Author Topic: EM Drive Developments - related to space flight applications - Thread 3  (Read 1800948 times)

Offline OttO

  • Member
  • Posts: 81
  • France
  • Liked: 91
  • Likes Given: 11
It is funny how while hunting in the internet I found that our EM problems have analog in water, sound and light.

When you google about tapered cavity a lot of work about light is going out. And with or without dielectric. What some of you guys talk about with horizon, gravity seems to have been explored.

http://extremelight.eps.hw.ac.uk/publications/CQG-optical_BH_laser-Faccio(2012).pdf

http://relativity.livingreviews.org/Articles/lrr-2011-3/download/lrr-2011-3BW.pdf

there was even an experience with light bullets preventing a violation of CoM.




Offline OttO

  • Member
  • Posts: 81
  • France
  • Liked: 91
  • Likes Given: 11
No, no toaster elements allowed.

Silly as it seems I think it would be a cheap and strong way to prove that the thermal effects are not a problem.
Put on the resistors to red hot and measure. If the Z displacement is inferior that the one with EM...
« Last Edit: 06/10/2015 02:49 PM by OttO »

Offline Star One

  • Senior Member
  • *****
  • Posts: 8013
  • UK
  • Liked: 1280
  • Likes Given: 168

It can measure thrust by its vertical Z displacement up or down

Do you plan to put in it toaster resistors to measure the infrared influence  :)

No, no toaster elements allowed.

I will be using a plastic container to keep any magnetic components from the EMdrive acting on the side walls. And don't laugh as this will work fine and it is inexpensive.

Are you making a comment there as you appear to be testing it in a dustbin.;)

Offline TMEubanks

...

The chart posted above does NOT seem to include atmospheric drag (which dramatically changes orbital lifetimes etc. at low altitudes). Note that most cubesat launches are at 300 - 400 km - the ISS is 330 km, and that is probably the easiest platform to launch from.

A cubesat is 0.1x0.1 meter (1U), so its area is 10^-2 m^2. Its mass will be ~ 1 kg.

Assume 0.1 N/kW or 10^-4 N/W or ~ 5 x 10^-5 N for a 0.5 W drive. That means we want forcing to be
(ideally) << 5 x 10^-3 N/m^2 to be sure a thrust observed is actually from the thruster. (If drag is large, then you will never be able to model it well enough to say that <thrust - drag> is actually meaningful.)

Solar radiation pressure is 4.5 (absorption) to 9 (reflection) micro N / m^2, so radiation force will be
< 10^-7 N, which is fine and can be ignored. (For LEO, the radiation pressure from the Earth is also substantial, and hard to model as it depends on cloud albedo, but it will be < solar and so also can be ignored).

Drag at altitude depends heavily on the solar activity, and thus the solar cycle (which brought Skylab down).  We are near peak right now, which is bad, but in 2 or 3  years or so things could be a lot better. See this prediction:

http://en.wikipedia.org/wiki/Solar_cycle_24#/media/File:Solar_cycle_24_sunspot_number_progression_and_prediction.gif

Looking at the old Harris-Preister model atmosphere (see Figure 2 of
http://stk.com/downloads/support/productSupport/literature/pdfs/whitePapers/A%20Critical%20Assessment%20of%20Satellite%20Drag%20.pdf ) we would want the altitude to be > 300 km. At 400 km, Harris-Preister drag prediction is 3 x 10^-4 N/m^2, which might be OK, but is a little too close for comfort for me.

That says to me that a CASIS launch of a test from Station would not be adequate, but a launch to 500 or 600 km circular orbit would be fine. Launches at that altitude still count as LEO, and are available as get-away specials. (For various reasons, get-away specials basically never seem to be available for launches to GEO and higher.)

