59th Conference on Mass Spectrometry and Allied Topics
As the “shoreline” of the Earth’s atmosphere, the mesosphere/lower thermosphere (MLT) region is home to many interesting and important phenomena, the most visible of which are the auroras. Geomagnetic storms, in addition to causing very intense auroral activity, also deposit large amounts of energy into the earth’s ionosphere. Recent analysis of data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument aboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite suggests that 5.3μm emission from vibrationally excited NO is the main method of energy dissipation from energy deposited by geomagnetic storms. Additionally, NO+ has been shown to be the major contributor to geomagnetic storm induced 4.3μm nighttime emission.
In order to better physically understand these two large sources of geomagnetic storm energy dissipation, a sounding rocket mission, ROCKet-borne Storm Energetics of Auroral Dosing in the E-region (ROCK-STEADE) is being proposed. The ROCK-STEADE instrument suite consists of several photometers, an interferometer, an IR spectrometer, and two time-of-flight mass spectrometers (TOFMS). The TOFMS will measure the ion and neutral compositions in the atmosphere as the sounding rocket travels through the MLT.
Due to the use of microchannel plate (MCP) detectors in TOFMS, one of the major challenges to making measurements in the MLT is the high ambient pressure. Other challenges and sources of error and background include stray UV photons, scattering of gas molecules from the interior surfaces of the instrument, dissociation of molecules in the bow shock caused by the supersonic rocket flight, and reactive recombination at the surfaces of the instrument. Methods of dealing with these challenges include:
• Recent advances in MCP technology allowing MCP operation into the mtorr range
• Cooling the front surface of the TOFMS using liquid He to eliminate the bow shock (thus making possible the direct sampling of the ambient atmosphere)
• Cryogenically cooling the interior of the instrument to eliminate scattering of gas from instrument walls and therefore also reducing the contribution of reactive recombination
• Rigorous error analysis to account for the background contribution of stray UV
Everett, Addison E.; Sanderson, W.; Allen, D.; Dyer, J.; Smith, B.; Watson, M.; Mertens, C. J.; and Syrstad, E. A., "An Axial Time-of-flight Mass Spectrometer for Upper Atmospheric Measurements" (2011). 59th Conference on Mass Spectrometry and Allied Topics. Graduate Student Posters. Paper 32.