Browsing by Author "Sample, John"

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Daedalus: a low-flying spacecraft for in situ exploration of the lower thermosphere–ionosphere
(2020-04) Sarris, Theodoros E.; Talaat, Elsayed R.; Palmroth, Minna; Dandouras, Iannis; Armandillo, Errico; Kervalishvili, Guram; Buchert, Stephan; Tourgaidis, Stylianos; Malaspina, David M.; Jaynes, Allison N.; Paschalidis, Nikolaos; Sample, John; Halekas, Jasper; Doornbos, Eelco; Lappas, Vaios; Moretto Jorgensen, Therese; Stolle, Claudia; Clilverd, Mark; Wu, Qian; Sandberg, Ingmar; Pirnaris, Panagiotis; Aikio, Anita
The Daedalus mission has been proposed to the European Space Agency (ESA) in response to the call for ideas for the Earth Observation program's 10th Earth Explorer. It was selected in 2018 as one of three candidates for a phase-0 feasibility study. The goal of the mission is to quantify the key electrodynamic processes that determine the structure and composition of the upper atmosphere, the gateway between the Earth's atmosphere and space. An innovative preliminary mission design allows Daedalus to access electrodynamics processes down to altitudes of 150 km and below. Daedalus will perform in situ measurements of plasma density and temperature, ion drift, neutral density and wind, ion and neutral composition, electric and magnetic fields, and precipitating particles. These measurements will unambiguously quantify the amount of energy deposited in the upper atmosphere during active and quiet geomagnetic times via Joule heating and energetic particle precipitation, estimates of which currently vary by orders of magnitude between models and observation methods. An innovation of the Daedalus preliminary mission concept is that it includes the release of subsatellites at low altitudes: combined with the main spacecraft, these subsatellites will provide multipoint measurements throughout the lower thermosphere–ionosphere (LTI) region, down to altitudes below 120 km, in the heart of the most under-explored region in the Earth's atmosphere. This paper describes Daedalus as originally proposed to the ESA.
Evidence of Microbursts Observed Near the Equatorial Plane in the Outer Van Allen Radiation Belt
(2018-08) Shumko, Mykhaylo; Turner, Drew L.; O'Brien, T. P.; Claudepierre, Seth G.; Sample, John; Hartley, D. P.; Fennel, Joseph; Blake, J. Bernard; Gkioulidou, Matina; Mitchell, Donald G.
We present the first evidence of electron microbursts observed near the equatorial plane in Earth’s outer radiation belt. We observed the microbursts on 31 March 2017 with the Magnetic Electron Ion Spectrometer and Radiation Belt Storm Probes Ion Composition Experiment on the Van Allen Probes. Microburst electrons with kinetic energies of 29–92 keV were scattered over a substantial range of pitch angles, and over time intervals of 150–500 ms. Furthermore, the microbursts arrived without dispersion in energy, indicating that they were recently scattered near the spacecraft. We have applied the relativistic theory of wave-particle resonant diffusion to the calculated phase space density, revealing that the observed transport of microburst electrons is not consistent with the hypothesized quasi-linear approximation.
The FIREBIRD-II CubeSat mission: Focused investigations of relativistic electron burst intensity, range, and dynamics
(2020-03) Johnson, A. T.; Shumko, Mykhaylo; Griffith, B.; Klumpar, David; Sample, John; Springer, Larry; Leh, N.; Spence, H. E.; Smith, S.; Crew, A.; Handley, M.; Mashburn, K. M.; Larsen, B. A.; Blake, J. B.
FIREBIRD-II is a National Science Foundation funded CubeSat mission designed to study the scale size and energy spectrum of relativistic electron microbursts. The mission consists of two identical 1.5 U CubeSats in a low earth polar orbit, each with two solid state detectors that differ only in the size of their geometric factors and fields of view. Having two spacecraft in close orbit allows the scale size of microbursts to be investigated through the intra-spacecraft separation when microbursts are observed simultaneously on each unit. Each detector returns high cadence (10 s of ms) measurements of the electron population from 200 keV to >1 MeV across six energy channels. The energy channels were selected to fill a gap in the observations of the Heavy Ion Large Telescope instrument on the Solar, Anomalous, and Magnetospheric Particle Explorer. FIREBIRD-II has been in orbit for 5 years and continues to return high quality data. After the first month in orbit, the spacecraft had separated beyond the expected scale size of microbursts, so the focus has shifted toward conjunctions with other magnetospheric missions. FIREBIRD-II has addressed all of its primary science objectives, and its long lifetime and focus on conjunctions has enabled additional science beyond the scope of the original mission. This paper presents a brief history of the FIREBIRD mission’s science goals, followed by a description of the instrument and spacecraft. The data products are then discussed along with some caveats necessary for proper use of the data.
