Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, June 2003. / Thesis advisor(s): Hal A. Titus. Includes bibliographical references (p. 89-90). Also available online.

The motivation for this research was an improvement of the quality of the Earth’s gravity solutions from the GRACE mission data through an instrument-level study. The objective was a better understanding of the characteristics and sources of the highfrequency noise in the range of (0.02 ~ 0.1 Hz) in the dual one-way ranging (DOWR) and its effect on the gravity solution. For this purpose, the mathematical model of the DOWR observation was derived and the Allan variance was computed to establish an upper bound on the level of frequency instability of the ultra-stable oscillators (USO) to determine their contribution to the high-frequency noise. Because they are dominated by the high-frequency noise, the postfit residuals of the time derivative of the DOWR ranges were also examined to evaluate the contributions of various other factors such as system noise from the microwave signal receiver, external influences, and internal influences. The results indicate that the system noise is the dominant source of the excessive highfrequency noise. As one method of mitigation, a tighter bandwidth filter was applied to the DOWR processing, resulting in modest improvements in gravity solutions. / text

The twin Gravity Recovery and Climate Experiment (GRACE) satellites were successfully launched on March 17, 2002. The mission goal is to make significant improvement in current measurements of the Earth’s gravity field. The satellites are linked by a K-band ranging system, which measures the range change due to the gravitational and non-gravitational accelerations. The non-gravitational accelerations can be obtained by transforming the accelerometer measurements into the inertial frame of reference based on the star camera observations, and will be used to separate gravitational effects in the range changes. However, the accelerometer’s proof mass offset from the center of mass of the spacecraft must be minimized and the misalignment between star camera frame and accelerometer frame must be known accurately in order to reduce the accelerometer data error. In addition, the phase center of the K-band horn must be known to make antenna offset corrections to the range and range change data. The objective of the center of mass calibration is to determine the proof mass offset, and then, to use the center of mass trim assembly mechanism to eliminate this offset. The main purpose of the K-band ranging system calibration is to determine the phase center of the K-band antenna, which will be used to adjust the satellite attitude orientations and make the antenna offset corrections to the K-band ranging system phase measurements. Furthermore, this calibration allows the misalignment between star camera frame and accelerometer frame to be determined. The calibration maneuvers have been designed for the real mission. Estimation algorithms have been developed and complete simulations have been performed. Finally, the real calibration data have been processed. Analysis shows that the proof mass offset has been determined better than the requirement value of 0.1 mm and trimmed well below this value. The boresight error of the K-band horn’s phase center has been determined better than 0.3 mrad and the resultant antenna offset correction error of range and range rate will be much less than the system resolution (10[mu]m ,1[mu]m/ s) and the frame misalignment parameters have been determined better than (0.04o ,1[delta] ) . Overall, the goal of calibrations has been successfully achieved. / text

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The existing air navigation services have many shortcomings and a reform was necessary. The new systems (CNS/ATM systems) will be largely dependent on Global Navigation Satellite Systems (GNSS) which can bring significant benefits to air navigation in terms of safety, efficiency, capacity, and economy. However, GNSS have weaknesses which can be reduced but will never be fully eliminated. Depending solely on a system that can be disrupted is not acceptable for safety of life applications, such as aviation. The implementation of GNSS also raises unique legal issues and ICAO has been working on the establishment of a legal framework for GNSS since 1992. Nevertheless, disagreement between states on the need for an international convention remains significant. Legal discussions should not slow down the implementation of GNSS which, when used in conjunction with terrestrial navigation aids, have the potential to revolutionize air navigation.

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