The present invention relates to a process for producing trajectories for an airborne vehicle.
It applies in particular, although not exclusively, to civil or military aviation and to airborne vehicles flown or alternatively guided from the ground.
In general, correct execution of the mission of an airborne vehicle relies on the defining of a flight plan which is produced during mission preparation. This flight plan comprises, among other things, a nominal trajectory to be followed during the mission, defined in a five-dimensional space: latitude, longitude, altitude, flight time and fuel reserves. However, unforeseen events may occur during execution of the mission, making the nominal trajectory envisaged during mission preparation unsuitable, or even obsolete. These events may, for example, consist in a breakdown of a vital part of the airborne vehicle, new weather conditions, a change in objective, or the emergence of a danger area crossed during that part of the nominal trajectory that remains to be covered. It is therefore necessary, during flight, to alter that part of the intended nominal trajectory that remains to be covered, with a view to jeopardizing the mission objectives as little as possible.
The nominal trajectory chosen during mission preparation is defined by a series of compulsory waypoints to pass through according to altitudes, headings, schedules, with minimum fuel reserves and, possibly, by positions and extended areas of danger that are to be avoided.
A modification, during flight, of a part of the nominal trajectory assigned during mission preparation that has yet to be covered, in order to take account of an event which was not taken into consideration during mission preparation is a difficult task because it has to be finalized quickly even though there are a great many obvious options for reconfiguring the nominal trajectory, among which it is difficult to discern, quickly, the one which best satisfies the numerous constraints encountered, whether these be associated with the airborne vehicle flight conditions, its maneuverability, its fuel-dependent range or the objectives of the mission, this difficulty being all the greater as these constraints often translate into contradictory requirements such as safety, economy, effectiveness, for example.
Attempts have therefore been made at easing the task of an aircraft pilot when the need to modify the nominal trajectory arises during flight, by providing him with the assistance of an automatic device which proposes to him a reconfigured trajectory that can be used by an automatic pilot system and by a cartographic display, and which is optimized from the point of view of satisfying the instantaneous constraints imposed by the flight conditions of the airborne vehicle, its maneuverability, its fuel-dependent range, the objectives of the mission and the relative importance attributed to these at that particular time.
The various processes for recalculating trajectories can be executed by an on-board computer which may or may not be assisted by an operator, allowing the pilot of an airborne vehicle in the course of performing a mission to be proposed a reconfiguration of his nominal trajectory by an automatic pilot system and by a cartographic display and minimizing the impact that an unforeseen event has on the safety and effectiveness of his mission.
Some of these processes call on cost optimization methods. These determine, as a function of the spatio-temporal position and of the maneuverability of the airborne vehicle, all of the detour paths that satisfy the new constraints imposed by the unforeseen event and which allow the nominal trajectory to be regained as quickly as possible keeping to the schedule and fuel-dependent range envisaged at the time of mission preparation and then proceed to select, of all the possible detour paths, the one which presents the minimum cost, that is to say the one which is optimum in terms of mission safety, economy and effectiveness. The cost of a trajectory is evaluated on the basis of its routing over a cost area superposed on the region overflown during the mission. The cost area is defined using a grid of points with a uniform mesh size, the actual size of which depends on the desired accuracy, each point in the grid being allocated a preference score devised according to the mission constraints in terms of effectiveness and safety. The cost of a trajectory corresponds to the inverse of the sum of the preference scores allocated to each point encountered on the cost area. These processes require an on-board computer with high processing power and a great deal of memory to implement them because they involve updating the cost area in real time to take account of the advent of an unforeseen event, followed by the detailed calculation, still in real time, of a number of possible detour paths and a calculation of their respective costs.
Other processes, calling upon levels of representation of a mission in greater or lesser detail, attempt to study a great many alternative solutions with a view to assigning them an effectiveness or risk criterion. However, in order to be able to provide an answer in real time, these processes require a great deal of processing power which is incompatible with the power of the computers which currently are fitted on board airborne vehicles. Furthermore, they require the intervention of the pilot, who has to divert his attention from the current mission to examine all the proposed solutions, of which there may be a great many, in order to select one of them. In this context, the pilot does not have control over the time when he has to make his choice, because the solutions put forward very soon become obsolete because of the speed with which the airborne vehicle is moving. What this means is that these processes are ineffective when the pilot needs to give his full attention to flying or the use of other systems (for example weapons or communications systems).
