Abstract:
A parafoil recovery system capable of autonomously controlling the descent profile of a payload to a recovery area and maneuvering the parafoil to execute a soft landing in the recovery area is disclosed. A descent profile management system determines wind speed and direction, altitude, heading, and position of the payload based on sensor input. The descent profile management system also determines a gliding flight path profile from the launch point to the desired recovery area. A flare and stall maneuver is executed at the end of the landing sequence by braking the parafoil to slow the vertical descent speed and groundspeed for a soft landing. The pitch attitude of the payload can be adjusted by the descent profile management system to prevent nose-first impact with the ground. The parafoil canopy is released from the payload upon touchdown to prevent the canopy from dragging the payload on the ground after landing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 09/922,167 entitled Autonomous Control of a Parafoil Recovery System for UAVs”, filed Aug. 6, 2001, now abandoned. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an apparatus for the parachute recovery of a payload, and more particularly to a system for autonomously steering an airborne payload to a recovery area and soft landing of the payload. 
     2. Description of the Related Art 
     Current parachute recovery systems use an uncontrolled round (or ballistic) parachute. The parachute descends at a vertical speed depending on the relation of the size of the parachute to the weight of the payload. The, recovery systems also have a horizontal speed and direction equal to that of the surface wind. The round parachute system drifts with the wind and impacts the ground at a random orientation. This ground impact usually results in damage to the payload due to the vertical descent rate and the horizontal speed which causes the payload to tumble and/or slam into rocks, trees, etc. In addition, since the round parachute is difficult to steer and drifts with the wind, the ground impact location is random. 
     Clearly there is a need for a parachute recovery system that can be steered to a precise recovery area and then execute a soft landing, all autonomously. 
     The related art teaches several parachute recovery systems for the controlled steering of the system to a predetermined recovery area, but none include the soft landing offered by the present invention. For example, U.S. Pat. No. 5,201,482 to Ream, U.S. Pat. No. 5,620,153 to Ginsberg and U.S. Pat. No. 5,899,415 to Conway all use parafoils (or ram air parachutes) for controlling the glide path of the recovery system. These systems all rely on human piloting of the parafoil (i.e.; non-autonomous). U.S. Pat. No. 6,122,572 to Yavnai teaches an autonomous command and control unit for a powered airborne vehicle that uses a programmable decision unit capable of managing and controlling the execution of a mission by using subsystems and a data base capable of holding and manipulating data including pre-stored data and data acquired by and received from the various subsystems. U.S. Pat. No. 6,144,899 to Babb et al. discusses a recoverable airborne winged instrument platform for use in predicting and monitoring weather conditions. The platform is taken aloft by balloon means, accurately determines its present position and uses the data to execute a predetermined flight plan and ultimately guide its descent to a predetermined landing site. This is achieved by installing the instrument package payload in the aerodynamic exterior housing of the recoverable airborne instrument platform. 
     None of the systems available in the prior include components for autonomously managing and controlling a parafoil recovery system to a pre-selected recovery area, adjusting the orientation of the payload before landing, or executing a landing sequence that includes parafoil canopy flare and stall maneuvers. 
     SUMMARY 
     A parafoil recovery system capable of autonomously controlling the descent profile of a payload to a predetermined recovery area and manipulating the parafoil to execute a soft landing in the recovery area is provided. 
     One advantageous feature of the system is a descent profile management system (DPMS) that can determine wind speed and direction, as well as altitude, heading and position of the payload, based on sensor input. The DPMS determines an optimum gliding flight path from the launch point to the desired recovery area, and then controls the recovery system to land the payload at or near the desired recovery site. 
     Another advantageous feature of the system includes one or more attitude control lines that allow the attitude of the payload to be adjusted either before or during flight to prevent nose-first impact with the ground. 
