This paper describes the Experiments in X-Ray Characterization and Timing (EXACT) mission, an on-orbit demonstration of pulsar-based positioning, navigation, and timing. EXACT will validate the Hard and Fast X-ray spectrometer (HaFX), a sensor designed to generate phase and Doppler measurements from X-ray pulsar observations. Deployed on the International Space Station as part of the Space Test Program's H-12 mission, HaFX will observe and tag the arrival time of photons from the Crab pulsar (PSR B0531+21). The time tagging will be synchronized with the GPS pulse-per-second. The performance of HaFX will be quantified in post-process by comparing phase (range) and Doppler (velocity) estimates derived from it with estimates from GNSS. The paper outlines the mission design, payload design, and expected results from the on-orbit experiment.

No instrument is currently capable of consistently measuring all three components of the DC and low frequency electric field (E-field) throughout the heliosphere with sufficient accuracy to determine the smallest, and most geophysically relevant component: the E-field component parallel to the background magnetic field. E-field measurements in the heliosphere are usually made on spinning spacecraft equipped with two disparate types of double probe antennas: (1) long wire booms in the spin plane, and (2) ~10 times shorter rigid booms along the spin axis. On such systems, the potential difference (signal + noise) is divided by the boom length to produce a resultant E-field component. Because the spacecraft-associated errors are larger nearer the spacecraft, the spin plane components of the E-field are well measured while the spin axis component are poorly measured. As a result, uncertainty in the parallel E-field is usually greater than its measured value. The new design proposed by the Grotifer team is a way to overcome this difficulty. It consists of mounting detectors on two rotating plates, oriented at 90 degrees with respect to each other, on a non-rotating central body. Each rotating plate has two component measurements of the E-field such that the Twin Orthogonal Rotating Platforms provide four instantaneous measurements of the E-field, and the three E-field components are well-measured by the rotating detectors. Grotifer marks a profound change in E-field instrument design that represents the best path forward to close the observational gap that currently hampers resolution of significant science questions at the forefront of space plasma physics research. Here, we present recent advances in the development of the Grotifer design and we demonstrate the feasibility of its implementation in a 27-U CubeSat designed for a Low Earth Orbit mission.

The Integrating Miniature Piggyback for Impulsive Solar Hard X-rays (IMPISH) is a solar X-ray spectrometer that features large-area scintillators, fast readout electronics, and good energy resolution in the hard X-ray band. IMPISH is a low-cost spectrometer designed to measure subsecond variation in hard X-ray time profiles from solar flares, with the goal of constraining particle acceleration timescales. To meet these requirements, we carried out a systematic optimization of the scintillation design, focusing on maximizing photon collection, reducing noise level, and improving energy resolution. We tested two high-yield scintillating crystals (LYSO, lutetium yttrium oxyorthosilicate, and GAGG, gadolinium aluminum gallium garnet), two reflector types (specular and lambertian), two kinds of surface finishes (all sides polished and readout face only polished), different optical coupling materials and thicknesses, multiple geometries, and readout face angles. Our studies show that light collection improves with increasing the crystal's effective area, breaking its symmetry, and reducing the photon's travel length. These minimize photon loss due to self-absorption and total internal reflection. Through combined simulation and laboratory tests, we achieved an optimal energy resolution with the LYSO trapezoid-shaped crystal coupled to a Broadcom NUV-MT SiPM with an approximately 0.25 mm thin Sylgard 184 optical pad.

Microbursts are impulsive injections of energetic (few keV to >MeV) electrons into the atmosphere, primarily caused by nonlinear scattering driven by whistler mode chorus waves. While the relative importance of microburst precipitation as a loss process has not been fully quantified, many studies have shown microbursts may play a significant role in the loss of outer radiation belt electrons. We present a multi-platform statistical analysis of chorus and energetic electron precipitation in an attempt to constrain the azimuthal spatial extent (triangle $\mathit{{\increment}}$MLT) of the microburst precipitation region and determine how this extent varies with geomagnetic activity. Statistical upper bounds of this azimuthal extent are determined with observations of general energetic electron precipitation that can include direct microburst detections, while statistical lower bounds determination requires direct microburst detections. The resulting distributions of both upper and lower bounds azimuthal extent suggest that microbursts may frequently constitute an important source of electron loss from the outer radiation belt. We find that 36% of upper bound events in the dawn sector span more than 5 hr in MLT. This azimuthal extent increases with geomagnetic activity, particularly in the dawn and noon MLT sectors.

