Abstract:
Providing separation management of vehicles is disclosed. In an embodiment, a separation management system includes a data input module for receiving and filtering aircraft information and airspace information related to a control aircraft and a relevant aircraft, the aircraft information enabling the calculation of a trajectory window for each aircraft. A conflict monitoring module may be included in the system for monitoring the trajectory window for each aircraft with respect to time and probabilistic location, the conflict monitoring module determining when a trajectory overlap occurs resulting from the intersection of the trajectory window for the control aircraft and the relevant aircraft. In addition, the system may include a separation routing module for rerouting the control aircraft when a trajectory overlap for the control aircraft is detected by the conflict monitoring module.

Description:
TECHNICAL FIELD 
       [0001]    The disclosure relates to systems and methods for vehicle separation management and routing and, more particularly, to systems and methods for time-based automated airspace separation management and air vehicle routing in an information-centric net-enabled environment. 
       BACKGROUND 
       [0002]    Controlling assets or vehicles operating in a defined space is a task that has both civilian and military applications. In a common situation, air traffic control may involve moving commercial airplanes through airspace. Civilian air traffic control and military aircraft (asset or vehicle) tasking include the coordinated movement of multiple aircraft (assets or vehicles) through a crowded space filled with terrain, weather, and other obstructions. Aircraft may include both manned and unmanned aerial vehicles (UAV). 
         [0003]    In practice, traditional methods of airspace separation management are usually geared to operating in a voice-based procedural control airspace environment, typically including geographical boundaries to separate potentially conflicting aircraft from one another. These methods may generally rely on rigid procedures and traffic patterns to maintain safety under the large latencies and uncertainties that necessarily exist in a voice based system. 
         [0004]    The current methods generally include highly structured airspace routing plans that are created after intensive planning. The large number of aircraft managed in the airspace makes the structured plans complex. Therefore, the structured plans may not easily handle large scale on-line disruptions. In extreme situations, an entire portion of airspace may be cleared during an airspace disruption as a precautionary measure, which in some cases unnecessarily disrupts aircraft routed along otherwise predictable flight paths. 
         [0005]    Other airspace management methods include reactive collision avoidance and may be used in conjunction with the structured plans. For example, potential or impending conflicts may be handled by short term collision avoidance measures using a human controller or automated collision avoidance system (ACAS) methods. However, short term collision avoidance may not be effective within an airspace shared by UAVs or when structured plans experience large scale disruptions. 
         [0006]    Generally speaking, traditional airspace management methods may benefit from improved flexibility and by taking a reactive approach to collision avoidance resulting in a reduced density of aircraft in the airspace. As implemented, the traditional approach may become overburdened with increased density when the preplanned routes become disrupted. Accordingly, there is need for improved techniques that create flexibility and more effective use of airspace when routing aircraft. 
       SUMMARY 
       [0007]    Embodiments of methods and systems for providing separation management of vehicles are disclosed. Embodiments may advantageously increase an aircraft density of airspace while creating more flexibility for establishing routes through airspace while avoiding conflicts and disruptions 
         [0008]    In an embodiment, a method for maintaining a safe separation distance between vehicles includes receiving time-referenced position and state data for vehicles including a control vehicle and a relevant vehicle, the vehicles having initial locations within a time-space zone of interest. Maneuver characteristics for the vehicles may be determined within the time-space zone of interest. A probabilistic position zone for each vehicle may be calculated within the time-space zone of interest for a plurality of time intervals, the probabilistic position zone based on a received time-referenced position, speed and direction data, the vehicle maneuver characteristics, and attitude data. The control vehicle may be rerouted when the distance between the probabilistic position zone of the control vehicle is less that a specified distance from the probabilistic position zone of the relevant vehicle. A reference point may be selected for the control vehicle when the control vehicle is rerouted. A plurality homotopically distinct paths may be calculated between the time-referenced position of the control vehicle and the reference point based on the maneuvering characteristics of the control vehicle and the probable probabilistic position zone of interest for the vehicles. 
         [0009]    In another embodiment, a separation management system includes a data input module for receiving and filtering aircraft information and airspace information related to a control aircraft and a relevant aircraft, the aircraft information enabling the calculation of a trajectory window for each aircraft. A conflict monitoring module may be included in the system for monitoring the trajectory window for each aircraft with respect to time and probabilistic location, the conflict monitoring module determining when a trajectory overlap occurs resulting from the intersection of the trajectory window for the control aircraft and the relevant aircraft. In addition, the system may include a separation routing module for rerouting the control aircraft when a trajectory overlap for the control aircraft is detected by the conflict monitoring module. 
