In space, an object like a shuttle would continue to move at a constant velocity even if it is no longer generating any force due to the principle of inertia. This principle, which is one of Newton's laws of motion, states that an object will remain in its state of motion (either at rest or moving with a constant velocity) unless acted upon by an external force.
When a shuttle is launched into space, it initially generates a large amount of thrust from its engines to overcome Earth's gravity and achieve orbital velocity. Once it reaches that velocity, the shuttle essentially enters a state of freefall around the Earth, continuously falling towards the Earth but simultaneously moving forward at a sufficient speed that it keeps missing the planet.
In the vacuum of space, where there is no significant atmospheric resistance, there are only minimal external forces acting on the shuttle. The primary force acting on it is gravity, which causes it to be in a constant state of acceleration towards the Earth. However, because the shuttle and its occupants are in freefall, they continuously experience the same acceleration due to gravity. As a result, they remain in a state of apparent weightlessness and continue moving forward at a constant velocity.
In summary, the shuttle continues to move in space at a constant velocity because there is no significant external force to change its state of motion once it has achieved the desired orbital velocity.