Forecasting ICME induced Satellite Orbit Decays

Geomagnetic storms are capable of triggering thermospheric density variations which in turn have an influence on the trajectory of low Earth orbiting satellites (LEO). The strongest of these disturbances of the thermosphere are caused by interplanetary coronal mass ejections (ICMEs). Due to increases in the neutral mass density during such ICME induced geomagnetic storms the altitude of satellites will decrease. Therefore, ICME induced orbit decays are important for long-term orbit prediction as well as short-term as the prominent example of the so called ‘Starlink’ event of February 2022 showed where 40 satellites reentered the atmosphere.

In order to calculate the ICME induced orbit decay we calculated the thermospheric neutral mass density through the deceleration due to drag. This is done either with an observation approach using the high orbiting global navigation satellite system (GNSS) or calibrated data from onboard accelerometers. We then relate the solar wind plasma and magnetic field measurements taken at L1 from the ACE (Advanced Composition Explorer) and the DSCOVR (Deep Space Climate Observatory) satellites to the calculated ICME induced orbit decays. 299 ICMEs occurred during the operation of the GRACE (Gravity Recovery And Climate Experiment) satellite which orbits at an altitude of around 490 km. Analysis of the ICME induced orbit decays and the interplanetary magnetic field at L1 show a strong correlation as well as a time delay between the ICME and the associated thermospheric response of around 15 hours on average. This correlation is implemented in the real time forecasting tool SODA (Satellite Orbit DecAy). Because the ICME induced orbit decay strongly depends on the altitude we additionally processed data from the CHAMP (CHAllenging Minisatellite Payload) satellite mission to cover the range of 400 km altitude. The GRACE focused forecast algorithm SODA is part of the project SWEETS and ESPRIT, which will be implemented in the ESA Space Safety Program (Ionospheric Weather Expert Service Center) in 2023.