[AR] Re: NASA test of quantum vacuum plasma thruster (was "Anyone heard of this?")
- From: Willow Schlanger <wschlanger@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sat, 02 Aug 2014 19:50:28 -0700
I personally am skeptical as well, but if conservation of energy is not
being violated here at all (and if momentum conservation proved only to
be "violated" if we fail to take into account the full system -- I
realize this is being optimistic!) then we'd be OK from a physics point
of view.
Still I'm not optimistic either; I would suppress judgment until linear
acceleration of an actual spacecraft is demonstrated (either changing
its orbital plane, i.e. transitioning between two orbits of equal energy
in a way that gives us a change in the direction of linear momentum, or
an outright measured acceleration) -- or found not to exist.
When I read the original Shawyer paper in 2006 I thought maybe the
effect was just a wobble of the outside part of a device, against the
center of mass. (Imagine a trapezoid with its angles changing due to
internal photon pressure or similar. The center of mass would not
experience any acceleration, but the thing could wobble vertically
against the center of mass due to changes in geometry).
This could easily be mistaken for a "force" if measured by a scale or
other instrument (which would really be measuring the wobble of the
outside of the device and would not show a continuous force for long
enough to take into account corresponding counter-momentum changes in
the interior). NASA's measuring devices were most likely not in
freefall, but were connected to a massive Earth that can absorb some
changes in momentum without us realizing it.
The use of the word "pendulum" in the AIAA paper makes me feel more
skeptical: did they measure only something that happened in pulses? If a
child is on a swing and wobbles against their center of mass in the
right way, an outside observer might see them speed themselves up
without exhausting anything (if they get the frequency of their
movements right), but this won't be impressive at all: the Earth itself
participated and was responsible for keeping momentum conserved.
Still, this could be a real effect and it deserves investigation. Also
the "energy conservation" problem (i.e. in most or all reference frames)
does not exist if momentum is indeed truly conserved.
(A true "reactionless" propulsion system would violate this, unless it
was interacting with a massive body via a field, in which case it
wouldn't be reactionless [an example is a gravitational slingshot].
However, we only know the EmDrive thing is supposed to be
"propellantless"; if it works, perhaps energy is indeed lost for some
field effects that somehow make it non-reactionless, i.e. to somehow
allow momentum to ultimately still be conserved?)
An optimistic view is as follows: I can walk very efficiently, more so
than you can if you're traveling via a rocket; the reason is I have the
whole earth to use for momentum conservation. Since the Earth is so big,
to conserve momentum as I push against the ground and walk, the Earth
hardly needs any change in velocity at all; so, I don't waste a lot of
energy making up for a change in kinetic energy for the Earth. Rockets
by contrast have an (empty mass) to (exhaust mass) ratio that is
generally between 1 and 10 or so. That's way different than the Earth's
mass divided by my mass.
Not surprisingly, I can spend only a little bit of my internal energy
changing my kinetic energy (i.e. increasing my speed -- since I have the
whole Earth to push against, this can be done quite efficiently).
A traditional rocket gets its energy by reacting chemicals that then
become exhausted, so they double as both a source of energy and
propellant. This means the mass of the rocket's propellant times its
energy density (i.e. Joules per kg) provides an upper limit on the
energy available for doing work on both the rocket and its exhaust.
Since the rocket's exhaust travels at a slow 1 km/s to 5 km/s speed (we
can't do much better using only a traditional chemical reaction and what
we have to work with), we wind up needing a large amount of propellant
for our space missions and also a lot of energy winds up as the kinetic
energy of the exhaust and not the empty rocket or payload's kinetic
energy (or potential also, if we're going up a gravity well).
The most obvious way to increase efficiency are to increase the
propellant's effective energy density in J/kg (i.e. using less safe
things that don't presently last the duration required for spaceflight;
or things that are radioactive; or use toxic chemicals--Hydrogen and
Fluorine release a lot of energy and so does ozone; even Beryllium and
Oxygen release a lot of energy).
I don't think anyone wants to pursue this approach, though an energy
storage or even transmission breakthrough could change the interest here.
Another way to increase efficiency is to reduce our delta-V requirements
or demands on the rocket -- if you have a 1,000 km vacuum tube / tunnel
and a dedicated hydro-electic dam, we might be in business here. The
rocket would be used after the ship reaches escape speed, and it would
coast to orbit (presumably the drag would slow it to orbital speed with
the rocket controling it; some kind of plasma-based spike thing would be
needed to keep it from burning up, and this wouldn't be legal in the
continental United States as we'd be way over mach 1 when the ship left
the tunnel).