Also note that a 600 km circular orbit is about as high as you can go with a reasonable expectation of a 25 year post mission lifetime for a cubesat, which is needed to meet IADC guidelines on limiting space debris :
http://mstl.atl.calpoly.edu/~bklofas/Presentations/DevelopersWorkshop2011/8_Leveque_Orbital_Decay.pdf

Thank you Marshall, this is an excellent explanation as to why nobody has reported launching the EM Drive yet to the International Space Station or such a low Earth orbit.  Launching it to a low orbit where it would be subject to air drag would just serve to continue the present state of uncertain experimental results at ground level, but at a low earth orbit would mean a much higher cost, where the experimental uncertainty of the ground tests with the EM Drives is such that there is no scientific demonstration that an EM Drive force that can be used for space propulsion is being measured, since the experimental variations and uncertainty overwhelm the present results.

It is still fortunate that one can rescue some positive news from this, that launching at >500km circular orbit would be fine and that still qualifies for relatively low rates [but this rules out the International Space Station is definitely out since its orbit is too low 417 km]   :):

Quote
a launch to 500 or 600 km circular orbit would be fine. Launches at that altitude still count as LEO, and are available as get-away specials


That's about the orbit of the Hubble Telescope, isn't it ?  (559 kilometers)





I believe that's the altitude they raised the Hubble to in the last servicing mission (Wikipedia says ~ 550 km). If nothing is done, of course, it will eventually come down in a few decades.

Here is a plot of Station altitude versus time. You can see the various boosts and the altitude now is indeed more like 400 km. It needs frequent boosts to maintain its orbit, and there is a tendency for the mean height to decline some over time (even with boosting) requiring a big boost every few years to raise it again.

http://www.heavens-above.com/IssHeight.aspx


Offline SeeShells

  • Senior Member
  • *****
  • Posts: 2326
  • Every action there's a reaction we try to grasp.
  • United States
  • Liked: 2956
  • Likes Given: 2589

It can measure thrust by its vertical Z displacement up or down

Do you plan to put in it toaster resistors to measure the infrared influence  :)

No, no toaster elements allowed.

I will be using a plastic container to keep any magnetic components from the EMdrive acting on the side walls. And don't laugh as this will work fine and it is inexpensive.

Are you making a comment there as you appear to be testing it in a dustbin.;)
No comment here and I'm sorry it had to be a Trash can, but it is cheap, strong, non-ferrous plastic and the right size.

I know some here will say ... And if it doesn't work just put it out by the curb.

Offline SeeShells

  • Senior Member
  • *****
  • Posts: 2326
  • Every action there's a reaction we try to grasp.
  • United States
  • Liked: 2956
  • Likes Given: 2589
Why not just launch 2 in tandem? One without an EM thruster and get real baseline data comparing the two orbits? Eliminate a lot of unknowns in your test.
Shell

Offline vulture4

  • Full Member
  • ****
  • Posts: 987
  • Liked: 305
  • Likes Given: 89
No, no toaster elements allowed.

Silly as it seems I think it would be a cheap and strong way to prove that the thermal effect are not a problem.
Put on the resistors to red hot and measure. If the Z displacement is inferior that the one with EM...

An excellent idea. Start with a simpler experimental setup (heating only) and measure generated forces.

As I noted before, the Shawyer data (based on the measured thrust) requires an incident flux of at least 15 megawatts on the end of the frustrum to produce the measured force through radiation pressure even if there is no counteracting forceat all on the opposite end. This level of power would have produced obvious thermal and electromagnetic leakage. The radiation flux can be (and apparently was) measured with a small dipole inserted into the resonator. This would be of interest, and would provide an upper limit to the force that could have been generated based on the total radation pressure on the large end of the resonator. Anything in excess of this must be the result of an experimental artifact.

There has been quite a bit of discussion suggesting that the measurement must be one of actual motion of the device in response to the force, using air bearings, flotation, or weightlessness, rather than measurement of the force under static test conditions. I cannot see any rationale for this, it appears to violate the equivalence principle. Nevertheless the most accurate way to measure thrust under dynamic conditions is simply to mechanically apply any desired movement profile to the device and measure the force it produces. Allowing the device to move freely permits any unanticipated force to remain unmeasured and produce unpredictable accelerations.

