Talk-Polywell.org

Carl White wrote:It looks like they're paying Heidi Fearn to basically speculate about an "if Mach thrusters work, then.." situation.

kunkmiester wrote:Frequency yes, I recall they wanted an electrical engineer with a master's to design a new power supply though. Apparently they don't come off the shelf at the lower levels Woodward needs at the frequencies a better thruster would operate at.

GIThruster wrote:
Most piezoactive materials have their capacitance drop off dramatically about 1 Mhz. You'll therefore need to measure the capacitance on frequency.

GIThruster wrote:
Instead of calculating what the resonance should be given any specific amount of damping (and you can find the equations online at PiCeramics.com in their online piezo university), what you might do is use a PLL tuned generator that seeks out the natural resonance of the actuator and runs at that frequency. There's a great little one you can often get cheap on EBay I think made by Sonotec. Note though, this is ultrasonic, not VHF, and I'm not sure where you can find a PLL circuit for that frequency. Most piezo manufacturers sell some power supply, but PLL circuits are rare and fantastically useful. Eagleworks got nowhere until they built their own PLL circuit.

GIThruster wrote:
This stuff is hard. I know it sounds simple, but it is very hard to do. Most people don't realize it, but it takes about a year just to build and characterize the balance. So don't jump in until you know what the entire project will cost in time and effort. Trust me, lots of people have the reaction to do this, and almost none of them get it done.

GIThruster wrote: If you find your experiment will run on a Mettler H20, let me know and I'll have mine sent to you. I think the max load is 260mg and 0.005mg precision.

GIThruster wrote: If you can stray that low on the mass scale, which gets easier when you go to higher frequency; you might use a Mettler. Duncan Cummins built an entire MLT experiment for 2 Mhz inside a coke can, power system included.

GIThruster wrote: It's amazing what you can do with modern switching power supplies. That sort of experiment holds promise for a budget, but you're looking at around 1-5 Mhz I would say, and you need to check that your capacitance doesn't drop off at whatever frequency you run at.

GIThruster wrote:
I'd do that before you buy more than the ceramic, which is very cheap. Here's your likely first, best choice which I put Jim onto and where he has gotten all his PZT the last 5 years:

http://www.steminc.com/ They also sell on Ebay and you can get reduced rates if you buy what they have on clearance. They often offer little bits that are the proper thickness for VHF.

Jim will offer advise and you should contact him and take it if you proceed, as otherwise, you'll just repeat old mistakes.

GIThruster wrote: This stuff is not nearly as easy as one would guess. And let me know what you're doing and I'll be as supportive as I can.

birchoff wrote:Not sure what centripetal force masquerading like gravity gets you from the perspective as an energy source.

Also, in case you saw the earlier discussions on using ME thrusters on a flywheel

kunkmiester wrote:The "semi" I use for Earth deliveries will require several times the power of the one I use for the moon, and will thus require greater resources. They may not be much, but it'll be enough to justify a larger or smaller ship.

GIThruster wrote:I don't know if what Dio was suggesting was that the only requirement to generate a Mach Effect is to charge a capacitor, but the two requirements are this large change in internal energy (shape change materials like perovskite crystals being charged as capacitors) and that the material needs to be accelerated relative to the distant stars. Dio is certainly correct that smaller is better and this is in Jim's book. Not only do you reduce spurious resonances that kill your mechanical Q by reducing the thruster cross section, but you mitigate heating issues and solve a handful of other practical concerns. We don't know if the gravinertial flux propagating from these things at c can be constructively and destructively interfered with yet, so we know what we don't know about arrays. It may turn out there are very specific concerns for large arrays that limit how they're designed, as well as create new possibilities depending upon how they're designed. In fact, the bootstrapping method of running two wormhole generators out of phase that are linked at a distance that causes them to constructively interfere, that is explained in Jim's book; is one possible way of using arrays, but as I have said to those holding this position, I don't then see a salient distinction between small elements in an array, and the very molecules of any particular element. This quickly turns into a nightmare of calculation. We'll have to wait and see what we see.

Oh and BTW Dio, all 1/4 wave acoustic resonators have an inverse proportional relationship between their thickness and their frequency, so at 1 Mhz, you have to have very small elements, at least in their thickness. At 500 Mhz, these thicknesses are measured in microns and microwave resonators are near the limits of how thin we can make things.

The problem facing the Mach Effect experimenters today is the magnitude of the thrust is not big enough to offset the weight of just the thruster (much less the thruster and its power source).

Surprisingly, not. What you're describing is what I like to distinguish as between "low thrust efficiency" and "high thrust efficiency" applications. Low thrust efficiencies where the thruster is much more massive than the force it generates, are still quite useful. Hall thrusters on geosynchronous orbit telecommunications satellites weigh much more on Earth than the thrust they put out, but in microgravity they can still achieve the results needed. So really when you look at thrust to mass, you are looking at general classes of applications. (Same with thrust to power so I lump these two together into the high and low classes.) If you want a flying car, or a spaceship that can fly direct from the surface of the planet, then yes, the thruster has to produce several times more thrust than the weight of the thruster and power supply. If all you want to do is create a space tug to tote Dragon 2 to the Moon or Mars, then you can make due with far less thrust. In fact someone did some decent calcs here in the forum a few weeks ago and found that it doesn't take much thrust at all to reposition all of ISS from its highly inclined orbit to equatorial, given 6 months to do this. Even I was surprised how easy things can be when you can't run out of propellant. And really the calcs that describe what we would be able to do with a nanosat with just a few mN's continuous thrust are astonishing. If you can loiter in the VAB without being cut to shreds, you can send 15,000 nanosats to LEO with a single Falcon 9 and fly them to the asteroid belt. THAT is the kind of thing that can make space exploration cheap, even without high thrust efficiencies.

But of course we want the high thrust efficiencies, flying cars and Millenium Falcon's too. Just they need to wait a bit.

If we can produce 20 mN thrust continuously, that can be reversed on command, with very little power and from a thruster and power supply that can last hours on a smallish battery, we will have hundreds of millions in development funds available. It is EASY to sell such things, when people cannot doubt what they're looking at, and have explained to them what is suddenly possible. For instance, DARPA has been looking for years for some method of repositioning sats on command and constantly maneuvering on orbit with sat killer craft, etc. This is probably what X-37 is all about but it still runs out of propellant and needs to come home. Even very low efficiency METS can make X-37 obsolete, because they cannot run out of propellant.

The problem facing the Mach Effect experimenters today is the magnitude of the thrust is not big enough to offset the weight of just the thruster (much less the thruster and its power source).