So do I understand this right?
The argument is that there is a time varying electric field offset from the central axis and you wind up with a Lorenz force?
F= q (E + v cross B)
I mean if that’s what he’s talking about then it sounds like the force is coming from interacting with the earth’s magnetic field. That’s not particularly magical.
Ars Technica is skeptical.
It sounds a bit like Steorn Orbo in the sense of having discovered some assymetry of reversibility in the laws of thermodynamics
Alternatively, I’d be happy with a single practical example of the device–say, installed on a satellite with no other propulsion system and being able to maneuver properly.
Same thing with “over unity” devices. If you have some small effect that is only just barely visible in a lab… then yes, I’m going to demand several independent confirmations of the result. If you instead build a small 1 kW generator that requires no fuel and runs long enough that it couldn’t be battery powered–well, that would be compelling enough that I wouldn’t be concerned about the theoretical backing.
Satellites in geostationary orbit also need to use fuel for station-keeping. Gravity from the sun and the moon perturbs the orbit, and each satellite has to stay in a very precise location. Wiki sez the delta-V requirements for geostationary station keeping are about 45 m/s per year, which is pretty considerable if you want your tremendously expensive satellite to be useful for a decade or two.
To be clear, they’re not “propellantless”; they used charge particles found in the orbital space medium (which are collected and concentrated in certain parts of an orbit by the Earth’s magnetic field and replenished by solar wind and cosmic radiation interactions with the upper atmosphere) and direct them along the tether axis to obtain small but fairly continuous amounts of thrust (and in the case of a tether that is off-axis of the system center of mass, torque) which can be used for station-keeping, maneuvering, and attitude control. There is nothing extra-physical about this, although the amount of thrust that can potentially be developed is so small that it is only practical for very lightweight spacecraft, e.g. femtosats.
On a high level, the “Cannae drive” works in a physically sensible fashion (using net radiation pressure as the propellant) and at least doesn’t appear to violate any thermodynamic laws (you have to put energy in to get work out) but since nearly all the links that purportedly describe the theory and application of the effect are 404’ed, it is impossible to make any kind of credible assessment other than that there are literally hundreds of claims of devices which can extract a net force from either the ambient electromagnetic environment or from some kind of virtual particle plasma, and almost none of them either offer reproducible results or offer enough thrust (or reduction of inertia or whatever) over a large enough range to ever be practicable. However, there is still considerable interest in resonant cavity propulsion, and here is a non-peer reviewed paper from a NASA test of a resonant EM thruster (the previously mentioned EmDrive) using a torsion pendulum (a device capable of measuring thrust forces in the micronewton range).
So, I wouldn’t bet the mortgage payment on it, or for that matter, your bubblegum money, but I also wouldn’t utterly dismiss the possibility that it may demonstrate future viability.
Stranger
Just wanted to add that reactionless drives are possible in principal. But they require a very powerful gravitational force to be measurable. This takes advantage of quirks of general relativity and involves a “swimming” motion. Of course the thing mentioned in the OP is a crock.
I’m sure you are right about the charged particles, but I am under the impression that even if there were no charged particles (say in the space surrounding a planet with no atmosphere but with a substantial magnetic field) an electrodynamic tether could still achieve propulsion by pushing against the field itself; in this case the propellant would be the planet, since it would move infinitesimally in the opposite direction to the tether.
This is interesting; do you have any more details? I’ve read about several different reactionless drives, mostly those described by Marc Millis in his Breakthrough Propulsion Physics program (also supported by NASA). Nothing much came from that, since each method required at least one impossible thing before breakfast.
Not the body must be large enough (or alternatively the spacetime ‘curved’ enough) so that the symmetry of the body in spacetime is far enough away from Lorentz symmetry for the effect to be noticeable.
Fascinating; thanks!
The reactionless drive that I always admired most is the Diametric drive, which uses a lump of negative matter (with negative inertia) to pull the ship across space-time. Of course not one single (negative) picogram of negative matter has ever been manufactured, nor is it likely to be.
Not even just radiation, these forces are so small, I’d be worried about vibration in the building throwing off their numbers. If those load cells can pick up micro and millinewtons, I’ll bet they can sense someone walking down the hallway 100 yards away or ‘background’ seismic activity. Don’t get me wrong, physicists are smart people and I’m sure they think about all this stuff.
Well, there was that antimatter gun in Rocky Horror Picture Show, but it just sort of knocked people out and didn’t really make anything disappear.
Sorry, let me clarify; the “thrust” is applied against the magnetic field by moving electric charges. That the charge is convey by the tether doesn’t matter; the equivalent momentum change is applied to the particles between the termini of the tether such that work is done and energy (except for ohmic heating of the tether) is conserved. There is nothing reactionless or aphysical about this; it is like using a propeller on a boat to redirect the flow of water to change speed or direction, and like the amount such a maneuver has on the effective of a lake or ocean, the work done on the Earth is minimal. However, momentum is locally conserved, which is not the case with a true “reactionless” drive. Whether such a system would conserve momentum in a global context depends on how it is implemented; systems which work within the existing mechanics of General Relativity and assume that space is continuous and well-behaved have to make alter the field elsewhere to ensure that momentum is globally conserved, but any in system which allows topological singularities to be arbitrarily created momentum does not have to be conserved.
Stranger
Those charges stay within the tether, though. As such, they don’t really qualify as “propellant” (the Earth as a whole, does, though).
There’s been some talk of using tethers not for thrust, but to clean out the Van Allen belts. Any charged particle interacting with the tether would have its orbit changed from roughly circular to something that (hopefully) either intersected Earth or was on an escape trajectory. It couldn’t eliminate the belts entirely, since charged particles are always being captured, but it would reduce the equilibrium level significantly.
This would only apply though to asymptotically flat spacetime and a few other spacetimes with certain symmetries. In general global momentum cannot be defined meaningfully.
No, charge (electrons) are definitely expelled in order to create the current. Of course, it isn’t the same electrons which are captured at the other end, but work is done nonetheless, either by or on the thin plasma of the thermosphere in order to generate the current which creates a magnetic field operating against that of the Earth. Here is a page from Tethers Unlimited (one of the leading developers and suppliers of spacecraft tether systems) which explains the operation of an electrodynamic tether.
Stranger
All right; I see that that’s the normal mode of operation, though it’s not clear to me that it must be the case. At least for non-equatorial orbits, a tether will experience a changing magnetic field over the course of the orbit and thus a varying induced voltage. That implies a current, which implies ohmic heating, which implies that the Earth’s magnetic field is doing work on the tether.
Here’s the thing; if momentum is conserved locally but not globally, there might be a way of tapping into this hypothetical distant unconserved momentum. The gods of the universe as a whole don’t really seem to care about the momentum copybook headings.
But how this might be achieved I can’t imagine.