The Copernicus Sentinel-2 mission, part of the European Space Agency’s (ESA) Copernicus Programme funded by the EU and ESA, comprises a constellation of identical satellites delivering high-resolution optical imagery of Earth’s land and coastal regions. Currently, three Copernicus Sentinel-2 satellites operate in sun-synchronous orbit with a 10-day repeat cycle, providing data across 13 spectral bands — from visible to short-wave infrared — at spatial resolutions of 10–60?meters.
During the commissioning of Copernicus Sentinel-2C, a 40-day tandem phase with Copernicus Sentinel-2A following its launch on September 5, 2024, proved highly valuable for cross-comparison and measurement characterisation. An orbit control concept was developed and successfully applied during this phase, though it relied on a time-intensive manual process. For the upcoming Copernicus Sentinel-2A/Sentinel-2B tandem, the same concept will be implemented using ESA’s Earth Observation Orbit Control (EOOC) software — its first automated application for this type of operation. EOOC integrates manoeuvre planning, threshold-based decision logic, and execution monitoring into a closed operational loop. Its control law computes orbital elements corrections to counteract drift caused by different perturbations, mainly the J? effect and atmospheric drag, ensuring compliance with stringent formation requirements — most notably maintaining an along-track separation of 25–30?s and a cross-track separation between ±200?m and ±700?m at all latitudes.
To validate EOOC for the upcoming tandem phase, the S2C/S2A scenario was repeated in simulation. High-fidelity perturbation models demonstrate that EOOC can apply the orbit control strategy and maintain the required along-track separation within ± 2?km of the target drift envelope and cross-track bounds within ±100?m, achieving this far faster than the previous manual approach. EOOC can also be executed repeatedly throughout the planning cycle, supplying successive optimised solutions that further refine the manoeuvre strategy.
The EOOC architecture includes modules for manoeuvre optimization under propellant constraints, and contingency handling. This paper presents the EOOC control concept for repositioning and tandem phase concepts, manoeuvre planning algorithms, and operational thresholds. It also reports on in-flight performance during the tandem phase, covering manoeuvre execution statistics, achieved accuracy, and robustness against environmental uncertainties.
Results confirm that EOOC provides a scalable and efficient solution for formation flying in LEO, enabling compliance with stringent mission requirements and paving the way for increased automation in orbit control operations for future multi-satellite Earth observation missions.