The title remains extremely biaised, especially after the discussion...
Since there is no released error analysis, the degree to which the news confirms or disconfirms the EmDrive is based solely on the belief or disbelief that the remaining one-fifth is attributable to some other error, just as most of it already was.What happened was that someone at NASASpaceFlight referred to various calculations made by Sonny, especially derivations of the Bohr radius, in support of the Q-thruster idea. I simply looked this up—most of the physics part that I picked apart was from a pdf hosted at ntrs.nasa.gov and attributed directly to Sonny. Unless there are serious shenanigans at the actual NASA website, there's no reason to disbelieve that those calculations indeed come directly from Eagleworks Labs, and so are not just some random person on the web.
We need to create a commission for thread titles in Brussels.
We'll need to make a commission for that.
Yeah, when I was reading up on the author's introduction to MiHsC, I started getting really annoyed about a lack of a source of momentum for photons, which his explanation for the EM Drive banks on. If he'd suggested the walls reacting to the bouncing photons in an asymmetric way, there'd be a ready mechanism for his theory of inertia to create interesting results. As is, it's just bizarre.
I did, actually, but I was grabbing the "quantized inertia" thing straight from title because I hadn't refreshed myself on which alternate model of cosmology it was yet.
"Argumentum ad lapidem (Latin: "to the stone") is a logical fallacy that consists in dismissing a statement as absurd without giving proof of its absurdity."
Whether or not the EmDrive itself has been "debunked," the idea that it has been "confirmed" almost certainly has.
The problem there is that you're then basically using the drive itself as reaction mass, meaning that the rocket equation applies in full force.
wikipedia said:Energy efficiency[edit]
Ion thrusters are frequently quoted with an efficiency metric. This efficiency is the kinetic energy of the exhaust jet emitted per second divided by the electrical power into the device.
Plot of instantaneous propulsive efficiency (blue) and overall efficiency for a vehicle accelerating from rest (red) as percentages of the engine efficiency- note that peak vehicle efficiency occurs at about 1.6 times exhaust velocity.
Ion thrusters are frequently quoted with an efficiency metric. This efficiency is the kinetic energy of the exhaust jet emitted per second divided by the electrical power into the device.
The actual overall system energy efficiency in use is determined by the propulsive efficiency, which depends on vehicle speed and exhaust speed. Some thrusters can vary exhaust speed in operation, but all can be designed with different exhaust speeds. At the lower end of Isps the overall efficiency drops, because the ionization takes up a larger percentage energy, and at the high end propulsive efficiency is reduced.
Optimal efficiencies and exhaust velocities can thus be calculated for any given mission to give minimum overall cost.
One of the few things I do understand is that this is unlikely because the thrust profile they get off their instruments while testing this thing has an abrupt start of force when electricity happens and an abrupt end of force when they turn it off. If it was a thermal effect or some similar sort of whatsit that would use the chamber as reaction mass, it would slowly ramp up as power was applied and then tamper off when it stopped.
Heh. The last bit explains the first: the objective is to find an equation that fits the data, not find a physically coherent mechanism. That's why McCulloch's idea is 'simpler' than a 2000 element thermodynamical model. It's pretty typical behavior among cranks. Hell, McCulloch himself is probably aware of this at least on some subconscious level, since he explicitly states that photons aren't supposed to work that way but proceeds regardless.Yeah, when I was reading up on the author's introduction to MiHsC, I started getting really annoyed about a lack of a source of momentum for photons, which his explanation for the EM Drive banks on. If he'd suggested the walls reacting to the bouncing photons in an asymmetric way, there'd be a ready mechanism for his theory of inertia to create interesting results. As is, it's just bizarre.
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Amusingly, the author has a rant about how his model is totally simpler and how a 2000 element finite element model is overly complex and can't be trusted. You know, because overturning one of the fundamentals of physics is simpler than modelling thermodynamics using industry standard practices.
I've never heard of Tajmar, but looking him up just now, he's a pretty interesting contrast to McCulloch.
