Initial Ionospheric Observations and ISS Frame Charging During the March and April 2023 G4 Solar Storms

The Falcon Electric Propulsion Electrostatic Analyzer Experiment (henceforth “ÉPÉÉ”) is a fourth-generation follow-on to a family of electrostatic analyzers flown five times on the International Space Station (ISS) and on six additional spacecraft in Low Earth Orbit (LEO) since 2009. The instruments are designed, built, and tested at the United States Air Force Academy (USAFA) allowing cadets to perform basic research “learning space by doing space”. The ÉPÉÉ is a compact, rugged Electrostatic Analyzer (ESA) that measures ion populations in the local space environment. ÉPÉÉ operated nearly continuously on-board the International Space Station (ISS) as a manifested payload on the United States Department of Defense Space Test Program - Houston 9 (STP-H9) platform from March 15th, 2023 to April 24th, 2024. The sensor serves as an energy bandpass filter and from the in-situ measurements the ambient density and temperature of the local space plasma can be obtained. Additionally, the resulting spacecraft charge can be observed to provide real-time data concerning the local space environment and potentially hazardous levels of differential frame charging. We present the ÉPÉÉ design and initial observations of the ionospheric plasma environment during the increased solar activity as Solar Cycle 25 heads towards the solar maximum. Specifically, we examine the impact of two G4 solar storms on ionospheric plasma density and resulting ISS frame charging.