Back to the "EmDrive" (the one in the AIAA papers use a new name that
starts with a C) to be useful at all they'd only have to match ion
rockets performance-wise with a longer mission duration being possible
(or a lower mass for the drive itself). Beating an ion rocket, or
scaling better would be icing on the cake.
I mentioned slingshots above as an example propellant-less "propulsion"
system. It's propulsion in the sense that it changes momentum for a
ship; but it's not reactionless, as it changes the momentum of
whatever's being slingshotted, just a little bit--that change in kinetic
energy represents the lost energy of a slignshot, and is very small.
Aside from that, there's likely close to or exactly no extra energy lost
as heat, and a massive amount of energy goes to changes in the satellite
or rocket's kinetic energy due to a desirable momentum increase.
This is a field effect, but it doesn't violate conservation laws. If you
just looked at a satellite before and after a slingshot encounter, or
even during if you couldn't see the body it's sling-shotting, it would
mysteriously be accelerated -- in a appellant-less way -- at high
efficiency, the input energy coming from a chemical rocket that put it
at the right place and time for the encounter to happen, but the output
kinetic energy being seemingly too high based on energy burned by the
rocket.
It would even look as if momentum weren't being conserved! So the
"EmDrive" could perhaps be like that; perhaps it pushes against the
whole visible universe somehow, using its mass like the way I push
against the Earth when I walk, at high efficiency?
I realize this is an optimistic estimate, but I don't think an
efficiency of 0 is required, but an efficiency of 100% is not possible
either. So getting some kind of number for efficiency would be a
positive step (and the computed number shouldn't require use of some
special reference frame; it should even take into account energy lost to
whatever's making sure momentum is indeed being conserved -- assuming
the effect is real).
Willow Schlanger
On 08/02/2014 06:31 PM, Ian Woollard wrote:
> On 3 August 2014 02:02, Nathan Mogk <nm8911@xxxxxxxxx> wrote:
>
>> That's exactly what things like rail guns do. They work by pushing against
>> a field, rather than by expelling propellant.
>>
>
> In a real sense this is false, rail guns do not violate Newton's third law,
> whereas the emdrive would have to.
>
>
>> This is just supposed to push off of the field of virtual particles. I
>> can't judge whether or not the physics is correct, but the quantum vacuum
>> is at the heart of how forces like magnetism are understood to work, and
>> there is experimental evidence for being able to produce forces from it (a
>> la, the Casmir Effect).
>>
>
> The Casimir effect does not violate Newton's third law either. The two
> plates are pushed equally and oppositely.
>
>
>> I'm fairly certain the physicists involved don't believe any conservation
>> laws have been violated, and not because they haven't checked them.
>>
>
> That bit in the NASA paper where they say they haven't validated the
> physics? Yeah, that bit; is where they haven't checked them.
>
> Hey, perhaps we do live in a universe where some processes violate
> conservation of energy. That would be nice, because my electricity bill
> could go down. But I'd need a heck of a lot more evidence than this to
> believe in it.
>
> On Sat, Aug 2, 2014 at 5:09 PM, Ian Woollard <ian.woollard@xxxxxxxxx> wrote:
>>
>>> There's essentially no chance that a thruster can work where you turn it
>>> on, feeding only electricity through it, and with nothing leaving it; where
>>> you switch it off, and you're now moving faster. This is what the emdrive
>>> is claimed to do.
>>>
>>> If you could do that, we're in perpetual motion territory; because it
>>> violates both conservation of momentum, and (more subtly) it can be shown
>>> to violate conservation of energy.
>>>
>>> The emdrive paper tried to fix that by using the kinetic energy equation
>>> in one frame of reference, but you can show that energy is violated in
>>> every other frame of reference except the one he did the calculation in. So
>>> he's done something wrong. You can fix it, if you introduce an efficiency
>>> variable, and set the variable to zero.
>>>
>>> On 2 August 2014 23:44, Willow Schlanger <wschlanger@xxxxxxxxx> wrote:
>>>
>>>> I just bought the AIAA paper (it's a 21 page PDF) from this location:
>>>> http://arc.aiaa.org/doi/abs/10.2514/6.2014-4029
>>>>
>>>> I also discovered I have an old paper on the EmDrive from "Satellite
>>>> Propulsion Research Ltd." The filename is "theory paper V9.3.doc" and I
>>>> received it September 16, 2006 from (if I remember correctly) Roger
>>>> Shawyer. Here is the first sentence from the Abstract: "A new principle
>>>> of electric propulsion for spacecraft is introduced, using microwave
>>>> technology to achieve direct conversion of d.c. power to thrust without
>>>> the need for propellant."
