Observations of Particle Loss due to Injection-Associated Electromagnetic Ion Cyclotron Waves

We report on observations of electromagnetic ion cyclotron (EMIC) waves and their interactions with injected ring current particles and high energy radiation belt electrons. The magnetic field experiment aboard the twin Van Allen Probes spacecraft measured EMIC waves near L = 5.5–6. Particle data from the spacecraft show that the waves were associated with particle injections. The wave activity was also observed by a ground-based magnetometer near the spacecraft geomagnetic footprint over a more extensive temporal range. Phase space density profiles, calculated from directional differential electron flux data from Van Allen Probes, show that there was a significant energy-dependent relativistic electron dropout over a limited L-shell range during and after the EMIC wave activity. In addition, the NOAA spacecraft observed relativistic electron precipitation associated with the EMIC waves near the footprint of the Van Allen Probes spacecraft. The observations suggest EMIC wave-induced relativistic electron loss in the radiation belt

Two Generations of CubeSat Missions (CSSWE and CIRBE) to Take on the Challenges of Measuring Relativistic Electrons in the Earth’s Magnetosphere

The Colorado Student Space Weather Experiment (CSSWE) CubeSat, carrying the Relativistic Electron and Proton Telescope integrated little experiment (REPTile) to measure 0.5 to \u3e3.8 MeV electrons and 8-40 MeV protons, operated for over two years, 2012-2014, in low Earth orbit (LEO). There have been 25 peer-reviewed publications, including two in Nature, and five Ph.D. dissertations associated with CSSWE. Another 3U CubeSat mission: Colorado Inner Radiation Belt Electron Experiment (CIRBE), has been under development to address an unresolved science question: Where is the break point in terms of electron energy below which electrons can be transported into the inner belt from the outer belt but above which they cannot? This requires clean measurements of energetic electrons with fine energy resolution in an environment where all instruments are subject to the unforgiving penetration from highly energetic protons (tens of MeV to GeV). An advanced version of REPTile has been designed and built, REPTile-2. It has been integrated into the CIRBE bus, which has active attitude control, deployable solar panels, and a S-band radio, provided by Blue Canyon Technologies. CIRBE advances our science capabilities and has significantly improved performance vs. CSSWE and is ready to be launched into a LEO in early 2023

Understanding Enhancements in Outer Radiation Belt Electrons through Measurement and Modeling

Electrons in Earth\u27s magnetosphere typically originate with energies below ten kiloelectron volts (keV). Electrons trapped in the radiation belts can have energies that exceed 10 MeV and must be naturally accelerated within Earth’s magnetosphere. Still, the processes that govern this highly dynamic region are not fully understood. The outer radiation belt is not only a scientific puzzle but understanding it is an operational necessity, as these high energy electrons are capable of damaging spacecraft and can even result in spacecraft failure. In this work, we investigate our ability to observe these particles and understand the natural acceleration processes that generate them. We approach the problem on three fronts: (i) from an instrumentation perspective we develop a first-of-its- kind miniaturized particle telescope flown on a CubeSat platform, (ii) from an observational perspective we investigate in detail an outer belt enhancement case-study, and (iii) from a modeling perspective we develop a data assimilation model to better understand the mechanisms causing the acceleration. Finally, we construct an event-specific method to estimate electron lifetimes for diffusion models using CubeSat data, and use it to fully investigate the case study using the assimilative model, ultimately combining the three approaches. The ensuing results substantiate CubeSats as scientific observatories, demonstrate new data assimilation applications to the radiation belts, and strengthen our understanding of magnetospheric dynamics and the role of acceleration mechanisms

Characterization and Testing of an Energetic Particle Telescope for a CubeSat Platform

The Relativistic Electron and Proton Telescope integrated little experiment (REPTile) instrument has been designed, built, and tested by a team of students at the University of Colorado. It is scheduled to launch on a 3U CubeSat, the Colorado Student Space Weather Experiment (CSSWE), this August, 2012. The instrument will take measurements of energetic particles in the near-Earth environment, which are vital to understand, predict, and mitigate hazardous space weather effects | an area identifed as a critical area of research by NASA\u27s Living With a Star program. However, the task of designing a payload to return accurate and reliable data is extremely challenging due to the resource limitations imposed by a CubeSat platform. REPTile has undergone rigorous testing and calibration to verify its functionality and certify the validity of its measurements. This paper focuses on characterizing the telescope detectors and individual electronic components, as well as the integrated space craft system. The response to environmental conditions is quantified, and the variability minimized through on-board data handling as well as post-processing during mission operations. Thorough testing and calibration validates the data as a valuable contribution to outstanding questions in the study of space weather. The ability to address these questions by making differential energy measurements of energetic particles with an affordable, robust, and simple instrument design is what sets this instrument apart from others

REPTile: A Miniaturized Detector for a CubeSat Mission to Measure Relativistic Particles in Near-Earth Space