         [0010]    In yet another embodiment, a method includes generating a virtual predictive radar (VPR) screen including a plurality of trajectory paths for a control vehicle, the plurality of trajectory paths originating at an initial point and ending at a destination point, the VPR including time rings predicting the location of the control vehicle in 3-D space on the VPR. A plurality of constraints on the VPR may be created for the control vehicle based on the maneuverability characteristics and velocity of the control vehicle. At least one relevant vehicle may be located proximate one of the time rings of the VPR, the relevant vehicle creating a conflict along at least one of the plurality of trajectory paths. A homotopy route may be generated along a subset of the plurality of trajectory paths to enable the control aircraft to maintain a safe separation between the control vehicle and the relevant vehicle when the control vehicle traverses from the initial point to the destination point. 
         [0011]    The features, functions, and advantages can be achieved independently in various embodiments of the present invention or may be combined in yet other embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Structures and techniques in accordance with various exemplary embodiments of the present invention are described in detail below with reference to the following drawings. As used herein, the term “exemplary” identifies an example and not necessarily an ideal. 
           [0013]      FIG. 1  is a schematic view of an illustrative environment including aircraft in communication with at least one of other aircraft or ground based systems, the aircraft configured with a separation manager in accordance with an embodiment of the present invention; 
           [0014]      FIG. 2  is an illustrative chart depicting a relationship between time and airspace complexity used to determine a safe separation region of phase space, which may be increased by implementation of an automated separation manager in accordance with an embodiment of the present invention; 
           [0015]      FIG. 3  is a schematic view showing illustrative safe separation windows for aircraft with varying degrees of uncertainty in accordance with another embodiment of the present invention; 
           [0016]      FIG. 4  is a flow diagram of an illustrative configuration of a separation manager in accordance with an embodiment of the present invention; 
           [0017]      FIG. 5  is a schematic of an illustrative virtual predictive radar that depicts aircraft trajectory with respect to time as implemented by a separation manager in accordance with yet another embodiment of the present invention; 
           [0018]      FIG. 6  is a flow diagram of the illustrative virtual predictive radar in accordance with another embodiment of the present invention; and 
           [0019]      FIG. 7  is a flow diagram including of additional illustrative details of the flow diagram in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Overview 
         [0021]    Methods and systems for providing a separation manager are described herein. Many specific details of certain embodiments of the present invention are set forth in the following description and in  FIGS. 1 through 7  to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present disclosure teaches various additional embodiments, or that one or more embodiments of the present invention may be practiced without several of the details described in the following description. 
         [0022]    Current airspace management methods are not able to adequately take advantage of current data communications and networking capabilities. Increased situation awareness, situation analysis, speed of action, and flexibility that can be gained through networking and computational capability is not realized by current methods. Therefore, network centric and information centric systems, methods, processes, and techniques are described herein to provide improved airspace separation. 
         [0023]    Generally speaking, the disclosure describes various embodiments of a separation manager configured in an information centric environment including network-enabled data transmission capabilities. Embodiments of the present invention may be implemented in one or more physical environment, including a maritime, space, or ground environment. For example, the automated separation manager may be used with one or more aircraft in an airspace, maritime vessels in a maritime environment, ground vehicles on in a ground environment, and/or space platforms in space. Although embodiments may be implemented in various environments, the separation manager will be described in an airspace environment including various aircraft, as one of many possible. As used herein, the term “aircraft” is intended to include airplanes, unmanned areal vehicles (UAVs), missiles, ordinance, gliders, helicopters, and other objects that travel thorough airspace. Based on the disclosure, a person of ordinary skill would be able to use the separation manager in other environments. 
         [0024]      FIG. 1  is a schematic view of an environment  100  including aircraft in communication with at least one of other aircraft or ground based systems, the aircraft configured to perform techniques provided by a separation manager in accordance with an embodiment of the present invention. The environment  100  includes an airspace  102  with a number of aircraft  104 . The aircraft  104  may include manned aerial vehicles and/or unmanned aerial vehicles (UAV) employed in military use, commercial use, or private use, or any combination thereof. The aircraft  104  each include a trajectory path  106  in a trajectory window  108  of possible trajectories. In one implementation, the separation manager may cycle through each of the aircraft  104 , such as aircraft  104 ( 1 ),  104 ( 2 ),  104 ( n ), checking for conformance to commands from the separation manager and for potential conflicts. The separation manager may continually update commands to adjust for deviations and/or to maintain an optimally controlled environment. 
         [0025]    In some embodiments, the separation manger may be configured as distributed system where each aircraft may implement the separation manager, or a portion thereof, and may compile data, analyze, and provide separation management to surrounding aircraft via inter-aircraft communications  110 . For example, the first aircraft  104 ( 1 ) may communicate the trajectory path  106  associated with the first aircraft to the second aircraft  104 ( 2 ). The second aircraft  104 ( 2 ) may process the first aircraft&#39;s trajectory path  106 , the trajectory window  108 , or other data related to or communicated from the first aircraft, such as velocity, acceleration, and altitude for processing by the separation manager. The quality of the data exchanged between the aircrafts, either directly or indirectly, may influence decision making processes by the separation manager. The separation manager implemented by the second aircraft  104 ( 2 ) may generate a separation window for the second aircraft to enable the second aircraft to avoid a predefined airspace adjacent to the first aircraft  104 ( 1 ) at a future point in time (when a potential conflict would have been present). In other embodiments, the aircraft may communicate to each other thorough intermediaries, such as a satellite or an antenna  118 , which may relay transmissions from a first aircraft to a second aircraft. 
