Question: Is it right that if you let go of a rocket or satellite in space you will keep on travelling at that speed and keep on travelling for ever??

Evan Keane answered on 22 Jun 2011:

You probably have heard one of Newton’s Laws that says that if you are not moving or moving at some speed you will stay either not moving or going at that speed unless some force acts on you. So if you set off at 100 miles per hour you will stay going at 100 miles per hour, as long as there is no force to stop you. On Earth there are forces that work against you – like air resistance and friction. But in space there is not much stuff so no air resistance and or friction. There is a little bit of stuff but this will not slow you down very much. The big issue in space is gravity. If you fire a rocket up into space you need to fire it fast enough so that it first escapes the gravitational field of the Earth. Otherwise that will slow you down and eventually drag you back down. But if you go fast enough (it is 11 kilometres per second needed to escape Earth’s gravity) then you will be free of gravity.

If you are way out in space, free from the gravity of planets, stars and moons, and you let off a rocket or anything then yes it will keep going forever at that speed unless something acts against it to slow it down. As I said there would be a TINY amount of resistance from the small amount of particles in space which you have to barge through but this would be very small. You would certainly not slow down unless you hit something like an asteroid or if you went too close to some planet and were sucked in by its gravity. Great question. 😀