Vehicular trajectory collision avoidance maneuvering method

Details Vehicular trajectory collision avoidance maneuvering method Vehicular trajectory collision avoidance maneuvering method

2002-07-30

2004-02-10

Louis-Jacques, Jacques H. (Department: 3661)

Data processing: vehicles, navigation, and relative location

Relative location

Collision avoidance

C701S302000, C340S436000, C340S961000, C342S029000

Reexamination Certificate

active

06691034

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to the field of collision prediction and avoidance of airborne and spaceborne moving vehicles. More particularly, the present invention relates to flight path trajectory conflict prediction and maneuvering avoidance methods for airplanes and spacecraft.
BACKGROUND OF THE INVENTION
Aircraft conflict prediction and resolution are performed manually by the pilots and air traffic controllers with the help of automated tools. The increase in air traffic is stressing the ability of the Air Traffic Management System to keep aircraft safely separated. Air traffic growth is expected to continue. The FAA Operation Evolution Plan is aimed at supporting a thirty percent overall growth in commercial aviation operations by 2010. Computer controller aids are expected to help relieve air traffic congestion. Such tools also enable free flight, which saves fuel and time. One such controller aid is the User Request Evaluation Tool, which is a conflict probe that looks ahead twenty minutes and helps en route controllers identify potential conflicts above 18,000 feet. Such tools require efficient computational methods to predict conflict.
Aircraft are usually routed between way points with constant altitude, speed and heading. Heading corrections and throttle adjustments are made to prevent each aircraft from deviating too far off course. Nevertheless, navigation errors, uncertainty in winds and aircraft altitude result in position prediction error. These prediction errors were found to be Gaussian and can be represented by error covariance matrices. Between state vector updates, the error covariance matrices grow. Lateral errors are controlled to about ±1.0 nmi one sigma. Vertical error is roughly ±100 ft one sigma. Along-track errors grow at a rate of about ±15 nautical miles per hour between updates. During climb or decent, position uncertainty increases by an amount that depends on the details of the particular route being studied. Therefore, when aircraft routes are near each other, aircraft position uncertainty results in a probability of the aircraft coming within a specified keep out distance. If the probability value exceeds a threshold, a conflict is declared. A conflict can be resolved by maneuvering one or both of the affected aircraft.
Predicting cumulative collision conflict probability for aircraft with constant velocity is very similar to space vehicle collision probability prediction. For aircraft, the probability of a conflict collision depends on the conflict volume, the relative position error, and the trajectories of the respective aircraft. First, one propagates the aircraft for thirty minutes. Next, coarse screening is performed to identify potential conflicts. Finally, collision conflict probability is predicted. The cumulative collision conflict probability method assumes that the relative velocity is constant and that the relative position error covariance matrix is constant during the encounter. These assumptions are not always valid, because aircraft routing involves turns at way points. In addition, along-track position errors grow between position data updates, The vertical position errors also grow during ascent or descent. Thus, a constant error covariance matrix throughout the encounter between the two aircraft produces uncertain risk of collision. The cumulative collision conflict probability formulation assumes both aircraft were traveling from minus infinity to plus infinity. This assumption can result in small errors in the collision probability. A slight increase in the predicted collision conflict probability could result. For these reasons, a general formulation for collision conflict probability is needed.
A conventional conflict keep-out box is a conflict volume that may be a cylinder 5.0 NMI in radius and 4,000 ft in height for aircraft flying above 29,000 ft. For aircraft flying below 29,000 ft, the cylinder height is reduced to 2,000 ft and a conflict occurs for aircraft with less than 5.0 NMI separation having altitudes that differ by less than ±1,000 ft. The cylinder is centered on the flying aircraft and oriented vertically with its height corresponding to altitude. Thus, when an aircraft is predicted to come within 5.0 NMI lateral distance or ±2,000 ft vertical distance, a conflict exists. The time of conflict resolution is a tradeoff between efficiency and error uncertainty. When the maneuver is too far in advance, it is efficient and therefore smaller but growth in position uncertainty reduces confidence in the computed collision conflict probability. When the maneuver is not far enough in advance, confidence in the computed collision probability is high but less time is available for the maneuver to avoid the conflict and a larger less efficient maneuver must be made. Thus, there is an optimum maneuver time to resolve a conflict efficiently. The ability to predict conflicts efficiently is needed to help air traffic controllers.
In level flight, the conflict determinations can be partitioned into vertical and horizontal portions because the cylindrical conflict volume is symmetric in the horizontal plane and there is no cross correlation between vertical and horizontal errors. The probability density is integrated from minus infinity to plus infinity along the relative velocity direction. The result is always unity because the probability density is normalized. The resulting two dimensional integral can be partitioned into two separate error function integrals with limits defined by the dimensions of the conflict cylinder. Thus, the conflict probability reduces to the product of two error function integrals.
Vertical and horizontal errors are correlated in the case of non-level flight. In addition, the cylindrical conflict volume takes a more complex shape when the conflict volume is projected to an encounter plane, which is normal to the relative velocity. An approximate solution and a Monte Carlo simulation approach has been proposed to overcome the difficulties of computing conflict probabilities for more complex shapes of the keep-out volume. The computational requirement is significantly greater with the Monte Carlo method. Although the FAA is currently modernizing the traffic control system by increasing automation, effective computerized methods to predict aircraft conflict and avoidance maneuvering are needed.
Collision conflict prediction methods have been used to determine when a spaceborne or airborne vehicle is likely to have a significant collision risk with another object. A contour integration method has already been used on asymmetric space vehicle collision probability and collision probability for space tethers. When there is a significant collision risk, it is then desirable to perform a collision avoidance maneuver prior to the collision time for both aircraft and spacecraft. Spacecraft collision avoidance is also becoming an increasing concern as the number of space objects continues to increase over time. There are currently over 9,500 tracked orbital objects. The need for collision avoidance maneuvers is correspondingly increasing as the number of operational satellites and associated debris objects increase. The narrow altitude bands associated with communication satellite constellations in both low earth orbit and geosynchronous earth orbit requires improved collision prediction and avoidance methods because satellites occupying the same altitude range have increased risk of collision. The collision hazard posed by debris and other operational satellites has been increasing to the point where collision avoidance maneuvers should be considered as a means to mitigate the collision risk. The increasing collision hazard is forcing manned vehicles to perform unwanted collision avoidance maneuvers. Such maneuvers are disruptive to mission operations. For example, the Space Shuttle performs a maneuver, when the predicted miss distance is less than two kilometers radially, five kilometers in-track and two kilometers out-of-plane. The International Spa

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