
Close Look at Recent EmDrive Paper - sohkamyung
http://www.centauri-dreams.org/?p=36890
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walrus01
Something I'm confused about, and I do RF/microwave engineering work...
There's a lot of debate about whether the "thrust" produced is real or is an
artifact of the test environment.

But they're only testing at relatively low power levels like 40W, 60W, 80W.
There are lots of commercially available sources for Klystron and TWT type
amplifiers rated up to 3000W (used for C, Ku and Ka-band satellite earth
station Tx applications). If the question is whether it's real, would it not
make sense to build a HUGE FUCKING HIGH POWERED test rig with >1500W input?

If we're measuring possible "thurst" in micronewtons, and the claim of the
original research is that the thrust will scale somewhat proportionally with
the power level applied, does it not make sense to develop an unambiguous
result by building a very high powered test rig?

In a theoretical scenario where a high powered test rig produces real
measurable thrust that is far too great to be a measurement error, it would be
an amount in millinewtons that is far too great to be explained by a non-
thrust variable such as thermal expansion/contraction in the power cables,
etc.

If the claim is 260 micronewtons at 60W, use COTS klystron and/or TWTA
technology to build a 3000W test rig. Question answered.

here are some examples of high powered units for satcom purposes:
[http://www.cpii.com/product.cfm/4/13](http://www.cpii.com/product.cfm/4/13)

edit: The thing is described as a "resonant cavity" and operates at 1.9 GHz:
[http://arc.aiaa.org/doi/10.2514/1.B36120](http://arc.aiaa.org/doi/10.2514/1.B36120)

Looks damn near identical to a weird feed horn to me. The test article looks
like a cone or horn antenna with a feed horn stuck onto the back of it. High
power capable waveguides and feed horns for big-ass satellite telecom things
(like an 11 meter sized C-band Tx/Rx earth station) are a well known science.
You can buy them from a myriad of COTS sources.

~~~
ridgeguy
From following EmDrive work a little, my impression is that nobody has the
budget to do a high power setup right. Budget was a major limitation in the
published NASA work. Also, some artifact sources (e.g. power lead/B field
artifacts) would scale up along with power.

~~~
flukus
Yet there are a couple of separate plans to send it into space for testing. I
would of thought more terrestrial testing would be much cheaper than sending
something to space.

~~~
kobeya
Actually cube sats can be pretty damn cheap. A cube sat test rig with off the
shelf components could be cheaper than a custom ground experiment.

~~~
walrus01
Sufficient watt hours per day to prove this are not available from the PV
cells you can mount on a cubesat.

~~~
euyyn
Plus you have to pay for launch, even if you piggyback.

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sethbannon
All quite interesting but the important bit is in the conclusion: "In addition
to mechanical and related considerations, the authors’ methods of analysis of
sensor data to derive thrusts rests on untenable grounds... Therefore, until
more control tests are performed allowing a more accurate method for
estimation of thrusts, no faith can be placed in the thrust magnitudes
reported in the paper."

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madengr
I'm still curious to know if it could be rectified DC currents in the cavity
as I posted here:

[https://news.ycombinator.com/item?id=13249730](https://news.ycombinator.com/item?id=13249730)

One of the comments in this threads story, was to place the apparatus is a
faraday cage. That does not shield against static magnetic fields. For that
you need chambers of multiple layers of high permeability materials, separated
by air.

~~~
sandworm101
Doesnt a vac chamber already make for a reasonable faraday cage?

~~~
madengr
Yes, though not up to standards of a room for RF testing. Though, classic
faraday cage does not shield static magnetic fields, like the Earths field.

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Analemma_
Previous discussion:
[https://news.ycombinator.com/item?id=13286160](https://news.ycombinator.com/item?id=13286160)

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powera
Article summary - the science and the experiment behind the EmDrive claims are
flawed.

My take - the people pushing this are charlatans and should be ignored
completely.

~~~
dpark
I don't see why they should be ignored. Right now what we have is an
unexpected and unexplained effect. The scientific thing to do is to understand
what is happening. The fact that the initial claims may be from charlatans is
irrelevant.

"We don't understand it and the explanation is likely boring, so let's ignore
it" might be a decent engineering tradeoff, but it comes from a goal of cost
savings, not from a goal of improving our knowledge of physics. Science is
about improving our knowledge and understanding.

~~~
powera
> Right now what we have is an unexpected and unexplained effect.

It's expected that the people working on this for 15 years would claim to find
an effect, since they clearly have an agenda that they want to be seen as
right. It's explained by this very article how there are many reasons other
than "propulsion-less thrust" that would cause the reported results.

~~~
kobeya
Except that the recent work is by new people who were skeptics trying to
refute the idea and failed. That's why people are so interested now while no
one cared 15 years ago.

~~~
euyyn
> new people who were skeptics trying to refute the idea and failed

Jelly beans cause acne. But if you investigate further, only green ones.
Unless you keep pouring money down the drain with it, in which case it's only
the green ones of a certain weight.

[https://xkcd.com/882/](https://xkcd.com/882/)

~~~
kobeya
That has zero relevance to the current situation.

~~~
euyyn
No. The relevance is that you aren't going to read of the cases in which
someone built the thing and didn't find any effect at all.

~~~
kobeya
Except I have. There have been multiple groups working on this, and they have
shared their results. Some published, some on blogs. Some have been
unsuccessful in getting their noise floor low enough to detect the effect.
Those who have (multiple groups now), have found _something_. That's why this
is interesting.

This sort of experiment requires a very expensive, delicate laboratory. No one
is going to run a replication of this and then not publish in some form, even
on a blog or a conference poster.

------
Zikes
Can somebody just put one of these in space already? We're seeing a post every
week refuting the previous week's posts.

[http://i.imgur.com/W6CyRnB.gif](http://i.imgur.com/W6CyRnB.gif)

~~~
superkuh
That'd just add _more_ uncontrolled variables. What they need to do is stop
assuming they can disassociate effects from a superposition with a trend
fitted by eye.

~~~
stale2002
Not really. You put it in space, turn on the engine, and see if it STAYS in
space.

If it crashes to earth after a year, then it clearly doesn't work.

If it steadily starts to escape earth's orbit, then it DOES work.

~~~
cjensen
The forces they are claiming are not sufficient to stay in space. Also, some
sources of error would provide actual boosts in orbit without being useful as
spacecraft engines.

~~~
taneq
Wouldn't an 'actual boost in orbit' be useful in and of itself?

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monocasa
Not if it's as inefficient as is claimed.

