Who We Are As the nation's largest producer of clean, carbon-free energy, Constellation is focused on our purpose: accelerating the transition to a carbon-free future. We have been the leader in clean energy production for more than a decade, and we are cultivating a workplace where our employees can grow, thrive, and contribute. The Mechanical System Engineer position is based out of our LaSalle County Generating Station in Marseilles, IL. Our culture and employee experience make it clear: W