Methods to improve the accuracy of in-orbit thruster parameter estimates
- Paper number
IAC-08.C1.8.6
- Author
Mr. Julio Rodríguez Navarro, ZARM - University of Bremen, Germany
- Coauthor
Dr. Stephan Theil, DLR, German Space Agency, Germany
- Coauthor
Mr. Daniel Bindel, ZARM - University of Bremen, Germany
- Year
2008
- Abstract
New scientific space missions, which need precision pointing and/or drag-free control, are using active actuator systems for the spacecraft attitude and translation control. Such a control system requires precise actuators, which are able to generate forces and torques in the order of mN and µN. The control system performance depends on several factors. One of them is the accurate knowledge of the actuator system such as stochastic errors as well as the configuration, including alignment errors or side effects. The success of a mission depends basically on the knowledge of a such actuator system.
Thrusters are arranged in a system in order to generate forces and torques in all directions and it is known as the thruster-configuration. It may vary due to the extreme environmental conditions, and mechanical effects during the launch. In addition, there are uncertainties in this configuration because it can be determined only with a limited accuracy before the launch. For that reason an in-orbit calibration is needed.
Estimation methods, like least-squares or Kalman-filter, can be applied to solve the problem. However, the data used for the estimation process has many noise sources, and the satellite itself is under the influence of many disturbances resulting in errors on the estimates. To overcome such problems, methods to improve the accuracy of the estimates are proposed and evaluated. A full satellite’s simulation generates the data and real spacecraft values, noises and physical restrictions, that are used to have a real approximation of the problem.
The in-orbit calibration of the thruster configuration matrix was already proposed and some results were presented in various publications by other authors. However they based their study in only one estimation method. Such studies show the convergence of the parameters but not the accuracies of the estimates and, most important, they do not mention the problems presented in the calibration procedure. In this paper different estimation methods are used and compared, and some methods to improve the accuracy of the estimates are suggested. Furthermore, the research about the excitation methods gave the necessary information to choose the better option for the calibration in terms of estimation algorithm, control method, and type of excitation. The problems generated by the spacecraft AOCS in the parameter estimation were recognized and identified. A depth discussion is carried out and a calibration procedure is proposed.
- Abstract document
- Manuscript document
IAC-08.C1.8.6.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.