     A further feature of the system that offers advantages over known systems includes executing a flare maneuver near the end of the landing sequence by braking the parafoil to slow the descent of the payload for a soft landing. When the payload is within a predetermined height above ground, the canopy of the parafoil is stalled to decrease the ground speed and vertical descent speed at touchdown. The parafoil canopy is released from the payload upon touchdown to prevent the canopy from dragging the payload on the ground after landing. The parafoil recovery system thus delivers a payload at or near a specified recovery location with minimal ground impact damage. 
     Although the present invention is briefly summarized, the fuller understanding of the invention is obtained by the following drawings, detailed description, and appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects, features and advantages of the present invention will become better understood with reference to the accompanying drawing, wherein: 
     FIG. 1 is a diagram depicting an embodiment of a parafoil attached to a payload. 
     FIG. 2A is a diagram of an embodiment of a harness and control line system for retaining the payload to the canopy, and for controlling the descent and landing of the payload. 
     FIG. 2B is a diagram of another embodiment of a harness and control line system for retaining the payload to the canopy, and for controlling the descent and landing of the payload. 
     FIG. 3 is a diagram of components included in an embodiment of a control system for controlling the descent of the parafoil and payload shown in FIG.  1 . 
     FIG. 4 is a flow diagram showing some of the functions performed by the control system of FIG.  3 . 
     FIG. 5 is a diagram showing an embodiment of a controlled descent and flared landing profile of the parafoil and payload shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, an embodiment of parafoil recovery system  100  for recovering payload  101 , such as an unmanned air vehicle, at a desired location at the end of a flight is shown. To simplify notation, reference numbers suffixed with “R” (right) or “L” (left) in the figures are, in some instances, designated collectively or in the alternative herein by the reference number without the “R” or “L” suffix. 
     Parafoil canopy  102  had a leading edge  104 , trailing edge  106 , and sides  108 R,  108 L. Canopy  102  is typically a rectangular or oval shaped fabric wing with a spanwise series of cells that are inflated by ram-air pressure during flight. Canopy  102  can be deployed from payload  101  automatically when a predetermined event occurs, such as reaching a specified location or being aloft for a specified time period. Alternatively, an operator can command deployment of canopy  102  from a remote location via a data uplink/telemetry system (not shown). 
     Main risers  110 R,  110 L connect respective sides  108  of canopy  102  to one end of harnesses  112 R,  112 L. The other end of harnesses  112  are attached to payload  101 . Brake line risers  116 R,  116 L connect left and right outer portions of trailing edge  106  to brake lines  120 R,  120 L. 
     Referring now to FIGS. 1 and 2A, FIG. 2A is a diagram of an embodiment of a configuration of harnesses  112  and brake line risers  116  is shown for retaining the payload  101  to canopy  102 , and for controlling the descent and landing of payload  101 . Any suitable type of releasable or fixed attachment mechanism can be utilized to implement attachment points  202 . In some embodiments, attachment points  202  are positioned at or ahead of the center of gravity  122  of payload  101  to prevent payload  101  from having a nose-down orientation during the landing. Harnesses  112  can be fabricated using any suitable rigid or flexible material. 
     Main risers  110  are coupled to harnesses  112  via quick-release connectors  204 R,  204 L. Similarly, brake line risers  116  are coupled to brake lines  120  via quick-release connectors  206 R,  206 L. When payload  101  touches ground, quick-release connectors  204 ,  206  disconnect risers  110 ,  116  from harnesses  112  and brake lines  120 , respectively, to prevent payload  101  from being pulled along the ground by canopy  102 . In other embodiments, quick-release connectors  204 ,  206  may not be used. In still other embodiments, main risers  110  can be coupled to a single harness  112  with or without a quick release connector  204 . Any suitable type of quick-release-connector can be utilized to implement quick-release connectors  204 ,  206 . 
     Reel motors  208 R,  208 L are mounted on payload  101 . A length of brake lines  120  is wound around a spindle on reel motors  208 . The spindle is rotated to wind or unwind the brake lines  120 , thereby adjusting the length of brake lines  120 . The resulting force is applied to the outer trailing edge portions of canopy  102 . Other suitable types of devices for adjusting the length of brake lines  120  can be utilized in addition to or instead of reel motors  208 . 
