Neutral gas pressure measurements in low Earth orbit (LEO) can facilitate the monitoring of atmospheric gravity waves, which can trigger instabilities that severely disrupt radio frequency communication signals. The Space Neutral Pressure Instrument (SNeuPI) is a low-power instrument detecting neutral gas density in order to determine neutral gas pressure. SNeuPI consists of an ionization chamber and a logarithmic electrometer circuit. The Rev. 1 SNeuPI electrometer prototype does not function as designed. A Rev. 2 electrometer circuit must be designed and its performance characterized across specified operating temperature and input current ranges.
This document presents a design topology for the Rev. 2 electrometer and a derivation of the theoretical circuit transfer function. Component selection and layout are discussed. A range of predicted operating input currents is calculated using modeled neutral density data for a range of local times, altitudes, and latitudes corresponding to the conditions expected for the Lower Atmosphere/Ionosphere Coupling Experiment (LAICE) CubeSat mission. Laboratory test setups for measurements performed both under vacuum and at atmospheric pressure are documented in detail. Test procedures are presented to characterize the performance of the Rev. 2 electrometer at a range of controlled operating temperatures. The results of these tests are then extrapolated in order to predict the operation of the circuit at specified temperatures outside of the range controllable under laboratory test conditions. The logarithmic conformance, accuracy, sensitivity, power consumption, and deviations from expected response of the circuit are characterized. The results validate the electrometer for use under its expected flight conditions. / Master of Science / Neutral gas pressure measurements in low Earth orbit (LEO) can facilitate the monitoring of atmospheric gravity waves, oscillations that transfer energy from weather events or other disturbances through the atmosphere and can severely disrupt radio frequency communication signals. The Space Neutral Pressure Instrument (SNeuPI) is a low-power instrument detecting neutral gas density in order to determine neutral gas pressure. SNeuPI is part of the instrument payload for the Lower Atmosphere/Ionosphere Coupling Experiment (LAICE). LAICE is a CubeSat–a small satellite format utilizing commercial o↵-the-shelf (COTS) parts to minimize development cycle time and cost–developed with the goal of observing atmospheric gravity waves. SNeuPI utilizes an ionization chamber, which ionizes neutral gas molecules, an ion detector that ouputs an electron current proportional to ion density, and an electrometer circuit, which outputs a voltage logarithmically related to the magnitude of the detector electron current. The Rev. 1 SNeuPI electrometer prototype does not function as designed. A Rev. 2 electrometer circuit must be designed and its performance characterized across specified operating temperature and input current ranges.
This document presents a circuit design for the Rev. 2 electrometer and a mathematical derivation of the relationship between its input current and output voltage. Component selection and layout are discussed. A range of predicted operating input currents is calculated using modeled neutral density data for a range of local times, altitudes, and latitudes corresponding to the conditions expected for the LAICE mission. Laboratory test setups for measurements performed both under vacuum and at atmospheric pressure are documented in detail. Test procedures are presented to characterize the performance of the Rev. 2 electrometer at a range of controlled operating temperatures. The results of these tests are then extrapolated in order to predict the operation of the circuit at specified temperatures outside of the range controllable under laboratory test conditions. The logarithmic conformance, accuracy, sensitivity, power consumption, and deviations from expected response of the circuit are characterized. The results validate the electrometer for use under its expected flight conditions.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/74916 |
| Date | 02 February 2017 |
| Creators | Rohrer, Todd Edward Bloomquist |
| Contributors | Electrical and Computer Engineering, Earle, Gregory D., Wang, Anbo, Sable, Daniel M. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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