Field propulsion

Field propulsion is the concept of spacecraft propulsion where no propellant is necessary but instead momentum of the spacecraft is changed by an interaction of the spacecraft with external force fields. The concepts for such means of propulsion range from schemes using the presently accepted physics paradigm to other more speculative means using "frontier physics" that may or may not be discovered in the future. Schemes for field propulsion that operate within presently within the present physics paradigm , such as the commonly used gravity assist trajectory, which uses planetary gravity fields and orbital momentum, schemes that use electromagnetic fields such as radiation pressure such as solar sails or photonic drive, and even aerodynamic fields such as solar wind and aerobraking. Concepts for field propulsion that rely on physics outside the present paradigms are various schemes for Warp drive and antigravity. All such schemes worthy of discussion rely on momentum transfer from the spacecraft to the external force field and from there to other masses in the cosmos in order to satisfy conservation of momentum.