IRSU - In Orbit or Landed?

[MrCynical]

I find it very difficult to make a case for having the refinery in orbit. Having the ISRU and drills on the same ship is more straightforward. So long as you include a big enough engine to get it into orbit without staging and with fuel to spare it can serve as the tanker as well. That's very easy on low gravity moons - like Ike, Minmus etc. I find the ISRU just isn't heavy enough to be significant relative to a decent load of fuel and/or ore, and having it on the ground means you can always launch with completely full fuel tanks.