Abstract:
To avoid an uncontrolled flight of a remotely controlled unmanned air vehicle (UAV), upon loss of radio contact between a control station ( 6 ) and the UAV ( 1 ), the UAV ( 1 ) flies on a preprogrammed safety route ( 3 ), as required the UAV is guided to a flight path ( 2 ) that is remote-controlled from the control station ( 6 ), and, in the event of an interruption of the radio contact, the UAV will fly on a substitute route calculated with on-board equipment, without active intervention from the remote control station.

Description:
FIELD OF THE INVENTION 
     The invention relates to a remote control method for operating an unmanned air vehicle (also called an unmanned airborne vehicle and an unmanned aerial vehicle), and to an unmanned air vehicle for performing the remote control method. 
     BACKGROUND INFORMATION 
     Unmanned air vehicle (UAV) missions are essentially based on pre-programmed flight paths. The planning of the flight paths requires precise knowledge of the terrain to be flown over and the expected threat of anti-aircraft defense. Very precise knowledge of the target area is particularly necessary in order to carry out target combat. This often occurs with additional support of final approach sensors that operate by comparing or matching images. These sensors thus require exact images of the targets and, under certain circumstances, images from various perspectives may be required. With preprogrammed flights it is impossible to react to unforeseen events. 
     The execution of such difficult tasks can be significantly improved if the UAV is remote-control guided via a radio wave transmission link, whereby the “pilot” operates the UAV from a remotely-situated control station. The control station can be located either on the ground or in flight in a manned aircraft. The remote control is carried out with the aid of a television or video image. The image is recorded by a camera in the unmanned UAV and transmitted to the control station where it is presented in a suitable manner (see, e.g., Predator; UAV Annual Report FY 1997, Nov. 6, 1997, page 5). 
     The above conventional method has the disadvantage that it depends on the reliability of the radio wave link. Loss of radio contact would, as is known, bring the UAV into an uncontrolled flight phase, which eventually results in the UAV crashing. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to avoid the occurrence of an uncontrolled flight of a remotely controlled UAV in the case of loss of radio contact. 
     The above objects have been achieved according to the invention in a method of remotely controlling an unmanned air vehicle (UAV) from a remote control station by radio transmitting control signals from the control station to the UAV and radio transmitting images from the UAV to the control station. According to the method, the UAV initially flies on a pre-programmed safety route, and then, as required, the UAV is guided by remote control to a flight path by correspondingly radio transmitting appropriate control signals from the control station to the UAV. In the event of an interruption of the radio contact between the control station and the UAV, then the UAV will fly on a substitute route calculated on-board the UAV using on-board equipment of the UAV, without active remote control intervention from the control station. 
     The invention is based on a method of continuing the flight of the UAV in the case of loss of radio contact by means of a substitute flight program calculated on-board. In this way, the threatened loss of the UAV can be avoided in an advantageous manner: and the mission can possibly be successfully concluded despite the radio interference. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention may be clearly understood, it will now be described in connection with an example embodiment thereof with reference to the accompanying drawing, of which the single Figure is a schematic plan view representing a portion of a flight path of a UAV. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An example embodiment of the invention will now be explained in greater detail, based on the drawing. The Figure shows partial views of a scenario of a UAV mission, with the representation of a remotely controlled flight path  2 , a pre-programmed safety route  3 , and shadow zones  4  and  5  (i.e. areas in which control signals that are radio-transmitted from a control station  6  will be interrupted) resulting from the example terrain formations such as mountains or hills  7 , and the position of the control station  6  in the illustrated terrain. 
     A progression of the method according to the invention is marked with the characteristic points A to H along the remotely-controlled flight path  2 . The method steps allocated to the individual points are given below: 
     A beginning of the remotely-controlled flight path  2  through intervention-in the safety route  3 ; 
     B remotely-controlled flight along flight path  2 , monitored by continuous extrapolation of the instantaneous flight path; 
     C entry of the UAV  1  into a shadow zone  4 , thus causing the impending beginning of uncontrolled flight, followed by recognition and analysis of the interruption of the remote control; 
     D continuation of the flight of the UAV along a substitute flight path in accordance with the substitute flight program, generated-on-board the UAV  1 ; 
     E transition back to the remote control of the UAV  1  upon leaving the shadow zone  4 ; 
     F termination of the remote control of the UAV  1  upon entering another shadow zone  5 ; 
     G guidance of the UAV  1  back to the-safety route  3  in accordance with the substitute flight program generated on-board the UAV  1 ; 
     H continuation of the flight along the safety route  3 . 
