A propellant-free superconducting solenoid thruster driven by geomagnetic field

Introduction: Space travel nowadays relies on physical ejection of propellants, which is challenged by reachable distance of a vehicle in desirable time. In contrast, electromagnetic propulsion was proposed to be a potential solution without need of carrying bulky mass of propellants, by using force interaction of local magnetic dipoles with the external natural magnetic field. Further development of this technique, however, has been daunted by extremely small magnetic induction that can be obtained. Objectives: To generate a significant thrust by a system with a reasonable scale, we propose an alternative concept of design, based on the variation of local magnetic dipole moments that has not been considered. Methods: A magnetic dipole is created by wrapping a solenoid around an iron core. It is varied spatially by changing the cross-sectional area of the solenoid, hence giving a gradient of magnetic dipole moment. The interaction force is measured by an in-house force sensor based on a cantilever, which has a high sensitivity of one micro-Newton. In addition, numerical simulation is used to calculate the magnetic field and created force via the Maxwell stress tensor. Results: As shown by experimental measurements and numerical simulations, a substantially larger magnitude of force is obtained on the solenoid with varying cross-sectional area, indicating a much stronger interaction with the geomagnetic field. Furthermore, to enhance electric current with negligible dissipation, a superconducting solenoid can be adopted at low temperature in space. With readily attainable conditions of operation, we demonstrate generation of a thrust comparable to that of present electric propulsion thrusters which are deemed as the most promising techniques for long-term space travel. Conclusions: By incorporating supplementary means, we provide a breakthrough solution for constructing an efficient thruster with minimal energy consumption and nearly null propellant load for near-Earth transportation and deep-space exploration.