Looking at the first six months of 2014's launch schedule for spacecraft visiting the ISS we have:
- Jan 8 - Orbital Cygnus - Node 2 zenith CBM
- Feb 5 - Progress - Russian segment port
- Feb 22 - SpaceX Dragon - Node 2 zenith CBM
- Mar 25 - Soyuz - Russian segment
- Apr 9 - Progress - Russian segment port
- May 1 - Orbital Cygnus - Node 2 zenith CBM
- May 28 - Soyuz - Russian segment
- Jun 6 - SpaceX Dragon - Node 2 zenith CBM
- Jun 17 - ESA ATV - Russian segment (aft Zvezda port)
- Jul 1 - JAXA HTV - Node 2 zenith CBM Jul 24 - Soyuz - Russian segment
That is a fair bit of traffic. (Now to be fair, these are probably the last ATV missions, and who knows how long JAXA will keep up the HTV flying, it is so expensive).
We know the Russian segment uses an automated docking system (Kurs) and the ATV buys Kurs from the Russians for the ATV.
Yet someone still has to be on hand in case a manual override is required.
The Berthing of the Dragon, HTV, and Cygnus is very manpower intensive, since the spacecraft gets to about 30 meters (? feet?) away, and the CanadaArm2 reaches out to grab, and then retracts/rotates/etc as needed to berth the craft to the CBM port on the bottom of Node 2 module. (Turns out the CBM port on the top, is the backup, but requires that CanadaArm2 relocate itself first so it can move a craft from the earth facing to space facing port. The plan is to move the PLM on the zenith port of Node 1 to forward facing CBM port on Node 3 to free up a real spare berthing port.)
I remember reading Allen Steele's book Orbital Decay, where there is a scene where a module docks, and people sneak aboard Freedom (The ISS predecessors name, when he first wrote that book in the 80's or 90's) and the astronauts aboard do not 'notice' initially. I remember reading how unlikely that seemed. But now I wonder, with so many craft arriving, each year, and no doubt automation being pushed as much as possible, if it will become a real possibility.
Anyway, the specific question is perhaps two fold.
For the Russian segment it is clearly different than the US Segment. Additionally, all current US Segment cargo craft berth, which requires CanadaArm2 time. But future manned spacecraft to the US segment will all dock (at a PMA, on the forward end of Node 2, and the backup will be the PMA from Node 3 move to the space facing CBM port on Node 2) which in principle should be more automated.
So how does a visiting craft disrupt operations on the station?
Does a Russian segment visitor disrupt much? (I.e. Perhaps only one crew member needs to be dedicated to watching the incoming craft, ready for manual override).
Does a US segement visitor disrupt much? (Clearly at least one crew member is required to drive the CanadaArm2 over several hours of work).