Space Weather is influenced by phenomena operating across a multitude of scales, from the large-scale expulsion and evolution of coronal mass ejections from the solar corona, to particle-scale interactions within the Earth’s radiation belts. My interests within plasma simulations focus on both large-scale fluid physics and kinetic particle-scale processes and the interplay between them. In this seminar I will start with Sun-to-Earth studies of coronal mass ejections and review some of the largest geomagnetic storms on record and examine under what conditions “Carrington-scale” events are possible.  I will then discuss how these impulsive injections of energy flow through the coupled Sun-Earth system and present an imminent danger to our increasingly technology-reliant society. In particular, I will focus on how non-thermal particle distributions can be created within the magnetosphere and feedback to influence the large-scale dynamics.  Following this, I will examine how these plasmas act to charge orbiting spacecraft and show how the outer solar system provided a novel class of spacecraft-plasma interactions for the Cassini spacecraft during its Grand Finale plunge into Saturn.