Focus: Platform tilt and deflections

The platform tilts as the dome moves in az,za:

• The platform is not balanced. The dome weighs 100+ tons while the carriage house weighs 17.5 tons. As the dome moves up in za, the platform tilts down in the direction of motion.
• The azimuth rails deflect differently as we move in azimuth. The beams of the triangle deflect more in the center than in the corners.
• We correct for this tilt and deflection by shimming the elevation and azimuth rails so the horn will move along the paraxial surface.

• Setup the tilt sensor on the rotary floor to measure the pitch and roll of the dome.
• Set the dome at za=10 degrees and then spin the azimuth by 360 degrees while we measure the tilt sensor. Adjust the tiedowns so there is no 1 azimuth term in the tilt sensor measurements. This removes any residual tilt in the platform caused by the tiedown cables.