Testing of Prototype Mass Spectrometer for Earth Atmospheric Studies, 15-R8475
Inclusive Dates: 06/18/14 – 10/18/14
Background — The NASA sounding rocket program provides the ideal opportunity to prove the flight-readiness and scientific capabilities of instruments that currently lack the flight heritage required for major NASA missions. The goal of this project was to propose a simplified configuration of an SwRI-built mass spectrometer for in situ measurements in support of a NASA sounding rocket project. The NASA project requires measurements of the total neutral density and the composition of neutrals in the region above 250 km. Neutral composition is poorly understood in this region of the atmosphere due to a serious gap in measurements. At the present time, atmospheric models are the only method for estimating composition at these altitudes, and these models are subject to large uncertainties because no composition measurements have been made since the 1980s. Currently, the predictions for atmospheric density and temperature can only be validated with satellite drag data, which determine the total mass density (in kg/m3) of the exosphere based on the drag induced by atmospheric particles on a satellite. They do not provide the composition of the atmosphere as a function of altitude. Recent estimates of the composition of the winter polar exosphere have found differences between densities estimated by satellite drag measurements and atmospheric models that ranged between 25 and 70 percent.
Approach — The primary objective of this project was to characterize the operation of a linear time-of-flight mass spectrometer (TOF-MS) for the simultaneous detection of hydrogen, oxygen, nitrogen and carbon dioxide at the range of pressure regimes expected during a sounding rocket ascent and descent stage. This effort was used to establish the required data integration times and leak rates into the analyzer for the measurement of the compounds of interest above 250 km. Completion of this project required four primary tasks:
- Preparing the Multi-Bounce Time of Flight (MBTOF) to be calibrated in linear mode
- Calibrating of MBTOF in linear mode for relevant gas mixtures
- Testing of the pulser under vacuum
- Testing of the power supply under vacuum
Accomplishments — Each of the proposed tasks was completed successfully. We were able to demonstrate that the mass resolution of the linear TOF-MS was clearly sufficient to resolve H, H2, and He, as well as N2, O2 and CO2. The sensitivities were determined for each of the constituents relevant to the science measurements proposed and were found to be sufficient for the LCAS proposal. Both the pulser and power supply operated successfully under vacuum.