Quote from: Mulletron on 11/10/2014 07:15 amI can see that the experimenters recognize heat contributions to the thrust plots. Look at the screen shot below. Table 2 isn't reporting 130uN of thrust for TE012, it is reporting just 55uN, after subtracting artifacts from the total 130uN peak.They recognize da heat, which is apparent by that gentle rise over 30 seconds followed by a gentle fall over 30 seconds.The sudden rise and sudden fall is the real thrust here..../...If it were that sudden, why there is not the characteristic overshoot magnitude clearly visible for the calibration pulses (of similar magnitude) that are known to be "instantaneous" ?You must see there is a huge difference between the result of rectangular force signals of calibration pulses vs thrusts pulses : the explanation is that for the later the rise is steep but not as steep. Still working on quantitative estimates but this is strongly hinting a time constant (time to asymptotically reach the plateau) that is likely much higher than anything electromagnetic in nature. Likely below 2 seconds but likely more than .1 s (analysis will tell).
I can see that the experimenters recognize heat contributions to the thrust plots. Look at the screen shot below. Table 2 isn't reporting 130uN of thrust for TE012, it is reporting just 55uN, after subtracting artifacts from the total 130uN peak.They recognize da heat, which is apparent by that gentle rise over 30 seconds followed by a gentle fall over 30 seconds.The sudden rise and sudden fall is the real thrust here..../...
Quote from: frobnicat on 11/10/2014 09:04 amQuote from: Mulletron on 11/10/2014 07:15 amI can see that the experimenters recognize heat contributions to the thrust plots. Look at the screen shot below. Table 2 isn't reporting 130uN of thrust for TE012, it is reporting just 55uN, after subtracting artifacts from the total 130uN peak.They recognize da heat, which is apparent by that gentle rise over 30 seconds followed by a gentle fall over 30 seconds.The sudden rise and sudden fall is the real thrust here..../...If it were that sudden, why there is not the characteristic overshoot magnitude clearly visible for the calibration pulses (of similar magnitude) that are known to be "instantaneous" ?You must see there is a huge difference between the result of rectangular force signals of calibration pulses vs thrusts pulses : the explanation is that for the later the rise is steep but not as steep. Still working on quantitative estimates but this is strongly hinting a time constant (time to asymptotically reach the plateau) that is likely much higher than anything electromagnetic in nature. Likely below 2 seconds but likely more than .1 s (analysis will tell).There is an overshoot with the "thrust" impulse. Why do you feel it needs to be the same magnitude as the cal pulse overshoot? Do they share the same dynamics? I would say not.
The test article and the calibration system overcome the inertia of the test rig in different ways.
Well it does take time for energy to build up in the cavity.
The fact that there is a sudden rise and fall when rf is on and off is enough.
Quote from: Mulletron on 11/10/2014 09:56 amWell it does take time for energy to build up in the cavity.Yes it does. On the order of Q * typical_length / c = 20000 * .3 / 300000000 = 20 µsWe are not talking about a delay bellow ms here. Admittedly we must provide a clear quantitative estimation but there is no question that the difference in overshoot is due to way higher than 1ms delay in rise (and fall) times.
Quote from: frobnicat on 11/10/2014 10:04 amQuote from: Mulletron on 11/10/2014 09:56 amWell it does take time for energy to build up in the cavity.Yes it does. On the order of Q * typical_length / c = 20000 * .3 / 300000000 = 20 µsWe are not talking about a delay bellow ms here. Admittedly we must provide a clear quantitative estimation but there is no question that the difference in overshoot is due to way higher than 1ms delay in rise (and fall) times.For clarity's sake, you're saying that the impulse delays could be caused by the amplifier warming up, and the undershoot at lower power levels, rather than higher level ones, is evidence of that?
The "undershoot" signature appears to occur more for the low power experiment (at 2.6 W) than for the higher power (around 16.8W) :- This would be a natural parameter dependency for a thermal effect.Meaning the thermal artefacts (be it at the place of the amplifier or the thruster) takes longer to reach a plateau at lower powers, so that thermal explanations are in good qualitative agreement.
1) Someone is stating that we don't know the mass on the inverted torsional pendulum. This is an incorrect statement. Paul March gave us the mass.
