The Jet Propulsion Laboratory at NASA fired him for performance reasons.

Ars Technica’s John Timmer has the story:

Coppedge had worked on the Cassini mission to Saturn, starting as a contractor in 1996, and later becoming a full-time employee. But one of the projects he pursued on his own time was the promotion of intelligent design, the notion that the Universe and, most prominently, life itself, is too orderly to have come about without a designer. (Like many others in that movement, Coppedge is a self-identified evangelical Christian.)\

In 2009, he apparently got a bit aggressive about promoting these ideas at work, leading one employee to complain. … he had also aggressively promoted his opinion on California’s gay marriage ban, and had attempted to get JPL’s holiday party renamed to “Christmas party.” …. Coppedge was warned about his behavior at work, but he felt it was an infringement of his religious freedom, so he sued … part of a set of cutbacks on the Cassini staff, he was fired.

From another source:

JPL attorney Cameron Fox, however, contended Coppedge was a stubborn and disconnected employee who decided not to heed warnings to get additional training, even when it became clear the Cassini mission would be downsized and computer specialist positions eliminated.