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German Test Reveals That Magnetic Fields Are Pushing the EM Drive (arstechnica.com)
"Researchers in Germany have performed an independent, controlled test of the infamous EM Drive with an unprecedented level of precision," writes PvtVoid. "The result? The thrust is coming from interactions with the Earth's magnetic field." From the report: Instead of getting ahold of someone else's EM drive, or Mach-effect device, the researchers created their own, along with the driving electronics. The researchers used precision machining and polishing to obtain a microwave cavity that was much better than those previously published. If anything was going to work, this would be the one. The researchers built up a very nice driving circuit that was capable of supplying 50W of power to the cavity. However, the amplifier mountings still needed to be worked on. So, to keep thermal management problems under control, they limited themselves to a couple of Watts in the current tests. The researchers also inserted an enormous attenuator. This meant that they could, without physically changing the setup, switch on all the electronics and have the amplifiers working at full noise, and all the power would either go to the EM drive or be absorbed in the attenuator. That gives them much more freedom to determine if the thrust was coming from the drive or not.
Even with a power of just a couple of Watts, the EM-drive generates thrust in the expected direction (e.g., the torsion bar twists in the right direction). If you reverse the direction of the thruster, the balance swings back the other way: the thrust is reversed. Unfortunately, the EM drive also generates the thrust when the thruster is directed so that it cannot produce a torque on the balance (e.g., the null test also produces thrust). And likewise, that "thrust" reverses when you reverse the direction of the thruster. The best part is that the results are the same when the attenuator is put into the circuit. In this case, there is basically no radiation in the microwave cavity, yet the WTF-thruster thrusts on. So, where does the force come from? The Earth's magnetic field, most likely. The cables that carry the current to the microwave amplifier run along the arm of the torsion bar. Although the cable is shielded, it is not perfect (because the researchers did not have enough mu metal). The current in the cable experiences a force due to the Earth's magnetic field that is precisely perpendicular to the torsion bar. And, depending on the orientation of the thruster, the direction of the current will reverse and the force will reverse. The researchers' conclude by saying: "At least, SpaceDrive [the name of the test setup] is an excellent educational project by developing highly demanding test setups, evaluating theoretical models and possible experimental errors. It's a great learning experience with the possibility to find something that can drive space exploration into its next generation."
Even with a power of just a couple of Watts, the EM-drive generates thrust in the expected direction (e.g., the torsion bar twists in the right direction). If you reverse the direction of the thruster, the balance swings back the other way: the thrust is reversed. Unfortunately, the EM drive also generates the thrust when the thruster is directed so that it cannot produce a torque on the balance (e.g., the null test also produces thrust). And likewise, that "thrust" reverses when you reverse the direction of the thruster. The best part is that the results are the same when the attenuator is put into the circuit. In this case, there is basically no radiation in the microwave cavity, yet the WTF-thruster thrusts on. So, where does the force come from? The Earth's magnetic field, most likely. The cables that carry the current to the microwave amplifier run along the arm of the torsion bar. Although the cable is shielded, it is not perfect (because the researchers did not have enough mu metal). The current in the cable experiences a force due to the Earth's magnetic field that is precisely perpendicular to the torsion bar. And, depending on the orientation of the thruster, the direction of the current will reverse and the force will reverse. The researchers' conclude by saying: "At least, SpaceDrive [the name of the test setup] is an excellent educational project by developing highly demanding test setups, evaluating theoretical models and possible experimental errors. It's a great learning experience with the possibility to find something that can drive space exploration into its next generation."
This is what we should be teaching in schools and promoting in daily life/culture.
No problem... we will just have to take the Earth with us.
... it's the field being created by the planetary body we call Earth. Surprise! No one has ever tested an EM Drive beyond the influence of Earth. If they had, its efficacy would have quickly been dis-proven.
Could it at least be used to reposition satellites? It appears to be an energy hog but if one first accumulates sufficient solar power then it might work.
It was presented at the Space Propulsion 2018 conference.
Starships were meant to fly, Hands up and touch the sky - Nicky Minaj
The EM drive, if it works, violates conservation of momentum, which can easily be used to also violate conservation of energy. (/. commenters on previous EM drive stories have gone into this at some length.)
The EM drive was originally designed using standard physics (I think electromagnetism and possibly special relativity) and the inventor's calculations showed it would produce thrust. They did not realize that as the input physics conserved momentum but their calculation result violated it, this guaranteed their calculation was in error.
The chances of this result being real were always really tiny. I'm happy there is now a good explanation for the anomalous experimental results.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
The EM drive does use fuel - just not a propellant. It also gives such a small amount of thrust, one can only measure it with a carefully controlled setup. This experiment basically proves the thrust is created from the charged craft interacting with Earth's magnetic field.... and the thrust doesn't go up much if any as the power on the craft goes from 5 watts to 50 watts. So, we're basically looking at motion powered by Earth's EM, not the craft's EM.
We have about as much of a chance of boosting a craft into low Earth orbit with this as we do using a compass.
Perhaps it'll be useful for something one day, but all I can come up with right now would be Back to the Future II style hoverboards, but for dust mites instead of people given what little thrust it gives -- also it is hard to steer given it tends to only move in alignment with Earth's magnetic field.
Once you've taken an EM drive and removed the useless cavity and microwave emitter, what you are left with is an electrodynamic tether which may indeed be useful, but doesn't owe anything to the EM drive.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
Yep. In 5 billions years, give or take, our sun will become a liability.
