[extropy-chat] unidirectional thrust

[Hal Finney]

Mike Lorrey writes, quoting me:
> > Where the heck does that equation come from?  Do you realize that to
> > produce a force of 0.3 Newtons, as Naudin measured in his lab (see
> > the link above, raising 35 grams takes 0.3 Newtons), you'd need V =
> > 4 billion?!  If V is kilovolts then we're talking about 4 teravolts
> > to power Naudin's lifter.  You're off by 8 orders of magnitude.
>
> These numbers are from research done under USAF contract and mentioned
> in Cravens study. This equation is for vacuum. Naudins numbers are all
> at 1 atm. The study he cites a thrust that is for a low pressure, but
> not a vacumm. I am not sure what thruster configuration this pertains
> to though.

Okay, I found that formula on page 87 of the report by D.L. Cravens,
<http://www.foldedspace.com/Electric%20Propulsion%20Study,%20Dr.Cravens%201989.pdf>.
This comes from work at Veritay Technology, an experiment by R. Talley,
"Twenty-First Century Propulsion Concept."  I found several references
to Talley's report, but the document itself does not seem to be online.
It's a little confusing because some references to the report indicate
that it did not observe steady thrust in vacuum, but that Talley did see
some anomalous transient effects as the voltage was switched on and off.
However this reference seems to claim that Talley observed a steady
thrust in a vacuum.

In doing this search I found a new report on the NASA web site from
within the past 6 months, doing more experiments on lifters in vacuum,
<http://gltrs.grc.nasa.gov/reports/2004/CR-2004-213312.pdf>, "Asymmetrical
Capacitors for Propulsion", October, 2004.  Here is how they characterize
Talley's report:

"Robert Talley of Veritay Technology 5 performed tests of ACTs in a vacuum
in the late 1980's under Air Force contract.  The tests did not let
the ACTs spin, but instead suspended it from a torsion wire.  This gave
him the sensitivity to be able to measure small forces.  His report is
the only written report we have found from the last half-century that
describes a measurement of a force while in a vacuum chamber.  Talley
ultimately attributed the force that he observed to the electrostatic
interaction between the chamber and the device. Talley wrote, 'Direct
experimental results show that under high vacuum conditions... no
detectable propulsive force was electrostatically induced by applying
a static potential difference... between test device electrodes...'
Talley concluded (page 91 of his report 5), 'If such a force still
exists and lies below the threshold of measurements in this program,
then the force may be too small to be attractive for many, if not most,
space propulsion applications.'  While this work makes a strong case
against the ability of these devices to produce a force in a vacuum,
it did not address the use of asymmetrical capacitors in the atmosphere."

Here is what the new NASA study observed: "After several days of tests,
we found that no device showed signs of rotation at a pressure less
than 300 Torr, with one exception.  When Device 2 wired according to
Circuit A was placed in the chamber and immediately pumped down to a
pressure of 5.5E-5 Torr, something interesting happened.  The voltage
on it was increased to 44 kV, and through the viewing port a large arc
was observed.  At that same moment, the device was seen to move about
an eighth of a rotation and stop.

"The large arc that was observed suggests that this movement was most
likely caused by material being ejected from the device. This material
might be either the copper on the plates or it might be water vapor."

So aside from this one arcing event, they failed to observe any thrust in
even a very mild vacuum of 300 Torr (normal air pressure is 760 Torr).
And according to them, Talley also did not claim to see thrust in a
vacuum in a steady state that could not be explained by electrostatic
attraction to the walls.  I don't know why Cravens characterizes Talley's
result so differently.

In any case the formula F = 3.55e-8 * V^0.722 does not make sense as a
general guideline, because F will depend not just on V, it will depend
on the size and design of the device.  Presumably by making the device
bigger we can increase the thrust even with constant voltage.  It makes
more sense for thrust to depend on power.

Cravens goes on to quote Talley with the other figure you gave, .00025
N/W.  That one makes more sense and as I pointed out is, coincidentally
or not, almost exactly the one I used (.00030 N/W) in my calculation.

> You have a good point there, but it isn't a point that doesn't cause
> problems also for a Bussard Ramjet, worse yet because the ramjet
> performs better at higher velocity.

