Abstract:
An air vehicle comprises a satellite receiver having messaging capability. The receiver is configured to process a command and control (C 2 ) message when alternative communications are required. The air vehicle further comprises avionics for taking a course of action according to instructions in a C 2  message received by the satellite receiver.

Description:
BACKGROUND 
       [0001]    In the past, unmanned air vehicles (UAVs) mainly supported military and security operations. Now, however, these remotely operated vehicles have additional uses, such as border patrol, disaster relief, traffic reporting, aerial photography, and environmental surveys. 
         [0002]    With these additional uses, the UAVs share the National Airspace System (NAS) with commercial aircraft and other manned vehicles. UAV flight operations may be granted by the Federal Aviation Administration (FAA). 
         [0003]    When manned aircraft are flying in the National Airspace System, they are required to retain the ability communicate with the FAA at all times. If a manned aircraft loses two-way radio communications, its transponder broadcasts squawk code 7600, which notifies air traffic control (ATC) that communications has been lost, and its pilot follows FAA regulations to safely land the aircraft (see, e.g., 14 CFR 91.185). 
         [0004]    UAVs do not have these same capabilities as manned vehicles. If the communications system of a UAV fails, the UAV will be unreachable and, consequently, might enter restricted airspace. 
         [0005]    The FAA is concerned about the consequences of UAVs that lose radio communications. The ability to re-establish communications with UAVs is needed. 
       SUMMARY 
       [0006]    According to an aspect herein, an air vehicle comprises a satellite receiver having messaging capability. The receiver is configured to process a command and control (C 2 ) message when alternative communications are required. The air vehicle further comprises avionics for taking a course of action according to instructions in a C 2  message received by the satellite receiver. 
         [0007]    According to another aspect herein, an unmanned air vehicle (UAV) comprises a transponder for transmitting a discrete transponder code indicating that alternative communications are required; a GPS receiver having text messaging capability for receiving satellite status information and also for receiving command and control messages; and UAV Command and Control for instructing the UAV to take a course of action according to a command and control message received by the GPS receiver. 
         [0008]    According to another aspect herein, an alternative communications method is used for an air vehicle equipped with a GPS receiver having capability to decode messages. The method comprises receiving a request for alternative communications for the air vehicle, formulating a command and control message that instructs the vehicle to take a course of action, and transmitting the message to the GPS receiver via a GPS satellite. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an illustration of an air vehicle. 
           [0010]      FIG. 2  is an illustration of an unmanned air vehicle in an airspace. 
           [0011]      FIG. 3  is an illustration of an alternative communications method performed by an Airspace Control Administrator and a satellite operator. 
           [0012]      FIG. 4  is an illustration of an alternative communications method performed by an air vehicle. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Reference is made to  FIG. 1 , which illustrates an air vehicle  110 . The air vehicle  110  includes an avionics system  120  that performs various functions and includes, but is not limited to, navigation controls  130 , flight controls  140 , radio communication controls  150 , a transponder  160 , and a satellite receiver  170  having messaging capability. The functions performed by these components may be implemented in standalone hardware, or several of these functions may be integrated into hardware systems. As a first example, the satellite receiver  170 , navigation controls  130  and flight controls  140  may be integrated into a single navigation and flight controls system. As a second example, the radio communication controls  150  and transponder  160  may be integrated into a communications system. 
         [0014]    The air vehicle  110  may or may not include a propulsion system. The air vehicle  110  may be a manned vehicle (e.g., a commercial aircraft, a commuter aircraft, or General Aviation aircraft) or an unmanned air vehicle (e.g., an aircraft, or balloon). If the air vehicle  110  is unmanned, the navigation controls  130  and flight controls  140  may be part of an automated navigation and flight controls system. 
         [0015]    Additional reference is made to  FIG. 2 , which shows an unmanned air vehicle (UAV)  110  flying in an airspace. The UAV  110  is controlled remotely by a ground or airborne UAV operator  200 . The UAV flight controls  140  respond to flight commands from the UAV operator  200 , and a payload  180  may send data back to the UAV operator  200 . 
         [0016]    The flight of the UAV  110  is monitored by an Airspace Control Administrator (ACA). In the United States, for example, the ACA may be a governmental agency such as the FAA, or it may be a non-governmental agency. The UAV radio communication controls  150  maintain two-way radio communications with the ACA  220 . The ACA  220  also monitors other air vehicles  210  sharing the airspace. 
         [0017]    The UAV satellite receiver  170  communicates with one or more satellites  230 . For instance, a Global Positioning System (GPS) receiver  170  receives signals from several GPS satellites  230  to determine the precise position of the UAV  110  in airspace. The GPS receiver  170  also has messaging capability. A text code field allows the GPS receiver  170  to receive and display satellite status information. This is the conventional use of the messaging capability. 
         [0018]    The messaging capability of the GPS receiver  170  has another use: the text code field is used to re-establish communications with the ACA  220  in the event alternative communications is required. Alternative communications might be required in the event of two-way radio communications failure between the UAV  110  and the ACA  220  or between the UAV operator  200  and the UAV  110 . Such failure might result, for instance, from a primary communications system failure, line-of-sight restrictions, or jamming of a primary communications link. 
