Will having an engineer on board let me extract more fuel from an asteroid?
OK, so I did some testing, and it would seem that:
- 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.
- 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.