ORBS: The Complete Four Book Series by Nicholas Sansbury Smith

While training for a manned mission to Mars, Dr. Sophie Winston and her team of scientists find themselves cut off from the rest of the world. Trapped inside a biosphere deep within the confines of Cheyenne Mountain, Sophie and crew discover they are the survivors of a brutal alien invasion. But as they struggle to stay alive, they realize their safe haven is far from safe and that they must team with other survivors around the world to defeat the aliens before it’s too late for humanity, and the Earth.

Category: Science Fiction – First Contact