Fullerenes as Ion Propellants

[sanman]

I'm x-posting this from the Aerospace Engineering forum, to see if I can get more responses here
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I'd read about the investigation into using C60 fullerenes as propellant in an ion engine, due to their high molecular weight and low ionization energy:

http://linkinghub.elsevier.com/retrieve/pii/S0094576502001157

By this reasoning, shouldn't buckyonions be even better candidates as propellant, since they have many layers, each of which would be influenced/polarized by the ionization/polarization of the adjacent layers?

Furthermore, I'd also read about Silicon fullerenes, like Si60, which not only have even higher molecular weight, but also have high magnetic spin properties as well.

http://www3.interscience.wiley.com/journal/93513554/abstract

Wouldn't it be possible to use Silicon fullerenes as propellant under the Lorentz force, for even better thrust performance?
What would be the main challenges or difficulties in doing so?

 

[Astronuc]

Fullerenes would be undersirable for ion propulsion precisely because of the large mass. Ideally one wants a low mass propellant that can be accelerated to highest possible speed. Low work function or ionzation energy is also desirable.

 

[sanman]

While I understand the desire for maximum kinetic energy per unit of propellant relative to the amount of energy expended, I've noticed that many feel that ion thrusters are handicapped by their lower thrust and thus their slower acceleration time, especially for missions to nearer bodies with their larger gravity wells.

Consequently, for missions to the Moon, wouldn't it be useful to have an ion engine and/or propellant capable of providing comparatively better acceleration relative to existing ion thrusters, in order to reduce transit time?
I realize that chemical rockets are better for acceleration and thrust, but at the same time they're far less efficient than ion engines on a propellant mass basis.
If some compromise is to be made between mass efficiency and acceleration, wouldn't a higher-thrust ion engine be a better choice?

The C60 ion propellant study I linked to claimed a better power to weight ratio relative to propellant mass. I assume that's because of better coupling between the fullerenes and the electric field of the thruster. That's why I was thinking that the Si60 with its unique magnetic properties might be better, because it would couple with both electric and magnetic (aka. "Lorentz") forces in a more efficient way.

I was also thinking that the newer DS4G ion thruster design would work better with fullerene propellants, since it seems designed to avoid erosion of its grids by the ion propellant.

Whether or not DS4G plus fullerenes are the optimal ion thruster combination, I'm wondering what the upper limit is on ion thrust, and whether it could ever be used for lunar liftoffs/landings by being scaled up beyond mere milliNewtons?