The primary reflector of the GBT will be an offset paraboloid of 100-meter projected aperture. The offset design provides an aperture that is completely free of blockage. The following paragraphs define the coordinate systems and nomenclature used throughout this document. In the following, all dimensions are in meters and angles in degrees, unless otherwise noted.
V o is the vertex of the paraboloid.
A prime focus receiver mount will be provided for receiver and feed combinations weighing up to 1500 pounds. Feed translation along its boresight axis of 50 inches will be provided. The feed boresight will be along a line tilted 45.5 degrees with respect to the paraboloid axis. Receiver motion orthogonal to this line and in the Y-Z plane will be provided to track the focal point motion due to gravitional deformations. These motions, together with specifications on speeds and repeatability, are further described in Figure 2-1 .