     The embodiment shown in FIG. 2A shows reel motors  208  mounted behind the center of gravity  122  of payload  101  to retain payload  101  in a substantially horizontal orientation during the descent. Brake lines  120 R,  120 L are coupled to reel motors  208 R,  208 L, respectively, and are threaded through pulleys  210 R,  210 L in harnesses  112 . Reel motors  208  are coupled to a control system (not shown), which issues commands to operate reel motors  208  to lengthen or shorten brake lines  120 R,  120 L. When one of brake lines  120  is shortened, the corresponding outer portion  118  of trailing edge  106  is pulled downward, thereby increasing drag and causing canopy  102  to turn toward the side  108  with the increased drag. When brake lines  120  are the same length, canopy  102  will descend without turning. When both brake lines  120  are shortened the same amount, drag increases over the entire canopy  102 , thereby slowing the descent rate and horizontal glide speed (also referred to as “braking”) of canopy  102 . The control system (not shown) is capable of combining commands to turn and brake canopy  102  simultaneously. 
     Referring to FIGS. 1 and 2B, another embodiment of harnesses  112  is shown in FIG. 2B including pitch control line  220  to control the nose-up/nose-down orientation of payload  101  during descent. In the embodiment shown in FIG. 2B, pitch control line  220  is connected between a point behind the center of gravity  122  and another point ahead of the center of gravity  122  of payload  101 . The length of pitch control line  220  is adjusted via reel motor  222 , thereby controlling the pitch orientation of payload  101 . Reel motor  222  is operated by a control system (not shown) capable of determining a desired orientation for payload  101  and coupled to feedback sensors regarding the actual orientation of payload  101 . 
     In other embodiments, pitch control line  220  can be a fixed length attached at various points to payload  101  to provide the desired pitch orientation for payload  101 . Such embodiments eliminate the need for reel motor  222 , and corresponding feedback sensors and control logic. Pitch control line  220  is shown in FIG. 2B as including two segments  224 R,  224 L branching to harnesses  112 R,  112 L, however, a variety of configurations and any suitable type of material can be utilized to implement pitch control line  220 . Additionally, attitude control lines and reel motors configured to adjust the orientation of payload  101  in other directions in addition to pitch can also be utilized. 
     In the embodiment shown in FIG. 2B, brake lines  120  are configured to thread through a central pulley  228  instead of pulleys  210  on harnesses  112 . Such a configuration eliminates any influence adjustment of the brake lines  120  may have on the pitch attitude of payload  101 . 
     Referring now to FIGS. 1 and 3, FIG. 3 shows a block diagram of an embodiment of a descent profile management system (DPMS)  300  that can be used to control parafoil canopy  102  in flight. The control functions are performed by generating commands in control computer  302  and transmitting the commands in the form of electrical pulses to actuators (not shown) in reel motors  208 ,  222  via motor controller  304 . Reel motors  208  are physically connected to brake lines  120 , which are used for right and left turns as well as to control the descent rate of payload  101 . 
     Pitch reel motor  222  is also coupled to receive position commands to adjust pitch control line  220  so that payload  101  has the desired pitch attitude. For example, when payload  101  includes external components, such as wings, that can influence the descent profile, the pitch attitude of payload  101  can be adjusted during the landing sequence to help achieve the desired descent profile. Additionally, the pitch attitude of payload  101  can be adjusted before touchdown to avoid a nose-first impact with the ground, as required. 
     DPMS  300  includes several sensors that provide information such as heading, speed, location, and altitude to control computer  302 . When available, instrumentation and equipment in payload  101  can be coupled to DPMS  300  to provide sensor information, as well as to implement and provide power to control computer  302 . Control computer  302  determines the resulting change to the descent profile of payload  101  based on feedback from GPS receiver  308 , heading indicator  310 , and AGL sensors  312 , which enables control computer  302  to make further adjustments to achieve the desired state including descent rate, ground speed, position relative to the desired recovery point, and heading orientation relative to the wind speed and direction. While the embodiment of DPMS  300  in FIG. 3 shows certain sensors to provide information such as position, speed, heading, and altitude, other types of sensors can be used to provide information to DPMS  300  in addition to, or instead of, the sensors shown in FIG.  3 . 
