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#3440
by
SeeShells
on 15 May, 2015 20:58
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The search function aren't that super here euuuuu.
Why is the RF injected into the side of the EM Device. I know it's a basic question but can someone expand on it a little more?
Shells
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#3441
by
deltaMass
on 15 May, 2015 21:15
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About Bae's PLT:
The technique will come into its own when alignment over at least one million Km is feasible.
Now you'll notice that they were in a clean room (albeit in air) so that should give pause to anyone considering using this as a launch system for extremely light payloads directly from Earth's surface. Nevertheless, a little noodling would not go amiss on this topic.
The available motive power is Q*P (Q=200, P=800 W in the video), so the force F = 2*Q*P/c (1.1 mN in the video), so the acceleration a = F/m (m=0.45 Kg, a = 2.5 mm/s2 in the video).
What would it take to get up to 1 gee for an Earth-based launch?
The acceleration needs to be increased by a factor of ~4000x.
Putting this all together we get
a = 2 Q P / (m c)
Leaving m alone for the moment, Bae states that Q could improve by a factor ~5x (200->1000).
Now we need 4000/5 = 800x improvement.
Using a 800 kW laser does that for us (1000x).
Alternatively we can use a lower mass and thus a lower power laser.
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#3442
by
deltaMass
on 15 May, 2015 21:22
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The search function aren't that super here euuuuu.
To be blunt, it totally sucks
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#3443
by
jmossman
on 15 May, 2015 21:32
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The search function aren't that super here euuuuu.
Why is the RF injected into the side of the EM Device. I know it's a basic question but can someone expand on it a little more?
Shells
No one else has chimed in, so I'll give this a shot.
I believe the choice of antenna position is predominantly a function of the antenna beam pattern, and the desire to couple maximum energy into the cavity.
A simple dipole antenna radiates/couples well in the perpendicular direction, so placing a dipole antenna perpendicular to the cavity wall would allow direct coupling into the dominant resonant direction (i.e. between the concave/convex end plates).
(attached image from
http://www.trevormarshall.com/byte_articles/byte1.htm)
I had proposed (many pages back) that the use of a waveguide to inject a magnetron's signal had the effect of a directional beam pattern that was much better at injecting energy than removing energy from the cavity. (since resonanting energy is dominantly between the end plates, a waveguide input roughly perpendicular to the walls would inject energy better than remove energy) However, I'll readily admit my reasoning may be overly simplistic.
Thanks,
James
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#3444
by
Rodal
on 15 May, 2015 21:48
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About Bae's PLT:
The technique will come into its own when alignment over at least one million Km is feasible.
Now you'll notice that they were in a clean room (albeit in air) so that should give pause to anyone considering using this as a launch system for extremely light payloads directly from Earth's surface. Nevertheless, a little noodling would not go amiss on this topic.
The available motive power is Q*P (Q=200, P=800 W in the video), so the force F = 2*Q*P/c (1.1 mN in the video), so the acceleration a = F/m (m=0.45 Kg, a = 2.5 mm/s2 in the video).
What would it take to get up to 1 gee for an Earth-based launch?
The acceleration needs to be increased by a factor of ~4000x.
Putting this all together we get
a = 2 Q P / (m c)
Leaving m alone for the moment, Bae states that Q could improve by a factor ~5x (200->1000).
Now we need 4000/5 = 800x improvement.
Using a 800 kW laser does that for us (1000x).
Alternatively we can use a lower mass and thus a lower power laser.
See:
http://ykbcorp.com/downloads/Bae_photon_propulsion_STAIF2_Paper_Circulation.pdf
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#3445
by
deltaMass
on 15 May, 2015 22:16
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Props to anyone who spots the error in my calculation
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#3446
by
phaseshift
on 15 May, 2015 23:59
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Does the Flight Thruster have a slightly concave top and convex bottom? Would appear so from the gaps.
Enhanced the photo as much as I can for those wishing to try to extract dimensions as this photo is better that the original as it has no distortion.
If we can find the dimensions of the bottom Rf connector flange, we can set pixels per cm and start doing measurements.
Most N connectors like that are 1" square, and the holes are .718" center line to center line.
Pixel away. 
Thanks. Have fine rotated to vertical / horizontal and lined up. Attached if anyone else wants to have a go.
Using the enhanced photo I built a Google SketchUp model such that when overlayed with the image it matches. Then I scaled the model so that the RF connector plate measured 1 inch along one side. The resulting cone has dimensions of sD: 122.2mm, bD: 223.8mm, L: 153.98mm. Not sure the margin of error but the numbers should look fairly close I hope.
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#3447
by
zellerium
on 16 May, 2015 00:06
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Random thought but;
1- Could someone please try an em cavity with the bottom (large curved end) not electrically bonded to the sidewalls & top. ie place a circular insulating gasket between the contact point of the sidewall bottom edge and the actual bottom curved plate, just the wall/plate boundary NOT covering the internal surface area of the curved plate.
What do you think will be different if the bottom plate is electrically insulated?
I think we could easily incorporate this into our design, we have planned to leave a small clearance between the bottom movable plate and the frustum. Our bottom plate may not be as curved as Shawyer's, but we'll be able to provide a small amount of curvature by tighting the screws to different lengths.
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#3448
by
deltaMass
on 16 May, 2015 00:15
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Accurate to about 5% = 1-cos(18o). Could be better were you to use my observation about the distortion in the 1" dimensions.