         [0026]    Alternatively or additionally, a centralized separation management system  112  may implement the separation manager for the aircraft  104 . In such an instance, the centralized separation management system  112  may communicate with the aircraft  104  using satellite systems, including a ground based transceiver  114  and the satellite  116 . The aircraft  104  may include satellite transceiver (not shown) to facilitate communications with the satellite  116  to exchange data with the centralized separation management system  112 . Other communication configurations may be implemented, such as a radio based communication system using the antenna  118 , or other communication techniques. The centralized separation management system  112  may compile aircraft data, analyze the data, and provide separation management to the aircraft  104 . In some embodiments, the centralized separation management system  112  uses techniques for separating aircraft according to time based allocation of the airspace  102 , among other techniques, which will be more thoroughly described below. 
         [0027]    Alternatively or additionally, aircraft implementing the separation manager may provide a centralized separation management system component with route options. The centralized system may choose final separation routes for the aircraft, which are communicated to the aircraft in accordance with an implemented communications configuration. Additionally, the centralized system component may carry out separation for those aircraft not configured with a separation manager. 
         [0028]    In one implementation, the separation manager may use aircraft flight management system (FMS) data as a source for aircraft location and behavior and may use additional airspace/aircraft related information when it is available. A subset of functionality can be obtained by working with data obtained from sources such as radar, sonar, optical, or infrared sources. In some embodiments, the separation manager continually monitors aircraft for potential conflicts. In addition or alternatively, the separation manager may improve airspace configuration by sending aircraft control commands to modify aircraft trajectories. The separation manager may be fully automated or include human interaction and/or oversight to the separation manager processes. In addition, by using a subset of separator functionality, operation of the separation manager may be applicable to traditional radar and sense and avoid systems. 
         [0029]      FIG. 2  is an illustrative chart  200  depicting a relationship between time  202  and airspace complexity  204  used to determine a safe separation phase space which may be increased by implementation of an automated separation manager in accordance with an embodiment of the present invention. The chart  200  includes information for two aircraft, such as a control aircraft  206  and a relevant aircraft  208 . The control aircraft  206  is an aircraft that may be “controlled” or otherwise maneuvered to create a safe separation distance from the relevant aircraft  208 . Although descriptions herein may be limited to the control aircraft  206  and the relevant aircraft  208 , it should be understood that the separation manager may be configured to provide airspace separation management for any number of aircraft in a substantially simultaneous process. For instance, the control aircraft may consider the trajectory of many relevant aircraft when determining a safe trajectory through a portion of airspace. 
         [0030]    The chart  200  may include maneuver curves  210  which depict the time necessary to maintain a safe separation distance between the aircraft  206 ,  208 . The control aircraft may include varying degrees of maneuverability and speed. For example, a first maneuver curve  210 ( 1 ) may be plotted for the control aircraft  206  having a first velocity, such as a velocity of  50  knots. A second maneuver curve  210 ( n ) may be plotted on the chart  200  and indicate a second velocity, such as  400  knots, of the aircraft  206 . In addition, the chart includes predication time curves  212  that determine the time necessary for initiating maneuvers to maintain the safe separation distance between the aircraft  206 ,  208 . For example, using current airspace management techniques, the prediction time curve  212 ( 1 ) and maneuver curve  210 ( 1 ) may determine a safe preparation phase space  214  in which the control aircraft  206  may successfully maneuver to maintain a safe separation from the relevant aircraft  208 . Implementation of embodiments of the present invention may shift the prediction curve to the right to create the new prediction curve  212 ( n ), thus expanding the safe preparation phase space  214  by an additional safe space  216 . Accordingly, a shift from the maneuver curve  210 ( 1 ) to the maneuver curve  210 ( n ) may further expand the safe zone. As shown, implementation of embodiments of the present invention may enable an increase in airspace density and/or flexibility of aircraft travel through the airspace. 
         [0031]      FIG. 3  is a schematic view showing illustrative safe separation windows for aircraft with varying degrees of uncertainty in accordance with another embodiment of the present invention. A first safe separation window  302  includes the relevant aircraft  208  and the control aircraft  206 , each having a trajectory window. The relevant aircraft includes a trajectory window R 1  that represents the navigational uncertainty from a planned trajectory path  304 . The trajectory window R 1  may be a result of environmental conditions (e.g., wind, air mass, etc.) instrumentation limitations and/or tolerances, or other factors influencing aircraft trajectory. The navigational uncertainties represented by the subset trajectory window R 1   308  are typically small and may be assumed to be approximately constant over time. The control aircraft includes a control trajectory window  306 . 
