First Results From REPTile-2 Measurements Onboard CIRBE

CIRBE (Colorado Inner Radiation Belt Experiment), a 3U CubeSat, was launched on 15 April 2023 into a sun synchronous orbit (97.4 degrees inclination and 509 km altitude). The sole science payload onboard is REPTile-2 (Relativistic Electron and Proton Telescope integrated little experiment-2), an advanced version of REPTile which operated in space between 2012 and 2014. REPTile-2 has 60 channels for electrons (0.25-6 MeV) and 60 channels for protons (6.5-100 MeV). It has been working well, capturing detailed dynamics of the radiation belt electrons, including several orders of magnitude enhancements of the outer belt electrons after an intense magnetic storm, multiple "wisps"- an electron precipitation phenomenon associated with human-made very low frequency (VLF) waves in the inner belt, and "drift echoes" of 0.25-1.4 MeV electrons across the entire inner belt and part of the outer belt. These new observations provide opportunities to test the understanding of the physical mechanisms responsible for these features. Energetic electrons of 100s of keV (1,000 electric volt) to MeV (million electric volt) existing in the near-Earth environment have detrimental effects on spacecraft subsystems and the bodies of astronauts during their extravehicular activity (e.g., Baker, 2002, ). Their source, loss, and variations have been a long-standing research topic. Recent advancements in miniaturization of spacecraft and instrumentation make CubeSats (in the shape of a cube, easier for launch and deployment) a viable means to conduct space-borne research. Colorado Inner Radiation Belt Experiment (CIRBE) is a 3U (10 cm x 10 cm x 34 cm) CubeSat with only one science instrument onboard: Relativistic Electron and Proton Telescope integrated little experiment -2 (REPTile-2), which is an advanced version of the previously flown REPTile. REPTile-2, thanks to its high energy and time resolution, revealed detailed dynamic features of the radiation belt electrons, which will further our understanding of and ability to predict the dynamics of these energetic electrons. Detailed variations of relativistic electrons over a wide energy range, 0.25-6 MeV, in the Earth's magnetosphere were captured Multiple "wisps," an electron precipitation phenomenon associated with human-made VLF waves in the inner belt, were measured "Drift echoes" or "zebra stripes" of 0.25-1.4 MeV electrons across the entire inner belt and part of the outer belt, have been observed