The active hydrogen maser atomic frequency standard is widely used in modern radio science astronautics research due to its outstanding short-term frequency stability. Short-term frequency stability is critical to radio science applications because the accuracy and resolution of spacecraft range and Doppler measurements are directly associated with the stability of the communication system’s timing reference. Due to the design of the hydrogen maser and the sensitivity of the hydrogen ground state hyperfine transition, the achievable frequency stability of the hydrogen maser is degraded by temperature fluctuations in its operating environment. This temperature sensitivity results from the influence of Doppler shifts, cavity pulling, and wall shifts associated with the temperature of the maser microwave cavity. Modern hydrogen masers are designed to compensate for temperature sensitivity through the use of a precision thermal control system.
This thesis details the development of a reduced-order multiphysics model of a precision thermal control system intended to mimic the internal regulated thermodynamics of a hydrogen maser. The developed electro-thermal model includes individual components representing the thermal plant, temperature sensors, and the associated temperature controller. The model is tuned to agree with empirical measurements from a simplified vacuum testbed, and it is empirically validated in both the time and frequency domains. The validated model is also leveraged to analyze the performance of the precision thermal control system within the Microchip MHM-2010 hydrogen maser. Analysis of this controller demonstrates that while the existing design meets performance specifications, there exists room for improvement in both the dynamic and steady-state tracking performance of this system. Overall, the proposed methodology presents a powerful approach for analyzing and improving the performance of a precision thermal control system.
|Commitee:||Baker, John, Branam, Richard, Freeborn, Todd|
|School:||The University of Alabama|
|School Location:||United States -- Alabama|
|Source:||MAI 82/1(E), Masters Abstracts International|
|Subjects:||Aerospace engineering, Electrical engineering, Thermodynamics|
|Keywords:||Frequency stability, Hydrogen maser, Modeling, Multiphysics, Precise time, Thermal control|
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