     One sensor included in the embodiment of DPMS  300  shown in FIG. 3 is a global positioning system (GPS) antenna  306  and GPS receiver  308  to provide latitude, longitude, and altitude of payload  101 . GPS antenna  306  represents one or more antenna devices that are capable of receiving radio frequency (RF) signals transmitted from GPS satellites (not shown). GPS receiver  308  receives RF signals from GPS antenna  306 , tunes the desired frequency(s), and detects/demodulates the position information in the signal(s). Various embodiments of GPS receiver  308  can include components for handling analog and/or digital data, as required. Other suitable systems that provide position information for payload  101 , such as an inertial navigation system, a dead reckoning navigation system, differential GPS, distance measuring equipment, and/or a combination of position information systems can be utilized in addition to, or instead of, GPS antenna  306  and GPS receiver  308 . 
     Another sensor that is shown in the embodiment of DPMS  300  in FIG. 3 is heading indicator  310  that provides signals to control computer  302  that indicate the magnetic heading of payload  101 . Any suitable heading indicator, such as gyroscope-based systems, magnetic compasses, or other magnetic flux detecting/heading indicator devices can be utilized. Control computer  302  can include logic to compensate for magnetic lead and lag errors that are observed during turns with magnetic compasses. 
     One or more sensors for providing information regarding the height of payload  101  above ground level (AGL) to control computer  302  is also included in DPMS  300 , as represented by AGL sensor(s)  312  in FIG.  3 . In some embodiments, a radar altimeter provides very accurate height above ground information by transmitting radio frequency signals directly below payload  101  and receiving reflections of the signals as they return from the ground. The time measured between transmission and reception of the same signal is used to determine the distance from payload  101  to the ground. Other suitable types of sensors can be utilized to implement AGL sensor(s)  312 , in addition to, or instead of, a radar altimeter. 
     Control computer  302  includes logic to determine the ground speed of payload  101  based on the change in position of payload  101  over time. Control computer  302  also includes logic to estimate wind speed and wind direction based on the ground speed, the change in position, and the heading of payload  101  over time. Outer trailing edge portions  118  of canopy  102  can be adjusted to account for the effect of the wind on the descent profile of payload  101 , and to help insure that payload  101  lands at or near the desired recovery site. 
     DPMS  300  can also include telemetry/uplink communication equipment (not shown) that allows an operator at a remote location from payload  101  to enter/update information being used by control computer  302  regarding wind speed and direction at various altitudes, location of payload  101 , and the desired recovery location. DPMS  300  can also include equipment to receive transmissions from automated flight information services to update information such as position, and wind speed/direction in the vicinity. 
     Power supply  316  provides power at the required voltage(s) to components in DPMS  300 . A portable battery or set of batteries capable of supplying different voltages can be utilized to implement power supply  316 . Other suitable devices, such as solar energy cells, can also be utilized in addition to, or instead of, batteries. 
     In some embodiments, control computer  302  includes a data processor that includes electronic circuits capable of executing logic instruction, memory for electronically storing data and software, and interfaces that allow control computer  302  to communicate information with other components of DPMS  300 . Other embodiments of control computer  302  can include data recording facilities for post-landing analysis. Control computer  302  can be implemented using a suitable combination of hardware, firmware, and software components. 
     Referring to FIGS. 1,  2 B,  3 ,  4  and  5 , FIG. 4 shows an embodiment of a flow diagram of logic processes included in control computer  302  to execute a descent and landing sequence when canopy  102  is deployed. FIG. 5 shows a profile diagram of the descent and landing sequence outlined in the processes in FIG.  4 . 
