Set in 2109 A.D., it tells of a comet on collision course with Earth, and Capt. Robert Singh's attempts to divert/destroy it. Capt. Singh is in command of the Goliath, a research ship originally designed to deflect Earth-threatening asteroids. The ship is engaged in reasearh when the comet is discovered. The story's 'current timeline' starts aboard the Goliath and moves back to show Capt. Singh's early life. It then comes back to the present, showing on the way the socio-religious situation that eventually leads to the partial failure of the mission.
Among other things, Arthur C. Clarke has outlined the 'SPACEGUARD' project, which is an early-warning system against meteors.
This is not a linear story: there are several flashbacks, giving a panoramic view of life in the 22nd century. This story may well come true someday....