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Electroplating inside of a tank

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LAN_403

klugesmith

Sun Nov 01 2009, 04:00PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

IntraWinding wrote ...
I think you should try the tank cleaned but unplated first. It might work fine.

I'll second that. Both links in my previous post find 10^-5 torr satisfactory for metal film deposition, so IMHO that's high enough vacuum for testing an ion thruster. The mirror-coating guy's tank looks like plain steel, at least on the outside.

[Now about the main project, but drifting away from this thread's topic]
Have you figured the pumping speed necessary to keep up with your deliberate gas emission?
Are you planning to directly measure reaction thrust, or to measure the ion plume?
"Dawn's engines have a specific impulse of 3100 s and a thrust of 90mN."

Turkey9

Tue Nov 03 2009, 03:07AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

On second thought, I think you guys are right about using the tank cleaned and unplated first. No point fixing a problem that might not exist, right? And if it is unsatisfactory, the plating can be done later.

I haven't figured out what pumping speed I'll need but that shouldn't be too big of a factor as I'll be operating with a single pulse configuration with as long of a time is needed in between pulses.

I'm also planning on measuring thrust directly with either an accelerometer (If thrust is high enough to move entire thruster on pendulum stand) or a piezoelectric force transducer. I have documented thrust down to the mN with the force sensor so I'm sure that will work.

I would like to analyse the ion plume and determining thrust from that would help verify my results. I don't know how I could determine the velocity of the ions, but I'm sure it can be done.

Thanks!
-Jesse

rp181

Tue Nov 03 2009, 03:37AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Somewhat like that:

have you tested the force sensor in a vacuum?

klugesmith

Tue Nov 03 2009, 03:43AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Turkey9 wrote ...
I'm also planning on measuring thrust directly with either an accelerometer (If thrust is high enough to move entire thruster on pendulum stand) or a piezoelectric force transducer. I have documented thrust down to the mN with the force sensor so I'm sure that will work.

Since OP is leading this thread away from electroplating, I'll follow suit.

I would be concerned about your thrust sensors being "glitched" by the high current capacitor discharge and associated strong magnetic fields. Also direct magnetic forces (in mN range?) on all wires in the high-current circuit, and magnetic interaction between the work coil and the steel vacuum chamber. In general terms, the thing will slightly "jump" even without directed emission of ions. I bet even the capacitors will jump from release of electrostatic stresses. Might be mitigated by design for mechanical symmetry around the center of gravity. You might be able to zero it all out by measuring the mechanical impulse with & without release of propellant gas.

Turkey9

Tue Nov 03 2009, 03:55AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

I have tested the force sensor in a vacuum and it works well.
With a previous thruster design I verified my thrust by firing without any ions and by firing with. It proved to be very difficult to isolate the pulse from thrust for the very reason of all the other factors that can mess with the signal.

I'm hoping that my next design stage will produce enough thrust to outweigh all the other factors. In the tens of Newtons range.

Oh yeah, I forgot about the langmuir probe... I am planning on building one of those for testing.

IntraWinding

Tue Nov 03 2009, 04:18PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Yes, don't fix it if it ain't broke...
Give it a really good clean and bakeout.
Also, plating is going to be a whole project in itself. It might even make things worse if the plating has pores filled with trapped plating solution and gasses which I'm guessing would act as 'virtual leaks'.
With that in mind, if you do have to plate I definitely think you should try coating by evaporation in vacuum as suggested earlier.

rp181

Tue Nov 03 2009, 09:46PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

I would love to see your progress on a Langmuir probe, I am also in the process of making one.

Turkey9

Tue Nov 03 2009, 11:51PM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

I'll make sure and post when I get around to making it. Might not be till after christmas though... gotta get the thruster built first! And if you have success would you mind giving me some tips? I'm sure it's not as easy as it looks.

rp181

Wed Nov 04 2009, 12:08AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

It seems the only difficult part is getting a stable electrode potential, and measuring the changes accurately, along with electrode shape. After that, it seems its just all math.

Turkey9

Wed Nov 04 2009, 01:36AM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

Ok, that doesn't sound too bad.. we'll see how that goes

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