Online Rodal

  • Senior Member
  • *****
  • Posts: 5838
  • USA
  • Liked: 5919
  • Likes Given: 5259
Why not just launch 2 in tandem? One without an EM thruster and get real baseline data comparing the two orbits? Eliminate a lot of unknowns in your test.
Shell
Because as Marshall said, " (If drag is large, then you will never be able to model it well enough to say that <thrust - drag> is actually meaningful.)"  the atmospheric drag force at a particular location is too difficult to model and the thrust force of the EM Drive is too small to differentiate.

Similar situation we are facing now with the tests on the ground, as the skeptics, for very good scientific reasons point out that the experimental uncertainty overwhelms what is being claimed as having been measured.

Even with all the "do it  yourself" experiments coming up, we will face pretty soon a situation similar to "cold fusion" which persists to this date with some claiming success and others not.

What is needed is to have scientific measurements that are repeatable and where the level of uncertainty is much lower than what is being claimed to be measured.
« Last Edit: 06/10/2015 03:48 PM by Rodal »

Offline vulture4

  • Full Member
  • ****
  • Posts: 987
  • Liked: 305
  • Likes Given: 89
Why not just launch 2 in tandem? One without an EM thruster and get real baseline data comparing the two orbits? Eliminate a lot of unknowns in your test.
Shell
The problem is that the thruster itself may produce unanticipated artifactual forces, e.g. interactions with the Earth's magnetic field, electrostatic interactions, vacuum arcing, variations in orbital drag acceleration due to differences in mass between the two spacecraft, etc. These forces are not huge but they can be comparable to the small force postulated for the EM thruster.

Online Rodal

  • Senior Member
  • *****
  • Posts: 5838
  • USA
  • Liked: 5919
  • Likes Given: 5259
Height of the International Space Station vs time, look at the effect of air drag at 416 to 398 km

(hat tip to TMEubanks )

« Last Edit: 06/10/2015 03:29 PM by Rodal »

Offline foob

  • Member
  • Posts: 7
  • Texas
  • Liked: 3
  • Likes Given: 9

It can measure thrust by its vertical Z displacement up or down

Do you plan to put in it toaster resistors to measure the infrared influence  :)

No, no toaster elements allowed.

I will be using a plastic container to keep any magnetic components from the EMdrive acting on the side walls. And don't laugh as this will work fine and it is inexpensive.

Are you making a comment there as you appear to be testing it in a dustbin.;)
No comment here and I'm sorry it had to be a Trash can, but it is cheap, strong, non-ferrous plastic and the right size.

I know some here will say ... And if it doesn't work just put it out by the curb.

If the water is heated by the DUT, you must resist the urge to get in until the data is collected.

Offline Prunesquallor

  • Full Member
  • *
  • Posts: 174
  • Currently, TeV Brane Resident
  • Liked: 157
  • Likes Given: 73
Re. the recent flyby reference to the Aachen group's Baby EmDrive and CubeSats, I'm reminded that their team leader has already flown a couple of amateur space missions with an outfit called PoqetQub (from memory).

This is a NASA forum, so presumably packed to the brim with orbital mechanics specialists!! So... what value of k (N/W) is needed to get EmDrive up from LEO, O Experts?

ETA: On reflection that's a dumb question  :-[
Any positive k value will do.

You would have to determine what constitutes an orbit change that is outside the natural decay forces.  Cubesats don't have much power, so they may not get much thrust.  Would a retardation of orbital decay convince anyone?  That is a tricky deal, because orbit decay is sensitive to upper atmosphere expansion/contraction, which is affected by solar activity, etc.

If the thrust was significantly greater than the decay forces, you can use something like the Edelbaum approximation to determine the altitude change you should see with constant, tangential acceleration.  If there is interest, I'll run some quick parametrics to see what that might be.

Here's some analysis of what kind of orbital raising one could expect given constant, tangential, in-plane orbit thrust acceleration starting from a 600 km circular orbit (an average CubeSat altitude). It is not dependent on the type of thruster.

