After a freak occurrence brought down the 30 year old original telescope in 1988, a $75 million replacement was designed, which called for a larger 100m diameter, fully steerable radio telescope. Weighing 7500 tons travelling on a 200 foot diameter track, it is the world's largest. To build this gigantic structure, a 500 ton capacity stiffleg derrick was selected, which had a 250 foot long boom and stood on top of a 200 foot tower. Somerset was hired by the contractor to develop the erection scheme for the derrick together with the rigging & lift layouts for the modules of the telescope. As the existing derrick tower was designed for a 400 ton model, we checked the stresses on the tower and engineered reinforcing to increase capacity, designed new tiedowns and foundations and the new members to fit the larger 500 ton derrick footprint.