Spaceship Mechanics

A spaceship is launched radially away from the earth with the help of a rocket. When the spaceship acquires speed $v_{0}$
the rocket used is switched off. As the spaceship proceeds further away from the earth, its speed $v$ decreases with time $t$ as shown in the graph and eventually the spaceship acquires a constant velocity that is one fifth of $v_{0}$
How far away from the centre of the earth, was the rocket switched off?

Answer comes in the form of $\alpha v_{0} t_{0}$
Find $\alpha=?$

Note:
1) The graph wants to show that when the rocket is switched off from that instant $t=0$ is considered .
2) See the graph carefully, it also wants to show that the spaceship reached its terminal velocity at time $8t_{0}$ .