Mechanical systems performance of the HET wide-field upgrade

We have completed a major Wide Field Upgrade (WFU) of the Hobby-Eberly Telescope (HET) and reentered scheduled queue science operations in mid-2016. This paper assesses the performance of the various mechanical systems which were upgraded, or added to HET, including the Telescope Structure, the star Tracker (aka, WFU Tracker), Prime Focus Instrument Package (PFIP), and VIRUS Support Structure (VSS). The upgrades were required to increase the field of view of HET, from 4 arc-minutes, to 22 arc-minutes, increasing the observed area of sky by 30 times the original FoV. In the process, the total weight of the system increased from 100 tons, to 153 tons, requiring a complete overhaul of most of the mechanical, servo, and control systems. The new 13-axis Tracker and control system was tested extensively prior to shipping and installation, and followed up with laser tracker measurements, which brought the tracking system to within 1 arc-minute RMS pointing, and followed up with on-sky derived mount-models, which has improved the pointing and guiding to within 12 arc-seconds RMS, and 0.1 arc-seconds, respectively. A completely new structural support system was implemented to house and connect a total of 156 VIRUS spectrographs, plus 4 new Low-Resolution Spectrographs (LRS2). The VIRUS units are arrayed in two large enclosures mounted to either side of the telescope. Each enclosure is approximately 1.3m deep x 6.7m wide x 6.2m tall and weighs 38 tons fully loaded. This structure is attached to HET in a way that allows it to be positioned by, but stand independent of, the HET during observation. As commissioning has transitioned to phased-science/engineering operations, and subsequently, to science operation, the tracking software and mechanical performance of the Tracker and VSS have been improved to meet specification. Performance data and lessons learned are provided.