[simpits-chat] Advance Space Propulsion Lab

Brian Sikkema simpits-chat@simpits.org
Fri, 28 Feb 2003 03:57:42 +0000

>Cool lab, tell me more about Ion Thrusters. How does one work?
Well this is going to be a very simplified explenation, because I only 
understand it very simply ;) But basically what it does is this:
The thruster consists of 2 parts, the anode and the cathode. In the pics the 
anode is the larger box-shaped part on the bottom, and the cathode is the 
little cylander mounted on the top. The thruster takes the fuel, in our case 
Krypton, and barrages it with a field of electrons, which ionizes the 
Krypton, giving it a negative charge. When the Krypton has a negative 
charge, it is repelled from the field of electrons, and by propelling it out 
the back thrust is produced.

Again, just a very simple explenation, but I'm learning much of this myself. 
And I'm just an undergrad wrench monkey, so I'm not required to have as 
in-depth an understanding as the grad students who are doing the research.

>Does your lab maintain a vacuum or near vacuum in the test cell?
Yes, when we want to run the thruster we have to have it in as close to a 
perfect vacuum as we can get, to the point where we're basically counting 
the number of particles left in the tank. We bring it down to vacuum using a 
mechanical pump, until it can't pump anymore, at which point we turn on the 
cryopump. That isn't really a pump in the traditional sense of the word, its 
just a set of liquid nitrogen-cooled vanes, so that when we cool them down, 
any remaining particles in the tank will eventually bounce around and hit 
them, freezing to the vanes instantly and therefore stop bouncing around the 
chamber, which is of course the definition of a vacuum, no particles 
bouncing around.

And when I say counting particles, I mean it. We get to the point where 
traditional pressure sensors dont do squat. In the picture of the back of 
the tank, you may notice something that kinda looks like a vacuum tube 
sticking off the side. That's our very-low pressure sensor. The way it works 
(if I remember correctly) is it shoots a beam into the tank, and senses when 
the beam is broken. In this way we can figure out how much "stuff" is left 
in the tank.

>By the way, I am getting a complete T-37 simulator and have to dispose of 
>four more for a friend of mine. Know any one who wants/needs one?
*pout* I want one! :( Define "dispose." If you mean "Throw at" I might be 
able to talk the detachment cadre into taking one. Maybe. If you mean sell, 
well, I dunno. Not us. I'd really love one, though, its a beautiful plane.


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