[XorNot]

By not testing it in a vacuum, which would eliminate most of the immediate problems with thrust being produced by outgassing from heated wires (10kW is more power then your stove top) or coronal discharge.

I don't know what's going on with whoever is doing this at NASA, but the joke of testing IN A VACUUM CHAMBER while not actually pumping it down is ridiculous. These people are scientists who have access to the device - how did they not turn it on? For lack of a suitable capacitor? That's a nothing part for such a massive potential breakthrough.

[pavlov]

The OP (Wired article) says that the vacuum chamber was indeed pumped down:

While the original abstract says that tests were run "within a stainless steel vacuum chamber with the door closed but at ambient atmospheric pressure", the full report describes tests in which turbo vacuum pumps were used to evacuate the test chamber to a pressure of five millionths of a Torr, or about a hundred-millionth of normal atmospheric pressure.

[XorNot]

Yeah just saw that part. The abstract doesn't mention it, which is super-weird, and neither did the original Wired article.

But if they found the effect persisted when pumped down then that puts this way further into "interesting" territory.

EDIT: Ok I've just been through the paper, but it's buried at the end - "Vacuum compatible RF amplifiers with power ranges of up to 125 watts will allow testing at vacuum conditions which was not possible using our current RF amplifiers due to the presence of electrolytic capacitors"

There is a big description of the test rig, and how it can be pumped down to vacuum during tests, but they do not explicitly say that they pumped down to vacuum before running tests on the thruster. And the vacuum is never mentioned again until the very end, where we get this one ambiguous sentence. They might be referring to a new optimized thruster they couldn't test, or they might be saying they couldn't test in vacuum at all - it's never made clear and it's pretty damn important.

[chton]

This was not a huge experiment for NASA, most likely the budget wasn't there for vacuum-capable capacitors and the time to convert the equipment. It was either go with what they had, or don't go at all. I do hope that, with a tentatively positive result, they can now get a bit more budget to perform the test again with an improved setup.