     By way of example, the UAV  1  initially automatically follows a preprogrammed flight course on a safety route  3 . The “pilot” in the control station  6  intervenes as necessary in this preprogrammed course. As a result, the UAV deviates from the predetermined course and continues its flight along a remotely-controlled flight path  2  according to transmitted control signals or commands from the control station  6 . In this phase, the flight is dependent on the critical reliability of the radio contact. Should the radio contact between the control station  6  and the UAV  1  fail because of shadowing or interference, then the invention provides that the flight, which is threatening to become uncontrolled, is continued with a substitute flight program that is generated on-board, after the interruption has been recognized and its type discerned. The substitute flight program guides the UAV through the danger zone (i.e. the zone of shadowing or interference) until it enters an area in which there is once again radio contact and it is again possible to guide the air vehicle with remote control. 
     If such an area of re-established radio contact cannot be reached, then an automatic return flight to a predetermined landing strip shall be carried out, after a corresponding flight program has been recalculated on-board. 
     In a further mode of the method, it is provided that the UAV returns to the preplanned course and approaches an alternatively planned target, there executes the maneuvers desired by the pilot by remote intervention in the program control, and subsequently returns to the landing strip following the preplanned course. 
     The above described method and operation of the UAV require certain equipment and/or functional processes that are described below. 
     The UAV  1  is equipped with a per se conventional programmable flight guidance system that allows the UAV to autonomously approach in flight one or more target areas and to return to a predetermined landing strip. According to the invention the automatic flight guidance system is provided with an interface for intervention by the radio remote control. When the guidance commands arrive, this interface in effect makes the program control inoperative and the remote control operative. As a result, the UAV executes the movements commanded by the control station  6 . 
     The automatic flight guidance system has a per se conventional terrain databank, with the help of which the UAV orients itself during automatic flight over the terrain. During remote-controlled flight, an accompanying route planner uses the data in this databank to monitor continuously or in intervals the guidance commands of the control station  6  with respect to maintaining minimum altitudes and minimum distances from obstacles in order to avoid collisions. The route planner does this by extrapolating the instantaneous flight path, based on the guidance commands, and comparing it with the data in the terrain databank. 
     Recognized dangerous situations are reported immediately to the control station and displayed there, or an anticollision program is calculated on-board and suitable correction maneuvers are automatically executed. 
     In the case of loss of radio contact, a recognition is provided that differentiates between “loss through shadowing” and “loss through interference”. The recognition sensor is the radio receiver itself, which differentiates between “no input signal” and “existing input signal, but unreadable modulation”, which are respectively allocated to shadowing and to interference. 
     If radio contact is lost because of shadowing of the control station, the altitude-dependent shadow zones are calculated by means of on-board equipment, based on the accompanying terrain profile and the coordinate values x/y/z of the control station  6 . Using the data calculated on the shadow zone, an optimal flight path in the terrain for flying through the shadow zone is subsequently calculated and supplemented with the calculation of a transition point (e.g. point E) to return to the remote control at the planned point of exit from the shadow zone (e.g. shadow zone  4 ). 
     In the case of loss of the radio contact due to receiver “interference”, the interference source is located in the terrain (coordinate values x/y) using on-board equipment. The z-coordinate value is determined from the known terrain profile. The altitude-dependent interference zone in the terrain is calculated from the location data. In the case of a known interference zone, an optimal flight path for flying through the interference zone, supplemented by the transition point to return to the remote control at the end of the interference zone, is calculated. 
     If a transition point to return to the remote control is not found, or if it is no longer of interest to continue the remotely-controlled flight, a route will be calculated with on-board equipment to return the UAV  1  to the safety route  3  and continue the mission to the next planned target area. If no further target area is planned, then the mission is terminated and a route is planned to the preplanned return flight course. Alternatively, a route can be planned to a new return flight course if this is more advantageous than the originally planned course. 
     Substitute route planning can also be executed during an interference-free remote control phase as a preventive measure, either continuously or in intervals, in order to have a calculated substitute flight program already available when a dangerous situation occurs.