Spacecraft floating potential measurements for the $\mathit{Wind}$ spacecraft

TL;DR

This study analyzes over 8.8 million electron velocity distribution functions from the Wind spacecraft to determine its floating potential, revealing spectral and temporal variations linked to solar activity and large-scale solar wind structures.

Contribution

It provides a comprehensive dataset of spacecraft floating potentials at 1 AU and identifies their spectral and temporal variations related to solar phenomena.

Findings

Floating potential mostly 5-9 eV due to spacecraft design.

Spectral enhancements at frequencies related to solar rotation.

Potential peaks correlated with solar maximum and solar wind structures.

Abstract

Analysis of 8,804,545 electron velocity distribution functions (VDFs), observed by the $\mathit{Wind}$ spacecraft near 1 AU between January 1, 2005 and January 1, 2022, was performed to determine the spacecraft floating potential, $\phi{\scriptstyle_{sc}}$. $\mathit{Wind}$ was designed to be electrostatically clean, which helps keep the magnitude of $\phi{\scriptstyle_{sc}}$ small (i.e., $\sim$5--9 eV for nearly all intervals) and the potential distribution more uniform. We observed spectral enhancements of $\phi{\scriptstyle_{sc}}$ at frequencies corresponding to the inverse synodic Carrington rotation period with at least three harmonics. The 2D histogram of $\phi{\scriptstyle_{sc}}$ versus time also shows at least two strong peaks with a potential third, much weaker peak. These peaks vary in time with the intensity correlated with solar maximum. Thus, the spectral peaks and histogram peaks are likely due to macroscopic phenomena like coronal mass ejections (solar cycle dependence) and stream interaction regions (Carrington rotation dependence). The values of $\phi{\scriptstyle_{sc}}$ are summarized herein and the resulting dataset is discussed.