Black Knight Down (Stone Soldiers #5‪)‬

When a coven of witches conspire to bring down a prehistoric satellite orbiting the earth for millennia, the Stone Soldiers spring into action, encountering a mysterious, superhuman priest spouting dire warnings that the Black Knight satellite must not be opened. 

Defying orders to leave the satellite in the hands of the Air Force, Colonel Mark Kenslir launches his own investigation into the satellite's origins and finally discovers the dark forces it contains.