Fifth Luna was a mining asteroid that orbited Earth. It was used by the Earth Federation to provide resources for space colony construction.
The Earth Federation moved several asteroids from the Asteroid Belt into the Earth Sphere and placed them in orbit around Earth to provide resources for construction. These asteroids were fitted with thermonulcear pulse thrusters on their surfaces to provide propulsion to move them into orbit. These thrusters were also used to move the asteroids out of orbit once their resources had been depleted.
Fifth Luna was one of these asteroids. It served civilian mining purposes.
The Federation deployed special task force Londo Bell to intercept the asteroid but they failed to stop its descent or change its course. Fifth Luna crashed into Lhasa and destroyed the city.