The roof panels, made of a PTFE (polytetrafluoroethylene) coated fiberglass fabric, are much lighter than a traditional clad roof. But the roof isn't the only thing that comes and goes.

The natural-grass playing surface sits in a 16.9 million-lb tray that is 234 400 ft, the first of its kind in North America. The roll-out field should save an estimated $50 million as it is cheaper to move the field outside than retract the entire roof to let the sunshine in.

The stadium-mechanization designer Uni-Systems, Minneapolis, partnered with ABB Inc., New Berlin, Wis., using ABB ACS800 Direct Torque Control drives to open and close the giant stadiumroof panels. Uni-Systems' resume also includes work on Minute Maid Park and Reliant Stadium, Houston, Tex.; Miller Park, Milwaukee; and RFK Stadium, Washington, D.C.

ABB Inc.,
(800) 752-0696,

(763) 536-1407,