Yeah, but it's the complete lack of address about the equivalence principle that prevents it from being considered to be some correction to GTR. Even with weak equivalence, test particles fall the same way in a gravitational field, regardless of mass or composition, and weak equivalence actually has very impressive experimental tests (to about 10-13). So messing with mass shouldn't do anything at all to the Pioneer probes as far as gravity is concerned, for any metric theory of gravity (not just GTR).
Exactly.
Hell, he says it explicitly:
Nice smilely. Have you ever read the articles on Podkletnov and his experiments? They read like N-Rays, only without the contingent of French "replications" to lend it credence. There are some really sad quotes from him about how his work proves that UFOs are totally real. It reminds me of this SMBC comic:
I just desperately hope that White will live up to Tajmar. He'd made noises in that direction before he started publishing his wacky quantum vacuum theory.I've never heard of Tajmar, but looking him up just now, he's a pretty interesting contrast to McCulloch.
Tajmar had an idea that the Cooper pair mass anomaly in spinning superconductors can be explained by a gravitomagnetic field. The gravitomagnetic field should be thirty-something orders of magnitude weaker than the magnetic field, so this part doesn't make any sense to me, but I'm not going to try to sort it out right now, so let's just roll with it... Tajmar did an experiment in 2006 that supported his theory. At STAIF 2006, he repudiated Podkletnov. In 2007, an independent experiment failed to replicate his results [pdf]. Finally, another experimental test by Tajmar (2011) was a hundred times more sensitive than any before it and yielded no result, contradicting his own earlier experiments.
To summarize, Tajmar had a somewhat far-out idea and proceeded to test it pretty thoroughly. Tajmar: +3. McCulloch: -eleventybillion. My favorite part:
"It's obviously very difficult to actually [replicate experiments]. The replication aspect in experimental physics—that's a very, very important aspect." — Martin Tajmar at STAIF 2006Some people in this thread could also learn a bit from this man.
There's some confusion in how he describes what's going on, but I think the idea is more that the Pioneer probes are running into a minimum acceleration that's essentially causing them to pinwheel slightly, like stars at the edge of a galaxy. Looking at his Pioneer anomaly paper, it seems that mass comes in from an explicit violation of equivalence at low acceleration. The probes retain their gravitational mass, but lose a small amount of inertial mass, getting more acceleration for the same amount of force. This explanation is, of course, completely incompatible with GR.
But looking at Greece, then we have to consider how to rename that commission once it gets unpopular...
Oh my.
I haven't read Podkletnov's papers, but his research is conspiracy theory fodder that I've encountered before, and that's even without getting to the UFO stuff. About fifteen years ago, NASA spent a bit over half a million dollars on trying to replicate Podkletnov's experiment, but the team fell apart allegedly because the lead, Ning Li, was more interested in proving her pet theory of how antigravity works than actually doing a careful experiment. Add in Li getting funded by DOD soon afterward and then abruptly disappearing and you're on your way to the perfect tinfoil brew.
Once upon a time I posted this on SV while cutting out the evening part... and it wasn't just to save space. I will thus proceed to once again distract myself from this aspect of the comic by munching on some beef tensors instead.It reminds me of this SMBC comic:
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"We have proof of principle of gravity shielding and gravity beams! Rockets are obsolete! Gravitational radiation is harmful to the body! UFOs are real! Why won't they listen?!"
"I know, buddy. I know."
It gets even more confused when one considers that this is his proposed explanation for both dark matter and dark energy, even though this would require opposite direction for the minimum acceleration. And one can't posit one way for internal galactic dynamics and opposite way for inter-galactic interactions; not only would that be completely ad hoc, but the dark matter content of galaxies affects the cluster and supercluster dynamics too.
There could be a variety of effects, both transient and steady, so things are not nearly so clear-cut, especially since their temporal resolution is not so great, the last year's graph showing a ramp-up in about three seconds—so not necessarily all that abrupt either.
