# Accelerating a spaceship to near speed of light

Hypothetically, suppose we have the ability to accelerate a spaceship to near speed of light (lets say 0.9c). From what I remember of relativistic kinematics, the energy required to accelerate the ship to that speed be given by:

$$KE = mc^2 (\gamma -1)$$

If so, let us suppose the spaceship is to travel to the nearest neighbouring star. What would be the energy for the spaceship to maintain that velocity of 0.9c.

• The problem is not coasting but decelerating at the destination. Mar 1, 2021 at 23:04
• I see! Hypothetically speaking, what forces could cause a deceleration of such spaceship? Would the gravitational potential of a nearby blackhole cause such disturbance? Mar 2, 2021 at 2:14