A rocket moves through empty space in a straight line with constant speed. It is very far from any star or planet. Under these conditions, the force that must be applied to the rocket in order to sustain its motion is

analysis the force is zero

Explanation:

Let's apply Newton's second law

         F = m a

In this equation we see that the force is directly related to the acceleration, as they indicate that the rocket is far from any planet or star has no force applied to it, therefore they also relate it to zero.

Change we can analyze the exercise with Newton's first law, which indicates that an object maintains its constant speed in a straight line has no forces applied to it.

In either analysis the force is zero

think its the third option