Will having an engineer on board let me extract more fuel from an asteroid?

Question

Here's a simple question that I couldn't easily find an answer to:

Will having a skilled engineer on board my asteroid resource harvester (equipped with a Convert-O-Tron 250 and a pair of Drill-O-Matic Mining Excavators) let me extract more total fuel from a given asteroid?

Both of these parts have a note in their in-game descriptions saying:

"When operated by a skilled engineer, you will be able to operate with better efficiency."

but it's not entirely clear whether "better efficiency" here actually means a better asteroid mass → ore and/or ore → fuel conversion ratio, or if it simply means higher drilling and conversion speed. It's also not totally clear to me if the better efficiency for the drills affects both asteroid and surface mining, or only one or the other.

In particular, the wiki entry for the Drill-O-Matic (linked above) seems to suggest (but not quite explicitly say) that drilling efficiency only affects the speed of resource extraction, but not the total amount of ore gained from a given asteroid. If that's the case, and if the ISRU conversion ratio is also not affected, then there doesn't seem to be much point in bringing an engineer along on asteroid missions, given that asteroid drilling with the large Drill-O-Matic is pretty fast even without one.

Obviously, this is something I could test pretty easily, but I figured I'd check if anyone else has already done the testing or confirmed this by other means. If not, I may fly a test mission and post a self-answer later.

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PS. Note that I'm specifically asking about KSP 1.2.2 (and potentially later versions, once they're released), since it appears that the effect of engineers on resource harvesting was buggy in earlier versions. Specifically, the KSP 1.2.2 change log lists the following bugfix:

• Apply Engineer bonuses to drills and ISRU correctly.

However, I have no clear idea what this fix actually changed in terms of actual gameplay.

Answer 1

OK, so I did some testing, and it would seem that:

1. The presence of an engineer on the vessel has no effect on the ore to liquid fuel conversion ratio of the Convert-O-Tron 250.
2. The presence of an engineer on the vessel also has no effect on the ratio of asteroid mass consumed to ore extracted by the Drill-O-Matic. (This ratio did vary slightly between runs, but only in the sixth decimal place. I'm inclined to ascribe this negligible variation to roundoff errors in the game.)

Thus, it would seem that having an engineer present does not increase the amount of fuel one can obtain from a given asteroid.

All that said, the presence of an engineer does dramatically increase the speed at which ore can be extracted and converted. Thus, you may still want to bring one along just to make the process less tedious. Also, having a Kerbal on the ship lets you collect samples from asteroids for science.