     Payload  101  can be any type of item or system that flies or is drop-shipped from the air. In a system capable of flight, canopy  102  can be deployed by DPMS  300  automatically based on fulfilling one or more criteria, such as duration of flight, operator control from a remote location, arrival at a destination, or an aborted mission. For drop-shipped items, canopy  102  can be deployed using any suitable means, such as operator control from a remote location, a static line on the vehicle from which payload  101  is dropped, or automatically using a release device coupled to control computer  302  that is activated upon reaching a predetermined altitude above ground. 
     Control computer  302  monitors sensor information, such as the heading, groundspeed, and descent rate of payload  101  to determine when canopy  102  is fully deployed in process  402 . Brake lines  120  are then adjusted on canopy  102  to achieve a pre-specified glide slope, shown for example, in process  404  as descending at a rate of 70 feet per second with a glide angle of approximately 23 degrees relative to the surface of the ground. The glide slope and/or descent rate to be achieved during various stages of the descent profile can be adjusted by control computer  302  based on various factors, such as groundspeed, wind speed/direction, and altitude of payload  101  above ground. 
     Process  406  can be included to determine the position of payload  101  with respect to a desired recovery location. If payload  101  is not within a desired distance of the recovery location, brake lines  120  are adjusted to steer toward the recovery location. 
     Process  408  adjusts brake lines  120  to enter a downward spiral flight path over the desired recovery location. Typically, one brake line  120  is reeled in to turn canopy  102 , however, both brake lines  120  may be adjusted at times during the spiral portion of the descent to correct drift of payload  101  from the recovery location due to the wind. The drift can be corrected by comparing the actual location of payload  101  to the desired location, and adjusting brake lines  120  accordingly to increase or decrease the turn rate to reposition payload  101  with respect to the recovery location. 
     Process  410  determines the wind speed and direction based on a constant rate turn over a period of time and drift from the desired recovery location during the turn. In the presence of wind W, the spiral deviates from a circular trajectory over a point on the ground. In some embodiments, the wind speed and direction can be determined from the differential distance covered during the short upwind leg and the long downwind leg. The direction of the wind W is in the direction of the long downwind leg and the wind speed is the difference in distance covered divided by the time to complete a quarter turn. The wind speed and direction information can be used to continually adjust brake lines  120  during the spiral to avoid drift. 
     Once the wind speed and direction are determined, process  412  determines the altitude h 1  above ground level at which to end the spiral descent. It is desirable to turn out of the spiral with front edge  104  of canopy  102  aligned heading into the wind W. By heading into the wind, the groundspeed of payload  101  is reduced, thereby reducing the potential for damage to payload  101  during landing. The height h 1  for ending the spiral descent is based on the altitude lost during each 360 degree turn in the spiral, the difference between the altitude of payload  101  and a second height above ground level h 2 , at which the final descent and landing sequence is started, and the direction and magnitude of the wind W. 
     Process  414  steers canopy  102  into the wind W at a specified descent rate until payload  101  reaches second height above ground level h 2 , as monitored by processes  416  and  418 . Some embodiments of process  418  also adjust pitch control line  220  to achieve a nose-up attitude for payload  101 . At altitude h 2 , control computer  302  commands reel motors  208  to simultaneously deflect trailing edges  118  downward to start the landing flare in process  420 . During the flare sequence, canopy  102  decreases the vertical descent of payload  101  to be at or less than a specified rate, such as 5 feet per second. 
     Process  421  determines the groundspeed of payload  101  based on the wind W. Process  422  utilizes the groundspeed of payload  101  to determine the amount of braking required to stall canopy  102  when the height of payload  101  above ground level is less than a specified distance, such as 10 feet. During a stall, the angle of canopy  102  with respect to the relative wind W increases until the air separates over the top of canopy  102 , thereby losing the lifting capability of canopy  102 . When canopy  102  stalls, payload  101  descends at a steeper angle until the tail portion of payload  101  touches the ground. The drag from the tail of payload  101  rapidly slows forward movement as the nose of payload  101  continues to descend. 
