The ISS is around 400km above us. A rocket needs a speed of at least 8km per second to get to space. If we cut out the acceleration part it could in theory reach the ISS in around 50 seconds. Even if we factor in the acceleration part etc. it should still be very quick up there. Yet the fastest possible time to get to the ISS is 4 hours. That would be an average speed of 100Km/h which is way slower than the speed of the rocket after a few seconds. Why the long journey?
In: Planetary Science
So the ISS is moving very fast, if you want to safely dock it, you need to have the right velocity, going too fast would be catastrophic, since you would slam into the ISS and break it, on the other hand going too slow would mean you wouldn’t catch up to it. So they fire the rockets so that the astronauts can go into orbit, where they can safely make sure that they get the right velocity, which takes time.
The Russians have done it in about 3 hours (Soyuz MS-17), but generally it takes longer, since it is much safer
hitting it directly would be impossible
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