Quote from: sghill on 02/12/2022 08:38 pmIs it normal for Progress cargo ships to spend two days in orbit before docking? The crewed missions go up and dock so fast, it raised my question.Two days is normal. If the phasing is exactly right, they can rendezvous in a few hours and then an hour or so to dock.A lot of the crewed missions use a 4 hour launch to docking because they deliberately wait on the ground for a quick opportunity and sometimes adjust the orbit of the station to make one possible. If they miss the launch window (for example, due to weather or technical problems), they usually won't have another quick docking opportunity for several weeks, so they launch as soon as possible on a 2-day docking.The quick docking is especially good for the Soyuz because of very limited supplies and fuel. I'm not sure, but they might have to load more fuel, food, water and oxygen for a 2-day flight and leave some station supplies on the ground to make up for it.Progress (and other cargo ships) don't have any people on board consuming supplies, so the constraints are much looser. They have launched Progresses on 4-hour docking flights, but I think that was mostly to test out the techniques before trying it with people, and they don't do that anymore.In principle, they could adjust the station phasing to allow quick dockings for other visiting vessels (shuttles, Cygnus, both crewed and cargo Dragons, etc.) but they all have much larger time, fuel and mass margins and don't really need it. Also, the Russians supply the fuel for station orbit adjustments, so they are more inclined to do it for their own benefit versus the benefit of station partners. I think some quick dockings have been done by other visitors, but that may have just been due to chance alignments that allowed it, and did not require any special station maneuvers.
Is it normal for Progress cargo ships to spend two days in orbit before docking? The crewed missions go up and dock so fast, it raised my question.