“…The purpose of this paper is to investigate optimal control problems governed by systems of ordinary differential equations of the forṁ Many models that enter into this framework can be found in practice and, in particular, in the existing literature. Among these we can mention: the Goddard's problem in three dimensions [24] analyzed in Bonnans et al [11], several models concerning the motion of rockets as the ones treated in Lawden [33], Bell and Jacobson [8], Goh [26,29], Oberle [40], Azimov [7] and Hull [31]; an hydrothermal electricity production problem studied in Bortolossi et al [13], the problem of atmospheric flight considered by Oberle in [41], and the optimal production processes studied in Cho et al [16] and Maurer at al. [36].…”