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Precise Absolute Orbit Control in Low Earth Orbit for Advanced Remote Sensing



                                 Artist illustration of TerraSAR-X (credits: Astrium)

The growing interest in Earth observation missions equipped with spaceborne optical and synthetic aperture radar (SAR) instruments drives the accuracy requirements with respect to spacecraft orbit determination, prediction, and control. Especially SAR interferometry with its capability to resolve the velocity of on-ground objects and to determine highly precise digital elevation models is pushing the demand of highly automated and precise space flight dynamics systems, either ground-based or autonomous.
This research investigates precise orbit control strategies for low Earth orbit advanced remote sensing spacecraft, including mission and requirements analysis, target/reference trajectory generation, orbit prediction and tracking error budgets, maneuver planning and commanding. The orbit control concepts are always devised and implemented in view of an operational flight dynamics deployment, being it autonomous on-board or automated on-ground.
This work has produced two of the most accurate orbit control systems published to date, namely the ground-in-the-loop orbit control system of the TerraSAR-X satellite (~100 m R.M.S., 514 km altitude), and the Autonomous Orbit Keeping (AOK) experiment on the PRISMA mission (~10 m R.M.S., 757 km altitude). The flight results and know-how gained from these missions are helping us to derive lessons learned and define future directions of investigation.
Current research is exploring the duality between absolute orbit control of a single spacecraft and relative orbit control of formation-flying spacecraft. New parameterizations are being introduced to describe the relative motion of two spacecraft sub-satellite points on the Earth surface to gain new insights into the orbit control problem. Model predictive control techniques are investigated to overcome the limitations of current closed-form or numerical approaches especially in terms of robustness to poorly modelled effects such as atmospheric drag and maneuver execution errors.
Recent Publications (2013-2014)
Kahle R., D’Amico S.;
The TerraSAR-X Precise Orbit Control – Concept and Flight Results;
24th International Symposium on Space Flight Dynamics, 24-28 Sep. 2007, Laurel, USA (2014).
De Florio S., D'Amico S., Radice G.;
The Virtual Formation Method for Precise Autonomous Absolute Orbit Control;
AIAA Journal of Guidance, Control, and Dynamics (2013).
De Florio S., D’Amico S., Radice G.;
Flight Results of the Precise Autonomous Orbit Keeping Experiment on the PRISMA Mission;
AIAA Journal of Spacecraft and Rockets, 50(3), 662-674, doi: 10.2514/1.A32347 (2013).
De Florio S.;
Precise Autonomous Orbit Control in Low Earth Orbit: from Design to Flight Validation;
Advisors: Radice G. and D’Amico S.;
PhD thesis, University of Glasgow (2013).
Impulsive Formation Keeping and Reconfiguration using Relative Orbital Elements



                                    Artist illustration of PRISMA (credits: DLR)

Advanced multi-satellite systems such as spacecraft formation flying or rendezvous&docking require the capability to maintain and reconfigure the relative motion in an autonomous, fuel efficient, and flexible manner. Realistic flight scenarios impose maneuvering time constraints driven by the satellite bus, by the payload, or by collision avoidance needs. In addition mission control center planning and operations tasks demand for determinism and predictability of the propulsion system activities.
This research addresses multi-impulsive solution schemes for formation maintenance and reconfiguration in the Relative Orbit Elements (ROEs) space. In contrast to the available literature, which focuses on case-by-case or problem-specific solutions, this work seeks the generalization and the systematic search and characterization of impulsive maneuvers of operational relevance. The inversion of the equations of relative motion parameterized using relative orbital elements enables the straightforward computation of analytical or numerical solutions and provides direct insight into the delta-v cost and the most convenient maneuver locations. The resulting general methodology is not only able to re-find and re-qualify all particular solutions known in literature or flown in space, but enables the identification of novel fuel-efficient maneuvering schemes for future onboard implementation.
This work has led to two flight demonstrations of formation keeping and reconfiguration technologies, namely in the TanDEM-X and PRISMA missions. In addition the relevant findings are being applied in the frame of upcoming on-orbit servicing missions. Current research is focusing on the embedding in actual space hardware of three-impulse solutions for arbitrary formation reconfiguration. Efficient ways to express operational constraints in terms of ROEs are being sought after. Future efforts will be put into the extension of the formation keeping and reconfiguration algorithms to orbits of arbitrary eccentricity. Furthermore graph theory and model predictive control seem to promise great potential when combined with relative orbital elements theory.
Recent Publications (2013-2014)
Gaias G., D’Amico S.;
Impulsive Maneuvers for Formation Reconfiguration using Relative Orbital Elements;
AIAA Journal of Guidance, Control, and Dynamics (2014).

Gaias, G., D'Amico, S., and Ardaens, J.-S.;
Generalized Multi-Impulsive Maneuvers for Optimum Spacecraft Rendezvous;
5th International Conference on Spacecraft Formation Flying Missions & Technologies (SFFMT), 29-31 May 2013, Munich, Germany (2013).