The Relativistic Electron and Proton Telescope integrated l little experiment (REPTile) is a solid-state Particle detector designed to measure solar energetic protons and relativistic electrons in Earth\u27s outer radiation belt. These particles pose a radiation threat to both spacecraft and astronauts in space, and developing a better understanding of these particles has been identified as a critical area of research by NASA\u27s Living with a Star program. REPTile has been designed specifically to meet the requirements for a CubeSat mission, namely the Colorado Student Space Weather Experiment, which is an example of how CubeSat can be employed to provide important scientific measurements for very low cost. This paper focuses on the REPTile design and functionality. The particular difficulties of energetic particle detection are introduced to provide a full understanding of the REPTile design, and then the design itself is covered in detail, including both mechanical and electronic aspects. The paper finishes with a detailed discussion of the various simulations that have been conducted to develop accurate estimates of the detector performance followed by a discussion of the instrument test plan

The Colorado Student Space Weather Experiment (CSSWE) On-Orbit Performance

The Colorado Student Space Weather Experiment is a 3-unit (10cm x 10cm x 30cm) CubeSat funded by the National Science Foundation and constructed at the University of Colorado (CU). The CSSWE science instrument, the Relativistic Electron and Proton Telescope integrated little experiment (REPTile), provides directional differential flux measurements of 0.5 to \u3e3.3 MeV electrons and 9 to 40 MeV protons. Though a collaboration of 60+ multidisciplinary graduate and undergraduate students working with CU professors and engineers at the Laboratory for Atmospheric and Space Physics (LASP), CSSWE was designed, built, tested, and delivered in 3 years. On September 13, 2012, CSSWE was inserted to a 477 x 780 km, 65° orbit as a secondary payload on an Atlas V through the NASA Educational Launch of Nanosatellites (ELaNa) program. The first successful contact with CSSWE was made within a few hours of launch. CSSWE then completed a 20 day system commissioning phase which validated the performance of the communications, power, and attitude control systems. This was immediately followed by an accelerated 24 hour REPTile commissioning period in time for a geomagnetic storm. The high quality, low noise science data return from REPTile is complementary to the NASA Van Allen Probes mission, which launched two weeks prior to CSSWE. On January 5, 2013, CSSWE completed 90 days of on-orbit science operations, achieving the baseline goal for full mission success. As the CubeSat continues to operate in its extended mission phase, the CSSWE team is working to understand and validate our design with on-orbit data. The power, data, and link budgets estimated prior to launch are found to be an accurate estimate of the on-orbit performance. Satellite interior temperatures are found to remain within their design range, even during periods of multi-week long insolation. However, not all systems have behaved as expected; an on-orbit anomaly occurred ten days after science operations began. An additional innovation is autonomous satellite operation, enabling uplink and downlink during all 8+ CSSWE passes per day and increasing monitoring capability. This was implemented in December to accommodate the lack of student operators over the holiday break and has been exceptionally beneficial. The student-led CSSWE team has grown in experience and knowledge throughout design, build, test, delivery, launch and operations of this small satellite. An overview of the CSSWE system, on-orbit performance and lessons learned will be presented

On the Cause of Two Prompt Shock-Induced Relativistic Electron Depletion Events

Dayside interplanetary (IP) shock-induced injections are known to be a source of highly relativistic electrons in Earth's outer radiation belt, and are possibly the only source of greater than 1 megaelectronvolt electrons in the inner belt. The associated electron energization process is well understood and modeled. Recently, relativistic electron depletion echoes have also been associated with IP shocks, but the processes driving the depletions are less well understood. In this study, we investigate in detail two shock induced greater than 1 megaelectronvolt electron depletion events observed by the Van Allen Probes, March 17, 2015 and May 24, 2013, and draw similarities to night-side substorm related enhancements and depletions. Both events exhibit shock induced enhancements on one of the Van Allen Probes and depletions on the other in greater than 1 megaelectronvolt channels, such observations have not previously been reported. The depletion of greater than 1 megaelectronvolt electrons during the March 17, 2015 event is associated with enhancements in 10 second - 100 second kiloelectronvolt electrons on the same spacecraft. The depletion is consistent with the effects of a lack of seed electrons at larger radial distances combined with inward motion due to asymmetric compression by the shock impact. The immediate enhancements and depletions of 75 kiloelectronvolt - 2.6 greater than 1 megaelectronvolt electrons are explained by the local phase space density radial profile. Observations of electron flux dynamics during the May 24, 2013 event can also be explained by a lack of a seed population at larger radial distances, supported by butterfly distributions observed during the event. The electron's inward radial motion can be attributed to the inward propagating impulse also associated with the greater than 1 megaelectronvolt electron enhancements observed on the complementary probe, rather than global asymmetric compression. This causal mechanism has parallels to substorm related depletions. Alternatively, evidence is provided to attribute the sudden depletions to losses due to a sudden but brief inward motion of the magnetopause