Now if one wanted to apply this to a CubeSat with a little bitty EM Drive, here is how the numbers might stack up:

Typical CubeSat available power: 0.5 W
http://www.diyspaceexploration.com/power-system-budget-analysis/

Typical CubeSat mass: 1.3 kg
http://en.wikipedia.org/wiki/CubeSat

Now, choose your assumed EM Drive efficiency and compute acceleration.  For example if you want to assume 0.1 N/kW, your acceleration would be (0.1 N/kW)*(0.5 W)*(0.001 kW/W)/(1.3 kg)/(9.81 m/s2/g) = around 4 micro-gs.

You can then look at the chart, find the 4 micro-g line and see the altitude gain as a function of thruster on-time.  You can decide for yourself if you want it to have constant thrust at constant power or if you want compute the time you think the universe will let the thruster operate and see how high it will get.

The chart posted above does NOT seem to include atmospheric drag (which dramatically changes orbital lifetimes etc. at low altitudes). Note that most cubesat launches are at 300 - 400 km - the ISS is 330 km, and that is probably the easiest platform to launch from.

A cubesat is 0.1x0.1 meter (1U), so its area is 10^-2 m^2. Its mass will be ~ 1 kg.

Assume 0.1 N/kW or 10^-4 N/W or ~ 5 x 10^-5 N for a 0.5 W drive. That means we want forcing to be
(ideally) << 5 x 10^-3 N/m^2 to be sure a thrust observed is actually from the thruster. (If drag is large, then you will never be able to model it well enough to say that <thrust - drag> is actually meaningful.)

Solar radiation pressure is 4.5 (absorption) to 9 (reflection) micro N / m^2, so radiation force will be
< 10^-7 N, which is fine and can be ignored. (For LEO, the radiation pressure from the Earth is also substantial, and hard to model as it depends on cloud albedo, but it will be < solar and so also can be ignored).

Drag at altitude depends heavily on the solar activity, and thus the solar cycle (which brought Skylab down).  We are near peak right now, which is bad, but in 2 or 3  years or so things could be a lot better. See this prediction:

http://en.wikipedia.org/wiki/Solar_cycle_24#/media/File:Solar_cycle_24_sunspot_number_progression_and_prediction.gif

Looking at the old Harris-Preister model atmosphere (see Figure 2 of
http://stk.com/downloads/support/productSupport/literature/pdfs/whitePapers/A%20Critical%20Assessment%20of%20Satellite%20Drag%20.pdf ) we would want the altitude to be > 300 km. At 400 km, Harris-Preister drag prediction is 3 x 10^-4 N/m^2, which might be OK, but is a little too close for comfort for me.

That says to me that a CASIS launch of a test from Station would not be adequate, but a launch to 500 or 600 km circular orbit would be fine. Launches at that altitude still count as LEO, and are available as get-away specials. (For various reasons, get-away specials basically never seem to be available for launches to GEO and higher.)

Also note that a 600 km circular orbit is about as high as you can go with a reasonable expectation of a 25 year post mission lifetime for a cubesat, which is needed to meet IADC guidelines on limiting space debris :
http://mstl.atl.calpoly.edu/~bklofas/Presentations/DevelopersWorkshop2011/8_Leveque_Orbital_Decay.pdf

You are absolutely correct - there are no other forces accounted for in that plot other than spacecraft thrust acceleration.  As I mentioned in the above quote, I think you need to be clearly above the region where predicted drag deceleration is within an order of magnitude of your expected thrust acceleration.  As time permits, I was going to try to do some calculations and include them as a "keep out zone" in that plot.

I am actually NOT a big fan of a space test, especially CubeSat.  I think the prospect of introducing error sources is much higher than in the lab.  Drag is one, but for example most CubeSats do NOT have active attitude control - they just tumble.  You have no ability, really to shield thruster electronics from spacecraft electronics and vice versa - you just don't have the space or mass available.

