Mach Effect progress

[MSimon]

Interesting that the crackpot "the aliens are here" folks called out Tau Ceti as one of the systems they claim aliens come from. If we find a planet in the habitable zone around Zeta Reticuli or Rigel I'll start to wonder how they guessed right twice. That would be an astonishing coincidence.

I would note though, we can't visit Tau Ceti ourselves. At 5X our gravity we wouldn't be able to move and it would cause heart failure pretty quickly. Imagine trying to move around with a pair of V8 engines strapped to your back.

You have enough people making enough guesses and from time to time some one will get something right.

[pbelter]

1.7g is a lot of gravity. Take your weight, then stuff 70% of it into a back- pack and try wearing it all day long. Even carrying 15% of your body weight in a backpack gets tiring after a while. I would say that 1.2g is about the maximum that people could live with. A planet with 1.7g gravity is not going to be a comfortable place to be.

Not comfortable but livable. After some time one would develop a lot of extra muscles.
Astronauts loose bone and muscle mass in 0 g and gain it back upon return. If this is scalable then we would gain more muscle and bone mass in 1.7g and it may be very livable. One just needs to be more careful not to fall. When elephants fall they crush their bones and die, yet they are still around.

The analogy with the backpack is not a good one since the weight it distributed evenly around your body. This is like saying all divers under 20 m of water should be crushed because there are tons of water on top of them. When we are kids we have much smaller mass but growing twice the size makes us feel just a bit heavier.

Anyway, everything depends on the chemical composition and most likely a planet with a higher gravity and the same chemical composition as Earth would have a higher density since there is more squeezing force on a unit of volume. So we wouldn't have 1.7 g but more.

All of that is speculation because the density has got to be different form Earth. The planet can have much smaller iron core and be richer in silicon and carbon, making it density lower and gravity weaker. Moon has a 60% of earth density and 1.7*60% =1.02g.
On the other hand it can have a larger iron core and higher density.
Higher rate of fission in the core would make it hotter and cause thermal expansion lowering surface gravity, probably not by much but we don't know.

There are too many unknowns

[93143]

1.7*60% =1.02g.

Not how that works.

Volume scales inversely with mean density. 5/0.6 = 8.333

Then redo the calculation: 5/cbrt(8.333)^2 = 1.216

You've still got 20% extra surface gravity.

...

Another issue is that things happen faster at higher gee. Human reflexes are generally fast enough to deal with 1 gee (for obvious reasons), and I suppose with training and/or acclimatization 1.7 gee wouldn't be unsurvivable...

[GIThruster]

The biggest problem would be with the heart. The strain on the heart would be like pumping blood through a 400 lb man who was 10 feet tall. That would kill most people in short order.

[pheolix]

Both the power into the stack needs to be on resonance and the acoustic action of the stack needs to be on resonance. .

I read the recent Fearn & Woodward AIAA paper and it states that the electrical and mechanical resonant frequencies don't necessarily coincide and can vary by 1-2kHz. Also when the two frequencies coincide the large thrusts occur. In the stack described there are 4 x 2mm PZT at one end and 8 x 1mm PZT at the other. Are the two sets of PZT both driven at the same frequency? if so would it be possible to modify the stack and control electronics to drive one PZT set (8x1mm) at electrical resonance and use the other set (4 x 2mm) to vary the mechanical resonance of the whole assembly so that it coincides with electrical resonance of the first set?

[GIThruster]

I think you misunderstand about there being 2 "sets". There is really only one set. The stack acts as a single unit. The divisions in the stack are there for two purposes. First, many thin layers of PZT are used instead of a single layer to keep the voltage requirements down. It's easier to run with an audio amplifier if you don't have to transform to very high voltage. Second, at each end of the stack and in one place between (what seems like makes the division between 2 stacks) there is a 0.3mm PZT accelerometer disc. These are not placed to make distinctions between the parts of the stack. They're only in place to allow them to monitor the mechanical action of the stack. Without that data they'd be flying blind.

[pheolix]

I think you misunderstand about there being 2 "sets". There is really only one set. The stack acts as a single unit. The divisions in the stack are there for two purposes. First, many thin layers of PZT are used instead of a single layer to keep the voltage requirements down. It's easier to run with an audio amplifier if you don't have to transform to very high voltage. Second, at each end of the stack and in one place between (what seems like makes the division between 2 stacks) there is a 0.3mm PZT accelerometer disc. These are not placed to make distinctions between the parts of the stack. They're only in place to allow them to monitor the mechanical action of the stack. Without that data they'd be flying blind.

Sorry, I over inferred, I thought that as there were two sets of piezoelectric crystals with different thickness and number that there was some unstated subtlety behind it. Also the paper states, "The end of the stack with the 1 mm thick
crystals was placed near the aluminum cap as that was where the greatest accelerations were expected." This led me to believe the 1mm set was primary in some way.

Going back to my original point: in the paper only one stack exhibited large thrusts and only for a limited period and it is suggested that the reason for this is that its difficult to simultaneously achieve electrical and mechanical resonance within the piezoelectric material. What I was suggesting is whether other mechanical input could be used to tune the mechanical resonance in the stack so that the piezoelectric elements could consistently experience electrical and mechanical resonance.

This was the reason I was suggesting to treat the two groups of PZT layers as separate entities. Driving one set of layers, the thinner ones just for the sake of argument, at electrical resonance and the use the thicker layers to achieve a matching mechanical resonance in the stack and consequently in the thinner layers, using the accelerometer to guide this process.

