
The Fact and Fiction of the NASA EmDrive Paper Leak - AliCollins
http://motherboard.vice.com/read/the-fact-and-fiction-of-the-nasa-emdrive-paper-leak
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david-given
James Woodward's one of the old names in propellentless thrust --- he's been
working on Mach Effect based systems for a long time now. His approach is my
favourite of all the anomolous science thruster systems, because (a) he
actually has a testable theoretical model to back up his experiments, and (b)
he doesn't talk about it much; in the fairly rare interviews, he tends to be
focused more on coming up with ways to _disprove_ his experiments, rather than
self-aggrandisement; which to my mind is the main mark of a serious scientist.

By which I mean to say, in the nicest possible way, that he's not an impartial
observer when talking about this thing, so it's worth being careful about what
he says.

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binarycoffee
As an electric propulsion engineer used to measure thrust in the uN range,
what disturbs me much more than thrust levels close to the sensitivity
threshold is the fact that thrust is only detected some 10-20s after the RF is
turned on (figs 9,8,13). I am rather confident that there is no physical time
scale in the RF generation process that would account for a 10-20s ramp, and
this would contradict their own report of the fast RF power stabilization. It
definitely looks like thermal drift; in fact, thermal drift is _always_ the
first thing to suspect when you get strange measurements with a low thrust
balance.

It appears as well that the authors have conveniently prepared an answer for
this objection with fig.5 which attempts to mislead the reader by suggesting
that the very slow evolution of the balance displacement is to be expected as
an artifact of the combined effect of thermal drift and RF pulse onset. But
conveniently, the time units are arbitrary so that hopefully nobody will
notice that RF onset was assumed in that figure to have exactly the same
characteristic time as the thermal drift... When all measurements actually
show that RF power stabilizes much faster.

~~~
dpark
> _which attempts to mislead the reader_

Even if you're right, assuming malice seems premature and pessimistic.

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Nokinside
NASA seems to be minimally involved.

The group has been working five years in their own time in this small
laboratory with shoestring budget. White has a day job in NASA and he and
others are working with this project in their free time. To best of my
knowledge - and correct me if I'm wrong - NASA only gave them $50,000 and a
room in Johnson Space Center 2011. They don't seem to be involved in any other
way but "NASA Eagleworks Laboratories" makes it sound like official NASA
organization.

Their results are consistently close to the detection threshold of their
sensors. They are always flirting with the measurement error.

~~~
sfifs
the paper is reporting milli newtons and claims the measurement device can
measure micro newtons - or am I missing something?

~~~
AcerbicZero
The paper is actually reporting measurement of millinewtons with 40/60/80
watts, and estimating that when pushed up to a 1kW it would generate
micronewtons.

~~~
lutusp
Wait ... a millinewton is 1000 micronewtons, not the other way around. Not
taking a position on this issue, just posting a clarification.

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danielmorozoff
Actual paper from NASA recently on EmDrive (from Eagle Works)
[https://news.ycombinator.com/item?id=12906254](https://news.ycombinator.com/item?id=12906254)

Actual paper:
[https://drive.google.com/file/d/0B7kgKijo-p0ibm94VUY0TVktQlU...](https://drive.google.com/file/d/0B7kgKijo-p0ibm94VUY0TVktQlU/view)

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jchung
So far I've failed to grok the many arguments for and against this drive's
"impossibility". I'd love to find an ELI5 for it.

I think at this point, I'm resigned to waiting for an emdrive cubesat to just
prove it once and for all:
[http://www.popularmechanics.com/science/energy/a22678/em-
dri...](http://www.popularmechanics.com/science/energy/a22678/em-drive-cannae-
cubesat-reactionless/)

~~~
cjensen
Against is pretty simple

Argument #1: it violates Newton's Third Law of Motion.

Argument #2: every time they improve the test apparatus, the measured force
declines and is "coincidentally" close to the measurement limits of the
apparatus.

Argument #3: It was originally designed based on a misunderstanding certain
principles of Physics. Now they are trying to find a new explanation for why
it works. What are the odds that you misunderstand physics, design something
based on that misunderstanding, and that it then works in a barely-detectable
way due to "unknown mechanism"?