Precipitation into the atmosphere is one of the main processes by which high energy electrons trapped in Earth's inner magnetosphere are lost from the system. Precipitating electrons can affect the chemical composition of the atmosphere and provide insight into the complex dynamics of the Van Allen radiation belts. This study compares energetic electron precipitation measurements at low-Earth-orbit by the Focused Investigations of Relativistic Electron Burst Intensity, Range, and Dynamics (FIREBIRD-II) CubeSats with NOAA Polar-orbiting Operational Environmental Satellite (POES) and ESA Meteorological Operational satellite (MetOp) satellites, which are equipped with the Medium-Energy Proton Electron Detector (MEPED). The analysis considers 51 high quality conjunction events at >300 keV during times of low to moderate geomagnetic activity. The spacecraft capture similar electron flux variability, and FIREBIRD-II observations fall between POES/MetOp 0 degrees and 90 degrees telescopes, likely a result of FIREBIRD-II sampling both precipitating and mirrored electrons due to uncertainties in pointing direction. Results demonstrate the value of high-resolution differential energy observations of electron precipitation by low-cost CubeSats such as FIREBIRD-II, especially during periods of low flux.

Microbursts are short duration intensifications in precipitating electron flux that are believed to be a significant contributor to electron losses in the magnetosphere. Microbursts have been observed in the form of bouncing electron packets, which offer a unique opportunity to study the properties of microbursts and their importance as a loss process. We present a collection of bouncing microbursts observed by the HILT instrument on SAMPEX from 1994-2004.We analyze the locations of the bouncing microbursts in L and MLT and find they align well with the properties of relativistic microbursts as a whole. We find that that the majority of bouncing microbursts observed by SAMPEX have scale sizes of 30km at the point of observation, or about 1500km when mapped to the equator.The time separation between the peaks of these bouncing microbursts is usually either half a bounce period or a whole bounce period.

Electromagnetic ion cyclotron (EMIC) waves are believed to play an important role in the dynamics of the inner magnetosphere, including the ring current, the radiation belts and potentially, the cold plasma. In this work, we investigate their occurrence in the magnetosphere and the geomagnetic and solar wind conditions which lead to their excitation. We use an automated detection algorithm of EMIC waves observed by Van Allen Probes over the entire mission duration between 2012 and 2019. Consistent with earlier studies, we find that the H+ band occurrence maximizes in the dayside magnetosphere during enhancements of solar wind dynamic pressure. Both the H+ and He+ band are also generated along the duskside magnetosphere during disturbed geomagnetic conditions. In addition, to H+ and He+ bands commonly surveyed, we investigate the occurrence of H+ waves above and below 0.5 H+ gyrofrequency, as well as wave occurrence in the N+ and O++ bands. Most H+ waves are observed in the band below 0.5fH+. We find several events in the N+ band, indicative of their very low occurrence. The O++ band is observed during disturbed geomagnetic conditions and high solar wind dynamic pressure at low L-shells. Its radial localization coincides with the O++ torus. This study provides a comprehensive picture of EMIC wave distribution and insight into ion composition in the inner magnetosphere during variable geomagnetic conditions.

The Virtual Super-resolution Optics with Reconfigurable Swarms (VISORS) is a National Science Foundation (NSF) space physics mission which will detect and study fundamental energy-release regions in the solar corona. The VISORS mission will image extreme ultraviolet (EUV) features on the Sun at a resolution of at least 0.2 arcseconds from Low Earth Orbit (LEO). To accomplish this objective, VISORS will use a pair of formation flying 6U CubeSats: one of which carries the observatory optics while the other contains the detector instrument. VISORS will serve as a proof of concept for this distributed instrument approach by obtaining at least one 10-second exposure image during its six-month mission lifetime. Meeting the strict relative orbit requirements during science observations will demonstrate several technologies key to precise formation flying including intersatellite link, relative navigation, and autonomous maneuver planning. To satisfy these stringent mission requirements, a concept of operations has been established that requires maneuvering between a standby orbit where housekeeping tasks are performed and an actively maintained science orbit where observations are conducted. Formation acquisition, re-acquisition, fault recovery, and escape operations are also planned. This paper provides a description of the VISORS formation flying concept of operations: explaining the function and rationale of each operation mode, how these modes are designed, and how they collectively meet the mission requirements. Specific challenges and mission trades related to performing precision formation flight with CubeSats are discussed. A Failure Mode Effects and Criticality Analysis (FMECA) is conducted to assess the risk of collision under the most probable fault scenarios, which is used to inform the development of operational mitigation strategies and on-board fault tolerant collision avoidance (COLA) logic.

