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#340 by Bob Woods on 05 Sep, 2016 19:42
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Cannae states that they have a design max operating temperature of 45K. They want the ambient temperature within a closed loop system to not exceed 45K and they will undoubtedly shoot for an operating temperature of significantly less than that value.
Their claim is that the 90 square meters of heat sink, more than double the radiation they need to keep the system well under the 45K design.
Why choose Neon? It’s inert, is the least reactive noble gas, and has the narrowest liquid range of any element, between 24.55 K and 27.05 K. That means at 24 K or lower it’s in solid state. Helium on the other hand does not solidify until you hit 1K to 1.5K. That’s below the deep space ambient temp of 3 K.
If I wanted a closed system that manages phase changes with a radiative heat sink, it would seem to me that Neon is a better choice -
#341 by Monomorphic on 05 Sep, 2016 20:00
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Perfect TE013 in spherical end-plate geometry using novel "offset loop" antenna. Special thanks to Shell for the final clue that eliminated the hotspot from a standard loop antenna.
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#342 by Rodal on 05 Sep, 2016 20:04
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Cannae states that they have a design max operating temperature of 45K. They want the ambient temperature within a closed loop system to not exceed 45K and they will undoubtedly shoot for an operating temperature of significantly less than that value.
Their claim is that the 90 square meters of heat sink, more than double the radiation they need to keep the system well under the 45K design.
Why choose Neon? It’s inert, is the least reactive noble gas, and has the narrowest liquid range of any element, between 24.55 K and 27.05 K. That means at 24 K or lower it’s in solid state. Helium on the other hand does not solidify until you hit 1K to 1.5K. That’s below the deep space ambient temp of 3 K.
If I wanted a closed system that manages phase changes with a radiative heat sink, it would seem to me that Neon is a better choice
* need to address the economic benefit that trades off not exhausting propellant and instead has 3% losses of Ne a month
*where is the 40 m^2 coming from ?QuoteThe radiative surface area needed to radiate 73 watts from a temperature of 75 K to 3 K (the effective temperature of deep space) is 40 square meters.
If one calculates this, one would need more than the entire surface they write is available (90 m^2) when taking into account that:
*Not only the radiators have to be kept away from the Sun, but don't forget that the Earth's heat flux can easily be > 50 W/m^2 in LEO. Maybe 100 W/m^2 ? (*)
* unless Cannae is planning to put in a shield between the drive and the Earth and the drive and its radiators, or do both?
* if so, where is the design for that shield ?
* please show how all of this is feasible to do in a 6 U (10 x 20 x 30 cm).
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(*) Thanks to Marshall Eubanks for providing these estimates. I am responsible for any errors in using them. -
#343 by RERT on 05 Sep, 2016 20:16
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There was a clear statement in an earlier post here that the Cannae 6U cubesat thruster was not superconducting. So the question of how to fit cooling in 6U does not arise.
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#344 by Rodal on 05 Sep, 2016 20:26
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There was a clear statement in an earlier post here that the Cannae 6U cubesat thruster was not superconducting. So the question of how to fit cooling in 6U does not arise.
Where are the calculations that show that a 6U Cannae cubesat in LEO 150 km does not need to be superconducting to successfully accomplish that goal ?
Let's go over this:QuoteTheseus is going to be launching a demo cubesat which will use Cannae thruster technology to maintain an orbit below a 150 mile altitude. This cubesat will maintain its extreme LEO altitude for a minimum duration of 6 months.
Run the numbers for LEO at 150 km
http://www.sciencedirect.com/science/article/pii/0032063367900232QuoteThe satellite 1966-101G was launched on 2 November 1966 into an orbit with an initial perigee height of 140 km. A satellite with such a low perigee usually decays within a few days, but 1966-101G was exceptionally dense and remained in orbit until 6 May 1967. Analysis of the changes in its orbital period provides an unique opportunity for studying continuously for six months the variations in air density at a height near 150 km.
This paper records the results of such an analysis, applicable for the (medium) level of solar activity prevailing early in 1967. It is shown that at a height of 155 km the air density is greater by day than by night, with the maximum daytime density exceeding the minimum night-time density by a factor of 1.7: in contrast the COSPAR International Reference Atmosphere 1965 predicts that the density should be slightly greater by night than by day. It is also found that the night-time density increases as solar activity increases, and that the density scale height given by CIRA 1965 at heights near 150 km is too low, perhaps by about 20%.
orbital data from a cubesat http://space.stackexchange.com/questions/5792/minimum-orbit-altitude
They want 6 months on orbit at 150 km.