Quote1) Someone is stating that we don't know the mass on the inverted torsional pendulum. This is an incorrect statement. Paul March gave us the mass. Well I really need the mass of the test articles. The mass of the pendulum and the test articles would be so useful. Was that provided?You see, if I had the mass of the test article, I could work out all the other math, like Delta V and put a check on that specific impulse I found.
"And I just verified that Paul March wrote that the supported mass was a maximum of 25 lbm. That is 11.3398 kgm"
1) Paul March posted the information in this NASASpaceFlight.com forum and not in the Next big future webpage. Next big future just copied the information from this forum into their webpage. They recognized this by stating at the outset: "Paul March ... is providing information about the experiments on the NASA spaceflight forum." There is no need to give any credit to Next Big Future, on the contrary, it is Next Big Future that owes credit to NASASpaceFlight.com and to Paul March. NASASpaceFlight forum is the true source of this mass information.2) I do not recall information for mass of individual items. The total mass, dimensions and stiffness is what is required for the lowest natural frequency of the pendulum. Individual motion of items on the pendulum can only occur at much higher frequencies (and lower amplitudes) than the lowest natural frequency of the pendulum
Quote from: Rodal on 11/10/2014 12:33 pm1) Paul March posted the information in this NASASpaceFlight.com forum and not in the Next big future webpage. Next big future just copied the information from this forum into their webpage. They recognized this by stating at the outset: "Paul March ... is providing information about the experiments on the NASA spaceflight forum." There is no need to give any credit to Next Big Future, on the contrary, it is Next Big Future that owes credit to NASASpaceFlight.com and to Paul March. NASASpaceFlight forum is the true source of this mass information.2) I do not recall information for mass of individual items. The total mass, dimensions and stiffness is what is required for the lowest natural frequency of the pendulum. Individual motion of items on the pendulum can only occur at much higher frequencies (and lower amplitudes) than the lowest natural frequency of the pendulumAre you using that 25lb figure as total mass? Because that is just how much weight it can hold. That isn't the mass of anything.
we nominally restrict ourselves to a 25 pound total load limit on the torque pendulum arm
And how much lower than 25 lb do you think that the total mass on the pendulum would be and why?
This quote:Quotewe nominally restrict ourselves to a 25 pound total load limit on the torque pendulum armis from NBF dated 11Sep14.Where is it on here from March for sake of clarity?Your comments:http://forum.nasaspaceflight.com/index.php?topic=29276.msg1275117#msg127511722Oct14.Indeed NBF references NSF, but it is about electrical issues. First linked to. But they have slides from March which contain the mechanical data, which weren't posted here.I don't want to start a war over this, but I remain correct when I asserted that we don't know the mass of the things inside the test chamber. So how can we blindly throw numbers at them? We can't just say 25lb/11.34kg based off of the max weight it can hold.I'm not the first to comment on here about blindly throwing numbers at assumptions. It ends up being a waste of time and sends everyone on a tangent based on bad info.QuoteAnd how much lower than 25 lb do you think that the total mass on the pendulum would be and why?There is no "think" about this, just what the mass actually really is.You can't pass off quantitative results derived from qualitative data.
We don't know the mass. That is the point. I don't mean to be mean. I'm sticking to the facts. The methodology you describe is like guessing how massive my truck is based on its cargo capacity.If you had the data, you'd be right.I'm finished here.
I don't care about the pendulum frequency. The amplitudes are important. The force required to move a pendulum of x mass (in the first place) varies wildly depending on mass. The kinetic energy and potential energy of a moving pendulum varies wildly depending on the mass of the pendulum as well. None of my screen shots previously, pointing out the "bounce" had anything to do with frequency, but the amplitudes were different.Here's something for the folks out there to play with. Take 2 pendulums, give them wildly different masses. Set them in opposite motion. Timing is everything......You'll see frequency is unaffected by mass, yet PE and KE are. Also getting the pendulum to move in the first place is very much dependent on mass. F=MA as they say.Let your computer do the work for you.....This author never made any assertions of the mass of anything. Simply we don't know the masses of anything.http://phet.colorado.edu/sims/pendulum-lab/pendulum-lab_en.html