why when the international space station is only 250miles away does it take at least 4 hours to get there?

Question

I’m going to be very disappointed if the rockets top out at 65mph.

In: Planetary Science

Answer 1

With the rockets we have now it takes roughly two minutes to get enough height to reach the ISS. Then a further 8 minutes to match the speed as it is going pretty fast. So about 10-15 minutes to get to orbit. The problem is that we are not extremely accurate when trying to hit an orbit first try. Just like on a golf course a good driver shot may have the distance to go all the way to the hole but not the accuracy and you will probably land just in the rough proximity.

So on a golf course you might aim a bit closer to make sure you land on the fairway and not in the rough. You then walk up to the ball and start over again evaluating the balls position and its trajectory as well as wind and other factors before taking another shot. This will bring in closer to the hole but not quite there so you rinse and repeat until you finally put the ball into the hole.

We do the same when docking to the ISS. We first launch into an orbit slightly behind and under the ISS. Then we take measurements of the orbit we ended up in and plan the next orbit changes to get closer to the ISS. Finally getting to visual range and then slowly bring the spacecraft close to the space station without hitting it and finally dock very carefully. But unlike golf which is fairly two dimensional when you are docking a space station you need to match seven dimensions, three locational dimensions, three velocity dimensions and time. Getting these to match is very complex. And sometimes you can do nothing but sit and wait for the spacecraft to slowly drift closer to the space station.

The fact that we can launch and dock a spacecraft to the space station in as little as 4 hours is an impressive feat in itself. It used to take a full day and night. Compressing it all down to 4 hours requires a huge effort but allows the astronauts to stay in their launch suits in their seats all the way which is more comfortable then having to spend the day and night in the confined spacecraft.