According to special relativity, as an object with mass approaches the speed of light, its energy and momentum increase, and it requires an increasingly large amount of energy to accelerate further. As the rocket ship approaches the speed of light, the energy required to accelerate it becomes practically infinite. Therefore, from the perspective of an observer on the rocket ship, it would be impossible to reach or exceed the speed of light.
In terms of the rocket ship's own frame of reference, its acceleration would appear constant as long as no external forces act upon it. However, as the ship's velocity gets closer to the speed of light, the energy required to increase its speed even slightly becomes prohibitively large. This means that, in practice, the speed of light acts as a universal speed limit that cannot be surpassed by any object with mass.
It's important to note that the concept of acceleration and velocity becomes more complicated near the speed of light due to time dilation and length contraction effects predicted by special relativity. As an object accelerates closer to the speed of light, time dilation causes its internal clock to appear slower relative to a stationary observer. Additionally, length contraction causes the object to appear shorter in the direction of motion. These effects further limit the ability of massive objects to approach the speed of light.