The use of artificial intelligence techniques and more specifically of a system employing a knowledge base and rules, and known by the name of expert system, has also been proposed for determining the reconfigured trajectory to be proposed to the pilot as being the one that is the result of the best compromise between the various requirements of the moment. However, an expert system requires the compiling of a knowledge base and of rules which is difficult to develop for determining a three-dimensional trajectory which also involves time, speed and other parameters, and evaluating its effectiveness at meeting the objectives of the mission as a function of a great many other criteria.
In order to solve this problem, European Patent Application EP 0 617 349 has proposed the use of multiexpert techniques which allow a number of expert systems with knowledge bases and rules each specialized in a given area to collaborate with each other. The process for determining the new trajectory comprises:
analyzing the context and interpreting the event that justifies the reconfiguring of the trajectory in order to determine the actions to be carried out,
breaking said actions down into alternatives each consisting of a sequence of elemental actions that can be performed by at least one of the specialist modules,
selecting each alternative in turn, using a certain strategy,
processing the alternatives selected which, for each alternative, consists in using the specialist expert modules to produce a trajectory using the elemental actions that make up the selected alternative, and evaluating the benefit of the trajectory obtained against at least one criterion, and
selecting at least one trajectory which has the best evaluation and presenting it as a solution associated with its evaluation.
This process is still fairly unwieldy to employ because it involves determining a collection of trajectory reconfiguring solutions and choosing the best one from among these.
The present invention proposes a process for reconfiguring a trajectory in real time which, at each moment, results in the detailed determination, usable by an automatic pilot system or a cartographic display, of just one reconfigured trajectory, the choice between the various possible detours for taking account of the advent of an event not taken into consideration during mission preparation being condensed, following an analysis of the real-time airborne vehicle-mission context and the detection of an event that justifies reconfiguring the trajectory, to likening this realtime context to a predefined context category chosen from several stored in memory taking account of different context eventualities and each corresponding to a specific reconfiguration method that results in the detailed determination of just one reconfigured trajectory. The calculation load is lower than in the aforementioned known processes because the reconfigured trajectory is chosen very early on in its precise definition in a form that can be used by an automatic pilot system or by a cartographic display.
More specifically, this process is performed by a computer which, in real time, receives information supplied by equipments on board the airborne vehicle regarding the situation of the airborne vehicle with respect to its spatial and temporal environment, its range and its maneuverability, and stores data regarding the mission of the airborne vehicle which may be updated in the course of the mission, including a nominal trajectory in five dimensions: three spatial dimensions, a time dimension and a dimension which represents the fuel-dependent range, this information constituting a real-time airborne vehicle-mission context, this computer being connected to an automatic pilot device and to a display which gives, on a cartographic background, a depiction of the current trajectory and indicates the current position of the airborne vehicle with respect to this trajectory.
It comprises with a view to adapting the mission to suit a new situation which has arisen as the result of one or more disrupting events:
updating the data relating to the real-time airborne vehicle-mission context that has been altered by the occurrence of the disrupting event, and
detecting, within the updated real-time airborne vehicle-mission context, the occurrence of one or more events that justify reconfiguring the nominal trajectory.
It is characterized in that it involves, after the above stages:
selecting, according to the updated real-time airborne vehicle-mission context, a trajectory-reconfiguring method from a collection of predefined trajectory-reconfiguring methods available in memory, each one, when implemented, allowing a single reconfigured trajectory to be obtained, each of these reconfiguration methods being tailored to a specific and predefined category of airborne vehicle-mission context, said selection of a predefined trajectory-reconfiguring method being made by likening the real-time airborne vehicle-mission context to the closest predefined category of airborne vehicle-mission context on the basis of selection criteria relating, in particular, to the values of the spatial, temporal and fuel-dependent range differences observed with respect to the nominal trajectory, the selected predefined trajectory-reconfiguring method directly translating the operational strategy customarily employed by aircrew placed in the chosen predefined category of airborne vehicle-mission context,
executing the selected predefined reconfiguration method which, according to the mission data and the real-time context, determines a new trajectory that the automatic pilot system can execute,
displaying the new trajectory on the display as an overlay on the current trajectory, and
if the pilot validates this new trajectory, transmitting information characterizing this new trajectory to the automatic pilot device.