         [0032]    A second trajectory window R 2  is defined by the possible trajectories of the control aircraft  208  as a function of time, where the radius (R) of the trajectory represents distance from a straight path. For example, a maneuverable aircraft may have a very large R 2  because the aircraft may be able to execute a sharp maneuver in a relatively short distance whereas a less maneuverable aircraft may have a narrower R 2  value. Generally speaking, R 2  values define the maximum maneuvering uncertainty for an aircraft and the R 2  area characteristically grows rapidly with time. 
         [0033]    Implementations of the present invention may reduce the R 2 . In some implementations, the separation manager addresses the use of the R&#39;s (R 1 , R 2 , and R 3  described herein) in maintaining airspace separation and thus enlarge potential safe separation zones between the control aircraft  206  and the relevant aircraft  208 . For example, techniques may use probability curves to reduce the trajectory window R 2  to a minimum safe distance trajectory window R 3  illustrated in a second safe separation window  308 . For example, the trajectory window R 3  may represent a ninety-eight percent confidence interval for the trajectory of the relevant aircraft  208 . In some implementations, a greater or smaller control window confidence interval may be appropriate, which may vary across applications, such as military applications during a conflict and commercial flight implementations where risk avoidance is an utmost concern for the separation management system. 
         [0034]    As shown in the first safe separation window  302 , the control aircraft trajectory window  306  does not allow the control aircraft enough time to maneuver to avoid the maximum maneuver uncertainty trajectory window R 2 . In such an instance, the control aircraft  206  and the relevant aircraft  208  may be at a high risk for collision. In contrast, the second safe separation window  308  does not include an intersection of the trajectory window  306  and the trajectory window R 3 , therefore creating a safe separation distance between the two aircraft. Embodiments of the present invention use a trajectory window R 3  for relevant aircraft when implementing the separation manager to control the airspace. For reference, examples of the R 1 , R 2 , and R 3  are illustrated in chart  31   0 . However, one skilled in the art will appreciate the radius of R 1 , R 2 , and R 3  may greatly differ from the chart  310 , although the general relationship of R 2  being greater than R 3  is consistent. Further detail about an illustrative separation manager will be described in the subsequent section, followed by details of illustrative modules of the separation manager and operations thereof. 
         [0035]    Illustrative Separation Manager 
         [0036]      FIG. 4  is a flow diagram of an illustrative configuration of a separation manager  400  in accordance with an embodiment of the present invention. As shown, the separation manager  400  includes plurality of operations represented as blocks in the flow diagram. In implementation, the separation manager  400  may include fewer or more operations to implement embodiments of the present invention. 
         [0037]    Embodiments include data input  402  from an aircraft. The data input  402  may include any data related to the relevant aircraft and/or the control aircraft, such as information from a flight management system (FMS) of an aircraft, such as trajectory, altitude, velocity, flight plan data, information from sensors, or other data related to the aircraft, including environment info such as restricted regions, external threats, weather. The data input  402  may be continually updated for the aircraft, such as at a rate of 10 Hz. In other implementations, the data input  402  may be updated more or less frequently. An update rate can be dynamically adjusted depending on factors such as airspace complexity, aircraft behavior and type, signal space conditions. In instances where the data input  402  is not updated, such as instances where data is not received or the data is determined to be corrupt, the input data for the next cycle may be generated from the data of the previous cycle. The data input  402  may be preformatted and/or post formatted for used by the separation manager  400 . For example, additional processes may convert information from the FMS to usable data which may be used by the separation manager  400  to create a safe separation between the relevant aircraft, such as relevant aircraft  208 , and the control aircraft, such as control aircraft  206 . In addition, distinct data structures may be generated for low bandwidth implementations to expedite transmission to other aircraft and/or controllers. In addition, data may include intention flags from a pilot or a mission planner. Data may include data from the relevant vehicle. 
         [0038]    In accordance with some embodiments, the separation manager  400  may include airspace information  404  and aircraft information  406 . The airspace information  404  may include metrics for the airspace, including geographical information and other data related to the airspace. Airspace information may also include metrics such as airspace complexity, density, aircraft mix, and knowledge certainty level which can be used in setting parameters such as desired data update rate, separator cycle time, and other separation manager parameters. The airspace information  404  may include designations, such as combat, commercial use, and the like, which may be used to determine the R 2  value such as by increasing or decreasing a confidence interval value associated with the airspace information  404 . 
         [0039]    The aircraft information  406  may include performance metrics related to the aircraft. In addition, the aircraft information may include predictions, latency information, data processing information (e.g., formatting, bandwidth, etc.), behavior metrics, and location information (e.g., FMS derived data). For example, the aircraft information  406  may enable the separation manager to create the trajectory window R 2  using information specific to a particular aircraft or type of aircraft. The aircraft information  406  may identify an aircraft as a military fighter jet aircraft, such as an F-15 Eagle. The identified aircraft may have known flight characteristics which may be used to generate the trajectory window R 2 . Predictions may include typical trajectory information associated with the identified aircraft, including historical information. For example, some identified aircraft may typically fly relatively direct paths despite having a relatively high maneuverability potential. Behavioral metrics may include information on the status of an aircraft, such as a status of in-transit, dog-fight, attack, pursuit, or other status. The status of the aircraft may influence the size of the trajectory window R 2 . 
