Robust optimal control problem for flexible spacecraft/structures using on-off typediscrete actuators has been a subject of intensive research. Optimization by switchingtime parameterization can be used to minimize the maneuver time subject to equalityboundary constraints. Sensitivity of the switching times with respect to modal parameterscould be a critical factor degrading the performance of the time optimal solutions. Anew approach for the robustness enhancement of switching times with respect to modalparameter uncertainty is introduced. A new concept so-called augmented dynamic modelis added to account for the modal uncertainty. The proposed approach tums out to besimilar to some previous methods, but it essentially provides some new results.