Abstract We present a method to determine energy‐dependent geometric factors for charged particle instruments in electron energy range of 125–2,200 keV aboard the geostationary satellite GEO‐KOMPSAT‐2A (GK2A), stationed at 128.2°E longitude. As deduced from the GEANT4 Monte Carlo simulation, the response function of the instrument in a matrix form was employed to undertake forward‐fitting of the differential energy spectra against various functions such as the double Maxwellian (DM), relativistic kappa (KP), and power‐law (PL). Thereby, we determined the energy‐dependent geometric factors for each energy channel and instrument. The forward‐fitting method was performed for a selected period of geomagnetically quiet days from May to November 2019, by applying stringent conditions to geomagnetic indices and the residual from the fit. It was found that the KP and DM functions provided better fits overall, whereas the PL function yielded considerably worse fits to the measurements. For the KP and DM functions, the validity of the geometric factors was examined against the distributions of the measured count rates and inferred model fluxes. The estimated model parameters, such as the spectral index from the KP function or the temperature from the DM functions, were also analyzed. The present study shows that the instruments provided quantitative observations of the outer radiation belt at a vantage point of 128.2°E longitude and allowed for a simple and reliable means to obtain electron fluxes based on combinations of results from numerical simulation, ground calibration, and space measurements.

Abstract Interactions between whistler mode chorus waves and electrons are a dominant mechanism for particle acceleration and loss in the outer radiation belt. One form of this loss is electron microburst precipitation: a sub‐second intense burst of electrons. Despite previous investigations, details regarding the microburst‐chorus scattering mechanism—such as dominant resonance harmonic—are largely unconstrained. One way to observationally probe this is via the time‐of‐flight energy dispersion. If a single cyclotron resonance is dominant, then higher energy electrons will resonate at higher magnetic latitudes: sometimes resulting in an inverse time‐of‐flight dispersion with lower‐energy electrons leading. Here we present a clear example of this phenomena, observed by a FIREBIRD‐II CubeSat on 27 August 2015, that shows good agreement with the Miyoshi‐Saito time‐of‐flight model. When constrained by this observation, the Miyoshi‐Saito model predicts that a relatively narrowband chorus wave with a ∼0.2 of the equatorial electron gyrofrequency scattered the microburst.

We analyze the drivers, distribution, and properties of the relativistic electron precipitation (REP) detected near midnight by the Polar Orbiting Environmental Satellites (POES) and Meteorological Operational (MetOp) satellites, critical for understanding radiation belt losses and nightside atmospheric energy input. REP is either driven by wave‐particle interactions (isolated precipitation within the outer radiation belt), or current sheet scattering (CSS; precipitation with energy dispersion), or a combination of the two. We evaluate the L‐MLT distribution for the identified REP events in which only one process evidently drove the precipitation (∼10% of the REP near midnight). We show that the two mechanisms coexist and drive precipitation in a broad L‐shell range (4–7). However, wave‐driven REP was also observed at L < 4, whereas CSS‐driven REP was also detected at L > 7. Moreover, we estimate the magnetotail stretching during each REP event using the magnetic field observations from the Geostationary Operational Environmental Satellite (GOES). Both wave‐particle interactions and CSS drive REP in association with a stretched magnetotail, although CSS‐driven REP potentially shows more pronounced stretching. Wave‐driven REP events are localized in L shell and often occur on spatial scales of <0.3 L. Using either proton precipitation (observed by POES/MetOp during wave‐driven REP) as a proxy for electromagnetic ion cyclotron (EMIC) wave activity or wave observations (from GOES and the Van Allen Probes) at the conjugate event location, we find that ∼73% wave‐driven REP events are associated with EMIC waves.

When the first CubeSats were launched nearly two decades ago, few people believed that the miniature satellites would likely prove to be a useful scientific tool. Skeptics abounded. However, the last decade has seen the highly successful implementation of space missions that make creative and innovative use of fast-advancing CubeSat and small satellite technology to carry out important science experiments and missions. Several projects now have used CubeSats to obtain first-of-their-kind observations and findings that have formed the basis for high-profile engineering and science publications, thereby establishing without doubt the scientific value and broad utility of CubeSats. In this paper, we describe recent achievements and lessons learned from a representative selection of successful CubeSat missions with a space weather focus. We conclude that these missions were successful in part because their limited resources promoted not only mission focus but also appropriate risk-taking for comparatively high science return. Quantitative analysis of refereed publications from these CubeSat missions and several larger missions reveals that mission outcome metrics compare favorably when publication number is normalized by mission cost or if expressed as a weighted net scientific impact of all mission publications.

