Earthlight is one of Arthur C. Clarke's earlier works, dating back to 1955.
The plot centers around a fight between those with allegiance to the Earth/Moon and those working as traders between the planets.
It has been a long time since a war has been fought, and people are re-learning things. There is thought to be an intelligence leak somewhere on the moon base astronomy lab, and an accountant is pressed into becoming a spy to route out the traitor.
Both sides in the small war have got some new technology, the traders a new spacecraft engine technology, and the Earth-based people an interesting electromagnetic wave shield.
The final battle is witnessed by one of the astronomers and the accountant, with some interesting results.
It was last printed as a paperback in New York by Del Rey in 1998 ISBN 0345430700