Atmosphere Effects of Precipitation through Energetic X-rays (AEPEX) CubeSat Mission (AEPEX)

Precipitation into the upper atmosphere is one of the primary sources of loss from the radiation belts. Numerous spacecraft have attempted to measure this Energetic Electron Precipitation (EEP) from Low-Earth Orbit (LEO); however, current instrumentation is not able to resolve the loss cone angle nor measure the pitch angle distribution, and thus the energy deposition in the atmosphere has a large uncertainty. Furthermore, particle detectors on spacecraft provide in-situ detection only, and single-spacecraft missions cannot provide instantaneous spatial information about the precipitation patches. We propose a comprehensive measurement of EEP, by measuring precipitating electron distributions and imaging X-ray photons produced by bremsstrahlung in the atmosphere. This concept is similar to the recent and successful BARREL balloon mission, except we will detect photons from LEO rather than balloon altitudes. Measurements of X-rays at LEO will provide an estimate of energy deposition in the upper atmosphere, will provide spatial information about precipitation regions, will provide global coverage, and will enable longer-term measurements than dedicated balloon campaigns. The proposed AEPEX mission will i) quantify the energy deposition from the radiation belts due to precipitation, during both quiet and active conditions, and ii) provide spatial measurements of precipitation regions. These measurements will improve our understanding of radiation belt precipitation, radiation belt lifetimes, and the effects of radiation belt precipitation on the upper atmosphere, directly addressing the Heliophysics Decadal Survey Key Science Goal 2: "Determine the dynamics and coupling of Earth's magnetosphere, ionosphere, and atmosphere and their response to solar and terrestrial inputs." Methodology: The AEPEX instrument will use an array of 12 RedLen M1770 CZT detectors, which are commercial off-the-shelf X-ray imagers. Each detector is 4 X 4 cm and includes an array of 16 X 16 pixels. These pixels will be binned to provide more limited spatial resolution for the benefit of SNR and data volume. These detectors will measure 50-300 keV photons; shielding will be used to block electrons and protons. As an estimate of moderate precipitating fluxes, modeling calculations show that for a precipitating flux of 3000 electrons/cm^2/sec at 1 MeV, we can expect to measure ~150 photons/sec in this instrument. X-ray optics will provide better than 100 km spatial resolution across track and 100 km spatial resolution along track with 10-second time resolution. Additionally, a 0.5U solid-state particle instrument will be included in the payload to measure the precipitating electron spectrum, and will be used to constrain the inversion from X-ray fluxes and spectra to energy deposition in the atmosphere. Spacecraft: The AEPEX CubeSat will adhere to the Tyvak 6U dispenser requirements: mass no greater than 14 kg and volume no greater than 11.6 X 23.9 X 36.6 cm. The C&DH, ADCS, power, communication systems, solar panels, and structure will be provided by the Blue Canyon Technologies (BCT) XB1 bus system. This system reduces the development efforts of the AEPEX team and reduces risk by using established and proven technologies with flight heritage. Mission: We propose a minimum six-month mission to be launched into a circular LEO with altitude near 500 km, and inclination above 70 degrees to enable passes through the radiation belts. The X-ray instrument will look down at the atmosphere by pointing towards the nadir, while the particle instrument points towards the zenith. Data will be downlinked to CU Boulder's S-band ground station at LASP. Mission operations will be controlled from LASP, which has recent experience operating the CSSWE and MinXSS CubeSats.

Support NASA's Heliophysics strategic science objectives to understand the Sun and its interactions with Earth and the solar system, including space weather. This will be achieved by developing/demonstrating instrumentation technology necessary to address the following science goals: Explore the physical processes in the space environment from the Sun to the Earth and throughout the solar system; Advance our understanding of the connections that link the Sun, the Earth, planetary space environments, and the outer reaches of our solar system; Develop the knowledge and capability to detect and predict extreme conditions in space to protect life and society and to safeguard human and robotic explorers beyond Earth.

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