In less than 1 billion years earth will go into "moist earth" runaway with surface temperatures hot enough to melt iron.
We will *have* to move our planet if we want to keep it.
This is possible with current level of technology. You need only nudge a few asteroids close to earth to selectively transfer kinetic energy a few times per century to keep up with increasing output from the sun while still on the main sequence.
..If the folks over at nasaspaceflight are to be believed
Looks like the setup was very sloppy indeed.. with the wattage too low making any signal disappear into noise..
Quoting:
Looking at the pictures of Tajmar's experiment, no wonder they are seeing nothing but Lorentz. First of all their twisted pairs do not appear to be twisted enough. There should be at least two twists per inch. In the image below it appears that there is maybe one twist per two inches or so. And then look at the location of the main amplifier and the length of the main leads! :o
At only 2W of RF power, no wonder they are only seeing Lorentz. It's almost like they designed their experiment to be susceptible to this form of error.
It's the field being created by the planetary body we call Earth. Surprise! No one has ever tested an EM Drive beyond the influence of Earth. If they had, its efficacy would have quickly been dis-proven.
Good grief.
If it's the Earth's field, put the device inside a pair of helmholtz coils (or the slightly more complex coil systems that can smooth out the residual ripples further). Give them enough current to cancel the Earth's field and, if the gadget is getting its thrust from this interaction, the thrust will stop. Give them twice that, reversing the field, and the thrust will be in the opposite direction.
I thought this test had already been done, by pretty much everybody including NASA.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
Magnetotorquer bars have been used in space for dozens of years to desaturate the reaction wheels.
These are perfectly adjusted to their function (no need for fancy EM things) and generate pure torques when interacting with the Earth magnetic field.
Just, no forces, as, well, expected.
Herve S.
So, where does the force come from? The Earthâ(TM)s magnetic field, most likely. The cables that carry the current to the microwave amplifier run along the arm of the torsion bar. Although the cable is shielded, it is not perfect (because the researchers did not have enough mu metal).
Also: What's wrong with using twisted pair? The individual half-twists may interact with a DC magnetic field, but on the average across a twist they cancel out.
This has been used since at least the early days of telephony (where they used twisted pair - with the wires occasionally swapped as they go from pole to pole - not just to cancel out coupling to electrical noise from lots of sources (including power lines) but also - with different rates of twist on different pair and phantom-group - to cancel it out between different lines running along the same poles.
Just like the four pair in your cat-N Ethernet cable each have a different rate of twist, so their signals stay separate.
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(I DO like the idea of swapping in the dummy load and seeing whether the thrust disappears. B-) )
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
The researchers used precision machining and polishing to obtain a microwave cavity that was much better than those previously published. If anything was going to work, this would be the one.
Now that reminds me of a story, back in my programming-for-the-auto-industry days.
Seems that Rolls Royce, after sticking with manual transmissions for a long time, decided to consider manufacturing a car with an automatic transmission. So they got hold of the best on the hoi polloi market - the GM 350 turbo-hydramatic - to use as a reference.
First they tested the heck out of it - and found it did exactly what an auto-tranny should. So how could they make something better? So they tore it down to see if there was anything they could improve. But everything was beautifully designed and machined. Except for one surface on one part, which was a little rough.
So they machined it smooth and reassembled the transmission. And it didn't work at all. That surface was SUPPOSED to be a little rough. B-)
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Now personally, as much as I'd like to see a working reactionless electronic thruster, I'm not holding my breath waiting for a violation of the law of conservation of momentum. But it would be nice if something DID show up that worked.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
For interplanetary space travel, yes. But that's not very exciting. Chemical rockets work fine for interplanetary travel on the order of years and decades at most with ion drives showing promise as a next step.
The reason the EM drive was so exciting was because of the potential for interstellar travel in reasonable timeframes (sub-100 year) without having to lug around huge quantities of propellant (mass to throw out the back to accelerate you). If it actually worked, you could power it with a nuclear reactor and accelerate away without needing any propellant (violation of conservation of momentum).
Traveling to Alpha Centauri (4.367 light years) in 100 years (assuming constant acceleration to the halfway point, decelerating the second half of the trip, and ignoring relativistic effects) would require reaching a peak speed of
d = 0.5*vavg*t
vavg = 2*d/t = 2*(4.367 c years)/(100 years) = 0.08734 c
vmax = 2*vavg = 0.17468 c = 52,368 km/s
To accelerate, you need to dump the energy you're producing into the propellant that you're ejecting in the direction opposite you're accelerating. The energy needed reach Earth's escape velocity (11.2 km/s) and to escape the solar system from Earth's orbit (16.6 km/s) are roundoff error compared to the energy needed to reach Alpha Centauri in 100 years.
Energy for Earth escape velocity = 0.5*m*(11.2 km/s)^2
Energy for solar system escape velocity = 0.5*m*(16.6 km/s)^2 = 2.2 times the energy to escape Earth
Energy to reach Alpha Centauri in 100 years = 0.5*m*(52367 km/s)^2 = 21,861,469 times the energy to escape Earth
So a trip to Alpha Centauri in 100 years would require nearly 22 million times more energy (and propellant to absorb that energy) than needed to escape Earth's gravity.
Not embarrassing at all, this is how real science is supposed to work. People propose theories and then look for ways to test and verify results.