Robust Relative All-in-View KCPT Solution for Aircraft Carrier Landing Operations

Greg Johnson, Bryce Thornberg, Phillip Chesson, Lee Wellons and Tom Briggs

Abstract:	Providing precision guidance to an aircraft landing aboard a ship requires a robust and extremely accurate positioning system. Several carrier controlled approach aids (such as the AN/SPN-42A/46 Automatic Carrier Landing System) currently provide the required accuracy for the U.S. Navy. However, these systems experience reduced performance in precipitation and are difficult to maintain. A relative Global Positioning System (GPS) Kinematic Carrier Phase Tracking (KCPT) solution has the potential to provide a highly accurate solution for shipboard landing operations which is unaffected by weather. There are several problems with a GPS based shipboard landing system over and above its shore based counterpart. The touchdown point and the GPS reference station are in motion through six degrees of freedom, the ship’s dynamics are nearly as high as the aircraft dynamics and the reference station experiences more cycle slips and masking due to the high electromagnetic interference environment and the ship’s structure. With these considerations in mind, E-Systems, Montek Division has developed a relative, all-in-view, KCPT solution that is able to resolve and hold carrier cycle ambiguities indefinitely. Space Vehicle (SV) pseudorange and carrier phase data as well as ship’s motion data are uplinked to the landing aircraft to formulate an air derived solution. The system features a floating point solution (ambiguities not resolved) and employs a Kalman filter to estimate the magnitude and covariance of the ambiguities. The results of the Kalman filter are fed to an ambiguity resolution algorithm that operates continuously. The output of the GPS solution (either a floating or fixed solution) is blended with high rate inertial data in a filter developed by the Naval Air Warfare Center Aircraft Division (NAWCAD), Patuxent River to provide a final position solution. This three step process provides a continuous navigation solution through loss and reacquisition of SVs and cycle slips. The system has been evaluated with two sets of approach and landing data. The first set was collected during an FAA Category III Feasibility Study in which E-Systems successfully completed 100 approaches and landings with a Westwind 1124 airplane using laser tracker to provide ‘truth’ position data. The second set was collected during a series of at-sea approaches by a GPS equipped, Naval Rotary Wing Test Squadron, SH-60F Seahawk helicopter to the aircraft carrier USS ENTERPRISE (CVN-65). The production GPS antenna (used for these tests) on the SH-60F is located in an area susceptible to SV masking and cycle slips, and the data collected during the approach profiles contained multiple occurrences of both. In all cases the KCPT solution provided a seamless fixed ambiguity approach solution with an average of 42 seconds ambiguity fixing time.
Published in:	Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996) June 19 - 21, 1996 Royal Sonesta Hotel Cambridge, MA
Pages:	235 - 244
Cite this article:	Johnson, Greg, Thornberg, Bryce, Chesson, Phillip, Wellons, Lee, Briggs, Tom, "Robust Relative All-in-View KCPT Solution for Aircraft Carrier Landing Operations," Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996), Cambridge, MA, June 1996, pp. 235-244.
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