Solar sailing is a flight-proven low-thrust propulsion technology with strong potential for innovative scientific missions. All previous solar-sail missions employed a solar-sail system design consisting of four triangular sail quadrants supported by deployable booms. As an alternative to such a fixed and flat sail-system design, this paper investigates the dynamics of the heliogyro. The heliogyro is a helicopter-like sail design that utilizes a set of long slender blades which are deployed and flattened by spin-induced tension and whose orientations can be individually controlled. The main advantages of such a design are the easier stowage and deployment, and potentially lower structural mass. Moreover, the individual blade orientation allows higher authority on the forces and moments produced by the sail, but at the same time complicates the heliogyro dynamics. The heliogyro’s translational and rotational motions are strongly coupled, with non-trivial relationships between the control inputs and the forces and moments produced by the sail. The purpose of this paper is to investigate for the first time the coupled roto-translational motion of the heliogyro. As tantalizing application, the paper analyzes the heliogyro’s performance for Earth-to-Mars stopover cycler trajectories, which could aid the exploration of Mars by providing recurrent propellant-less logistics links between Earth and Mars. Two numerical models to describe the heliogyro coupled roto-translational dynamics are derived; a spin-averaged and a non-averaged model. To design time-optimal heliogyro Earth-to-Mars stopover cycler trajectories, a multiple shooting algorithm is employed and the feasibility of the concept is demonstrated. The resulting trajectories are then compared to those of a traditional fixed-area and flat sail-system design, demonstrating that the heliogyro can perform similar trajectories as the traditional fixed-area and flat sailcraft, without the need of an additional system to control the sailcraft attitude.

Despite having the advantage of a secondary flow pattern in coiled tubes, a very high Dean number is required to induce significant mixing in helical coils, usually implying high shear rates. At very high shear rates, polymer fluids with long molecular chains can be damaged. Therefore, in this study, we investigate the enhancement of mixing of a viscoelastic fluid in a coiled tube at low Dean numbers using the concept of a coiled flow inverter (CFI). Viscoelastic flow simulations were performed for CFIs of different curvature ratios, by changing the coil diameter, for a range of Weissenberg numbers (Wi) 0-125. An analytical method using velocity streamlines to quantify mixing is presented. The pressure drop per unit length increases with increasing Wi number. A more efficient mixing is predicted in the CFI, when compared with a helix of the same curvature ratio for all flow conditions. The mixing in the CFI is improved with an increase in flow rates (Wi). The mixing is enhanced at every bend because of flow inversion in the CFI.