Originally Posted by
DuncanDoenitz
In general, I thought that objects intended to rendezvous with the ISS would appear to approach from in-advance, rather than from the rear. In order to "pursue" the ISS, it would have to first achieve ISS-orbital-velocity plus overtake-velocity, which will clearly consume more energy. By initially positioning itself in front of the ISS, it only as to achieve orbital velocity as the ISS catches up to it. Similarly, on undocking, it will appear to lag the ISS's orbit.
Obviously, I'm not the proverbial scientist .....
Not sure if there's a ISS traditional way of doing this but the general answer is that it depends because there are various ways of doing this... putting the active vehicle into a lower orbit and approaching the passive vehicle from below/behind is one popular option but putting the active vehicle in a higher orbit than the target and then when appropriate descending from that to approaching the target from above is another
The permutations are almost endless.
i should add that what we're seeing here in the way of maneuvering is a bit atypical- Normal resupply missions/re-crewing missions to the ISS don't usually hang around in orbit for 8 days prior to docking...I haven't followed this in great detail but it looks like Nauka was put in an orbit that allows the Russians to road test it, so to speak, for few days before committing to going anywhere near ISS.