Assume that they present a surface of only 0.03 m^2.
A drag coefficient, CD= 2 (*)
Orbital velocity, v ~ 7835 m/sec (*)
Assume a margin of 2.5 (*) to make sure you would not deorbit if some event raised the density at high altitude.
For a 6 month mission, 150 km LEO, you will be in eclipse ~ 50% of the time (i.e., another factor of 2). (*)
Then the calculation is that one needs a thrust/power of at least 1 milli Newton / Watt.
To my knowledge, only the Cannae superconducting claims to provide 1 milliNewton/Watt. If a copper Cannae drive would provide the same 1 milliNewton/Watt thrust/InputPower as the superconducting version, then what is the point of their superconducting version, with all its complexity
See:
details of the Cannae superconducting design and experiments, in this US Patent Application
https://www.google.com/patents/US20140013724
http://emdrive.wiki/Experimental_Results
mN/kW
Cannae LLC, Superconducting 761.9 - 952.4
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(*) Thanks to Marshall Eubanks for providing these estimates. I am responsible for any errors in using them. -
#345 by Bob Woods on 05 Sep, 2016 21:07
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Calculations and feasibility is Cannae's job as it's their baby. I'm not qualified to do that level of work.
Why choose Neon? It’s inert, is the least reactive noble gas, and has the narrowest liquid range of any element, between 24.55 K and 27.05 K. That means at 24 K or lower it’s in solid state. Helium on the other hand does not solidify until you hit 1K to 1.5K. That’s below the deep space ambient temp of 3 K.
If I wanted a closed system that manages phase changes with a radiative heat sink, it would seem to me that Neon is a better choice
* you have not addressed the economic benefit that trades off not exhausting propellant and instead has 3% losses of Ne a month
*where does Cannae get 40 m^2 from ?QuoteThe radiative surface area needed to radiate 73 watts from a temperature of 75 K to 3 K (the effective temperature of deep space) is 40 square meters.
Have you checked those calculations?
One would need substantially more than what they say is available (90 m^2) for that
*Not only the radiators have to be kept away from the Sun, but don't forget that the Earth's heat flux can easily be > 50 W/m^2 in LEO. Maybe 100 W/m^2 ?
* is Cannae planning to put in a shield between the drive and the Earth and the drive and its radiators, or do both?
* if so, where is the design for that shield ?
* please show how all of this is feasible to do in a 6 U (10 x 20 x 30 cm).
I'd like to point out that the Cannae picture you posted is their futuristic Space Freighter for deep space work, NOT the cubesat they are sending up. In fact Cannae speciffically states on their website: "Cannae is also commercializing a thruster that does not require superconducting operation in order to generate thrust" . [/font][/size][size=78%]http://http://cannae.com/the-technology/[/size]
I guess you assumed they were doing the Freighter in their cubesat. I assumed they are not.
Doc I do not have experience in cryogenic cooling systems. So I don't know what the 3% loss is based on. Is there a difference in efficiency in those systems if you start with and store your material as a solid instead of a liquid or gas? I would guess it might be more efficient but that's only a guess.
What I do see is that Neon can be a solid, liquid and gas within a narrow temperature range of +/- 3.5 K at a temperature that seems to be within the range that Cannae is shooting for.
Basic chemistry shows energy absorbed in the change from solid to liquid, and again from liquid to gas. For neon in the operating parameters that Cannae indicates, you could have potentially 2 phase changes. Neon also has a much higher density and thermal conductivity than helium at their respective boiling points.
https://en.wikipedia.org/wiki/Noble_gas_(data_page)
If Cannae can prove THEIR (not mine) statements that they can radiate off the heat they will generate, then they seem to have the potential to store their coolant as a solid and benefit from two potentially manageable phase changes.
PS: Fetta apparently has a degree in Chemical Engineering FYI. -
#346 by Rodal on 05 Sep, 2016 21:14
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....
No, rather than assuming things, one has to start by figuring out what is the thrust/PowerInput that would be required for a 6 month 150 km LEO [a low perigee] mission. See: https://forum.nasaspaceflight.com/index.php?topic=40959.msg1578840#msg1578840 The calculation is that you need a thrust of at least 1 milli Newton / Watt.
I guess you assumed they were doing the Freighter in their cubesat. I assumed they are not.
....
To my knowledge, only the Cannae superconducting version claims to provide the calculated requirement of 1 milliNewton/Watt.