         [0040]    The separation manager  400  may use the airspace information  404  to generate an airspace/time allocation  408  which may determine an aircraft&#39;s current airspace allocation region relative to other aircraft. An airspace allocation region is a dynamically changing region surrounding the aircraft that no other aircraft may enter for safety or other reasons. For example, in a friendly (non-combat situation), the airspace/time allocation  408  for an aircraft may be larger than the airspace/time allocation during a combat situation when greater risks may be necessary to achieve a successful outcome to a planned mission. 
         [0041]    In accordance with one embodiment, the separation manager  400  uses the aircraft information  406  and/or airspace/time allocation  408  as inputs for a separation routing process  410 . The separation routing process  410  includes a virtual predictive radar (VPR) with a variety of dimensions. The dimensions may include time, altitude, latitude, and/or longitude. For illustrative purposes, the separation routing process will be presented as a 4D-VPR, including all four dimensions (4D), however other dimensions may be added or removed while effectively implementing the separation manager  400  with a VPR. 
         [0042]    As an overview, the separation routing process  410  includes a 4D-VPR conflict monitoring module  412  which receives data from the aircraft information  406  and/or the airspace/time allocation  408 . The conflict monitoring module  412  may search for upcoming potential conflicts with other aircraft by processing inputs to determine if a future conflict is possible. For example, the conflict monitoring module  412  may determine if the trajectory of the relevant aircraft  208  provides a safe separation from the control aircraft  408  at a future point in time, such as 10 seconds in the future. 
         [0043]    In one implementation, the conflict monitoring module  412  may include a look-ahead time. The look-ahead time may be implemented as a step function over a look-ahead time window for determining time points to check for possible future conflicts. In addition or alternatively, a region extent function may determine which aircraft to consider in checking for possible upcoming conflicts. For example, aircraft in a close proximity may be sampled more often than aircraft further from the control aircraft  206 . There may be different regions used for checking conflict with different aircraft types. The shape of the region considered may depend upon the control aircraft course and behavior of the aircraft. Finally, the regions may depend upon airspace conditions, such as density and complexity. 
         [0044]    As discussed above, a cycle time, such as without limitation 100 Hz to 0.5 Hz, determines how often to invoke the conflict monitoring module  412 . The cycle time may be static in some instances or it may be dynamically varied based upon current circumstances such as airspace density, local region aircraft behavior, or types of aircraft in the region. 
         [0045]    Thus far conflicts have been typically associated with other aircraft. However, further embodiments may include other possible threats to a control aircraft such as poor weather or dangerous regions, such as regions heavily fortified with armament such as surface to air missiles (SAM). In still further embodiments, the conflict monitoring module  412  may assess likely position of the aircraft based on possible control of the aircraft determined by space and time, such as via the look-ahead window. For example, there may be a minimal conflict approach distance function which keeps the control aircraft from making a premature trajectory change. In addition, the conflict monitoring module  412  may depend on other factors such as relative aircraft type/capability, absolute aircraft type/capability, relative aircraft behavior, and/or absolute aircraft behavior, and/or time into the future (time ahead along the proposed reroute). Factors such as aircraft behavior and type/capability affect the look-ahead time used in checking for potential conflicts. For example, a slow UAV checking for potential conflicts with a highly capable fast flying F-15 would use a longer look-ahead window than if it were checking for potential conflicts with an aircraft of similar capability and behavior. 
         [0046]    If a safe separation exists, there may be no further action by the conflict monitoring module  412  related to relevant aircraft, thus the separation manager  400  may cycle to another aircraft to implement conflict monitoring, such as using a 10 Hz processing cycle. However, if the conflict monitoring module  412  determines a potential conflict may occur based on the trajectory window R 2  and/or R 3  for the relevant aircraft  408  and the trajectory of the control aircraft  406 , then the separation manager  400  may determine at a decision block  414  to proceed to a 4D-VPR separation routing module  416 . 
         [0047]    In one embodiment, the separation routing module  416  may modify the trajectory of the control aircraft to prevent a possible future conflict or achieve a desired goal, including conflicts, avoidance situations, or action such as without limitation airspace, adverse weather, or making desired trajectory modifications. The separation routing may include a number of possible modes. In one mode, the routing for an aircraft may be based on ownership of the relevant aircraft. For example, if the relevant aircraft is friendly, the safe subset may be enlarged to provide more maneuvering flexibility for the control aircraft. In a second mode, multiple possible conflicts may occur for the routed aircraft over the routing time, whereas all the possible conflicts may be avoided in a routing. In a third mode, routing may involve simultaneous choices for multiple aircraft among outputs created for individual aircraft. Finally, routing may involve simultaneous choices for multiple aircraft where outputs are created concurrently for the aircraft. 
