The Active Plasma and E-field Sounders (APES) Mission Concept

Abstract

The Active Plasma and E-field Sounders (APES) mission concept aims to resolve orders-of-magnitude errors in modeling transionospheric radio propagation through the midlatitude trough, and to determine which physical mechanism(s) are responsible for generating plasma irregularities there. APES will observe ionospheric electron density profiles and signals from ground transmitters along its orbital track, allowing for a constrained test of propagation models. The mission will also perform small-scale in situ science, differentiating between the long-held temperature gradient instability and the Kelvin–Helmholtz/gradient drift instabilities as potential causes of irregularities in the trough. The centerpiece of the mission is the first-ever oblique topside ionospheric sounder, providing 2D electron density-altitude profiles along the orbital track through cooperative operation between two satellites. The leading satellite will produce swept-frequency HF transmissions that will reflect off the ionosphere before being received by the follower. The following satellite will also receive signals transmitted by the Super Dual Auroral Radar Network (SuperDARN). Both satellites will observe electron density at 1 m along-track resolution, while single-point electron temperature, vector electric field, neutral density and neutral wind will also be provided. The mission will operate in a nominal 350 × 800 km elliptical orbit, with along-track spacing varied from < 1 to 750 km over 12 months of science operations in an inclination between 50–87° and 103–130° (depending on the rideshare). Each bus carries a 250 m/s propulsion system to control eccentricity and for orbit maintenance. The orbital analysis has been used to select orbits with > 500 passes through the trough in each quarter.