So, it is not an assumption that a Freighter will be used, but instead it comes from a calculation of what is the thrust/InputPower required for a 6 month 150 km LEO mission, with a reasonable margin of safety, as discussed above.
If a copper Cannae drive would provide the same 1 milliNewton/Watt thrust/InputPower as what is claimed for the superconducting version, then what is the point of their superconducting version, with all its complexity
Also, my superconducting discussion was in response to this post by somebody else (which you marked with a "like"): https://forum.nasaspaceflight.com/index.php?topic=40959.msg1578614#msg1578614 that discussed superconducting operation of said Cannae EM Drive.
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#347 by Bob Woods on 05 Sep, 2016 22:01
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If a copper Cannae drive would provide the same 1 milliNewton/Watt thrust/InputPower as what is claimed for the superconducting version, then what is the point of their superconducting version, with all its complexity
Fair question, it's just that I've never seen any specific claim from Cannae as to what their superconductor thrust/watt is.
The overall truth should come out after they launch their baby: Does it work at all, and if so, how efficient? -
#348 by Rodal on 05 Sep, 2016 22:41
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...What I do see is that Neon can be a solid, liquid and gas within a narrow temperature range of +/- 3.5 K at a temperature that seems to be within the range that Cannae is shooting for. ...
One should not bunch together this huge temperature range (75 to 2 deg K)
He = 2.17 K (This is what Cannae tested at)
H2 = 13.8 K
Ne = 24.6 K (This is what Cannae shows in the above drawings)
N2 = 63.1 K (Cannae discusses 75 K in their write-up)
The Stefan-Boltzmann equation, which describes the rate of transfer of radiant energy, is as follows for an object in a vacuum
The formula for radiation heat transfer depends on the 4th power of the Temperature !
Such a nonlinear dependence is very unforgiving as the temperature goes down to absolute zero.
Comparing the 75 K in the write up with the 24 K for Ne is a factor of almost 100 times the radiator surface area
(75/24)^4 = 95
Comparing the 75 K in the write up with the 2 K they tested their superconducting at, gives a ratio of almost one and a half million:
(75/2.17)^4 = 1.4*10^6
Just trying to make sense with numbers here...
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#349 by Prunesquallor on 05 Sep, 2016 22:45
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If a copper Cannae drive would provide the same 1 milliNewton/Watt thrust/InputPower as what is claimed for the superconducting version, then what is the point of their superconducting version, with all its complexity
Fair question, it's just that I've never seen any specific claim from Cannae as to what their superconductor thrust/watt is.
The overall truth should come out after they launch their baby: Does it work at all, and if so, how efficient?
I know I sound like a broken record, but I would really like to know how they plan to separate out thrust effects from the high variability of atmospheric density at those altitudes.
Sent from my iPhone using Tapatalk -
#350 by FattyLumpkin on 05 Sep, 2016 23:47
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I hope there is no confusion re the various projects going on at Cannae...as folks know I've been conducting a study of them
1) for the cubesat, they say they are orbiting it at less than 150 miles...not kilometers. Mr. Feta told me there would be no super-cooling of this device. I'm left to conclude that the cooling of their thruster will be passive and that the thruster will be kept in shadow at all times
2)The LEO tug as seen in the pic (previous page(s)) is enclosed and I am not sure how the Neon is to be used to aid in cooling---the tug is reported to be able to work for many years without servicing...I think this would indicate a closed atmosphere around the cavities where the gas is circulated in and out via pump.(gets cold when released and hot when compressed: basic air conditioning) A radiator of X size would probably be required on the shadow side of the tug outside of the enclosure.
3) the "deep space" probe is passively cooled with a special coating on the cavities which is reported to aid in the radiation of heat. These cavities would also remain in shadow except for periodic trajectory change or communication. Based on Cannae's claims pertaining to thrust/watt I was underwhelmed at the probes speed performance, but am left to recon that if more power were injected into the cavities they would exceed their 45 degrees K "rating" and become less efficient.
Once again Cannae doesn't say much, so we're left with logical speculation (Mr. Spock would not like this)! -
#351 by Star One on 06 Sep, 2016 00:09
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Problem I have with all this is talk is cheap especially in the grey area of this technology. Verifiable actions are a whole other matter. Some of this talk has been going on for years so where is the practical nuts & bolts results?
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#352 by Rodal on 06 Sep, 2016 00:17
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I hope there is no confusion re the various projects going on at Cannae...as folks know I've been conducting a study of them
So they are using miles instead of kilometers to specify an orbit?
