Quantifying Radiation Belt Electron Precipitation Through Bremsstrahlung X-Ray Spectral Imaging

Energetic particle precipitation (EPP) is a phenomenon that couples planetary magnetospheres and atmospheres through high-energy charged particle transport into the atmosphere. Due to the large spatial scales over which this process occurs, it is difficult to observe directly and therefore the spatial and temporal scales of EPP are poorly constrained. Open questions of magnetosphere-atmosphere coupling relate to the driving mechanisms of EPP: how does EPP vary seasonally, temporally, and with magnetospheric conditions; and what are the spatial scales over which this process occurs? The study of EPP will improve current understanding of the behavior of the radiation belts and the atmosphere&rsquo;s response to EPP, and will lend a deeper understanding of the dynamic interactions of planetary magnetospheres and atmospheres. This work specifically focuses on electron precipitation involving the highest energy particles in the magnetosphere: the radiation belts. Obtaining global measurements of EPP is difficult due to the spatial scale and height above Earth&rsquo;s surface at which this process occurs; the drivers interact with charged particles in the heart of the radiation belts at 4 &ndash; 7 Earth radii, and the effects at Earth cover the entire globe, from mid-latitudes to the poles, and at altitudes too high for in-situ balloon measurements, and too low for radar remote sensing. Measuring EPP&rsquo;s effects through remote sensing in the ionosphere is difficult due to high atmospheric density driving fast recombination such that the atmospheric effects of EPP dissipate quickly. Perturbations in atmospheric chemistry can be measured as a proxy to precipitation inputs, but the complicated reactions and transport dynamics makes the inversion to precipitation characteristics uncertain. On the other hand, direct in-situ measurements of charged particles from spacecraft cannot easily obtain the spatial and temporal coverage necessary to quantify EPP due to the limited nature of a single (or a few) spacecraft in orbit. Additionally, charged particle instruments are often angular resolution-limited and are unable to resolve the loss cone at various points in the orbit, which is necessary to provide a global image of precipitation. EPP can instead be inferred through remote measurements of X- and gamma-ray photons, which are a byproduct of relativistic electron precipitation. Once an electron has entered the atmosphere it interacts with neutrals and can spontaneously generate a high energy photon via the bremsstrahlung (&ldquo;braking radiation&rdquo;) interaction. The resulting photon energy is correlated with the precipitating electron energy, such that statistical relationships can be formed between the two quantities. By measuring X- and gamma-ray photons that escape the atmosphere with a spacecraft-based imaging spectrometer, a global perspective of EPP can be obtained: the spatial scales of EPP can be directly measured by photon imaging of the upper atmosphere from low-Earth orbit, and by measuring in-situ electron spectra along with photon measurements, the photon flux and spectra can be inverted to estimate precipitating electron flux and spectra. This thesis is split into three parts. First, the design, development, and testing of the Atmospheric X-ray Imaging Spectrometer (AXIS) instrument onboard the upcoming Atmospheric Effects of Precipitation through Energetic X-rays (AEPEX) CubeSat mission is described. The detectors, shielding design, and signal-to-noise ratio calculations are described in detail. Second, the novel X-ray optics and algorithmic reconstruction technique of the AXIS instrument are developed and described. The wide field-of-view imager implements a coded aperture mask in order to obtain spatial resolution of X-ray photons. Finally, EPP simulations are performed with a kinetic model of precipitation built using GEANT4 to determine the X-ray signal and atmospheric effects of EPP at Earth and Jupiter in support of the AEPEX mission and other studies of planetary magnetospheres. The development of the AXIS instrument and tools developed herein are extended for a NASAfunded concept study of a spacecraft mission to Jupiter, which aims to address open questions of Jupiter&rsquo;s radiation belts.</p

The AEPEX CubeSat Mission: Quantifying Energetic Particle Precipitation through Bremsstrahlung X-Ray Imaging

Fundamental gaps exist in the understanding and observation of energetic particle precipitation (EPP),a solar-terrestrial coupling mechanism that is vital for climatelogical modeling of the atmosphere and magnetosphere. The Atmospheric Effects of Precipitation through Energetic X-rays (AEPEX) mission is a 6U CubeSat that will measure energetic electron spectra and X-ray images in order to quantify the spatial scales and amount of energy input into the atmosphere, and therefore lost from the magnetosphere, via EPP. AEPEX includes two instruments; AEPEX’s FIRE (Focused Investigations of Relativistic Electron) instrument (AFIRE), a TRL 9 electron detector previously flown on the FIREBIRD mission; and the Atmospheric X-ray Imaging Spectrometer (AXIS), an instrument being developed at CU Boulder that will take novel images and spectra of 50–300 keV X-ray photons. This work describes the AEPEX mission overview, the detailed design and operation of AXIS, and initial test and calibration results

