Archive for January, 2012

Closed Cell Foams

Propellant.  Engines need it and our ion engine is no exception.  Ours is an electrostatic ion engine that accelerates both ions and electrons, using lasers to boost the plasma flow rate through a novel nozzle.  The question then becomes, how do we get the raw material for a plasma?  The plan so far has been to use a small cylinder of compressed gas – perhaps an 8 gram nitrous oxide cylinder commonly used to make whipped cream to order.  The gas is stable and easy to obtain.  The only projected difficulty was metering the gas flow in orbit as most valves are simply too large physically for our satellite.

That was the plan until we looked back at our ConOps documentation.  After we ship our satellite to the launch provider, we can’t expect them to do substantial technical work installing our gas cylinder and checking flows immediately prior to launch.  We have to plan that they will only remove our “Remove Before Flight” pins and that our satellite could spend a month in desert temperatures.  It doesn’t seem practical to presume o-rings, screw threads, and a homemade micro valve will stand up to those temperature swings without leaking.

Our new idea: use a closed cell foam filled with pressurized nitrogen, vaporizing the supporting plastic and releasing the enclosed nitrogen using a spark system similar to that used by Pulsed Plasma Thrusters (PPTs).  PPTs create an arc across the face of a solid Teflon bar, turning a few micrograms of Teflon into plasma.  The plasma moves along the PPT’s cathode and anode by Lorentz forces, much the same way that a rail gun accelerates its conducting projectile.

We won’t be building a PPT of course, but will use the inspiration of eroding a fuel bar, making some plastic-based plasma and nitrogen-based plasma from a temperature stable storage media.

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