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#3449
by
aero
on 16 May, 2015 00:21
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I have this, but don't know what the small end chord, large end chord, or the perpendicular distance between the chords should be, in terms of wavelengths. Or the drive frequency for that matter.
What is your antenna like. A centered dipole (vertical in the images) works well, and the longer the better it seems to me.
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#3450
by
phaseshift
on 16 May, 2015 00:23
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Accurate to about 5% = 1-cos(18o). Could be better were you to use my observation about the distortion in the 1" dimensions.
It's an actual 3D Model and the projection lines up to a pixel, so the 'distortion' should be accounted for.
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#3451
by
phaseshift
on 16 May, 2015 00:25
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Random thought but;
1- Could someone please try an em cavity with the bottom (large curved end) not electrically bonded to the sidewalls & top. ie place a circular insulating gasket between the contact point of the sidewall bottom edge and the actual bottom curved plate, just the wall/plate boundary NOT covering the internal surface area of the curved plate.
What do you think will be different if the bottom plate is electrically insulated?
I think we could easily incorporate this into our design, we have planned to leave a small clearance between the bottom movable plate and the frustum. Our bottom plate may not be as curved as Shawyer's, but we'll be able to provide a small amount of curvature by tighting the screws to different lengths.
After building the 3D-Model I'm 'fairly certain' there is a rubber gasket between the end plates and cone. It's 1/16 of an inch thick in the model which reflects what I see in the image.
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#3452
by
phaseshift
on 16 May, 2015 00:29
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A little more detail - hidden edges can be seen in the xray rendering.
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#3453
by
Notsosureofit
on 16 May, 2015 00:34
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Random thought but;
1- Could someone please try an em cavity with the bottom (large curved end) not electrically bonded to the sidewalls & top. ie place a circular insulating gasket between the contact point of the sidewall bottom edge and the actual bottom curved plate, just the wall/plate boundary NOT covering the internal surface area of the curved plate.
What do you think will be different if the bottom plate is electrically insulated?
I think we could easily incorporate this into our design, we have planned to leave a small clearance between the bottom movable plate and the frustum. Our bottom plate may not be as curved as Shawyer's, but we'll be able to provide a small amount of curvature by tighting the screws to different lengths.
After building the 3D-Model I'm 'fairly certain' there is a rubber gasket between the end plates and cone. It's 1/16 of an inch thick in the model which reflects what I see in the image.
Typically, it would be a copper gasket w/ bevels on the plate edges, but rubber o-rings could be used. In any event, they would be used to make it vacuum tight. (the copper gaskets are ~1/16")
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#3454
by
Iulian Berca
on 16 May, 2015 00:38
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The search function aren't that super here euuuuu.
Why is the RF injected into the side of the EM Device. I know it's a basic question but can someone expand on it a little more?
Shells
It was first question in my mind also. Why not on top or bottom ?
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#3455
by
Rodal
on 16 May, 2015 00:57
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I am back with an updated draft after some terrible news around about NASA dismissing these researches. They should not as, otherwise, it could happen as with Galilei having his detractors even not trying to look in the telescope, just dismissing on faith.
I have analysed the case of the frustum and the results appear to be striking. One must admit that geometry comes to rescue not just general relativity. For this particular geometry the cavity can be made susceptible to gravitational effects if your choice of the two radii of the cavity is smart enough. This is something to be confirmed yet, just my theoretical result, but shocking anyway.
As usual, any comment is very welcome.
In page 8, equation 34 of
http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=36313.0;attach=830137,
for the integral on dr', should the limits, instead of
0 to ((r2-r1)/h) z' +
r2be
r1 to ((r2-r1)/h) z' +
r1 ?
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#3456
by
Notsosureofit
on 16 May, 2015 01:02
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I am back with an updated draft after some terrible news around about NASA dismissing these researches. They should not as, otherwise, it could happen as with Galilei having his detractors even not trying to look in the telescope, just dismissing on faith.
I have analysed the case of the frustum and the results appear to be striking. One must admit that geometry comes to rescue not just general relativity. For this particular geometry the cavity can be made susceptible to gravitational effects if your choice of the two radii of the cavity is smart enough. This is something to be confirmed yet, just my theoretical result, but shocking anyway.
As usual, any comment is very welcome.
In page 8, equation 34 of http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=36313.0;attach=830137,
for the integral on dr', should the limits, instead of
0 to ((r2-r1)/h) z' + r2
be
r1 to ((r2-r1)/h) z' + r1 ?
Good Point ! But volume integral ? 0 to ... ((r2-r1)/h) z' + r1 /l0 ? (seems circular that way)
It's Eq. 18 that still bothers me a bit. Invoking the Heaviside step function is OK, but I don't see the addl. components being detectable outside the cavity w/o a non-linear term. Maybe I'm missing something ?
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#3457
by
LasJayhawk
on 16 May, 2015 01:08
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The search function aren't that super here euuuuu.
Why is the RF injected into the side of the EM Device. I know it's a basic question but can someone expand on it a little more?
Shells
Beats me. And it looks like the placement would put part of the big end in the near near field and loading the bejesus out of the source.
I've also noted they use a simple loop antenna, but there seems to be no consideration to what we called at Collins the "look angle"
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#3458
by
deltaMass
on 16 May, 2015 01:14
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Collins used to make top line ham receivers back in the day
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#3459
by
ThinkerX
on 16 May, 2015 01:17
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The search function aren't that super here euuuuu.
Basically, you have to use a defined google search to find past items of interest on this thread.