         [0048]    The separation routing module  416  may include techniques to determine a set of routing possibilities using one or more metrics to determine route preferences. The route may consist of one or more preferred routes, a discrete set of route options weighted according to preference, and/or a continuum of route options with a weighting function. Routing may end at a specified point in space, such as a target destination. In some instances, a time window for arrival at the target destination may be used. A specified speed, heading, and pitch at the target destination may also be specified. 
         [0049]    As discussed above, metrics may be included in the separation routing module  416 . The metrics may include metrics to measure deviation from original planned route (in time, space, and behavior). Other metrics may measure deviation from linear constant speed motion, measure nearness in time and space to other aircraft, measure threat conditions of traversed airspace, measure certainty level of information on conditions of traversed airspace, and/or measure impact of higher level mission objectives. 
         [0050]    The separation routing module  416  may include a minimal separation approach distance function as a constraint that may not be violated. The minimal separation approach distance may depend on relative aircraft type, absolute aircraft type, relative aircraft behavior, and/or absolute aircraft behavior. In addition, the minimal separation approach distance may depend upon time into the future (time ahead along the proposed reroute). The separation routing module  416  may include a minimal time to minimal separation distance. 
         [0051]    The separation routing process  410  may lead to a command generation  418  for the controlled aircraft, the relevant aircraft, or other aircraft in the proximate airspace of aircraft evaluated by the separation manager  400 . The output of command generation  418  may be a trajectory window, trajectory path, trajectory options, or a no-fly command (airspace to avoid). Additionally, the command generation  418  may format command output in accordance to requirements of the intended recipient. 
         [0052]    Additional operations may be included in the separation manager such as a performance evaluation  420 , a control mode module  422 , a time and system health manager  424 , and/or setup implementation module  426 . The control mode module  422  will be discussed in further detail. 
         [0053]    In accordance with an embodiment of the separation manager  400 , the setup module  422  includes control mode options. The control mode options may contain a level of automation which further includes avoidance rules. For example avoidance rules may be determined on whether a vehicle is manned or unmanned (UAV). Avoidance rules may include having the UAV avoid the manned aircraft, a mutual avoidance rule between the UAV and the manned aircraft, a human controller providing some guidance to the UAV regarding avoidance, and/or the UAV entering a safe-hold pattern. In addition, control mode options may contain a level of centralization (e.g., ground based), distribution (e.g., aircraft based) or a hybrid of centralization and distribution. 
         [0054]    The setup module  422  may include varying separation levels. For example, a separation level may contain a minimal allowed approach distance along with a minimal time to approach. The minimal time to approach and approach distance may be a function of airspace conditions, aircraft behavior and capability, and/or objectives. Further, the setup module  422  may include data levels such as a data level update rate where various rates for different data types or data fields are implemented. A data level may contain a send rate for different data types or data fields. In addition, a data level may contain the ‘sophistication’ level of data requested, for example for specific sensors, predicted trajectories, pilot provided flags, aircraft internal sensors, and mission plan information. Finally, the setup module  422  may include an airspace and time allocation technique. The technique may include an allocation of airspace surrounding the control aircraft that other aircraft are not allowed to traverse. This may depend on relative aircraft capability and/or behavior, other aircraft capability and/or behavior, and the identity of particular aircraft and/or mutual mission objectives. 
         [0055]    Illustrative Separation Router (4D-VPR Module) 
         [0056]      FIG. 5  is a schematic of an illustrative virtual predictive radar (VPR)  500  that depicts aircraft trajectory with respect to time as implemented by a separation manager in accordance with yet another embodiment of the present invention. More specifically, the separation routing process  410  creates a 4D-VPR model  502 . The 4D-VPR  502  includes the four dimensions of time, latitude, longitude, and altitude, however more or fewer dimensions may be used to generate the VPR  500 . In some embodiments, there may be a discrete set of altitude levels specified with a distinct ‘sub’ VPR for each altitude and a set of altitude transition guides. Generally speaking, the separation router determines reroute options for a control aircraft by (1) generating a discrete frame work of trajectories and ‘time-range rings;’ (2) determining a weight for framework; and (3) routing the trajectories through intervening regions as efficiently as possible using the framework as a guide or by extending the weighting. A scale component determines the scale of the discrete frame work using information on certainty of airspace conditions, complexity of the airspace, and type of aircraft in the area. 