Microburst Scale Size Derived from Multiple Bounces of a Microburst Simultaneously Observed with the FIREBIRD-II CubeSats
(2018-07) Shumko, Mykhaylo; Sample, John; Johnson, Arlo; Blake, Bern; Crew, Alex; Spence, Harlan; Klumpar, David; Agapitov, Oleksiy; Handley, Matthew
We present the observation of a spatially large microburst with multiple bounces made simultaneously by the FIREBIRD‐II CubeSats on February 2nd, 2015. This is the first observation of a microburst with a subsequent decay made by two co‐orbiting but spatially separated spacecraft. From these unique measurements, we place estimates on the lower bounds of the spatial scales as well as quantify the electron bounce periods. The microburst's lower bound latitudinal scale size was 29 ± 1 km and the longitudinal scale size was 51 ± 1 km in low earth orbit. We mapped these scale sizes to the magnetic equator and found that the radial and azimuthal scale sizes were at least 500 ± 10 km and 530 ± 10 km, respectively. These lower bound equatorial scale sizes are similar to whistler‐mode chorus wave source scale sizes, which supports the hypothesis that microbursts are a product of electron scattering by chorus waves. Lastly, we estimated the bounce periods for 200‐800 keV electrons and found good agreement with four common magnetic field models.
Microburst Scale Size Derived From Multiple Bounces of a Microburst Simultaneously Observed With the FIREBIRD-II CubeSats
(2018-09) Shumko, Mykhaylo; Sample, John; Johnson, Arlo; Blake, Bern; Crew, Alex; Spence, Harlan; Klumpar, David; Agapitov, Oleksiy; Handley, Matthew
We present the observation of a spatially large microburst with multiple bounces made simultaneously by the Focused Investigation of Relativistic Electron Bursts: Intensity, Range, and Dynamics II (FIREBIRD‐II) CubeSats on 2 February 2015. This is the first observation of a microburst with a subsequent decay made by two coorbiting but spatially separated spacecraft. From these unique measurements, we place estimates on the lower bounds of the spatial scales as well as quantify the electron bounce periods. The microburst's lower bound latitudinal scale size was 29 ± 1 km and the longitudinal scale size was 51 ± 1 km in low Earth orbit. We mapped these scale sizes to the magnetic equator and found that the radial and azimuthal scale sizes were at least 500 ± 10 km and 530 ± 10 km, respectively. These lower bound equatorial scale sizes are similar to whistler mode chorus wave source scale sizes, which supports the hypothesis that microbursts are a product of electron scattering by chorus waves. Lastly, we estimated the bounce periods for 200‐ to 800‐keV electrons and found good agreement with four common magnetic field models.
Observations Directly Linking Relativistic Electron Microbursts to Whistler Mode Chorus: Van Allen Probes and FIREBIRD II
(2017-12) Breneman, A. W.; Crew, Alex; Sample, John; Klumpar, David; Johnson, Arlo; Agapitov, Oleksiy; Shumko, Mykhaylo; Turner, D. L.; Santolik, O.; Wygant, John R.; Cattell, C. A.; Thaller, S.; Blake, Bern; Spence, Harlan; Kletzing, C. A.
We present observations that provide the strongest evidence yet that discrete whistler mode chorus packets cause relativistic electron microbursts. On 20 January 2016 near 1944 UT the low Earth orbiting CubeSat Focused Investigations of Relativistic Electron Bursts: Intensity, Range, and Dynamics (FIREBIRD II) observed energetic microbursts (near L = 5.6 and MLT = 10.5) from its lower limit of 220 keV, to 1 MeV. In the outer radiation belt and magnetically conjugate, Van Allen Probe A observed rising-tone, lower band chorus waves with durations and cadences similar to the microbursts. No other waves were observed. This is the first time that chorus and microbursts have been simultaneously observed with a separation smaller than a chorus packet. A majority of the microbursts do not have the energy dispersion expected for trapped electrons bouncing between mirror points. This confirms that the electrons are rapidly (nonlinearly) scattered into the loss cone by a coherent interaction with the large amplitude (up to 900 pT) chorus. Comparison of observed time-averaged microburst flux and estimated total electron drift shell content at L = 5.6 indicate that microbursts may represent a significant source of energetic electron loss in the outer radiation belt.