Comments on 'quasi-continuous higher order sliding-mode controllers for spacecraft-attitude-tracking maneuvers'

In the paper 'Quasi-continuous higher order sliding-mode controllers for space-attitude-tracking maneuvers' (IEEE Trans. Ind. Electron., vol. 57, no. 4, pp. 1436-1444, Apr. 2010), higher order sliding-mode control laws are applied to the attitude-tracking maneuvers of spacecraft. It is pointed out in the author's comments that the proposed applications of higher order sliding-mode control, although in the form of second- and third-order sliding-mode controls, can only realize first-order sliding-mode dynamics because of the improperly chosen sliding vectors. The proposed sliding vectors in the paper are suitable when integrators or a first-order lag is added into the system. In the author's comments, alternative measures to realize second- and third-order sliding-mode dynamics are suggested.