Answer:
It will continue moving at a constant speed because no forces are acting on it.
Explanation:
By the second law of Newton, the force is proportional to the acceleration. If there is no force, there is no acceleration. So, when the astronaut turns off the engines, the rocket will have no acceleration which means that the speed will be constant.
Therefore, the answer is:
It will continue moving at a constant speed because no forces are acting on it.