Somewhere I saw that the AVERAGE CubeSat deployment altitude was 600 km, which is why I used it in that example, but the analysis was just to answer the question of what kind of altitude change you could expect as a function of predicted thruster performance.  I still maintain that an early CubeSat test at this stage that returns null results tells us nothing.
« Last Edit: 06/10/2015 04:08 PM by Prunesquallor »
Retired, yet... not

Offline TMEubanks

Height of the International Space Station vs time, look at the effect of air drag at 416 to 398 km

(hat tip to TMEubanks )



Thanks, Jose, I should have done that :)

I should point out that a huge effort in basically every space faring country has gone into understanding orbital drag and relating it to solar activity and other parameters. Some very sophisticated models are available and you would definitely want to use them in analyzing any advanced propulsion test in Earth orbit. I just wanted to provide some back-of-the-envelope information that would be useful in deciding what sort of test to run.

Note, also, that any proposed EM-drive in a CubeSat test would be considerably smaller and would have a considerably higher resonance frequency than the drives I am aware of. Any space test would need first a "CubeSat sized" thruster that had gone through a series of ground tests in vacuum first, and been shown to be producing (or possibly producing) anomalous thrust on the ground. "It would be bad" to actually fly something and then find it didn't even appear to work on the ground. Do that once, and you'll find it very hard to get resources for a second attempt.

Offline Giovanni DS

  • Regular
  • Full Member
  • *
  • Posts: 186
    • ChibiOS/RT Project
  • Liked: 44
  • Likes Given: 162
19 hours after posting their YouTube video, they still donīt know (or haven't reported) if there is thrust yet...



The cavity does not look in the right orientation in this video, is it?

Offline SeeShells

  • Senior Member
  • *****
  • Posts: 2326
  • Every action there's a reaction we try to grasp.
  • United States
  • Liked: 2956
  • Likes Given: 2589
Why not just launch 2 in tandem? One without an EM thruster and get real baseline data comparing the two orbits? Eliminate a lot of unknowns in your test.
Shell
Because as Marshall said, " (If drag is large, then you will never be able to model it well enough to say that <thrust - drag> is actually meaningful.)"  the atmospheric drag force at a particular location is too difficult to model and the thrust force of the EM Drive is too small to differentiate.

Similar situation we are facing now with the tests on the ground, as the skeptics, for very good scientific reasons point out that the experimental uncertainty overwhelms what is being claimed as having been measured.

Even with all the "do it  yourself" experiments coming up, we will face pretty soon a situation similar to "cold fusion" which persists to this date with some claiming success and others not.

What is needed is to have scientific measurements that are repeatable and where the level of uncertainty is much lower than what is being claimed to be measured.
That makes sense.

Seems like so many are building an EMdrive, even me.  I still have my doubts as to how any of the data I get will be accepted. I'll share but, because I'm just an old gal engineer and not an accredited lab I know the data will be under question like the cold fusion fiasco. That's to be expected and I knew this going in. So I'm going about this as a personal project.

 I still have some ideas as to the why it does what it does and those ideas come from an anomaly I saw 35 years ago doing sonar buoy research with a shape very similar to the Frustum. Funny, I never understood why and that has always bothered me. 

Maybe the container has thrown some people off in my test but if the other one I wanted (simply a barrel) wasn't so much more I would have gone with it. Honestly I did laugh at my solution but honestly it's just a container.

Offline TMEubanks

Re. the recent flyby reference to the Aachen group's Baby EmDrive and CubeSats, I'm reminded that their team leader has already flown a couple of amateur space missions with an outfit called PoqetQub (from memory).

This is a NASA forum, so presumably packed to the brim with orbital mechanics specialists!! So... what value of k (N/W) is needed to get EmDrive up from LEO, O Experts?

ETA: On reflection that's a dumb question  :-[
Any positive k value will do.

