Electronic Prognostics – A Case Study Using Global Positioning System (GPS)

Prognostic health management (PHM) of electronic systems presents challenges traditionally viewed as either insurmountable or not worth the cost of pursuit, but recent changes in weapons platform acquisition and support requirements has spurred renewed interest in electronics PHM, revealing possible applications, accessible data sources, and previously unexplored predictive techniques.

Many types of circuits compose avionics systems. One of the following categories can be used to classify each circuit topology at the time this research was performed:

  • High frequency analog

  • Low frequency analog

  • Low impedance

  • High impedance

Common failure mode mechanisms for analog circuits depend largely on the architecture and relative operating frequencies of the circuit. In this research, high frequency analog circuits are categorized as operating above 1GHz, while low frequency analog circuits operate below 1GHz. High frequency analog circuits are sensitive to small changes in device parameters, resulting in non-destructive, or operational, failure modes. Unlike physical device failures, the cause of operational failures cannot be traced back to individual components. Low frequency analog circuits are more likely to undergo physical device failure. The accompanying figure illustrates the relationship between the operating frequency of an analog circuit and the different types of failure modes.

Avionic systems containing high frequency analog circuits or RF circuits have high failure rates. Therefore, an avionics-related electronic system containing high frequency RF components was considered to test this theory. Evaluation of the following criteria led to the specific avionic system investigated in this report:

  • Critical avionics subsystems

  • Representative failure modes

  • Thorough documentation

  • Commercial availability for failure testing

One such avionics system that met all selection criteria is the Global Positioning System (GPS). The Garmin GPS 15L-W was selected for failure mode analysis and accelerated failure testing for the following reasons:

  • Thorough documentation

  • Commercial-off–the-shelf (COTS)

  • Embedded thermocouple

  • Small form factor

The global positioning system (GPS) is a space-based radio-navigation system managed by the U.S. Air Force (USAF). GPS, originally developed as a military force enhancement system, supports the existence of two different services: the Precise Positioning Service (PPS) and the Standard Positioning Service (SPS). The PPS is reserved for military use and requires special PPS receivers to access the system, while the SPS is available to civilian users throughout the world. Fundamentally, both services operate on the same principles. Accuracy is the main difference between the two systems; the SPS provides a less accurate positioning capability than its counterpart. All GPS systems consist of three major subsystems:

  • GPS Satellites

  • Transmission Paths

  • GPS Receivers

The GPS constellation consists of 24 satellites in continuous operation with six additional backup satellites, each having an orbital radius of 26559.7 km. All 24 satellites in the constellation are separated into six groups consisting of four satellites per group separated 60° apart with a maximum angle of inclination of 55° from the equator. Additionally, the satellites are designed to provide reliable service over a 7 to 10 year lifetime. Every active satellite broadcasts a navigation message based upon data periodically uploaded from the Control Segment (CS), which continuously monitors the reliability and accuracy of each satellite. This research focused on GPS reliability as a function of receiver degradation.

This work was done by Douglas W. Brown, Patrick W. Kalgren, Carl S. Byington, & Rolf F. Orsagh of Impact Technologies, LLC for the Naval Air Warfare Center. For more information, download the Technical Support Package (free white paper) below. NAWC-0005

This Brief includes a Technical Support Package (TSP).
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Electronic Prognostics – A Case Study Using Global Positioning System (GPS)

(reference NAWC-0005) is currently available for download from the TSP library.

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