devices include a color marker, an infrared marker, an acoustic beacon, and an electromagnetic beacon. In various embodiments, the air vehicle may use vision-based sensors, for example, to maintain a constant image of the target (e.g., a capture mechanism associated with the drogue) during the final stage of recovery. If the image “moves” while the air vehicle is approaching the drogue, the air vehicle may actuate its control surface(s) to reacquire the desired approach image by the vision-based sensors. It is worth noting that other sensor systems may be used. 
     At any stage of the method shown in  FIG. 1 , it may be advantageous to compensate for wind, which may cause the drogue recovery orbit to become “tilted.” A “tilt” refers to a situation in which the drogue experiences unintentional altitude variations while in the drogue recovery orbit. These altitude variations may be caused by the wind. 
     Compensation for the wind may be achieved by using several different techniques, alone or in combination. For example, as discussed above, the mothership recovery orbit may be “tilted” in one embodiment by varying the altitude of the mothership during the mothership recovery orbit. Also, the shape of the mothership recovery orbit (e.g., circular, elliptical, etc.) may be varied to compensate for wind. In other embodiments, the orbit of the air vehicle may be “tilted” by varying the altitude of the air vehicle as recovery of the air vehicle is attempted. In another embodiment, a winch may be used to deploy the tow cable (e.g., from the mothership) that is connected to the drogue, and thus, the winch may be used to vary the length of the tow cable to compensate for the effect of the wind on the drogue. In various embodiments, one or more of the control surfaces of the drogue may be actuated to control the flight path of the drogue to compensate for wind. 
     Referring now to  FIG. 2 , system  200  is shown that may be used to recover an air vehicle. System  200  includes mothership  202  that is shown flying in mothership recovery orbit  204 . Mothership  202  may be manned or unmanned. Mothership recovery orbit  204  has radius (R)  206 , and mothership  202  is traveling at speed (V)  208 . Drogue  210  is coupled to mothership  202  by tow cable  212 , which has length (I)  212 . 
     Drogue  210  is flying in drogue recovery orbit  214 . Drogue recovery orbit  214  has radius (r)  216 . In various embodiments, radius  216  of drogue recovery orbit  214  is significantly smaller than radius  206  of mothership recovery orbit  204 . Drogue  210  is shown traveling at speed (v d )  218 . In various embodiments, speed  218  of drogue  210  is significantly less than speed  208  of mothership  202 . 
     Air vehicle  220  (e.g., MAV) is shown flying towards drogue recovery orbit  214  in order to be recovered by drogue  210 . Air vehicle  220  is shown flying at speed (v)  222 . As discussed above, speed  218  of drogue  210  is less than speed  222  of air vehicle  220  so that air vehicle  220  may over take drogue  210  once air vehicle  220  has entered drogue recovery orbit  214 . 
     Referring now to  FIG. 3 , one embodiment of a drogue is shown. Drogue  300  includes aerodynamic main body portion  302  and control surfaces  304  located on main body portion  302 . Control surfaces  304  include elevons  304   a . Elevons are a combination of elevators and ailerons. Control surfaces  304  also include rudders  304   b . It is worth noting that other numbers, types, and configurations of control surfaces may be used. 
     Drogue  300  additionally includes catch mechanism  306  coupled to main body portion  302 . Catch mechanism  306  is an open cavity located within an interior of main body portion  302  and is designed to facilitate recovery of an air vehicle. In various embodiments, catch mechanism  306  is lined with one type of hook-and-loop fastening material, and the air vehicle to be recovered has a complementary type of hook-and-loop fastening material disposed thereon to facilitate recovery. Although, other material could be used to line catch mechanism  306  to facilitate recovery of an air vehicle. 
     Drogue  300  also includes homing device  308  coupled to main body portion  302  to guide the air vehicle during recovery. As mentioned above, homing device  308  may be active, passive, or have components that are both active and passive. Examples of passive homing devices include a color marker, an infrared marker, an acoustic beacon, and an electromagnetic beacon. 
     Drogue  300  has wings  310  coupled to main body portion  302 . Wings  310  are designed to impart lift to drogue  300  while in flight. Attachment mechanism  312  is coupled to the front of main body portion  302  and is designed to attach main body portion  302  to a mothership with tow cable  314 . 
