In situ Mass Spectrometer Measurements of Earth&#8217;s Upper Atmosphere for Enhanced Atmospheric Modeling
Authors: Iseli Alex , Fausch Rico , Wurz Peter 
Published: July 2024

Title: In situ Mass Spectrometer Measurements of Earth&#8217;s Upper Atmosphere for Enhanced Atmospheric Modeling&#160;Session: MITM5 In-situ planetary measurements&#160;Authors: Alex M. Iseli, Rico G. Fausch, Peter Wurz&#160;The exosphere represents the outermost layer of Earth's atmosphere, extending beyond 550 km and into low Earth orbit. This region is predominantly composed of neutral atomic hydrogen, helium, and atomic oxygen, alongside less abundant heavier species. It plays a critical role in various atmospheric processes influenced by solar activity and diffusion gradients. The current understanding is primarily based on outdated mass spectrometer data from the 1980s, utilized in recent models such as NRL-MSISE 2.0 [1]. This highlights a significant gap in contemporary in-situ data, particularly concerning the chemical composition and density profiles necessary for accurate modeling and predictions.&#160;This contribution discusses the necessity for current and reliable exospheric data to refine existing atmospheric models. Such data are crucial not only for scientific accuracy but also for practical applications such as modern space traffic management and climate change studies analyzing trends in the upper atmosphere. The dynamics of the exosphere are observed on various time scales. On the very shortest timescales, atmospheric chemistry is happening. On the medium time scales, a cooling of the atmosphere in low Earth orbit is observed, indicating an increased challenge in space sustainability and space traffic management related to climate change. On the longest time scale, atmospheric escape processes can be characterized for studying the different evolutionary pathways of atmospheres of rocky planets such as Venus, Earth, and Mars over the evolution of the Solar System.&#160;To address the need for new observations, we introduce the CHESS mission. Part of the science payload is the CubeSatTOF mass spectrometer [3]. This mission aims to provide detailed measurements of atoms, radicals, and molecules within the exosphere and thermosphere [2]. CubeSatTOF provides the unique capabilities of measuring trace species like argon, where a balance between high dynamic range and measurement duration is critical for maintaining spatial resolution. A simulation depicted in Figure 1 illustrates the expected number density for a satellite in a sun-synchronized orbit at 550 km, highlighting the impacts of measurement strategies on data quality. The shaded regions correspond to the dynamic range for different measurement durations. In the presented case CubeSatTOF requires an integration time of 10.5 minutes to detect argon, about 9 times per orbit. During this time the spacecraft will fly about 4800&#160;km. This contribution further discusses how the orbit influences the measurement strategy.&#160;In conclusion, CubeSatTOF mass spectrometer on board the CHESS mission will provide new in situ composition measurements of Earth's upper atmosphere. With these data we will enhance the accuracy of atmospheric models, and support both scientific research and practical applications in understanding the dynamics of Earth's thermosphere and exosphere region.Figure 1: Simulated encountered number density for a satellite on a sun synchronized orbit at a height of 550 km. The simulated number densities relay on data from the NRLMSIS 2.0 code [1].References[1]&#160;&#160;&#160;&#160;&#160; Emmert, J. T., Drob, D. P., Picone, J. M., Siskind, D. E., Jones, M., Mlynczak, M. G., Bernath, P. F., Chu, X., Doornbos, E., Funke, B., Goncharenko, L. P., Hervig, M. E., Schwartz, M. J., Sheese, P. E., Vargas, F., Williams, B. P., and Yuan, T. 2021. NRLMSIS 2.0: A Whole&#8208;Atmosphere Empirical Model of Temperature and Neutral Species Densities. Earth and Space Science 8, 3.[2]&#160;&#160;&#160;&#160;&#160; Fausch, R. G., Moeller, G., Rothacher, M., Martinod, N., Trebaol, T., Villegas, A., Kneib, J.-P., Corthay, F., Joss, M., Tieche, F., Tulej, M., and Wurz, P. uuuu-uuuu. CHESS: Measuring the Dynamics of Composition and Density of Earth's Upper Atmosphere with CubeSats. In 2022 IEEE Aerospace Conference (AERO). IEEE, 1&#8211;13. DOI=10.1109/AERO53065.2022.9843791.[3]&#160;&#160;&#160;&#160;&#160; Fausch, R. G., Zimmermann, C., Gerber, T., Schertenleib, J., F&#246;hn, M., Aebi, A. E., and Wurz, P. uuuu-uuuu. Monitoring Space Weather with a Sensitive 1 U CubeSat Mass Spectrometer. In 2023 IEEE Aerospace Conference. IEEE, 1&#8211;11. DOI=10.1109/AERO55745.2023.10115572.&#160;&#160;