Accurate knowledge of the full, three-dimensional electric field vector is of fundamental importance in understanding electrodynamics of a vast variety of space plasmas. However, heliophysics research still lacks access to the reliable parallel electric field measurements required to close many significant science questions. This uncertainty represents a significant barrier to progress in the field. The only way to close this major observational gap is a profound change in electric field instrument design. A new electric field instrument called Grotifer is now being designed to address the need for highly accurate three-dimensional electric field measurements while enabling lower cost missions and constellation missions in deep space. Grotifer (Giant rotifer) is a reference to the rotifer, also known as the “wheel animalcule.” Similarly, Grotifer consists of mounting detectors on two rotating plates, orthogonal to each other, on a non-rotating central body. The two rotating plates provide continuous high-accuracy three-dimensional measurements of both electric fields and magnetic fields. The Grotifer design leverages more than 50 years of expertise in delivering highly accurate spin plane electric field measurements, while overcoming inaccuracies generated by spin axis electric field measurements. Our current efforts focus on designing Grotifer as a SmallSat (27U CubeSat). That said, Grotifer could also become part of the payload on a much larger platform. In the future, one could imagine fleets of Grotifers studying electrodynamics at many points, facilitating differentiation between spatial and temporal dynamics. Plasma detectors could also be added to the rotating plates to cover the full phase space better than is done on spinning spacecraft, leading to more complete correlation studies of the fields and plasmas.

Microbursts are impulsive (<1 s) injections of electrons into the atmosphere, thought to be caused by nonlinear scattering by chorus waves. Although attempts have been made to quantify their contribution to outer belt electron loss, the uncertainty in the overall size and duration of the microburst region is typically large, so that their contribution to outer belt loss is uncertain. We combine datasets that measure chorus waves (Van Allen Probes [RBSP], Arase, ground-based VLF stations) and microburst (>30 keV) precipitation (FIREBIRD II and AC6 CubeSats, POES) to determine the size of the microburst-producing chorus source region beginning on 5 December 2017. We estimate that the long-lasting (∼30 hr) microburst-producing chorus region extends from 4 to 8 Δ MLT and 2-5 Δ L. We conclude that microbursts likely represent a major loss source of outer radiation belt electrons for this event.

Solar flares are some of the most energetic events in the solar system and can be studied to investigate the physics of plasmas and stellar processes. One interesting aspect of solar flares is the presence of accelerated (nonthermal) particles, whose signatures appear in solar flare hard X-ray emissions. Debate has been ongoing since the early days of the space age as to how these particles are accelerated, and one way to probe relevant acceleration mechanisms is by investigating short-timescale (tens of milliseconds) variations in solar flare hard X-ray flux. The Impulsive Phase Rapid Energetic Solar Spectrometer (IMPRESS) CubeSat mission aims to measure these fast hard X-ray variations. In order to produce the best possible science data from this mission, we characterize the IMPRESS scintillator detectors using Geant4 Monte Carlo models. We show that the Geant4 Monte Carlo detector model is consistent with an analytical model. We find that Geant4 simulations of X-ray and optical interactions explain observed features in experimental data, but do not completely account for our measured energy resolution. We further show that nonuniform light collection leads to double-peak behavior at the 662 keV $^{137}$Cs photopeak and can be corrected in Geant4 models and likely in the lab.

Resonant wave-particle interactions with plasma waves (e.g. plasmaspheric hiss, whistler mode chorus, and electromagnetic ion cyclotron (EMIC) waves) are often cited as one of the main loss processes that drive the variability of electron fluxes in the Earth's radiation belts . The evolution of our understanding of the radiation belt electron precipitation, the driving mechanism for such events, and its relative impact on radiation belt particle fluxes has moved from single point measurements to the dawn of simultaneous multi-point measurements and conjunction studies. The BARREL mission, as a mission of opportunity to the Van Allen Probes mission, deployed an array of balloon borne detectors to observe radiation belt electron losses into the atmosphere. This mission offered extended periods of time in conjunction with Van Allen Probes and polar LEO orbiting satellites. Conjunction studies have been used to correlate observed plasma waves on Van Allen Probes with electron precipitation observed on BARREL and further constrained the spatial scale of electron precipitation [1-3]. These studies, in combination with theoretical modeling, have shown that the parameter space involved in wave-particle interaction extends beyond our measurements. Therefore, in order to further advance our understanding of these phenomena and their impact on the radiation belts we need to broaden the scope of our measurements and narrow the assumptions and undefined parameters that go into the theory.

