Atmospheric Effects of Precipitation through Energetic X-rays (AEPEX)
The Atmospheric Effects of Precipitation through Energetic X-rays (AEPEX) mission is the crown jewel in our set of science CubeSats. AEPEX aims to image precipitation of energetic electrons from the radiation belts - one of the main loss mechanisms for radiation belt electrons - through their X-ray signatures. As energetic electrons collide with the atmosphere, they produce X-rays, many of which are backscattered into space. By imaging these X-rays, we can determine the flux of electrons precipitating, along with their energy spectrum, spatial extent, and temporal variation. but measuring "hard" X-rays, with energies above 50 keV, is difficult, and usually requires instruments with large mass. To get around this, we are designing an instrument that uses off-the-shelf X-ray detectors designed for security X-ray systems. These are compact and light, but the design of the X-ray optics is still quite complicated.
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The AEPEX mission was recently awarded funding through the Heliophysics Technology and Instrument Development for Science (H-TIDeS) program through Phase E launch and operation. The mission implementation began in Fall 2019 and is set to launch in 2021. The development of AEPEX involves novel design of instrument electronics and software, the primary design of the instrument itself, and integration with the spacecraft bus. AEPEX is a unique opportunity that combines spacecraft and systems engineering, space science, electronics, and fundamental particle physics.
Our Work
The AXIS (Atmospheric X-ray Imaging Spectrometer) instrument is being designed, tested, and built at CU Boulder by the LAIR team. It incorporates 12 pixelated Redlen CZT M1770 detectors, which have spaceflight heritage and measure X-rays from 50 - 300 keV. The AXIS instrument is a true imager, in that it will incorporate an X-ray optical aperture to provide 2D spatial coverage of the upper atmosphere. AXIS incorporates automotive-grade microcontrollers that are radiation-hardened to prevent space environment-related interruptions during the instrument’s operation. Two potential designs are being pursued and are shown below. One uses a slit aperture and baffles in the cross-track direction to provide a push-broom field-of-view. The other uses a coded aperture, which requires the data to be deconvolved in post processing to retrieve the image.
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Above: Early prototype board of the AXIS instrument.
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Top Left: AXIS instrument slit design, showing an array of 12 detectors and electronics stack (bottom) as well as cutaways of a detector pair. Top Right: AXIS instrument coded aperture design. Bottom Left: Energy spectrum testing results for the Redlen detector. Bottom Right: Detector image test, where you can see a point source distribution around the center of the detector, which is where we placed the radiation source. |
References
- Marshall, R. A., T. Woods, C. Cully, A. Jaynes, C. Randall, D. Baker, M. McCarthy, H. E. Spence, W. Xu, G. Berland, A. Wold, E. Davis. The AEPEX Mission: Imaging Energetic Particle Precipitation in the Atmosphere through its Bremsstrahlung X-ray Signatures. (Submitted to Advances in Space Research)