Doing Battle with the Sun: Lessons From LEO and Operating a Satellite Constellation in the Elevated Atmospheric Drag Environment of Solar Cycle 25

Abstract

Capella Space, which designs, builds, and operates a constellation of Synthetic Aperture Radar (SAR) Earth-imaging small satellites, faced new challenges with the onset of Solar Cycle 25. By mid-2022, it had become clear that solar activity levels were far exceeding the 2019 prediction published by the National Atmospheric and Oceanic Administration's (NOAA) Space Weather Prediction Center (SWPC). This resulted in the atmospheric density of low Earth orbit (LEO) increasing 2-3x higher than predicted. While this raises difficulties for all satellite operators, Capella's satellites are especially sensitive to aerodynamic drag due to the high surface area of their large deployable radar reflectors. This unpredicted increase in drag threatened premature deorbit and reentry of some of Capella's fleet of spacecraft. This paper explores Capella's strategic response to this problem at all layers of the satellite lifecycle, examining the engineering challenges and insights gained from adapting an operational constellation to rapidly changing space weather conditions. A key development was the implementation of "low drag mode", which increased on-orbit satellite lifetime by 24% and decreased accumulated momentum from aerodynamic torques by 20-30%. The paper shares operational tradeoffs and lessons from the development, deployment, and validation of this flight mode, offering valuable insights for satellite operators facing similar challenges in LEO's current elevated drag environment.