By virtue of these arrangements, all the operations in selecting a solution for reconfiguring the mission are performed before a trajectory that can be executed directly by an automatic pilot device is actually determined, this determination being expensive in terms of time and processing power. The process according to the invention thus makes it possible, in real time, to propose a trajectory capable of satisfying each new situation at the time it occurs. This speed of response can be obtained using the computers currently fitted on board airborne vehicles, without affecting the other functions performed by these computers and does not require new equipment.
Furthermore, the reconfiguration method selected more or less corresponds to the thought process that a pilot goes through in a similar situation. What this means is that if the pilot does not agree with the new trajectory proposed, he may, by direct action on the airborne vehicle flight controls (speed, heading or altitude), alter the real-time context of the airborne vehicle so as to force the process to calculate a new trajectory which corresponds to the pilot""s wishes. He may also force passage through a particular goal or alter one or more mission constraints.
Of course, when the event detected is that the airborne vehicle is ahead of or behind schedule, this new trajectory may correspond to the trajectory previously being followed, with simply a change in the speed at which this trajectory is covered.
The events may originate directly from the various parts connected to the computer. They may also be generated by a task of monitoring the surroundings of the airborne vehicle, which task evaluates parameters on the basis of real-time context data and compares them with thresholds or expected values, the crossing of a threshold or the detection of an unexpected value giving rise to the generating of an event.
Advantageously, the mission data involves three types of constraint, namely spatial constraints (initial trajectory, compulsory waypoints), temporal constraints (rendezvous times), and fuel-dependent constraints, the process according to the invention involving associating each of these types of constraint with a set of respective priority values which give the relative priority with which the constraints of this type are taken into consideration at each stage of the mission, the process according to the invention involving taking all of these sets of priority values into consideration when analyzing the real-time context and executing a reconfiguration method.
The fuel-dependent constraint corresponds to the ability of the airborne vehicle to carry out the mission and land with a sufficient reserve of fuel, given its range which may incorporate in-flight refuelling in the case of military missions.
Thus, if, for example, the spatial constraint takes priority and the airborne vehicle departs from the current trajectory, the process according to the invention will produce a trajectory for regaining that trajectory as a function of the current position of the airborne vehicle and of the presence of a compulsory waypoint near the airborne vehicle.
Advantageously, updating the real-time airborne vehicle-mission context involves analyzing the real-time situation otherwise known as monitoring the environment, to take account of:
the mission, defined by information recorded prior to flight or received during flight, including the five-dimensional nominal trajectory, notes on danger areas, compulsory waypoints, etc.,
data specific to the airborne vehicle, such as its spatio-temporal position, the amount of fuel actually available, its phase of flight, newly appeared obstacle zones, predicted changes in flight phase, any faults which may have occurred, changes in weather conditions, etc.
Advantageously, the predefined trajectory-reconfiguring methods each call on a specialist module chosen from a set of specialist modules common to them and each capable of solving a specific problem in the reconfiguring of an itinerary.
Advantageously, said specialist modules each solve a specific problem in the reconfiguring of an itinerary in the five dimensions in space, time and fuel-dependent range, such as:
cutting short the 5D trajectory,
extending the 5D trajectory,
5D trajectory for avoiding a new or otherwise threat,
5D trajectory for regaining a 5D itinerary with threat avoidance,
5D trajectory for regaining a 5D itinerary with threat avoidance and with a compulsory destination,
5D direct return/emergency return trajectory over terrain that is accessible in terms of weather/fuel,
modification of speed when behind schedule on SD trajectory,
modification of speed when ahead of schedule on SD trajectory,
5D trajectory for managing in-flight refuelling,
5D trajectory to take account of a change in constraint,
5D trajectory for constructing a modified flight plan.
Advantageously, the predefined configuration methods are of finite depth, that is to say that the specialist modules on which they depend resort to only a limited number of solution steps, each solution step consisting in solving a partial reconfiguration problem. That makes it possible to guarantee that a proposed reconfigured 5D trajectory best suited to the changing context of a mission will be produced and displayed in a limited amount of time. As the time taken to formulate a proposed reconfigured trajectory is controlled, this proposal can be updated periodically at a sufficiently high frequency, for example of the order of 1 hertz, to give the pilot of the airborne vehicle a constant picture of the available possibilities for reconfiguring his trajectory.