STEPHEI: a novel double-probe electric-field instrument for CubeSats in tenuous plasma environments

Abstract

The Small TEnuous Plasma Heliophysics Electric field Instrument (STEPHEI) represents a significant advancement in the miniaturization and cost-effective deployment of double probe electric field sensors for CubeSats and Small Sats operating in the magnetosphere. Leveraging advanced electronics, high-strain composite booms, and innovative design strategies, STEPHEI enables high-precision double probe measurements of quasi-steady (DC) electric fields in tenuous plasma environments. Unlike traditional electric field sensors, STEPHEI eliminates the need for bias currents due to its ultra-low leakage current and high input impedance front-end electronics. Featuring 4.5-meter deployable booms, the instrument offers a precision error of less than 0.3mV/m, making it ideally suited for multipoint CubeSat constellation missions where electric field measurements from a small form-factor payload are needed. This paper details the instrument's novel design, its technological innovations, and the challenges it overcomes in measuring the magnetospheric environment, while highlighting its alignment with key heliophysics science goals.