Answer:
P = 2 pi R / v period of space station
F / m = v^2 / R centripetal force per unit of mass
So F / m = 4 pi^2 R^2 / (P^2 * R) = 4 pi^2 R / P^2
Also, F / m = 9.8 m/s^2 earth's gravitational attraction
So 9.8 = 4 pi^2 R / P^2 or R = 9.8 P^2 / 4 * pi^2) = 195 m
Or D = 2 R = 390 m the diameter required