Robust Control for Low-thrust Interplanetary Trajectories
The purpose of this research project is to introduce novel approaches and methods for designing robust control for low-thrust interplanetary trajectories, in the case of physical perturbations and incertainties, or momentary engine failures.
As the technology matures, low-thrust propulsion systems appear as the most efficient choice for interplanetary missions. Recent experiences on low-thrust interplanetary missions (Smart-1) showed that designing a low-thrust mission is not simple considering trajectory corrections and engine degradation.
This issue is less prominent for impulsive trajectories as thrust to weight ratio is sufficient to make almost instantaneous correction maneuvers. Low-thrust propulsion systems do not allow by definition immediate correction maneuvers. New design tools and methodologies shall then be proposed for low-thrust trajectory design to include thrust margins during the design phase for possible long thrust correction maneuvers. For instance, future ESA BepiColombo mission includes coast arcs before planetary swing-bys in order to perform necessary trajectory corrections for the swing-bys maneuver to be realised as designed. BepiColombo will also have redundant ion thrusters in case of a premature degradation of the operating ion engines.
Robustness of the control with respect to the engine imperfections should thus be part of the design process. Two approaches have been followed so far:
- a-priori reduction of the thrust level
- introduction of coast arcs in the trajectory
For the second strategy, how these coast arcs could be optimally placed, regarding a given robustness criterion.
Current work, performed in the team, considers both deterministic and stochastic optimal control methods.
 Olympio, J., Designing Robust Low-Thrust Interplanetary Trajectories Subject to One Temporary Engine Failure, 20th AAS/AIAA Space Flight Mechanics Meeting, 2010, AAS 10-171. (link)