Difference between revisions of "Generic EM Drive Information"

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(Mode Shape: added link to new Dimensions page)
(Added information about how frequency, Q, and mode shape bundle together.)
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See calculations pertaining to the relationship between thrust and mode shape at [http://forum.nasaspaceflight.com/index.php?topic=36313.msg1317866#msg1317866 Notsosureofit's post] and [http://forum.nasaspaceflight.com/index.php?topic=36313.msg1318217#msg1318217 Rodal's response.]
 
See calculations pertaining to the relationship between thrust and mode shape at [http://forum.nasaspaceflight.com/index.php?topic=36313.msg1317866#msg1317866 Notsosureofit's post] and [http://forum.nasaspaceflight.com/index.php?topic=36313.msg1318217#msg1318217 Rodal's response.]
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An EM Drive is a cavity resonator that uses the Quality Factor Q to achieve greater response. There is definitely a peak resonant frequency to achieve the highest Q, though besides Q and frequency, mode shape must also be considered. The shape of the electric and magnetic fields inside the cavity at a given frequency.<ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1319407#msg1319407 Rodal on frequency, Q, and mode shape.]</ref>
  
 
The mode-shape to frequency relation is very sensitive to the exact [[Dimensions]] of the cavity. <ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1319117#msg1319117 Rodal's post on geometric relations to mode shape.]</ref>
 
The mode-shape to frequency relation is very sensitive to the exact [[Dimensions]] of the cavity. <ref>[http://forum.nasaspaceflight.com/index.php?topic=36313.msg1319117#msg1319117 Rodal's post on geometric relations to mode shape.]</ref>

Revision as of 12:32, 20 May 2015

This is a location for assorted information concerning EM Drives. Likely applies to all current experimental efforts.

Conservation of Energy Violation

Doctor White has proposed that the EM Drive is capable of producing constant thrust at a constant power output. User frobnicat has shown (in the following text and image) that if this were to be true, then the EM Drive could be utilized as a source of unlimited energy. [1] This of course constitutes a violation of Conservation of Energy.

"As often remarked : for any propellantless device yielding "given constant thrust for given constant power" (ie. a definite thrust/power ratio) there is a velocity relative to a power feedback loop system above which net power surplus can be generated (indefinitely, wear apart). This velocity is simply the inverse of the thrust/power ratio : V (m/s) = power (W) / thrust (N)." -frobnicat [2]

On the assumption that the results provided by the various experimenting groups are valid, then one of the following two options as provided by user deltamass[3] and clarified by user frobnicat [4] must be true. The options are as follows:

Option 1: Energy is conserved, but there is a preferred rest frame. In essence, the drive has a maximum change in velocity (a decreasing acceleration curve) that it can impart irrespective of its starting velocity. The idea of a preferred rest frame is at odds with general relativity.

Option 2: An apparent breach of conservation of energy is possible, where the mechanism by which conservation of energy is maintained is as yet unknown. An example of a possible solution to this problem is that the drive could in some way be emitting tachyons.[5]

Tachyons are fictional particles that can travel faster than the speed of light. Sending signals faster than light, leads to violations of causality, see: Tachyonic Antitelephone.

Since option 1 leads to a violation of general relativity and option 2 leads to a violation of causality, one concludes that, with constant input power supplied to the EM Drive, the acceleration cannot be constant. As remarked by WarpTech the acceleration must decrease with increasing velocity, as per Newton's 2nd law:[6]

Acceleration = Thrust / Mass = Power / (Mass*Velocity)

So, for constant input power to the EM Drive (and constant vehicle mass), the vehicle's acceleration must decrease in inverse proportion to the vehicle's velocity. To achieve constant acceleration, increasing power must be supplied to the EM Drive, in proportion to the increasing velocity.

Mode Shape

See calculations pertaining to the relationship between thrust and mode shape at Notsosureofit's post and Rodal's response.

An EM Drive is a cavity resonator that uses the Quality Factor Q to achieve greater response. There is definitely a peak resonant frequency to achieve the highest Q, though besides Q and frequency, mode shape must also be considered. The shape of the electric and magnetic fields inside the cavity at a given frequency.[7]

The mode-shape to frequency relation is very sensitive to the exact Dimensions of the cavity. [8]

References