You would have to determine what constitutes an orbit change that is outside the natural decay forces.  Cubesats don't have much power, so they may not get much thrust.  Would a retardation of orbital decay convince anyone?  That is a tricky deal, because orbit decay is sensitive to upper atmosphere expansion/contraction, which is affected by solar activity, etc.

If the thrust was significantly greater than the decay forces, you can use something like the Edelbaum approximation to determine the altitude change you should see with constant, tangential acceleration.  If there is interest, I'll run some quick parametrics to see what that might be.

Here's some analysis of what kind of orbital raising one could expect given constant, tangential, in-plane orbit thrust acceleration starting from a 600 km circular orbit (an average CubeSat altitude). It is not dependent on the type of thruster.

Now if one wanted to apply this to a CubeSat with a little bitty EM Drive, here is how the numbers might stack up:

Typical CubeSat available power: 0.5 W
http://www.diyspaceexploration.com/power-system-budget-analysis/

Typical CubeSat mass: 1.3 kg
http://en.wikipedia.org/wiki/CubeSat

Now, choose your assumed EM Drive efficiency and compute acceleration.  For example if you want to assume 0.1 N/kW, your acceleration would be (0.1 N/kW)*(0.5 W)*(0.001 kW/W)/(1.3 kg)/(9.81 m/s2/g) = around 4 micro-gs.

You can then look at the chart, find the 4 micro-g line and see the altitude gain as a function of thruster on-time.  You can decide for yourself if you want it to have constant thrust at constant power or if you want compute the time you think the universe will let the thruster operate and see how high it will get.

The chart posted above does NOT seem to include atmospheric drag (which dramatically changes orbital lifetimes etc. at low altitudes). Note that most cubesat launches are at 300 - 400 km - the ISS is 330 km, and that is probably the easiest platform to launch from.

A cubesat is 0.1x0.1 meter (1U), so its area is 10^-2 m^2. Its mass will be ~ 1 kg.

Assume 0.1 N/kW or 10^-4 N/W or ~ 5 x 10^-5 N for a 0.5 W drive. That means we want forcing to be
(ideally) << 5 x 10^-3 N/m^2 to be sure a thrust observed is actually from the thruster. (If drag is large, then you will never be able to model it well enough to say that <thrust - drag> is actually meaningful.)

Solar radiation pressure is 4.5 (absorption) to 9 (reflection) micro N / m^2, so radiation force will be
< 10^-7 N, which is fine and can be ignored. (For LEO, the radiation pressure from the Earth is also substantial, and hard to model as it depends on cloud albedo, but it will be < solar and so also can be ignored).

Drag at altitude depends heavily on the solar activity, and thus the solar cycle (which brought Skylab down).  We are near peak right now, which is bad, but in 2 or 3  years or so things could be a lot better. See this prediction:

http://en.wikipedia.org/wiki/Solar_cycle_24#/media/File:Solar_cycle_24_sunspot_number_progression_and_prediction.gif

Looking at the old Harris-Preister model atmosphere (see Figure 2 of
http://stk.com/downloads/support/productSupport/literature/pdfs/whitePapers/A%20Critical%20Assessment%20of%20Satellite%20Drag%20.pdf ) we would want the altitude to be > 300 km. At 400 km, Harris-Preister drag prediction is 3 x 10^-4 N/m^2, which might be OK, but is a little too close for comfort for me.

That says to me that a CASIS launch of a test from Station would not be adequate, but a launch to 500 or 600 km circular orbit would be fine. Launches at that altitude still count as LEO, and are available as get-away specials. (For various reasons, get-away specials basically never seem to be available for launches to GEO and higher.)

Also note that a 600 km circular orbit is about as high as you can go with a reasonable expectation of a 25 year post mission lifetime for a cubesat, which is needed to meet IADC guidelines on limiting space debris :
http://mstl.atl.calpoly.edu/~bklofas/Presentations/DevelopersWorkshop2011/8_Leveque_Orbital_Decay.pdf

You are absolutely correct - there are no other forces accounted for in that plot other than spacecraft thrust acceleration.  As I mentioned in the above quote, I think you need to be clearly above the region where predicted drag deceleration is within an order of magnitude of your expected thrust acceleration.  As time permits, I was going to try to do some calculations and include them as a "keep out zone" in that plot.

