Dynamic Soaring as a Means to Exceed the Solar Wind Speed

Author: Andrew Higgins, PhD, Aeronautics and Astronautics, Professor, McGill University

Background: A number of concepts exist for exploiting the solar wind as a means of propulsion: the MagSail, the e-sail, and the plasma magnet. All of these concepts work predominately as drag devices and thus are limited to velocities equal to the solar wind (~700 km/s), with only limited ability to generate force transverse to the local direction of the solar wind (i.e., lift). An interesting possibility to be explored is dynamic soaring: Exploiting the difference in wind speed in two different regions of space. Albatrosses and sailplanes are known to use this technique, circling in and out of regions of wind shear. Birch (JBIS, 1989) suggested such a technique could be used via a “MHD Wing” for interstellar travel applications, but did not explore the concept further.

Objective: The potential for dynamic soaring to enable a spacecraft using the dynamic pressure of the solar wind in order to greatly exceed the wind speed will be explored. Analysis of the concepts will be organized around passive (meaning simple wing- or sail-like structures) and active (wherein there is a power and thrust interaction with the solar wind) approaches.

Methods: For passive methods, charged particle interaction with static electromagnetic fields will be directly numerically simulated and the lift and drag values derived. Techniques of generating electromagnetic fields capable of providing ideally (specular) reflection of particles will be assessed. For active methods, the ability to extract power from the wind and accelerate a transverse flow—thus generating lift—will be analyzed. Simple analytic models of the fast/slow solar wind and the termination shock will be adopted to explore the required trajectories for soaring.  3-degree-of-freedom simulations of spacecraft trajectories will be performed to assess the potential gains that might be realized by the dynamic soaring maneuver.

Results: While passive methods appear capable of generating high lift-to-drag ratio, the requisite structural mass limits them to very low accelerations and thus not directly applicable to interstellar flight. Active concepts wherein plasma structures have a power and momentum transfer interaction with the solar wind are more promising, but have greater uncertainty associated with their principles of operation.