Investigating Satellite Attitude and Orbit Control System Performance of the SDRE Technique regarding Parametric Uncertainty

Resumo

The satellite attitude and orbit control subsystem (AOCS) can be designed with success by linear con-
trol theory if the satellite has slow angular motions. However, for fast maneuvers, the linearized models are not

able to represent all the perturbations due to the effects of the nonlinear terms present in the dynamics which
compromises the system’s performance. Therefore, in such cases, it is expected that nonlinear control techniques

yield better performance than the linear control techniques, improving the AOCS pointing accuracy without re-
quiring a new set of sensors and actuators. Nonetheless, these nonlinear control techniques can be more sensitive

to parametric uncertainties. One candidate technique for the design of AOCS control law under a fast maneuver

is the State-Dependent Riccati Equation (SDRE). SDRE provides an effective algorithm for synthesizing nonlin-
ear feedback control by allowing nonlinearities in the system states while offering great design flexibility through

state-dependent weighting matrices. The Brazilian National Institute for Space Research (INPE, in Portuguese)
was demanded by the Brazilian government to build remote-sensing satellites, such as the Amazonia-1 mission.
In such missions, the AOCS must stabilize the satellite in three-axes so that the optical payload can point to the
desired target. Currently, the control laws of AOCS are designed and analyzed using linear control techniques
in commercial software. Although elsewhere the application of the SDRE technique with opensource software
has shown to yield better performance for the missions developed by INPE, a subsequent important question is
whether such better performance is robust to parametric uncertainties. In this paper, we investigate whether the
application of the SDRE technique in the AOCS is robust to parametric uncertainties in the missions developed by
INPE. The initial results showed that SDRE controller is robust to ±20%, at least, variations in the inertia tensor
of the satellite.