     Referring now to  FIG. 4 , another embodiment of a drogue is shown. Drogue  400  includes aerodynamic main body portion  402 , which is designed to create lift while flying. The shape of main body portion  402  may be similar to that of stealth aircraft that have a “flying wing” design. Drogue  400  also includes control surfaces  404  located on main body portion  402 . Control surfaces  404  include elevons  404   a . Control surfaces  404  also include rudders  404   b . It is worth noting that other numbers, types, and configurations of control surfaces may be used. 
     Drogue  400  additionally includes catch mechanism  406  coupled to main body portion  402 . Catch mechanism  406  is a closeable cavity located within the interior of main body portion  402  and is designed to facilitate recovery of an air vehicle. As shown in  FIG. 4 , catch mechanism  406  is illustrated in an open configuration, ready to recover an air vehicle. The dashed line in  FIG. 4  indicates trailing edge  410  of main body portion  402  when catch mechanism  406  is in a closed configuration. In various embodiments, catch mechanism  406  is lined with one type of hook-and-loop fastening material, and the air vehicle to be recovered has a complementary type of hook-and-loop fastening material disposed thereon to facilitate recovery. Although, other material could be used to line catch mechanism  406  to facilitate recovery of an air vehicle. 
     Drogue  400  also includes homing device  408  coupled to main body portion  402  to guide the air vehicle during recovery. As mentioned above, homing device  408  may be active, passive, or have components that are both active and passive. Examples of passive homing devices include a color marker, an infrared marker, an acoustic beacon, and an electromagnetic beacon. Attachment mechanism  412  is coupled to the front of main body portion  402  and is designed to attach main body portion  402  to a mothership with tow cable  414 . 
     Referring now to  FIG. 5 , another embodiment of a drogue is shown. Drogue  500  includes aerodynamic main body portion  502  and control surfaces  504  located on main body portion  502 . Control surfaces  504  include elevons  504   a . Control surfaces  504  also include rudders  504   b . It is worth noting that other numbers, types, and configurations of control surfaces may be used. 
     Drogue  500  additionally includes catch mechanism  506  coupled to main body portion  502 . Catch mechanism  506  is a dragnet coupled to main body portion  502  and is designed to facilitate recovery of an air vehicle. In various embodiments, catch mechanism  506  is lined with one type of hook-and-loop fastening material, and the air vehicle to be recovered has a complementary type of hook-and-loop fastening material disposed thereon to facilitate recovery. Although, other material could be used to line catch mechanism  506  to facilitate recovery of an air vehicle. 
     Drogue  500  has wings  508  coupled to main body portion  502 . Wings  508  are designed to impart lift to drogue  500  while in flight. Attachment mechanism  510  is coupled to the front of main body portion  502  and is designed to attach main body portion  502  to a mothership with tow cable  512 . 
     Although not shown in the figures, the drogue may have an autopilot system that is capable of actuating the one or more control surfaces in order to establish and maintain a drogue recovery orbit. In addition, the drogue and the air vehicle may each have a Global Positioning System (“GPS”) receiver that can provide information that can be used to bring the drogue and the air vehicle within 3-5 meters of each other, at which point the air vehicle may utilize the homing device on the drogue for guidance during the final stage of recovery. The autopilot of the drogue may also be used to cooperatively maneuver the drogue during the final stage of recovery of the air vehicle. 
     In operation, each component of the system (e.g., mothership, drogue, air vehicle) may be controlled by software. In various embodiments, control software may be resident on each component, respectively (e.g., control software for mothership may be resident on the mothership). In other embodiments, the control software for all of the components may be resident in one location (e.g., mothership or on a remote computer system). In still other embodiments, the location of the control software may be a combination of these examples. 
     Regardless of the location of the control software, there may be a user interface in various embodiments for a user to control the overall system (e.g., programming one or more of the components, inputting environmental factors that need to be considered for recovery of an air vehicle, manually controlling one or more components, etc). In one embodiment, the user interface may be a laptop computer. In other embodiments, the user interface may be a desktop computer, a personal digital assistant, a tablet personal computer (“PC”), or other similar devices. The user interface may be physically connected to one or more of the system components. In other embodiments, the user interface may be in wireless communication with one or more of the system components. 
     The various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the disclosed embodiments. 
     The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is required for proper operation of the method that is being described, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims. 
     It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the systems, methods, and apparatus described herein without departing from the scope of the claims.