Comment by jcims | Hacker News Reader

Comment by jcims | Hacker News Reader

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Edit: Title has been changed, leaving this for posterity.

Apologies for formatting, but the title doesn’t match the conclusion of the paper.

“First measurement campaigns were carried out with both thruster models reaching thrust/thrust-to- power levels comparable to claimed values. However, we found that e.g. magnetic interaction from twisted-pair cables and amplifiers with the Earth’s magnetic field can be a significant error source for EMDrives.”

There was no experimental validation of this, just speculation based on their observations. They propose a simple fix, run the experiment in a magnetically shielded environment. They suggest Mu metal for maximum shielding, which would be good, but I’m a little skeptical that the vacuum vessels used in previous tests would have allowed a substantial flux of earths magnetic field through the environment. Using my phone's basic magnetometer, I get an order of magnitude reduction in field strength by placing it ~8" inside my oven and leaving the door open.

In any event they are probably on to something here. Certainly a more plausible explanation than any of the alternatives.

There was kind of. When they turn the EMDrive on its side the thrust doesn't come from the cone anymore it comes from an angle meaning that the angle at which the EMDrive/cone is placed has no relevance to the thrust's vector.

Imagine turning a rocket from horizontal to vertical and finding it still goes up, despite the exhaust from the engine going sideways.

That's not what Fig 13 says.

We changed the title to that of the article. Submitted title was 'EMDrive “thrust” caused by magnetic interaction from electric cables'.

Submitters: the site guidelines say "Please use the original title, unless it is misleading or linkbait. Don't editorialize." Please follow the rules when posting here.

https://news.ycombinator.com/newsguidelines.html

Why do you let people choose the title? Wouldn't it be easier to grab it from the page's title tag automatically?

I'd say while this might help, titles need editing by the submitter more often than not, be that for removing some extra tags/snippets/etc from the title, simplifying/abbreviating long titles, etc. (which is usually ok if you don't editorialize)

That alas is the sort of thing that works 80% of the time and fails the other 80% of the time.

What about a feature where the title is automatically populated and the user can modify it if incorrect?

The HN bookmarklet (in the footer) does that:

https://news.ycombinator.com/bookmarklet.html

Then half the submissions here would be “Github.com”.

The title is well supported by a statement in the paper (section 2.1, next to last para): "This clearly indicates that the “thrust” is not coming from the EMDrive but from some electromagnetic interaction." I think the conclusion is written in carefully understated scientific style.

The only thing they measured was that the thrust vector was decoupled from the cavity orientation and did not decrease when power to the cavity was heavily attenuated (fig 10). They therefore concluded that the forces measured are not thrust from the EmDrive. Everything else is (likely correct) speculation.

Yeah, it's odd that they make stronger claims in the middle of the paper (e.g. "This clearly indicates that the “thrust” is not coming from the EMDrive but from some electromagnetic interaction.") than in the conclusion.

Why not just replace the magnetron with a resistor. That keeps the DC effects while removing the RF.

Nevermind, they are not using a magnetron like the original concept.

Oh, they did that in a previous emDrive experiment. It still produced the same thrust. They ignored it. This is par for the course with reactionless drive "research."

Yep. This is going to be the next cold fusion - the device will soon be debunked, but we will still be hearing about it from conspiracy theorists for decades.

Quick comment on your oven test: The your oven's shell is probably some low-grade, magnetic steel. Vacuum chambers are typically stainless, aluminum, or titanium (if you want to break the bank) so non-magnetic. Their shielding effects would be much smaller.

Very good point! I tried adding a caveat to my comment but can no longer edit. Confirmed negligible impact in aluminum pot and large stainless bowl.

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