The ELFIN mission

The Electron Loss and Fields Investigation with a Spatio-Temporal Ambiguity-Resolving option (ELFIN-STAR, or heretoforth simply: ELFIN) mission comprises two identical 3-Unit (3U) CubeSats on a polar (∼93∘ inclination), nearly circular, low-Earth (∼450 km altitude) orbit. Launched on September 15, 2018, ELFIN is expected to have a >2.5 year lifetime. Its primary science objective is to resolve the mechanism of storm-time relativistic electron precipitation, for which electromagnetic ion cyclotron (EMIC) waves are a prime candidate. From its ionospheric vantage point, ELFIN uses its unique pitch-angle-resolving capability to determine whether measured relativistic electron pitch-angle and energy spectra within the loss cone bear the characteristic signatures of scattering by EMIC waves or whether such scattering may be due to other processes. Pairing identical ELFIN satellites with slowly-variable along-track separation allows disambiguation of spatial and temporal evolution of the precipitation over minutes-to-tens-of-minutes timescales, faster than the orbit period of a single low-altitude satellite (Torbit ∼ 90 min). Each satellite carries an energetic particle detector for electrons (EPDE) that measures 50 keV to 5 MeV electrons with Δ E/E 1 MeV. This broad energy range of precipitation indicates that multiple waves are providing scattering concurrently. Many observed events show significant backscattered fluxes, which in the past were hard to resolve by equatorial spacecraft or non-pitch-angle-resolving ionospheric missions. These observations suggest that the ionosphere plays a significant role in modifying magnetospheric electron fluxes and wave-particle interactions. Routine data captures starting in February 2020 and lasting for at least another year, approximately the remainder of the mission lifetime, are expected to provide a very rich dataset to address questions even beyond the primary mission science objective.Published versio

Experimental Investigation on the Magneto-Hydrodynamic Interaction in the Shock Layer on a Hypersonic Body

This paper describes the results of an experimental investigation on the effect of the MHD interaction with the plasma of the shock layer above a test body immersed into a hypersonic argon flow. The hypersonic flow is obtained from the high-enthalpy arc-heated wind tunnel of Alta-CPR (Pisa) at Mach 6. Test at heating chamber stagnation pressures of 0.65, 0.85, and 1 bar, and magnetic fields in the range of 0.15-0.35 T, are carried out. The experimental observations are done by means of a set of electrical probes, an optical multi-channel analyser, and a fast shutter CCD camera. In order to maximize the effect of the MHD interaction the Faraday field is shorted ad a magnetic field perpendicular to the test body surface is used. Due to the MHD interaction increases of the distance between the shock front and the body surface are observed. The MHD interaction effect is reduced by the low conductivity of the plasma in the boundary layer above the test body surface