Variable Mass Propellantless Propulsion Drive Authors: Matthew Gorban and Gerald Cleaver Background – In order to break through the confines of our solar system and travel to distant stars, new and groundbreaking propulsion techniques are needed that far exceed the capacity of even the most powerful and efficient modern engines. Objective – We introduce a gedanken experiment that generates thrust, through the construction of a propellantless propulsion drive, by using a variable mass object under the influence of a mass-dependent potential. Several methods of altering an objects mass are investigated, including the Casimir effect, and their realistic use when applied to this setup is analyzed. Methods – Our engine design uses a mass dependent potential to induce a displacement of a variable mass object in an isolated spring system. By carefully controlling the mass of the object, or conductivity in the case of a Casimir cavity, over the different portions of the harmonic cycle of a mass-spring system, one may generate a small amount of net thrust along the direction of cavity motion, while total conservation of momentum is necessarily maintained. Results – Preliminary gedanken experiment results reveal a small, but useful, amount of thrust that may be used to push a macroscopic system through space without the need to carry on-board propellant. (Energy must nevertheless be added to the system.) We also outline a way to scale the engine system by stacking additional variable spring-mass oscillators and developing a more efficient variable mass oscillator design. We demonstrate a change in the linear momentum of the system via careful consideration of the conservation of momentum. Conclusions – We present a new propellantless propulsion drive that takes advantage of a unique property imparted to a system with a variable mass object. This system possesses the advantage of macroscopic scalability and increased efficiency necessary for future in-space propulsion missions to distant targets at the boundary of our solar system and beyond.