Path planning for satellite slew maneuvers is considered as an optimal control problem. The goal is to determine rapid maneuvers with vibrational modes resting time as short as possible in order to provide more time for space imagery. In this paper, this optimal time and control effort problem is adressed by using flatness and B-spline collocation. First, the flatness allows us to reduce the optimal control problem into a tractable geometric programming problem with no numerical integration, and with a minimal number of decision variables. Second, to limit the energy spillover into flexible modes, the attitude parameters history is shaped by B-splines to get flexible trajectory with high level of continuity. A consequence of flatness is that the transformed constraints describe a generally non convex subspace. In the proposed approach, a flat suboptimal convex problem is formulated using off-line convex approximations of the feasible space and a measure of its conservatism is proposed. Numerical results are discussed and compared to the results coming from an in-service industrial path planner available at the CNES, the French Space Agency.