Military satelites looking up?

I was just reading an article on the largest explosion witnessed in our universe, and came across a strange passage:

Gamma ray bursts were unknown until the launch of U.S. military satellites designed to detect radiation from the explosion of atomic bombs. Later, scientific satellites were launched to study the bursts, but astronomers were still at a loss to explain them.

...What were they doing looking up if they were looking for radiation from atomic bombs?

It all depends on how high the sattelite is, if it's high enough, it might be able to see around the horizon of the earth and into space while looking at the surface of earth. It's cheaper to build 20 bigger satelittes and send them higher to get a bigger picture of earth, than to build 50 smaller sattelites and put them closer to earth for a smaller pictures.

[Edited on 1-1-2004 by muzz]