A multichannel electrometer voltmeter that employs a mechanical resonator maintained in sustained amplitude-stabilized oscillation has been developed for the space-based measurement of an Internal Electrostatic Discharge Monitor (IESDM) sensor. The IESDM is new sensor technology targeted for integration into a Space Environmental Monitor (SEM) subsystem used for the characterization and monitoring of deep dielectric charging on spacecraft. Creating a stable oscillator from the mechanical resonator was achieved by employing magnetic induction for sensing the resonator’s velocity, and forcing a current through a coil embedded in the resonator to produce a Lorentz actuation force that overcomes the resonator’s dissipative losses. Control electronics employing an AGC loop provide conditions for stabilized, constant amplitude harmonic oscillation.
The prototype resonator was composed of insulating FR4 printed-wire-board (PWB) material containing a flat, embedded, rectangular coil connected through flexure springs to a base PWB, and immersed in a magnetic field having two regions of opposite field direction generated by four neodymium block magnets. In addition to maintaining the mechanical movement needed for the electrometer’s capacitor-probe transducer, this oscillator provides a reference signal for synchronous detection of the capacitor probe’s output signal current so drift of oscillation frequency due to environmental effects is inconsequential.
This work was done by Brent R. Blaes and Rembrandt T. Schaefer of Caltech for NASA’s Jet Propulsion Laboratory. NPO-47336
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Amplitude-Stabilized Oscillator for a Capacitance- Probe Electrometer
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Overview
The document outlines a project led by the California Institute of Technology and NASA's Jet Propulsion Laboratory, focusing on the development of a Space Environment Monitoring (SEM) subsystem for spacecraft. The primary objective is to create an integrated suite of environmental sensors capable of continuously monitoring local space environments, particularly for deep space missions that face extreme radiation and temperature conditions. This real-time data is crucial for diagnosing operational anomalies and optimizing spacecraft design for future missions.
The project was divided into two fiscal years (FY09 and FY10) with specific objectives and results. In FY09, the focus was on developing requirements and integration architecture for the SEM subsystem, utilizing commercial off-the-shelf hardware. The goal was to design, build, and prototype a system that could function effectively in laboratory environments.
In FY10, the project advanced to the development and demonstration of a prototype multichannel high-voltage electrometer, specifically designed for measuring an Internal Electrostatic Discharge Monitor (IESDM). This new sensor technology aims to monitor deep dielectric charging on spacecraft, which is critical for ensuring the safety and functionality of electronic systems in space.
Key achievements from FY10 included the design and construction of a prototype voltage-sensing capacitance-probe resonator for the IESDM electrometer. This resonator was built on a printed-wire board with an embedded coil and featured floating electrodes suspended in a fixed magnetic field using flexure springs. The prototype resonator underwent testing to validate its electromechanical model, and oscillator electronics were designed and tested in conjunction with the resonator.
Additionally, the project involved the creation of signal-chain electronics for the IESDM-measuring electrometer, which underwent open-loop tests with the capacitance-probe resonator. During these tests, a measurement offset was observed due to parasitic capacitance couplings between the resonator's floating electrode and surrounding conductors at different potentials.
Overall, the document highlights significant advancements in sensor technology for space applications, emphasizing the importance of real-time environmental monitoring to enhance the reliability and performance of spacecraft in challenging deep space environments. The work represents a step forward in ensuring that future missions can effectively address the complexities of operating in space.