>>>>
>>>> It's been a while since I've read that paper (and I'm surprised I was
>>>> able to find a copy of it saved from all those years ago), but I don't
>>>> think it mentioned anything quantum related. I'm taking a quick look; I
>>>> think he attempted to use only special relativity and non-quantum
>>>> physics to describe the effect.
>>>>
>>>> I'm not sure I'll be able to figure out what any of this means, but I'll
>>>> try to do some reading and post my thoughts here, if I can decipher what
>>>> they're all talking about. The AIAA paper was $25.00, and the old
>>>> "theory paper" mentioned above was sent to me back in 2006 for free (but
>>>> both documents are copyrighted so I can't share them).
>>>>
>>>> Willow Schlanger
>>>>
>>>>
>>>> On Sat, Aug 2, 2014 at 1:26 PM, Satadru Pramanik <satadru@xxxxxxxxx>
>>>> wrote:
>>>>
>>>>> There's some discussion of the merits of this paper on reddit by this
>>>>> user here:
>>>>>
>>>>> http://www.reddit.com/user/dalovindj
>>>>>
>>>>> He says that the null article wasn't a control, but used to test under
>>>>> which conditions the effect occurred:
>>>>>
>>>>> "The null configuration (not the RF load - not the control but the
>>>>> *central* subject of a test) was one of two test articles. There are
>>>>> two competing theories as to how the phenomenon works. Fetta believes that
>>>>> it works based on asymmetry in the design, while White believes it works
>>>>> by
>>>>> pushing against the quantum vacuum.
>>>>>
>>>>> They tested an asymetric and a symetric design. The symmetric design
>>>>> (neither were "broken") is what they refer to as the null. It was meant to
>>>>> test a prediction of Fetta's theory on how the device produces thrust. He
>>>>> believes that the force is produced by an imbalance of the lorentz force
>>>>> caused by the asymmetric chamber. This test seems to indicate that Fetta's
>>>>> theory is incorrect (or at the very least innacurate). Dr. White's theory
>>>>> on how thrust is produced (pushing against the quantum vacuum), however,
>>>>> predicted that both test articles should produce thrust, which they did.
>>>>> It
>>>>> would seem an endorsement of White's theory over Fetta's."
>>>>>
>>>>>
>>>>> This is stated in the paper as such:
>>>>>
>>>>> Prior to testing, Cannae theorized that the asymmetric engraved
>>>>> slots would result in a force imbalance (thrust). As a result, a second
>>>>> (control) test article was fabricated without the internal slotting
>>>>> (a.k.a.
>>>>> the null test article).
>>>>>
>>>>> Let me know if anybody wants a copy of the paper. Seriously discussing
>>>>> the merits of the physics in this paper is currently above my pay grade.
>>>>>
>>>>>
>>>>>
>>>>> On Sat, Aug 2, 2014 at 11:15 AM, David Weinshenker <
>>>>> daze39@xxxxxxxxxxxxx> wrote:
>>>>>
>>>>>> William Blair (Redacted sender wbblair3@xxxxxxxxx for DMARC) wrote:
>>>>>>> How could they then be certain that air movement caused by the
>>>>>> differential heating
>>>>>>> of the air within the RF cavity hadn't caused the measured
>>>>>> micro-thrust? I must be
>>>>>>> missing something because this seems to be too obvious of a
>>>>>> potential flaw in the test.
>>>>>>
>>>>>> Well, the abstract (is the full text available anywhere?) did mention
>>>>>> a comparison
>>>>>> run they did with an "RF load" replacing the test device, which seems
>>>>>> to be intended
>>>>>> to control for effects such as you suggest. (If the test device wasn't
>>>>>> designed and
>>>>>> baked out for operation in vacuum, escaping air from crevices, and
>>>>>> outgassing of
>>>>>> surfaces, could conceivably create spurious forces of their own if the
>>>>>> chamber was
>>>>>> pumped down to vacuum.)
>>>>>>
>>>>>> -dave w
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>>
>>> --
>>> -Ian Woollard
>>>
>>
>>
>
>
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