They covered the topic of a natural comet impact in Lucifer's Hammer, from 1977.I read that. It was about as much fun as an after-the-deluge kind of book would be expected to be. :') With SpaceWatch, the only way such a scheme could succeed and perhaps be explained away as a fortuitous accident would be to keep the projectiles small. Aerodynamic tungsten projectiles would get through the atmosphere and deliver a nice sized bang, destroying a population center while minimizing regional effects. He wrote, cheerfully. ;')
They also have an Orion spaceship. The character meant to represent Jerry Pournelle explains that kind of ship this way:
"Take a big metal plate," Curtis said. "Big and thick. Make it a hemisphere, but it could even be flat. Put a large ship, say the size of a battleship, on top of it. You want a really good shock absorber system between the plate and the ship.
"Now put an atom bomb underneath and light it off. I guarantee you that sucker will move." He sketched as he talked. "You keep throwing atom bombs underneath the ship. It puts several million pounds into orbit. In fact, the more mass you've got, the smoother the ride."
And when they built it and finally launched it they described it this way in the book:
SLAM.
Commander Kennedy whooped. "They made it! They're up! It's--"
SLAM
"--first bomb fails you just start over."
SLAM
"If the second bomb fails, you're already--"
SLAM
"--already in the air. You'll fall. They're on their--"
SLAM
"--way, by God! You can give me that drink now."
SLAM
God was knocking, and he wanted in bad.