The effect of space weather on satellite orbits

Every now and then most of the people have thought about terrestrial weather and its forecast since it plays an essential role in our daily lives. Now, the main focus of project ESPRIT is space weather, which in a certain way can be considered analogous to the weather on Earth. It deals with the dynamic conditions in the Earths outer space environment including the physical processes on the Sun, in the solar wind, the magnetosphere and in the upper atmosphere. Accompanying with the rapid technological progress in the last decades space weather effects can directly be perceptible in peoples everyday life. Coronal mass ejections, huge clouds of magnetized plasma, and may lead to perturbations of electronic devices at technical infrastructure on Earth and also in space. Furthermore, they have the capability to interrupt navigation and communication services or even be the trigger for the loss of complete electricity grids, with far-reaching consequences in different areas. With this in mind, it becomes obvious that a precise forecasting of space weather effects is of vital importance. However, compared to the weather predictions on Earth, the forecasting of space weather effects, especially during solar eruptions, is still at the very beginning. The goal of project ESPRIT is the exploration of physical conditions of the solar wind plasma and interplanetary magnetic field parameters as well as solar radiation over varying solar activity levels and during different solar phenomena. On this basis, it is proposed to develop optimized algorithms to improve the modelling of the upper Earths atmosphere and the associated determination of satellite orbit decay rates. As we know, certain predominant chemical compositions like NO, CO2 and He in the upper Earth`s atmosphere may be the trigger to so called cooling effects. These effects have the capability to counteract the heating processes induced by the enhanced energy input from the solar wind. At first glance, one might think that this is beneficial, because it counteracts the negative effects of solar eruptions on the upper Earth atmosphere. However, since the sources of such cooling effects are not fully understood so far, unforeseen behaviours of the atmosphere are rather a disadvantage, especially for the accuracy of potential space weather predictions. For this reason, it is intended to additionally focus on this important topic in order to incorporate new findings regarding the interaction of heating and cooling processes in the upper Earth atmosphere in the modelling process.

Satellites are crucial for our daily lives, but they face a constant threat from space weather effects. The project "The effect of space weather on satellite orbits" (ESPRIT) was initiated to investigate the physical conditions of the solar wind and interplanetary magnetic field, with a particular focus on their impact during solar eruptions (coronal mass ejections, solar flares). A primary objective was to analyze how these phenomena affect the orbits of satellites in space. Over the project's duration, we analyzed individual aspects of this complex system, identified key shortcomings in existing models, and successfully developed new methods to address them. A foundational component of our work was the creation of a detailed, freely accessible database built from a thorough analysis of more than twenty years of measurements from diverse observation techniques. This database, which depicts correlations between various solar and magnetic parameters, served as the foundation for the forecasting tool, SODA (ESA Space Safety Program I.161). The SODA tool is designed to predict the impact of Coronal Mass Ejections (CMEs) on satellite orbits. In this context, our focus in ESPRIT was predominantly on complex, interacting CME events and on understanding the cooling effects within the Earth's thermosphere. We performed a rigorous comparison of in-situ nitric oxide (NO) measurements from the TIMED satellite with results from own atmospheric models (e.g., the Kompot Code). To better understand the production of NO molecules and their influence on thermospheric structure and satellite drag, we modeled Earth's background thermosphere with this 1D upper atmosphere model, taking into account the incident X-ray, EUV, and IR radiation during specific space weather events. A key scientific finding was the critical role of electron particle precipitation on thermospheric NO production, which, in turn, has a significant cooling effect. We demonstrated that integrating this phenomenon is of utmost importance for accurate thermosphere modeling. We also established that the impact of solar storms varies significantly depending on the satellite's altitude and the height of the exobase. Additionally, we showed that the merged electric field is a more reliable and stable proxy for predicting the expected impacts of CME events on satellites in low Earth orbit. This project not only yielded significant scientific advancements but also solidified a robust partnership between the participating research institutions within the scientific community of Graz. This successful collaboration laid the groundwork for new research ideas and questions that will continue to drive our work in the future.