Momentum is conserved in space due to space being A vacuum and there being no external forces which can act upon the objects, this is referred to as an isolated system. Planets in orbit never change course or the speed at which they orbit the sun due to their momentum being conserved. Their masses and velocities are constant and therefore will continue on their paths for eternity. According to Richard Garriott who is an American astronaut “linear momentum will be conserved since the external force of gravity is absent” and therefore linear momentum is not conserved on earth as in any system being dealt with it will lose energy in the form of heat or sound due to external forces acting upon them. These external forces present on earth result in momentum not being conserved, but In space there is a complete absence of all external forces which allows for momentum to be conserved. Astronauts need either A: a platform to push off or B: a handle to pull themselves on in order to move around the space ship, whatever force they pull/push themselves with, will determine their velocity and at what speed they move, they will get to their next location with the exact same velocity at which they left with, due to their masses staying constant and there being no external forces acting upon them and therefore their momentum is conserved as momentum is directly proportional to an objects mass and its velocity. Velocity is a vector and therefore direction has to be taken into consideration so when two objects (traveling in space) of the same mass are pushed together with the same velocity they will collide and bounce away from each other with the same velocity but in opposite directions, therefore the vector sum of the two objects will cancel each other out and momentum before the collision will be the same as after collision. Momentum in space is conserved due to it being an isolated where no external forces are present to act upon an object.