1) for the cubesat, they say they are orbiting it at less than 150 miles...not kilometers. Mr. Feta told me there would be no super-cooling of this device. I'm left to conclude that the cooling of their thruster will be passive and that the thruster will be kept in shadow at all times
...
150*1.60934=241
So their orbit is really 241 km ?
That makes a difference ! Thanks
I calculated with 150 km. (I recall pointing this out weeks ago, when they first announced, that instead of using customary SI units, Cannae is using Miles, oh well
)
Just like the probe that crashed on Mars years ago (different units !)
Will recalculate with 150 miles tomorrow (Is it US Miles )
US Survey mile = International mile =1.60934 km
Nautical mile = 1.852 km
Roman mile = 1.481 km
Chinese mile = 0.5 km -
#353 by RotoSequence on 06 Sep, 2016 00:28
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Will recalculate with 150 miles tomorrow (Is it US Miles
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I reckon it's either that or nautical miles
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#354 by FattyLumpkin on 06 Sep, 2016 00:33
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Star One, in reality the only data we have pertaining to Cannae is what we got from NASA. The rest is indeed marketing from/by Cannae...not to long ago I said they were a little to slick for me, and was criticized even for that comment. Unfortunately Monomorphic has been too busy to perform sims on several of Cannae's designs that I've dug up as part of my study.
I'm hoping for excellent results in his test campaign and look forward to digging into what IS out there about Cannae. I'm sorry if I disturbed you with the above mentioned...Cannae ticks me off (politely put) FL -
#355 by dustinthewind on 06 Sep, 2016 03:41
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Perfect TE013 in spherical end-plate geometry using novel "offset loop" antenna. Special thanks to Shell for the final clue that eliminated the hotspot from a standard loop antenna.
I am just curious what this "offset loop" antenna is supposed to look like. I would assume a loop symmetric with the axis of the cavity but in what way is it offset? Position maybe? Tried looking up images but didn't get anything definitive. Maybe I flunked my search. I remember Shell mentioning having one flat and one curved end plate. I am assuming this arrangement of plates helped with the placement of the antenna to maximize the interaction of the antenna with the radiation in the cavity. Possibly maximizing the electric field in its vicinity. -
#356 by FattyLumpkin on 06 Sep, 2016 04:19
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dustinthewind, probably like this antenna , but in a frustum instead of a Cannae RC.....by "offset" maybe he means suspended away from the wall, top or bottom plate, and not located on it.?
+ note it's a hoop (round) and not a loop...I wonder if that's a distinction without a difference : )
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#357 by Star One on 06 Sep, 2016 06:51
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Any wiser heads than mine want to comment on the criticism of the experiments contained in the OP here.
https://m.reddit.com/r/EmDrive/comments/51b1r8/nasas_eagleworks_em_drive_testing_searching_for/ -
#358 by RotoSequence on 06 Sep, 2016 08:18
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Any wiser heads than mine want to comment on the criticism of the experiments contained in the OP here.
https://m.reddit.com/r/EmDrive/comments/51b1r8/nasas_eagleworks_em_drive_testing_searching_for/
The only thing I've gleaned thus far is that my reading comprehension sucks at 1 AM.
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#359 by StrongGR on 06 Sep, 2016 09:31
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After the announcement of Dr. Rodal, I have modified my draft explaining NASA's results. The idea is that the theory to be used is a Brans-Dicke instead that a pure general relativity, inside the cavity. The question of what theory really describes our universe is widely open as the Brans-Dicke theory exactly recovers general relativity in all the known tests. But the former allows for a varying Newton constant as seems to be seen in NASA experiments.
If this would be confirmed, it would appear a breakthrough in our knowledge as it would seem that the Brans-Dicke theory is preferred to general relativity even if both theories coincide for all practical purposes.
The draft is here enclosed. It is my paper appeared on arxiv with added a new section before conclusions about Brans-Dicke theory. The computation shows that, just inside the cavity, the electromagnetic field can change the Newton constant because of its energy density. Outside the cavity, the ordinary Newton constant is recovered.
The new version of the paper appeared today on arxiv at
http://arxiv.org/abs/1505.06917
Here I get a general equation for the gravitational constant in the Brans-Dicke model determined by the square of the energy density of the e.m. field inside the cavity. As already said, the gravitational constant, in this case, is modified just inside the volume of the cavity making the effect markedly larger than expected from Einstein gravity. In such conditions, the device does not appear reactionless, as claimed by somebody, but just use gravity.
Brans-Dicke model is a serious contender to Einstein's general relativity since '60 when was formulated. Presently, cosmological tests constrain it but does not rule it out at all.
)