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.
Examples are a gravity assist trajectory, which uses planetary gravity fields and orbital momentum, schemes that use electromagnetic fields such as radiation pressure, e.g. solar sails or photonic drive, and aerodynamic fields such as solar wind and aerobraking.
Other concepts that have been proposed are more speculative, using "frontier physics" that may or may not become engineering practice in the future. Based on General Relativity, the Woodward effect is considered the leading candidate. (NASA, BPP)
Although speculative, ideas such as coupling to the momentum flux of the zero-point electromagnetic wave field hypothesized in stochastic electrodynamics have a plausible basis for further investigation within the existing theoretical physics paradigm. Examples of proposals for field propulsion that rely on physics outside the present paradigms are various schemes for faster-than-light, warp drive and antigravity, and often amount to little more than catchy descriptive phrases, with no known physical basis. Any such schemes worthy of discussion must rely on energy and momentum transfer to the spacecraft from some external source such as a local force field, which in turn must obtain it from still other momentum and/or energy sources in the cosmos, in order to satisfy conservation of both energy and momentum.
One possible method gaining some credibility involves magnetohydrodynamics, in which the entire vehicle acts like the armature of an electric motor and the external environment acts as the stator. Instead of the engine being a separate or distinct part of the vehicle, in this system the vehicle's power source, controls, payload and occupants are all inside the engine itself. This system seems to satisfy many of the requirements of a field propulsion system and is based on known field theory. It represents a radical departure from current ideas of aeronautics and rocket propulsion, and as such, might offer potential for a radical advance in performance capabilities.
Electrohydrodynamics is another method whereby electrically charged fluids are used for propulsion and boundary layer control.
In the Standard Model, force carriers include electromagnetism, weak force, and strong force. Electroweakhydrodynamics has the potential for propulsion systems. The strong interaction is dependent on the gluon of which there are eight types. These eight variations may prove difficult and challenging for a field propulsion system. In the future, the Higgs particle also be a candidate for high energy propulsion.
Just beyond the Standard Model but within mainstream science (which does not include gravity) are the gravitational field which does behave like a fluid. The Euler equations (fluid dynamics) can be extended to include gravity.  (see Misner Thorne and Wheeler: Gravitation). Einstein's General relativity provide the basis for gravity and inertia.
- Advanced Space Propulsion Investigation Committee
- Breakthrough Propulsion Physics Program
- Eugene Podkletnov
- United States gravity control propulsion research
- Reactionless drive
- Woodward effect
 Examples of current field propulsion systems for ships. http://www.ovaltech.ca/spctrvl/thryop3.html
 Example of a possible field propulsion system based on existing physics and links to papers on the topic. http://www.ovaltech.ca/spctrvl/oneinddrv.html
 Stoyan Sarg, Field Propulsion by Control of Gravity - Theory and Experiments, 2009, ISBN 978-1-4486-9308-5.
 Y. Minami., An Introduction to Concepts of Field Propulsion, JBIS,56,350-359(2003).
 Minami Y., Musha T., Field Propulsion Systems for Space Travel, the Seventh IAA Symposium on Realistic Near-Term Advanced Scientific Space Missions, 11–13 July 2011, Aosta, Italy
 Ed.T.Musha, Y.Minami, Field Propulsion System for Space Travel: Physics of Non-Conventional Propulsion Methods for Interstellar Travel, 2011, ISBN 978-1-60805-270-7.
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