     When the weight of payload  101  is removed from canopy  102 , quick release connectors  204 ,  206  release canopy  102  from payload  101  to prevent payload  101  from being dragged along the ground by the wind W until canopy  102  deflates. In some embodiments, pyrotechnic devices that are activated by DPMS  300  can be coupled between brake lines  120  and control lines  116 , and between main risers  110  and harnesses  112  instead of mechanical quick-release connectors, to jettison canopy  102  at touchdown, or at any other time whether canopy  102  is deployed or not. 
     Control computer  302  determines the amount of braking required to stall canopy  102  in process  422  based on the descent rate and the ground speed of payload  101 . The control logic adjusts brake lines  120  to minimize the vertical descent speed and the ground speed at impact. For example, full braking is typically required in no wind conditions, while little or no braking may be necessary when the magnitude of the wind W is equivalent to the horizontal glide speed of the system  100 . The weight of payload  101  and the lifting capacity of canopy  102  affect the horizontal glide speed and vertical descent rate of payload  101 . A proper combination of payload weight divided by canopy size (referred to as “parafoil loading”) is therefore selected to allow the descent of payload  101  to be controlled as desired. 
     As an example of the operation of one embodiment of payload recovery system  100 , when canopy  102  deploys at a parafoil loading of 2.14 pounds per square foot, an equilibrium glide is established at a horizontal glide speed of approximately 64 feet per second, a vertical descent speed of 26 feet per second, and a descent angle of 23 degrees with respect to the horizontal. DPMS  300  steers payload  101  to the recovery site, and enters a spiral descent The radial distance from payload  101  to the recovery site is monitored, and brake lines  120  are adjusted to maintain a spiral descent with the recovery site at the approximate center of the spiral. The wind direction and speed can be estimated based on logic in process  410  described hereinabove. DPMS  300  adjusts the tension on the brake lines  120  to retain the recovery site at the center of the spiral. 
     When the wind speed and direction are estimated, DPMS  300  determines the altitude h, at which payload recovery system  100  should turn out of the spiral to be heading into the wind for landing. The determination of altitude A, is based on the descent rate and time required for each complete turn in the spiral. Once payload  101  reaches altitude h 1 , DPMS  300  rolls out of the spiral and begins the final descent phase. DPMS  300  adjusts brake lines  120  to slow the descent rate of payload  101 . Attitude control line  220  can also be adjusted to help insure that payload touches ground at the desired orientation. The amount of braking required depends on the descent rate and wind speed. In one embodiment, DPMS  300  slows the descent rate to less than 5 feet per second when payload  101  is 10 feet above ground level. At that point, partial to full braking is applied to stall canopy  102  and slow the ground speed to less than 5 feet per second. Quick-release connectors  204 ,  206  disconnect canopy  102  from payload  101  once payload  101  is on the ground. 
     Recovery system  100  can thus deliver payload  101  at or near a specified recovery location with minimal ground impact damage. The attitude of payload  101  during touchdown can be controlled so that only a portion of payload  101  touches the ground first. The touchdown portion of payload  101  can be reinforced to resist any damage that may be inflicted upon impact with the ground. Further, the descent rate can be slowed to a minimum before touchdown to further prevent damage to payload  101 . Other descent and landing patterns can be programmed into DPMS  300 , either before takeoff or during flight. 
     While the invention has been described with reference to various embodiments, it will be understood that these embodiments are illustrative and that the scope of the invention is not limited to them. Many variations, modifications, additions and improvements of the embodiments described are possible. For example, those having ordinary skill in the art will readily implement the steps necessary to provide the structures and methods disclosed herein. Further, functions performed by various components can be implemented in hardware, software, firmware, or a combination of hardware, software, and firmware components. Variations and modifications of the embodiments disclosed herein may be made based on the description set forth herein, without departing from the scope of the invention as set forth in the following claims. 
     In the claims, unless otherwise indicated the article “a” is to refer to “one or more than one”.