Reactionless propulsion

A reactionless drive or inertial propulsion engine (also reactionless thruster, reactionless engine, bootstrap drive, and inertia drive) is any form of propulsion not based around expulsion of fuel or reaction mass.

The name comes from Newton's Third Law of Motion, usually expressed as: "For every action, there is an equal and opposite reaction." Such a drive would use a hypothetical form of thrust that does not require any outside force or net momentum exchange to produce linear motion, and therefore necessarily violates the conservation of momentum, a fundamental principle of all current understandings of physics. In addition it can be shown that conservation of energy is violated.

In spite of their physical impossibility, such devices have been often proposed in recent history.

Contents

Physics of reactionless drives

In a sentence: "The underlying problem [with reactionless drives] is that breaking the law of conservation of momentum shatters the entire mathematical framework [of physics]."[1] These devices by their very nature violate the law of conservation of momentum - if a ship with such a drive existed, then any motion of that ship, being unaccompanied by the motion of any other material, would cause the center of gravity of the universe to move with it. Furthermore, the total energy of the universe becomes reference frame dependent - energy can only be conserved in the presence of a reactionless drive in (at most) one reference frame, because in all other reference frames the change in kinetic energy of the ship differs from the power expended by the ship. Given that these two laws - the conservation of momentum and the principle of relativity - are so well established (and thoroughly verified) in physics, any ordinary mechanical system purporting to violate the laws is generally dismissed outright.[2]

(Even if we granted these violations, then it would not only change the sum of momentum in our nearby reference frame, but in fact render the concept of momentum entirely dependant of the observer. However it also means the movement of rotation of earth around itself, the sun and the milky way etc. etc. does not have to be taken into account, since all movement (and momentum, whatever it'd be in this scenario) happens in relation to the given point of observer in space. The earth moves in relation to other particles in space, not THROUGH the space as you may think.)

Hal Puthoff coined the term "metric engineering" for reactionless drives. The idea is direct control of the gravity field through its coupling to the electromagnetic field. Jack Sarfatti http://www.americanchronicle.com/articles/view/96198 has taken Hal Puthoff's suggestion to the next step noting that Ray Chiao's "gravity radio" claims to increase the coupling between electromagnetic microwaves and gravity microwaves by about 42 powers of ten in a thin film Type 1 superconductor. Chiao is testing his theory at the University of California Merced http://faculty1.ucmerced.edu/rchiao/2.cfm?pm=113&lvl=3&menuid=117 The equivalence principle says that there is zero g-force on timelike geodesics. The idea is to electromagnetically control the shape of the timelike geodesic that the ship freely-floats on (e.g. Alcubierre's toy model of warp drive). If there is an effective amplification of the gravity field coupling large enough, then the power requirements go down significantly.

Types

Oscillation thruster

An oscillation thruster (also known as a stiction drive, internal drive or slip-stick drive) uses the motion of internal masses to create a net thrust. These thrusters include either vibrational or rotating masses, in which one portion of the cyclical motion is high-speed, and the other low-speed, or alternately high and low impulse. The result is that for some of the motion there is a high force being generated, enough to overcome friction. However on the "return stroke" the force is not high enough, and any motion occurring in the first portion is not reset. In this way the devices "steal" working mass from their supporting surface, a fact that may not be apparent to casual observation.

Basically, an oscillation thruster works just like walking does, one mass is "thrown" backward, "thrusting" the device forward according to conservation of momentum (like a person taking a step forward), then the mass is more slowly brought forward to its initial position (like the person using their step to pull the rest of their body forward). The thruster is allowed to move forward in the first step because the mass is "thrown" back with large enough force to overcome static friction. The "thruster" doesn't move backward in the second step because static friction provides an outside force that overcomes the step (like the ground does when you're walking).

Although there have been many versions proposed, all oscillation thrusters have the following common components:

  • Chassis to support a system of masses,
  • Conveyor that moves the masses through an asymmetric cycle,
  • Power source for the conveyor.

A crucial feature is that these internal masses go through some sort of cyclic motion where the motion in one direction is quicker than in the return direction.

Inventors of oscillation thrusters extrapolate its behavior to mean that it can work in a vacuum in zero gravity.

One of the most famous proposed reactionless drives was the Dean drive. Although Dean himself gave few indications of how his "reactionless drive" was supposed to work, it appears to be an attempt at an oscillation thruster. Other examples of oscillation thrusters are:

Electrostatic anti-gravity

Electrostatic anti-gravity relies on oddly placed capacitors and a high-voltage source. Claims of electrostatic anti-gravity are explained by the Biefeld–Brown effect, which is distinctly not anti-gravity. Believers of this form of "anti-gravity" agree that the Biefeld–Brown effect is in action, but say that it does not account for all the upward force. This area of research has not been fully exhausted, but all verified experiments fail to show any new physics. Supposed "Electrostatic anti-gravity"-machines have been tested in vacuum, even in an episode of the Mythbusters, and either insufficient force or no force at all was produced by the test device able to levitate it, at the undeclared vacuum level that the experiment was performed. In the Mythbusters experiments in vacuum, the lowest unit of force detectable was the device ability to lift its own weight, which was not observed. A company by the name of Gravitec claims to have demonstrated this unaccounted force in an experiment conducted with NASA, but to date, no evidence exists of this claim, and NASA have no record of any such experiment.

Electromagnetic tethers

At first glance, a device called the electrodynamic tether might appear to constitute a reactionless drive[3] because it does not expel reaction mass. But it is still not reactionless, as electromagnetic fields can carry energy and momentum.[4]

The fundamental scientific problem is one of momentum transfer. If there is no momentum transfer, the postulated device is classified as a "reactionless" drive and labelled a fraud. If there is a mechanism for momentum transfer, then the device is classed as a reaction drive and is therefore by definition not a "reactionless" drive. Tethers do have a mechanism for momentum transfer and although they do not expel reaction mass like a rocket, they do transfer momentum and hence cannot be a true reactionless drive.

See also

References

  1. ^ Atomic Rockets: Reactionless drives
  2. ^ Sean Carroll, The Alternative Science Checklist
  3. ^ Tethers | Macmillan Space Sciences. Accessed 2008-05-04.
  4. ^ Special Projects Group via Internet Archive. Accessed 2008-05-04.

External links

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This page was last modified on 5 March 2010 at 07:49.

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