'Dynamic soaring' could help spacecraft zoom across interstellar space, study suggests

"Drawing inspiration from maneuvers practiced by seabirds and RC glider pilots, we show that a flight vehicle interacting with two different regions of wind can extract energy from the wind shear and accelerate to speeds greater than the wind," the team said in a tweet.

The scientists look into dynamic soaring - flying lifting trajectories that "bounce back and forth between the different regions of wind speed, like a tennis ball bouncing back and forth between two approaching trains."

Dynamic soaring exploits the difference in wind speeds

"In dynamic soaring as practiced terrestrially, a lift-generating vehicle executes a maneuver that exploits the difference in wind speeds between two different regions of the air, for example, the wind blowing over a hilltop and the quiescent air on the leeward side of the hill," Larrouturou and the team explained in the study. The same technique was invoked by seabirds for flight.

To elaborate, a lift is generated by extracting power in the direction of the medium blowing over the spacecraft and accelerating flow in the perpendicular direction. In the researchers' concept, however, no onboard reaction mass is used, resulting in a type of lift-generating wing sans a physical structure. 

The scientists picture a "magnetohydrodynamic wing," and as aforementioned, it wouldn't have a tangible structure but one with magnetic fields similar to the physical wing of a bird.

This wing could be produced by using a plasma wave antenna made of two plasma magnets. The field created by the magnets could interact with the solar wind flows in different directions, thereby creating lift.

Eliminating the usage of propellant

"A physical wing would be impractically heavy, so instead, we expand upon Jeff Greason's (commercial space innovator) idea of extracting power from the flow of plasma blowing over the vehicle. In this new paper, we push the idea one step further and eliminate using propellant entirely. Instead, the power extracted from the flow over the vehicle is used to accelerate the surrounding medium in the perpendicular direction, generating a transverse force: Lift!" the tweet said.

"Development of the concept of interacting with the solar wind as a means of propulsion will require experimental validation in stages, the first of which would be a demonstration of significant drag against the solar wind using a magnetic structure for propulsion," the researchers write.

"The plasma magnet appears to be the highest performing in terms of accelerations of the drag concepts reviewed in the Introduction, so a plasma magnet technology demonstration would appear to be the next logical step."

Reaching planetary bodies in just months

Their concept would help humanity reach planets like Jupiter in months.

The researchers also mention a 16U CubeSat demonstrator concept called Jupiter Observing Velocity Experiment (JOVE) that could transit the orbit of Jupiter just six months after launch from Earth and another application of the wind-riding plasma magnet technology called Wind Rider Pathfinder Mission. 

"These groundbreaking missions would provide validation that meaningful propulsive power could be extracted from the solar wind, providing a foundation for the more advanced concept of extracting electrical power from the wind for lift generation," the scientists added.

Their results are published in Frontiers in Space Technology.

Study Abstract:

A technique by which a spacecraft can interact with flows of ionized gas in space (the solar wind or interstellar medium) in order to be accelerated to velocities greater than the flow velocity is explored. Inspired by the dynamic soaring maneuvers performed by sea birds and gliders in which differences in wind speed are exploited to gain velocity, in the proposed technique a lift-generating spacecraft circles between regions of the heliosphere that have different wind speeds, gaining energy in the process without the use of propellant and only modest onboard power requirements. In the simplest analysis, the spacecraft motion can be modeled as a series of elastic collisions between regions of the medium moving at different speeds. More detailed models of the spacecraft trajectory are developed to predict the potential velocity gains and the maximum velocity that may be achieved in terms of the lift-to-drag ratio of the vehicle. A lift-generating mechanism is proposed in which power is extracted from the flow over the vehicle in the flight direction and then used to accelerate the surrounding medium in the transverse direction, generating lift (i.e., a force perpendicular to the flow). Large values of lift-to-drag ratio are shown to be possible in the case where a small transverse velocity is imparted over a large area of interaction. The requirement for a large interaction area in the extremely low density of the heliosphere precludes the use of a physical wing, but the use of plasma waves generated by a compact, directional antenna to impart momentum on the surrounding medium is feasible, with the excitation of R-waves, X-waves, Alfven waves, and magnetosonic waves appearing as promising candidates. A conceptual mission is defined in which dynamic soaring is performed on the termination shock of the heliosphere, enabling a spacecraft to reach speeds approaching 2% of c within two and a half years of launch without the expenditure of propellant. The technique may comprise the first stage for a multistage mission to achieve true interstellar flight to other solar systems.