         [0057]    In one embodiment, a method for maintaining a safe separation time and distance between vehicles includes receiving a time-referenced position, speed and direction (attitude) data for vehicles including a control vehicle, the vehicles having initial locations within a predetermined zone. Data describing maneuvering characteristics of the vehicles and information on mission plan may be received. In addition, pilot generated intentions may be assessed and incorporated in some embodiments. For each of a plurality of future time intervals, a potential time-position zone is calculated for each vehicle within the predetermined zone based on the received time-referenced position, speed and direction data, and vehicle maneuver characteristics. If the distance between the potential time-position zones for the vehicles is less than a specified distance, the control vehicle is rerouted. A reference point is selected as a next waypoint for the control vehicle. A plurality of homotopic regions are calculated between the initial location of the control vehicle and a destination point. The destination point is generated based on the maneuvering characteristic data for the control vehicle and potential time/position zones of each vehicle within the predetermined zone. Within each homotopy region, a set of path options is determined between the initial location of the control vehicle and the reference point based on the maneuvering characteristic data for the control vehicle. In other embodiments, methods may forego homotopy paths and instead find routes directly from guide curves. 
         [0058]    When using the homotopy paths, the guide curves determine the time rings. Homotopy paths are typically constrained by the time rings, and aircraft capability and/or desired behavior, but are not constrained by the guide curve. In some implementations, the time rings may be generated using constraints on desired aircraft performance. The time rings may be determined by a future location of the aircraft at a future point in time given desired constraints on aircraft motion. The time rings are drawn as lines on the picture but in actuality they are “fattened” rings with variable “diameter.” 
         [0059]    In some embodiments, the 4D-VPR  502  may include an initial reference point  504  (starting point) and an objective point  506 , which is the desired destination of a control aircraft  508 . The control aircraft  508  may reach the objective point  506  by traveling along any number of trajectory paths  510 , which are represented by dashed lines in  FIG. 5  that originate at the initial reference point  504  and continue through a three-dimensional representation plus time, thus a 4D representation, to the objective point  506 . The trajectory paths incorporate maneuverability of the control aircraft  508  and mission objectives, and therefore create a no-fly zone  512  that is outside the 4D-VPR trajectory paths  510 . The VPR  500  includes time rings  514  that indicate the amount of time necessary for the control aircraft  508  to travel along a particular trajectory path  510 . The time rings  514  are analogous to radar range rings except the time rings represent time rather than distance. 
         [0060]    In some embodiments, the 4D-VPR  502  includes representations of potential conflicts in the form of trajectory windows  516 , described above as R 3  trajectory windows, which are confidence regions for a predictive aircraft position of another aircraft. Typically, only potentially conflicting aircraft will be represented on the 4D-VPR and will affect the trajectory path  510  of the control aircraft  508 . Other conflicts and/or obstacles, such as weather conditions or geographical constraints (e.g., a mountain) may be represented on the 4D-VPR. 
         [0061]    Working in the context of time and considering the R 3  trajectory windows  516  in relation to maneuver capability enable management of separation distances between aircraft. The 4D-VPR  502  provides a technique to link time, maneuverability, and R 3  in determining possible reroutes for the control aircraft  508  to avoid possible conflicts based on the maneuvering capabilities of the control aircraft. A high uncertainty of future conditions may result in a short time frame representation of objects with high future uncertainty on the 4D-VPR  502 . A high airspace complexity or high speed aircraft may necessitate a fine scale frame work having many time rings  514 . 
         [0062]    The location of the R 3  trajectory window  516  across one of the time rings  514  determines a probability distribution over the time ring. The probability distributions may be used along with additional probability distributions induced by any number of metrics defined over time rings. For simplicity, the 4D-VPR  502  does not depict additional metrics however additional metrics may be included in further embodiments in accordance with the present invention. A weight may be determined by metrics specified by a metric component. Metric evaluations are approximations with the fineness of approximation determined by the scaling. Metrics may include a deviation from an original path metric, a time deviation metric, a behavior change metric, and/or a behavior deviation metric. The metric values may describe a worst case, average case, weighted average case. 
         [0063]    With continued reference to  FIG. 5 , reverse distributions  518  may be generated by the separation routing process  410  for any number of the time rings  514 . In particular, the reverse distribution may include weighted graphs showing separation as a function of confidence along the array of possible trajectories. A first distribution  518 ( 1 ) depicts a low confidence interval at a dip  520  which indicates a potential conflict in this region, a subset of trajectory paths  510 . The dip  520  is associated with the R 3  trajectory window  516 ( 1 ) that is the potential conflict requiring airspace separation. The right side of the graph depicts an increased confidence level which indicates less threat of a conflict or no conflict. Similarly, graph  518 ( 2 ) corresponds to the R 3  trajectory window  516 ( 2 ) while graph  518 ( n ) corresponds to the R 3  trajectory window  516 ( n ). Each time ring  514  represented along the distribution graphs  518  are adjusted to show possible ranges of the threats. The distributed graphs  518  represent ‘unrolled’ time rings  514  that are normalized for comparison purposes, therefore enabling a determination of safe trajectory paths for the control aircraft  508  to safely reach the objective point  506 . 