[williatw]

The biggest problem would be with the heart. The strain on the heart would be like pumping blood through a 400 lb man who was 10 feet tall. That would kill most people in short order.

The Metallacity of Tau Ceti is much lower than the sun's. According to wikepedia: In the case of Tau Ceti, the atmospheric metallicity is roughly:

or about a third the solar abundance. Past measurements have varied from −0.13 to −0.60.
http://en.wikipedia.org/wiki/Tau_Ceti#Metallicity

I assume this would mean any planets even ostensibly rocky metallic ones would tend to be made of lighter elements than earth, so lower density and therefore lighter surface gravity then you would expect from an earth dense planet of greater mass.

[williatw]

1.7g is a lot of gravity. Take your weight, then stuff 70% of it into a back- pack and try wearing it all day long. Even carrying 15% of your body weight in a backpack gets tiring after a while. I would say that 1.2g is about the maximum that people could live with. A planet with 1.7g gravity is not going to be a comfortable place to be.

http://esciencenews.com/sources/the.gua ... .milky.way

'Tens of billions' of habitable exoplanets in Milky Way

Wednesday, March 28, 2012 - 15:00 in Astronomy & Space

About 40% of red dwarf stars are thought to have a so-called 'super-Earth' planet orbiting in a habitable zoneAstronomers hunting for rocky planets with the right temperature to support life estimate there may be tens of billions of them in our galaxy alone

If this is true the answer is simple...as far as people are concerned Human Dwarfs will inherit the Cosmos. Who better to tolerate heavy gravity than someone shorter than 4ft 6in and 100lbs or so? Red dwarf stars have very long life spans as main sequence stars too, some of them 10X or even 100X longer than our sun will.

[GIThruster]

What I was suggesting is whether other mechanical input could be used to tune the mechanical resonance in the stack so that the piezoelectric elements could consistently experience electrical and mechanical resonance.

There are actually several ways to approach the problem, but running two actuators inside the same preload cage is not one of them as this would produce something other than a single resonance. The simplest and most effective is to use a PLL tuning circuit like that found in this small generator:

http://www.loettechnik.com/sono-tek/pdf ... ogue_e.pdf

page 9, and allow the amp to automatically tune to the acoustic resonance of the stack at any given moment. These stacks change in resoance as they heat up so as noted above, this sort of active PLL tuning would be a huge breakthrough. Then you just add a variable inductor to add the necessary inductance to bring the electrical circuit into resonance--something they're already using. Pretty simple, but Jim doesn't at present have a PLL circuit. I should note I missed bidding on one of these that sold on EBay for just $50 last October and I do have an eye out for one.

Note this is just 15W but when Jim is running on resonance, he only dissipates about 1 watt, so a tiny amp like this, designed to drive piezo actuators would be a great find.

The other way one can tune the stack mechanically is to put a DC offset on it. DC offset changes many of the variables in positive ways, enhancing the dielectric constant, the Young's modulus, the electromechanical linking coefficient and slightly raising the resonant frequency of the stack. Jim has a Krone-Hite 7500 that's good from DC-1 Mhz he can use that provides suitable DC offset, but to use it he needs to replace all the matching equipment and lose the step-up transformers. Paul March has the Krone-Hite matcher built to go with the 7500 and has offered to loan it to Jim, but I think Jim notes correctly that rebuilding the entire power system around a new amp is very time consuming, so he wants to do what tests he can with the current setup before he changes much. I'm not sure he intends to ever use the Krone-Hite. We'll have to wait and see.

I would certainly like to see him go this way with either of these other amps because they open the door to higher frequency experiments, but any sort of change like this one could take most of a working season to enable, so don't hold your breath.

[GIThruster]

If there is anyone interested to dabble with some chemistry, I have an interesting project for you to consider.

CCTO is fabricated half a dozen different ways in the literature the last decade or so. I can link the papers but each of these methods requires someone fairly familiar with doing this sort of chemistry. First the stuff is made in a batch. Then its pressed and sintered. Then it has electrodes put on. The size and shape of the ceramic as well as the way the electrodes are attached all effect the resulting effective k value of the package.

What we need is someone who can mix this stuff up and generate "green" pucks that then need to be baked/sintered/annealed at around 1000*c. Then if that works out, the next step is to try to use a laserscribe to attach electrodes.

Anyone is welcome to try any of the three steps, but success really requires all three. Let me know if you're interested in all or part of this project.

[AcesHigh]

Another issue is that things happen faster at higher gee.

falling is faster with a higher gee. Getting up from your bed at morning is slower.

[pheolix]

There are actually several ways to approach the problem, but running two actuators inside the same preload cage is not one of them as this would produce something other than a single resonance. The simplest and most effective is to use a PLL tuning circuit like that found in this small generator

Many thanks for the explanation.

Is anyone doing a DIY replication? with a minimal experimental configuration: a thrust balance beam + optical sensor (+ servo depending on sensor range); control system + power amplifier; PZT stack including accelerometers.

[GIThruster]

To the best of my knowledge there was a replication attempt about 10 years ago, but that person did not contact Jim for guidance and later decided his balance was not sensitive enough. That's the only UFG replication I'm aware of. Anyone who has an interest should write me and let me know so I can put them in touch with Jim. Would save a LOT of wasted effort.

[chrismb]

Is anyone doing a DIY replication?

there was a replication attempt about 10 years ago, but that person did not contact Jim for guidance

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