Researchers at TU Graz have successfully enhanced orbit predictions for satellites and space debris while also gaining deeper insights into Earth’s water masses through the use of satellite laser ranging.
How are the Earth’s gravitational field and the paths of satellites and space debris interconnected? The Earth’s gravitational field affects the orbits of objects in space. In turn, observing the changes in these orbits can reveal shifts in the gravitational field, indicating the presence of water masses. In the COVER project, TU Graz’s Institute of Geodesy integrated satellite gravity measurements with the satellite laser ranging (SLR) technique. This combination has significantly advanced both the accuracy of gravity field assessments and the tracking of space objects and their orbital predictions. The findings have been added to the gravity recovery object-oriented programming system (GROOPS), which the Institute of Geodesy makes available for free on GitHub.
Accurate Analysis of Earth’s Long-Wave Gravity Field
Sandro Krauss from TU Graz’s Institute of Geodesy noted, “Satellite missions like Grace, Grace Follow-on, and the earlier GOCE have yielded invaluable data for understanding the Earth’s gravity field. However, these missions struggle to accurately capture the long-wavelength gravity field associated with larger land masses.” In contrast, SLR measurements excel in resolving these long wavelengths. This process involves a network of SLR stations targeting a satellite equipped with retro-reflectors that bounce back the emitted laser light. By measuring the time it takes for the light to travel, the satellites’ positions can be determined within centimeters, and changes in their orbits due to surface mass variations can be detected. “By integrating SLR with other satellite measurement methods, we can compute the gravity field with greater precision, allowing for enhanced understanding of Earth’s water masses, while also significantly improving our ability to predict the locations and future paths of satellites and space debris, thereby increasing orbital safety.”
Currently, there are about 40,000 pieces of space debris larger than ten centimeters orbiting the Earth, with around a million objects measuring one centimeter or larger. Traveling at speeds of approximately 30,000 km/h and moving in various directions, a collision could have devastating effects, potentially damaging satellites and posing risks to astronauts aboard space stations and manned spacecraft. Hence, accurately determining the orbits and forecasting the future trajectories of these objects is crucial.
Centimeter Precision Rather Than Kilometer Estimates
Currently, radar measurements are used to track space debris, but their precision is lacking. Existing predictions often had an accuracy of just a few kilometers, complicating efforts to pinpoint their locations. Significant strides have been made in collaboration with the Satellite Laser Ranging Station at the Austrian Academy of Sciences’ Space Research Institute located at Lustbühel Observatory. The Institute of Geodesy applied its own force models, enabling them to determine satellite or debris positions to within approximately 100 meters. This capability improved tracking and detailing via laser surveying. Additional measurements during follow-up flybys provided even finer details on orbital behavior, enhancing predictive accuracy.
“To predict orbits, we must consider all forces acting on the satellites,” explains Torsten Mayer-Gürr from TU Graz’s Institute of Geodesy. “This includes the gravitational force from the Earth, which is affected by the presence of water masses. Our combined orbit modeling and SLR measurements have led to significantly improved calculations in our GROOPS software, which is open to the public. To our knowledge, we are unique in offering such a comprehensive, free resource for gravity field assessment, orbit determination, and SLR processing. This open-source approach allows us to receive rapid feedback for potential improvements.”
