Abstract: An orbital service bridge for positioning a work platform at desired positions within an overlying dome-shaped structure comprises inclined leg members pivotally mounted at one end near the top of the dome. A motor driven trolley positions the other end of the leg member along a track circumferentially disposed on the base of the domed area. A carriage movably supported on the leg members positions the work platform at the desired height, and a telescoping mounting assembly extends the work platform in either direction away from the leg members and into the desired position. The bridge may also be assembled with complimentary leg members to form a self-supporting bridge structure useful in assembling the dome and related systems.