I'll go ahead and explain about the ramjet in another message, just to
put the issue to bed.

> As Cravens noted, you can't talk
> about 'conservation of momentum' with a field thruster like this if it
> is thrusting against the entire universes inertial frame, because you
> have no external point of reference to base such a judgement on.

Physics is local.  That's the lesson from general relativity.  The sun
doesn't reach out across space and pull on the earth, let alone the
distant stars.  The sun warps space locally, right next to itself.
That warpage then warps the space out a little farther.  Each bit of space
warps the bit next to it, and eventually we get out to where the earth is.
The curvature of space manifests itself in the orbital path of the earth.

You can't thrust against an inertial frame.  Such a frame is merely a
mathematical convention for analyzing motions.  It's like suggesting that
you will climb up onto your roof using a ladder made out of the Y axis.

Now, if you wanted to claim that this device is reaching out to the
distant stars, physically grabbing onto them and pulling them backwards
as it goes forwards, at least that would not violate conservation of
momentum.  But it does violate the principle of locality of physics,
which is related to the principle of relativity - that there is no
absolutely preferred rest frame.  This is all mainstream physics.

And be reasonable - could a dinky little piece of aluminum foil with
a tiny little kilovolt electric field really reach out and pull on
the distant galaxies, billions of light years away?  That's not at
all credible.

> The
> best you can do is divvy the KE in half, because the universe is being
> pushed equally in the opposite direction, a division that generally
> isn't used with rocket engines because it is only accelerating a small
> amount of mass and where the observer isn't part of the equation. When
> you do that, your actual KE drops below the power put in, and
> conservation does in fact exist.

You're not being quantitative here.  You were pretty pushy when I was
doing my calculations - you even demanded that I supply an analysis
based on relativistic mechanics!  (For a device going 10 km/sec!)
Let's see you supply a thrust and power scenario in as much detail as
I did, where you can show that the device will never go over unity.

> WRT this device, the problem we run into is that we've never tested it
> at ANY sort of velocity but a lab test bench, so there is not any sort
> of sufficient experimental database upon which to even extrapolate what
> sort of attenuation law might apply in higher velocity ranges. Until
> that happens, making arguments like yours to justify dismissing this
> technology are tantamount to excuses why heavier-than-air flight was
> impossible prior to the wright brothers.

I'm not saying we should dismiss it.  I'm saying that any such device
either violates conservation of energy or the principle of relativity.
It if keeps thrusting through the 10 km/sec regime then it violates
conservation of energy.  If it stops working at that speed, then someone
who was moving past the device at 10 km/sec would disagree about whether
it should be working or not.

Heck, the earth's orbital velocity around the sun is 30 km/sec!
If there is really a preferred rest frame of the universe that this
device interacts with, and if moving 10 km/sec will make it stop working,
then it should be extremely sensitive to the earth's motion.  Whether the
device works or not should depend on the time of year.

And what are the odds that the sun is at rest relative to this magical
universal frame?  The sun is moving around the galactic center at 220
km/sec.  Who knows how fast the galaxy is moving.  We add 30 km/sec for
the earth, 220 km/sec for the sun, something more for the galaxy and
larger structures... the chances are basically zero that we are anywhere
close to being at rest with regard to the average motion of the universe.

If this device really did only achieve thrust with regard to such a
universal rest frame, such that moving 10 km/sec relative to that frame
would make it stop working, then it would never work here on earth,
because we're already moving far faster than 10 km/sec relative to
that frame.  This whole line of explanation just doesn't work.

Frankly, if you want to cling to the idea that this thing works, my
advice is to explain away the extra energy.  You're already invoking
this mysterious rest frame to explain where the momentum comes from,
so why not the energy?  There's always zero point, the catch-all energy
source for every perpetual motion machine inventor.  Or maybe you're
extracting energy from the distant stars.  That doesn't sound much harder
than grabbing onto them and giving them a push.  I don't understand why
you're so willing to excuse the obvious violation of conservation of
momentum but so reluctant to accept the problems with energy balance.
To me, they're equally bad.

Hal