         [0064]    The distribution graphs  518  may be multiplied or otherwise combined to create a final options relative safety graph  522 . The relative magnitude of the final options relative safety graph  522  indicates an increasing safety of a particular trajectory both represented by that portion of the graph. The final options relative safety graph  522  may be converted to a final options absolute safety graph  524  which indicates trajectory paths which are deemed acceptable (denoted by the higher line on the right of the graph) and trajectory paths that are deemed unsafe (denoted by the a line with no magnitude on the graph). In some instances, no mutually feasible direction for a reroute may be depicted on the graph without the using additional turns from one of the trajectory paths  510 , such as an instance where the control aircraft  508  jumps trajectory paths to avoid a conflict. 
         [0065]    The functionality of the separation manager results from the use of input streaming data and fast cycle rate along with techniques to quickly generate trajectory options and efficiently obtain approximate metric evaluations, and quick iterative inspection and continual refinement of trajectories. In addition a subset of functionality may be obtained through traditional radar or ‘sense and avoid’ data input. Further aspects of the separation router will be described in relation to an illustrative operation in the subsequent section. 
         [0066]    Illustrative Separation Router Operation 
         [0067]      FIGS. 6 and 7  are flow diagrams of an illustrative process  600  of the virtual predictive radar in accordance with another embodiment of the present invention.  FIGS. 6 and 7  include an arrangement of blocks arranged in a logical flow diagram, the blocks representing one or more processes conducted by the separation manager. In some embodiments, the blocks may be implemented in software and execute by a processor. The arrangement of the blocks is not intended as a limitation. In some implementations, the blocks may be executed in series or in parallel. 
         [0068]    The process  600  includes an input  602  which may include the data input  402 , information from the airspace information  404 , and/or aircraft information  406 . The input is received at  604  for generating a 4D-VPR radar screen  606 . The illustrative (default) radar screen  606  may be generated in association with the 4D-VPR from the block  604 , where the rings represent elapsed time from an initial reference point. Next, aircraft behavior and routing information may be added to the 4D-VPR at  608  and is represented by a populated 4D-VPR display  610  which includes time rings and trajectory paths. 
         [0069]    In accordance with one or more embodiments, the separation manager via the separation router adds R 3  trajectory windows and other constraints (e.g., conflict sources) to the 4D-VPR at  612 . A populated 4D-VPR and R 3  display  614  includes three R 3  trajectory windows  616  representing potential conflicts. Next, R 3  and other constraints are added to the 4D-VPR data to create a data structure display  620 . In some implementations, the data structure display  620  includes conflicts  622  (generated form R 3  potential conflicts), a no-fly zone  624  which may be based in part on the control aircraft&#39;s maneuverability, and a available travel route  626 . 
         [0070]    The separation router process  600  continues in  FIG. 7  at  628  where a decision block determines if a feasible route is determined by the separation router. If no feasible route is determined, the input of the separation manager may be reconfigured at  630  and the process may begin again at  604  to create another trajectory determination. For example, the input may be reconfigured by reducing the confidence intervals used in the final options relative safety, or other metrics that create the route display  620 . 
         [0071]    In one or more embodiments, the separation router may optionally include additional metrics values at  632 , including confidence intervals or other metrics which expand or narrow the route display  620 . Next, homotopically distinct regions are generated at  634  for specific trajectory routes that may enable the control aircraft  508  to traverse from the initial point of reference  504  to the objective point  506  while maintaining a safe separation from conflicts. For example, a first trajectory path  636  may include a more direct homotopic region while a second trajectory path  638  may include a less direct homotopic region for the control aircraft  508  to reach the objective point  506 . The homotopically distinct regions may be output for use to a pilot, controller, UAV, or for other uses in accordance with the present invention. 
         [0072]    In accordance with one or more embodiments of the present invention, the separation manager and/or the separation router may be configured to generate and/or output a guide route, such as a preferred route  642  depicted in the route display  644 . For example, in an implementation where the control aircraft  508  is a manned aerial vehicle, a guide route may not be necessary but may provide a more efficient route for the pilot to consider, among many other considerations. In an implementation where the control aircraft  508  is a UAV, the UAV may be automatically directed along the preferred route  642  without further action by a controller. Therefore, the UVA may be directed along a route providing a safe separation from a relevant aircraft, such as a fast flying fighter jet, therefore providing a safe separation and conflict free airspace proximate the control aircraft  508  and the fighter jet. 
         [0073]    Although only local airspace separation management was described for illustrative purposes, one skilled in the art would understand that many aircraft in a densely populated airspace may be controlled using the separation manager implementing a separation router as described herein. The separation manager, whether implemented in a centralized or disparate net-centric implementations, may assess aircraft and conflict interaction on a wide scale to create safe separation distances for the aircraft. 
         [0074]    While preferred and alternate embodiments have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the present invention. Accordingly, the scope of the present invention is not limited by the disclosure of these preferred and alternate embodiments. Instead, the scope of the present invention should be determined entirely by reference to the claims that follow.