Titanium is an interesting fuel for a couple of reasons. Firstly, it’s a pretty popular aerospace metal, so there is a fair bit of it floating up in Earth orbit ready for recycling. Secondly, as far as the base Neumann Drive goes, it is a well-behaved light refractory metal that does what it should. Thirdly, it responded really, really well to the magnetic nozzle, achieving marked increases in efficiency.
During the testing process in 2014, we hit a Titanium cathode with 460,000 eroding pulses, which sent approximately 3.8g into the exhaust. As far as fuel efficiency goes, Titanium had the best results using 30 joule pulses over 100 microseconds at 4 pulses per second, which resulted in about 2.5 Newtons over that time, with a specific impulse of about 4200.
Once we got the magnetic nozzle attached, the results changed for the better – but to compare them, we need to move to the work we did on ‘clean’, un-eroded cathodes. A brand new, “clean” cathode temporarily gets better results, but we generally don’t like talking about those results because nothing stays new in space for long, and a few hours of solid use will change a previously clean cathode to a used one.
A clean titanium cathode running 200 microsecond pulses at 50J per pulse will produce 3.75N of thrust over the length of the pulse, at around 3000s of specific impulse, without a magnetic nozzle. Adding the nozzle to the system improved the performance under similar conditions to producing about the same amount of thrust, but at around 4500s of specific impulse. This represents a 50% improvement in efficiency, with no added power or fuel required and with no reduction in thrust.