Comment by binarycoffee

Yes, operating a Hall or ion thruster on O2 and/or N2 is not new (and Busek was not the only one that did it either).

And it is definitely hard, but this is just part of the problem.

The really tricky thing is to get the whole system working. For instance it is not longer possible to use a "high pressure" (relatively speaking of course) propellant feed. Even with the passive compression stage discussed in the article, an off-the-shelf thruster wouldn't be able to operate due to the low inlet pressure.

Also, the intake/collector design is a problem of its own. AFAIK this was the first real-life test for the passive intake concept (the theory of operation and trade-off to be considered are discussed here [1]).

That being said there is still a long way to go before this can work in space...

[1] http://erps.spacegrant.org/uploads/images/2015Presentations/...