Answer:
Will remain in motion until an external force is applied.
Explanation:
According to Newton's first law of motion, a body continues to be in state of rest or motion, until and unless an unbalanced, external force acts on it.
In deep space, there is no external force. If a motionless spacecraft uses thrusters to give a push, the spacecraft will continue to be in motion until an unbalance external force acts on it again to stop it or increase its speed or change direction.
