A fascinating article on the NBC Science blog describes some of the things done to allow the recent Soyuz resupply ship to make a 6 hour rendezvous with the ISS, rather than the conventional 4-day rendezvous procedure.
I had surmised that this feat required upgrades to the Soyuz navigational and control systems to refine the trajectory on the way up, but that turns out not to be the case. The NBC article by James Oberg says that the real trick to this was adjusting the ISS’s orbit so that it would be in exactly the right place at the right time.
Of course, it did mean that the launch window for the Soyuz was much tighter than usual, but the actual flight itself was business as usual.
Soyuz spacecraft on it’s way to the launch site
James describes the maneuvering of the ISS to achieve this reposition, which involved increasing the altitude of the ISS by only 1.5 miles. Anyone who has played LEO – Low Earth Orbit will realise that increasing your orbital altitude slows you down, which can have a significant effect on your orbit. Bearing in mind that they were trying to arrange for the ISS to ...