CubeSat Active Thermal Control via Microvascular Carbon Fiber Channel Radiator

Small spacecraft rarely have space for any thermal control subsystems and often must perform operations in “burst” mode as a result. The few spacecraft who do have control rely on low-complexity thermal control systems which conduct heat to the bus structure and then radiate the heat away. These simplistic techniques are sufficient for low power missions in Low Earth Orbit (LEO) but are not capable of dumping the heat produced in new mission profiles that are in development. This is due to small spacecraft incorporating increasingly advanced subsystems which have difficult thermal control requirements such as propulsion systems or high-power antennas. The University of Illinois at Urbana-Champaign, in partnership with NASA Ames Research Center, is developing a thermal control system for small spacecraft. This control system uses a deployable radiator panel made from carbon fiber with micro-vascular circulatory system for coolant. This paper is a follow-up on the previous year’s SmallSat conference. A bench prototype of the thermal control subsystem was designed and built. The prototype underwent a range of thermal and vibration tests at NASA Ames. Test results and lessons learned are presented. Moving forward, test conclusions will require some design parameters to be changed and the subsystem will reach TRL 6 by the end of the two-year program

The AEPEX Mission: Imaging Energetic Particle Precipitation Into Earth’s Upper Atmosphere

Radiation belt electron fluxes can be enhanced during geomagnetic storms by two orders of magnitude; subsequently, these fluxes decay back to nominal levels in a few days. Precipitation into the upper atmosphere is a primary loss mechanism for these electrons, particularly during the decay phase. Upon impacting the upper atmosphere, these electrons create new ionization, leading to a chemical response that increases NOx and HOx and destroys ozone. Quantifying both radiation belt loss and the impact on the atmosphere requires an accurate estimate of the flux, energy spectrum, and spatial and temporal scales of precipitation. The NASA-funded Atmospheric Effects of Precipitation through Energetic X-rays (AEPEX) Cube-Sat mission is designed to quantify these parameters of radiation belt precipitation by measuring the bremsstrahlung X-rays created during the precipitation process, using a new instrument called the Atmospheric X-ray Imaging Spectrometer (AXIS). Hard X-rays (50-300 keV) emitted by Earth’s atmosphere have previously been measured from high-altitude balloons and satellites, but have never been imaged from space. The AXIS instrument will image the X-ray fluxes produced by the atmosphere, providing measurements of spatial scales, along with the X-ray flux and spectrum, using off-the-shelf pixelated detector modules and coded aperture optics. A solid-state energetic particle detector, with heritage from the FIREBIRD Cube Sat mission, will measure the precipitating electron energy spectrum, which is used to constrain the inversion from X-ray fluxes to electron fluxes. The AEPEX spacecraft is a 6U CubeSat, currently being built by the University of Colorado Boulder. It includes a custom-designed structure and a custom spacecraft bus consisting of an electrical power system, command and data handling, flight software, and instrument interface electronics designed by the Laboratory for Atmospheric and Space Physics (LASP) at CU Boulder. The system also includes custom-designed doubly-deployable solar panels. The mission will be launched into ahigh-inclination orbit to ensure coverage of high latitudes; launch is scheduled for early 2024

The AEPEX Mission: Imaging Energetic Particle Precipitation in the Atmosphere through its Bremsstrahlung X-ray Signatures

The Atmospheric Effects of Precipitation through Energetic X-rays (AEPEX) mission is a 6U CubeSat that will monitor energetic electron precipitation from the radiation belts into the upper atmosphere. The primary instrument will image energetic (50&ndash;300 keV) X-rays produced in the atmosphere by bremsstrahlung, providing a near-direct signature of electron precipitation. An energetic electron detector will measure the precipitating electron spectrum, while the X-ray observations will be used to determine the absolute flux. X-ray images will be produced with 10-s time resolution and 50&ndash;100 km spatial resolution. The 6U spacecraft uses flight heritage spacecraft bus subsystems, including the attitude determination and control, electrical power, and command &amp; data handling systems. AEPEX is designed to be operated from low-Earth orbit at ~500 km altitude with a high inclination in order to cover the outer radiation belt. AEPEX will be the first spacecraft mission to measure X-rays in the 50&ndash;300 keV energy range emitted by Earth&rsquo;s atmosphere in response to radiation belt precipitation, and the first to image that precipitation from above.</p