~~~
danielmorozoff
Aren't new physics drawn from violations of old laws?

~~~
mikeash
Yes, which is why violating a known law isn't automatically disqualifying. But
it is _highly_ suggestive, and requires extremely good evidence to surmount.
So far, such evidence has not been forthcoming, so this remains a good reason
to doubt.

Every so often, something comes along that overturns an established law, like
the photoelectric effect or the Michelson–Morley experiment. But the vast
majority of the time, the laws remain intact and it's the claim which is
somehow flawed. (See the Pioneer anomaly for a recent example where new
physics was long considered as a potential explanation, but it ended up being
a completely mundane effect.)

~~~
shuntress
So, thermal radiation slowed the Pioneer spacecrafts. 'Thermal' is a type of
Electromagnetic (EM) radiation, right?

Doesn't that make it an EM Drive?

Why the cone apparatus? What is preventing the intentional design of a
spacecraft that uses thermal radiation (or Thermal Recoil Force) similar to
the Pioneer spacecraft?

e: The replies indicate the answer is that this could be built but the effect
is to weak to be practical. Which I find to be a completely acceptable answer,
thanks.

~~~
Dylan16807
Light has effective mass. It's well known that you can shoot light in one
direction for a tiny amount of thrust the other way.

The device under consideration is special because if it works it is a
reactionless drive. Nothing is coming out of it.

~~~
triplepoint217
Light actually has momentum but not mass. Calling it effective mass isn't far
off, but sometimes my pedantic physicist kicks in.

~~~
Dylan16807
The proper term I'm used to is "relativistic mass", but I didn't want to make
the discussion complicated. Would you not phrase it that way?

------
ComputerGuru
I know absolutely zero about rocket physics or quantum mechanics but isn't
this a fairly easy and "cheap" thruster to prototype and test _in actual
space?_

Nothing beats real world results, and this doesn't seem that hard to test. It
might even be faster and cheaper than what's already been done, no?

~~~
huragok
No one will pony-up the millions of dollars it will need to design, build,
test and launch a satellite based on (possibly) unconfirmed science.

~~~
ComputerGuru
Yet they will gladly throw away ten times that amount investing in a silly app
idea on the off-chance it will be the next facebook or snap chat...

~~~
roywiggins
In fairness, we know Facebook is physically possible. Not so reactionless
drives. If a Facebook is unlikely, a reactionless drive is spectacularly so.

If they are possible, the question of where all the aliens are becomes much
more acute. If it's actually cheap to accelerate mass around the universe we
ought to be crawling with visitors.

~~~
dragonwriter
If it's cheap to accelerate mass around the universe, spreading beyond one
planet is easy, but provides less insulation against non-natural disasters,
like species-ending war.

~~~
arcticfox
Couldn't you theoretically take one of these way out from Earth, turn it 180,
and wait for a massively powerful kinetic energy weapon to return?

"Cheap to accelerate mass" just sounds like a crazy weapon

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jwtadvice
There's been breakthroughs in a fully quantified theory of how
electromagnetics can be used to create propulsion reliably and at (still
incredibly small but) orders of magnitude larger than prior designs provided
by the aeronautics research team from the Northwestern Polytechnical
University in Xi'an.

The research team published their breakthroughs in 2008, and excitingly,
they've been highly reproducible.

Unfortunately, the paper appears to be behind a paywall:
[http://en.cnki.com.cn/Article_en/CJFDTOTAL-
YHXB200805027.htm](http://en.cnki.com.cn/Article_en/CJFDTOTAL-
YHXB200805027.htm)

Does anyone on HN have the background necessary to explain the mechanics of EM
propulsion to laymen?

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jwatte
If they feed electricity into the microwave horn, how strong is the induced
magnetic field around the wires? Would that push against anything? How is that
compensated for in measurements?

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maverick_iceman
Sad to see this nonsense pseudoscience constantly making HN's front page.
Whenever it appears I debunk it using the same post[1] (in short, conservation
of momentum cannot be violated) but it keeps coming back. Looks like even
highly intelligent people like HNers are easily fooled by pseudoscience.

[1] [http://www.preposterousuniverse.com/blog/2015/05/26/warp-
dri...](http://www.preposterousuniverse.com/blog/2015/05/26/warp-drives-and-
scientific-reasoning/)

~~~
outworlder
> in short, conservation of momentum cannot be violated

Why?

~~~
piannucci
Speaking somewhat loosely, the relationship between the local state of
spacetime and its energy, the Lagrangian density, does not seem to depend on
where you are or when you are. Emmy Noether gave us a straightforward proof
that each such "differentiable symmetry" (in this case, translation
invariance) implies that the state of spacetime maintains a corresponding
"conserved current" (in this case, momentum and energy density).