         [0019]    There are various ways in which the ACA  220  may determine that alternative communications are required. As a first example, the UAV transponder  160  transmits a discrete code (e.g., 7200) signaling that two-way communications has been lost. As a second example, the ACA  220  suddenly loses communications with the UAV  110 . As a third example, the UAV operator  200  informs the ACA  220  FAA (e.g., via the link  215 ) that UAV communications are unavailable. 
         [0020]    Additional reference is made to  FIG. 3 . When the ACA  220  determines that alternative communications are required for the UAV  110  (block  310 ), it attempts to re-establish communications with the UAV  110  by having a command and control (C 2 ) message sent to the GPS receiver  170 , where the C 2  message instructs the UAV  110  to take a course of action (blocks  320 - 350 ). As a first example, the C 2  message specifies a longitude and latitude, and instructs the UAV  110  to fly to that specific location (for instance, where it lands or runs out of fuel). As a second example, the C 2  message instructs the UAV  110  to return to its starting location. As a third example, the C 2  message instructs the UAV to leave restricted airspace. As a forth example, the C 2  message instructs the UAV  110  to self destruct. 
         [0021]    The ACA  220  may have the C 2  message sent as follows. At block  320 , the ACA  220  sends a request to the satellite operator  240  (e.g., via link  225 ). The request will specify the course of action for the UAV  110 . 
         [0022]    At block  330 , the satellite operator  240  formulates a C 2  message. The C 2  message might include an identification field and an instructions field. The satellite operator  240  might formulate the C 2  message by filling these fields with a code identifying the message as a C 2  message and another code corresponding to a specific course of action. 
         [0023]    At block  340 , the satellite operator  240  transmits the C 2  message to one or more satellites  230 . At block  350 , the satellite  230 , in turn, sends the C 2  message to the GPS receiver  170  of the UAV  110 . The satellite  230  may send the C 2  message directly to the UAV  110 . In the alternative, the satellite  230  may broadcast the C 2  message to all air vehicles  110  and  210  in the airspace. However, the C 2  message may be read only by the UAV  110 . For instance, the message may be encrypted and may only be decrypted by the air vehicle having a corresponding decryption key and the correct ID. 
         [0024]    It may take as little as 0.5 seconds to transmit the C 2  message to the GPS satellite  230 , receive the C 2  message at the GPS receiver  170  onboard the UAV  110 , and decode the C 2  message. More time may be taken if the C 2  message is sent synchronously (e.g., every X seconds) instead of asynchronously (e.g., upon receipt of a request). 
         [0025]    Additional reference is made to  FIG. 4 , which illustrates the response by the UAV  110 . At block  410 , the satellite receiver  170  distinguishes the C 2  message from satellite status information by the type and format of the message that is sent. At block  420 , the satellite receiver  170  decodes the C 2  message to determine the commanded course of action. For example, the satellite receiver  170  uses a lookup table to look up a code in the appropriate field of the C 2  message. 
         [0026]    At block  430 , the commanded course of action is forwarded to UAV Command and Control, which is the flight control system that performs navigation and control. The UAV Command and Control commands the UAV  110  to take the commanded course of action. 
         [0027]    At block  440 , the transponder  160  may transmit discrete codes that acknowledge receipt and decoding of the C 2  message. For example, code 5601 may be used for such an acknowledgement. The transponder code may be received by the ACA  220 . 
         [0028]    At block  450 , the transponder  160  may also transmit discrete transponder codes indicating vehicle intentions or status. The codes indicating status and intention may be updated periodically. The ACA  220  may override the vehicle intention by having another message sent to the satellite receiver  170 . 
         [0029]    If the UAV  110  is not broadcasting transponder codes, it may be necessary to determine the location of the UAV  110 . Under these circumstances, the UAV  110  may be found via search. One method is to search “skin paint” with ACA active radars. 
         [0030]    The avionics  120  of the UAV  110  may be microprocessor-based. Microprocessor-based avionics allow the flight controls  140 , transponder  160 , and satellite receiver  170  to be implemented via programming. Flight controls, transponders and GPS receivers in general are typically found in all air vehicles. Thus, the alternative communications herein may be implemented without adding extra hardware, thereby saving weight and cost. 
         [0031]    Alternative communications herein are not limited to the embodiments above. A satellite receiver  170  other than a GPS receiver may be used to receive messages. As a first example, the satellite receiver  170  may be a Wide Area Augmentation System (WAAS)-capable GPS receiver. WAAS augments GPS by providing greater accuracy and integrity. A WASS receiver uses WAAS customizable data messages. Customizable messages are more flexible than GPS field codes because they enable more distinct commands to be sent (e.g., waypoints, landing sites, and velocity). 
         [0032]    The satellite receiver  170  is not limited to positioning systems. The satellite receiver may communicate with a commercial satellite such as XM radio or Sirius radio. Messages may be sent through a service provider for each of these alternative satellite systems. 
         [0033]    Alternative communications for manned and unmanned vehicles may be performed in the same basic way. A manned vehicle experiencing a communications failure may receive information from the ACA via its satellite receiver. For instance, the ACA may send a C 2  message specifying waypoint information for a new flight path. The satellite receiver decodes the C 2  message, and the avionics takes a course of action that includes displaying that information on a cockpit display so the pilot can fly the flight path ordered by the ACA.