Earth and Space Science Open Archive PosterOpen AccessYou are viewing the latest version by default [v1]Meet Grotifer: a CubeSat that Will Provide Highly Accurate Three-Component Electric Field Measurements throughout the HeliosphereAuthorsSolèneLejosneiDDavidAuslanderiDJohnBonnelliDDavidKlumparJeremyMcCauleyRubinMeuchelForrestMozeriDDavidPankowJohnSampleiDLarrySpringerSee all authors Solène LejosneiDCorresponding Author• Submitting AuthorSpace Sciences Laboratory, University Of California, BerkeleyiDhttps://orcid.org/0000-0003-4238-8579view email addressThe email was not providedcopy email addressDavid AuslanderiDMechanical Engineering DepartmentUniversity of CaliforniaBerkeleyiDhttps://orcid.org/0000-0002-1377-0624view email addressThe email was not providedcopy email addressJohn BonnelliDSpace Sciences Laboratory, University Of California, BerkeleyiDhttps://orcid.org/0000-0002-0675-7907view email addressThe email was not providedcopy email addressDavid KlumparSpace Science and Engineering Laboratory, Department of Physics, Montana State University - Bozemanview email addressThe email was not providedcopy email addressJeremy McCauleySpace Sciences Laboratory, University Of California, Berkeleyview email addressThe email was not providedcopy email addressRubin MeuchelSpace Science and Engineering Laboratory, Department of Physics, Montana State University - Bozemanview email addressThe email was not providedcopy email addressForrest MozeriDSpace Sciences Laboratory, University Of California, BerkeleyiDhttps://orcid.org/0000-0002-2011-8140view email addressThe email was not providedcopy email addressDavid PankowSpace Sciences Laboratory, University Of California, Berkeleyview email addressThe email was not providedcopy email addressJohn SampleiDSpace Science and Engineering Laboratory, Department of Physics, Montana State University - BozemaniDhttps://orcid.org/0000-0002-9516-9292view email addressThe email was not providedcopy email addressLarry SpringerSpace Science and Engineering Laboratory, Department of Physics, Montana State University - Bozemanview email addressThe email was not providedcopy email address

Intense bursts of precipitating electrons called "microbursts" were first detected in the 10-100 keV energy range using balloon-based instrumentation [ Anderson and Milton, 1964 ]. The balloon-borne detectors measure bremsstrahlung x-rays produced by energetic electrons that are scattered into Earth’s atmosphere from the Van Allen radiation belts. Direct low-altitude satellite observations of the precipitating electrons revealed that microbursts can extend up to relativistic energies [e.g, Imhof et al., 1992 , Blake et al., 1996 ] and may be a major loss process for trapped radiation belt electrons [ O’Brien et al., 2004 ].

This paper describes the mission concept for "RadPC-Lunar", a technology demonstration of a novel computer architecture that can recover from faults caused by ionizing radiation. RadPC-Lunar is a payload that was selected by NASA in 2019 to go to the Moon through its Commercial Lunar Payload Services (CLPS) project as part of the Artemis lunar program. RadPC-Lunar will travel to the lunar surface in 2022-23 onboard a commercial lander and will spend a minimum of 7-days in the Mare Crisium. This demonstration will serve two important purposes in support of future lunar missions. First, it will demonstrate a key technology for computationally intense autonomous lunar activities such as in situ resource utilization, robotic surface operations, and entry/descent/landing maneuverers while providing increased reliability over the state-of-theart in space computers. Second, it will provide a characterization of the radiation effects environment of the lunar surface by tracking upsets within the computing fabric and correlating them to data from on-board dosimeters. The payload can also provide a unique set of measurements on the ionizing radiation environment as it passes through the Earth's magnetosphere during transit to the Moon.This paper describes the overall mission concept of RadPC-Lunar in addition to the details of the design-of-experiments and the types of data that will be collected. This paper will be of interest to engineers and scientists studying the lunar transit and lunar surface radiation environment and those working with radiation tolerant avionics. The timing of the presentation will allow the RadPC-Lunar team to solicit feedback from the aerospace community that can influence its design-of-experiments prior to completion in order to maximize the return of the mission.