Publications

Engineers at Sandia National Laboratories are combining entertainment industry software with traditional data collection techniques to create an interactive visualization tool. By replacing the usual flight simulator joystick with a telemetry data stream, experimental data is combined with existing three-dimensional (3D) engineering models. Users are immersed in their experiment, allowing interaction with and comprehension of complex data sets. Software tools are currently under development for post flight data visualization, and their usefulness and reusability have been demonstrated on numerous spaced-based programs within Sandia. However, data from remote sensors are subject to transmission errors that yield nonphysical behavior in real-time data visualization applications. We propose to investigate the applicability of real-time processing algorithms and estimation theories, such as Kalman filters, that have been successfully applied in other fields. Results will be integrated into existing postflight visualization tools for Proof-of-Concept validation and for potential integration of real-time applications.

This report contains the results of a Sandia National Laboratories Directed Research and Development (LDRD) program to investigate the integration of Global Positioning System (GPS) and inertial navigation system (INS) technologies toward the goal of optimizing the navigational accuracy of the combined GPSANS system. The approach undertaken is to integrate the data from an INS, which has long term drifts, but excellent short term accuracy, with GPS carrier phase signal information, which is accurate to the sub-centimeter level, but requires continuous tracking of the GPS signals. The goal is to maintain a sub-meter accurate navigation solution while the vehicle is in motion by using the GPS measurements to estimate the INS navigation errors and then using the refined INS data to aid the GPS carrier phase cycle slip detection and correction and bridge dropouts in the GPS data. The work was expanded to look at GPS-based attitude determination, using multiple GPS receivers and antennas on a single platform, as a possible navigation aid. Efforts included not only the development of data processing algorithms and software, but also the collection and analysis of GPS and INS flight data aboard a Twin Otter aircraft. Finally, the application of improved navigation system accuracy to synthetic aperture radar (SAR) target location is examined.

Verifying the velocity accuracy of a GPS receiver or an integrated GPS/INS system in a dynamic environment is a difficult proposition when many of the commonly used reference systems have velocity uncertainities of the same order of magnitude or greater than the GPS system. The results of flight tests aboard an aircraft in which multiple reference systems simultaneously collected data to evaluate the accuracy of an integrated GPS/INS system are reported. Emphasis is placed on obtaining high accuracy estimates of the velocity error of the integrated system in order to verify that velocity accuracy is maintained during both linear and circular trajectories. Three different reference systems operating in parallel during flight tests are used to independently determine the position and velocity of an aircraft in flight. They are a transponder/interrogator ranging system, a laser tracker, and GPS carrier phase processing. Results obtained from these reference systems are compared against each other and against an integrated real time differential based GPS/INS system to arrive at a set of conclusions about the accuracy of the integrated system.