I am actually NOT a big fan of a space test, especially CubeSat.  I think the prospect of introducing error sources is much higher than in the lab.  Drag is one, but for example most CubeSats do NOT have active attitude control - they just tumble.  You have no ability, really to shield thruster electronics from spacecraft electronic and vice versa - you just don't have the space or mass available.

Somewhere I saw that the AVERAGE CubeSat deployment altitude was 600 km, which is why I used it in that example, but the analysis was just to answer the question of what kind of altitude change you could expect as a function of predicted thruster performance.  I still maintain that an early CubeSat test at this stage that returns a null results tells us nothing.

That is indeed a worry. Note, however, that reaction wheels (and, for that matter, micro thrusters) are now available for CubeSats. See

http://www.cubesatkit.com/docs/datasheet/DS_CSK_ADACS_634-00412-A.pdf (for example).

However, my thoughts have been moving in a different direction, and I would like to present that here.  I would suggest that a CubeSat test should be 3U, not 1 U, and should have two thrusters,  to enable a spin test, not a thrust test.

The proposed test would have two drives, oriented in opposing direction (i.e., 180 deg relative to each other), to enable the drives to spin the satellite up (i.e., in a "pin-wheel" mode). That way, drag becomes much less important. In Ascii Art mode, the directions of thrust would look (from above the long axis) like

>|
  |
  +
  |
  |<

where + denotes the center of Mass and <,> the directions of thrust.

A 3U CubeSat is 30 cm long (L = 0.3 m) and 10 cm high and wide (h = 0.1 m).  Assume the thrust is 2.5 x 10^-5 N per drive, they are separated by 25 cm, are each 12.5 cm from the center of mass , and the total mass is 3 kg.

The moment of inertia, I,  of a spin perpendicular to the L axis is ~ M * (L^2 + h^2) / 12, or 0.025 kg m^2 (a non-uniform distribution of mass might change that by up to a factor of two, which doesn't matter now but would have to be measured before launch). The torque, T,  from two drives would be 2 x 2.5 x 10^-5 N x 0.125 m = 0.625 x 10^-5 N m =  6.25 x 10^-6 kg m^2 / sec^2. The spin up (or down), d Omega / dt =  T / I =  6.25 x 10^-6  / 0.025 = 2.5 x 10^-4 radians sec^-2

A  d Omega / dt =  2.5 x 10^-4 radians sec^-2 means that in 1 day (86,400 seconds, assuming the orbit was in continual sunlight), the spin rate would be 21.6 radians / second, or a spin period of 0.29 seconds (or 206 rpms).

With two transmitters on either end of the CubeSat, you could easily see the 3 m/sec relative Doppler shift that 21.6 radians represents, and of course gyroscopes, accelerometers and sun-sensors (all for measuring rotation) are available and routinely used on CubeSats.

Even in 8 hours of Sun, the spin would be 68 RPM or 0.87 seconds.

I, personally, think that spinning a test satellite up to 200 rpms or even 68 RPMS in a day would be pretty conclusive. (Of course, you would need a "null mode," with power but no expected thrust, as a control.) And, note, this could be done at ISS altitude (or on a "next available" orbit, which is cheapest on commercial flights) - drag at those altitudes does not spin satellites up like that. If these thrusts are at all realistic, then the test would succeed or fail in a very short period of time (2 or 3 days), which is also a plus.

Also, the first such test you run, if successful (a big if in my opinion) would establish a market for EM drives for attitude control.

Online Rodal

  • Senior Member
  • *****
  • Posts: 5838
  • USA
  • Liked: 5919
  • Likes Given: 5259
...

