This paper regards small/midsize square sails on which a field of wrinkles appears owing to the necessary sail-membrane operations before and during the deployment. We collected a large amount of data in our laboratory. Many ten thousands of measurements had been statistically processed for characterizing some sail’s sampled membranes consisting of aluminized-polyimide layers (2.5+0.1)μm thin, and loaded at vertices. Such samples have exhibited area and orientation alterations, as a whole, which can affect the propulsive acceleration of a sailcraft. Wrinkled-sail orientation has been given a thrust-specialized meaning for trajectory computation. Three-dimensional heliocentric minimum-time orbit transfer between Earth and Mercury orbits had been investigated. This had resulted in wrinkled-sail sailcraft moving on trajectories remarkably different from those ones of the corresponding ideal unwrinkled-sail sailcraft. Nevertheless, at least in the current framework, the most important result is that sail-wrinkled sailcraft’s interplanetary trajectories could be optimized without resorting to stochastic differential equations.