Marshall, we might as well take advantage of having an Astrophysicist in our thread to learn even more from you.  I recall you telling me how the Cosmos is a great laboratory where a lot (all ?) of the processes that govern Nature have or can be observed.  This is relevant to a lot of the theories being considered here as they may already be denied (or confirmed ?) by astronomical observations.  One of the least controversial theories (least controversial because it does not involve extra dimensions or unknown particles, fields or forces) is the transfer of linear momentum from the quantum vacuum to a magnetochiral molecule, posited by Bart van Tiggelen and Manuel Donaire.  They have lots of papers, see this for example:  http://arxiv.org/abs/1404.5990 and http://qvg2013.sciencesconf.org/conference/qvg2013/program/Donaire_qvg2013.pdf.    They claim to have shown that the simultaneous breakdown of Time & Parity symmetries allows for the transfer of net momentum from the quantum vacuum to matter.  The breakdown of time and parity symmetry should be associated (in my view) with the weak force (although I do not recall their papers invoking the weak force).  They claim that this effect is similar to the Casimir effect of the Lamb-shift effect.

For common chiral compounds they estimate a deltaV Δv~ 1 nanometer/second for a magnetic field B=10 Tesla.

QUESTION:  Are there chiral (polymer ?) compounds floating in the Cosmos that astronomers have already observed (for example through spectroscopy)?  If so, is a deltaV Δv~ 1nm/s (admittedly extremely small (*) ) in the presence of 10 T magnetic field, a change in velocity that would observable, and if so do you know whether it has been observed ?

________
(*) For comparison Shawyer reported a maximum speed of 2 cm/s in his EM Drive on an air bearing test, that is twenty million (20*10^6) times greater deltaV, using an axial magnetic field (in TE012 mode) much smaller than 10 Tesla
« Last Edit: 06/10/2015 05:10 PM by Rodal »

Offline deltaMass

  • Full Member
  • ****
  • Posts: 955
  • A Brit in California
  • Liked: 671
  • Likes Given: 275
About that spinning idea. T = I dw/dt is the rotational equivalent of F = m a. T = F r and I is the moment of inertia of the thing being accelerated. So for a given F, what r maximises dw/dt?

dw/dt = F r / I, so naively maximum r results in maximum dw/dt
But I itself depends on r; I = m r2, the result of some integral and averaging, so
dw/dt = F / (m r), so here minimum r results in maximum dw/dt.

Which is it?

EDIT: If we assume the arm is massless in comparison to the device at the end of it, then I is constant and we need maximum r.
« Last Edit: 06/10/2015 05:28 PM by deltaMass »

Offline SeeShells

  • Senior Member
  • *****
  • Posts: 2326
  • Every action there's a reaction we try to grasp.
  • United States
  • Liked: 2956
  • Likes Given: 2589
No, no toaster elements allowed.

Allowing the device to move freely permits any unanticipated force to remain unmeasured and produce unpredictable accelerations.

By placing one of my tests in water, any and all abnormalities can show up and I'm looking to address any of them. Things you'll not see on a bench strapped down to a air bearing or simply pushing on a force gauge or hanging in free air with a wire. Being submerged with the device water cooled I can reduce the issues with the thermal expansion coefficients of the case. See any unknown effects and log them, measuring in real time the EmDrive to move freely in XYZ & T.  It's all about the data and getting data in 3D is better than in 2D.

Shell

Online Rodal

  • Senior Member
  • *****
  • Posts: 5838
  • USA
  • Liked: 5919
  • Likes Given: 5259

By placing one of my tests in water, any and all abnormalities can show up and I'm looking to address any of them. Things you'll not see on a bench strapped down to a air bearing or simply pushing on a force gauge or hanging in free air with a wire. Being submerged with the device water cooled I can reduce the issues with the thermal expansion coefficients of the case. See any unknown effects and log them, measuring in real time the EmDrive to move freely in XYZ & T.  It's all about the data and getting data in 3D is better than in 2D.

Shell

It will be very interesting.  My prediction is that you will see a random walk

« Last Edit: 06/10/2015 06:13 PM by Rodal »

Tags: