Following a 7-year, multi-million dollar effort to fabricate a 730 kg, 4 element Wide Field Corrector (WFC) for the Hobby-Eberly Telescope (HET) Wide Field Upgrade (WFU), it needed to be transported 820 km to its destination at the McDonald Observatory in West Texas. The final system optical test for the assembly required repeatability in the +/- 2μm range. Due to the size, mass, and ultimate destination of the payload, the only option available for transport was via roadway on a flat-bed trailer. While the route was primarily interstate highway, it presented a great variety of vibrational inputs due to poor paving conditions, and mountain roadways. Consideration also had be given to avoiding high ambient temperatures. Early in the design of the corrector assembly it was assumed that cable isolators would be the key element to isolate the payload from vibrational inputs, however, few documented references were available to provide the assurances required for transporting a load so key to the success of the telescope program. Tests were designed to simulate the load conditions, and inputs and outputs to the test load were measured for verification of the isolator performance. This was followed up with monitoring of vibration throughput during the actual shipment of the WFC. Upon arrival at the destination, the alignment of the assembly was checked and found to have no appreciable change in the alignment. Data and lessons learned are presented on the performance of air-ride trailers as well as the performance of cable isolators.
The Giant Magellan Telescope (GMT) is one of the extremely large telescopes of the next generation. The GMT adaptive optics (AO) system uses an adaptive secondary mirror and natural and laser guide stars to achieve diffraction-limited images. The AO calibration source provides sources at the telescope prime focus which replicate the properties of the natural and laser guide stars, to calibrate and verify the performance of the AO system. We present an optical design for this calibration source, and discuss the expected accuracy based on the tolerance analysis.
A 4-mirror prime focus corrector is under development to provide seeing-limited images for the 10-m aperture Hobby-
Eberly Telescope (HET) over a 22 arcminute wide field of view. The HET uses an 11-m fixed elevation segmented
spherical primary mirror, with pointing and tracking performed by moving the prime focus instrument package (PFIP)
such that it rotates about the virtual center of curvature of the spherical primary mirror. The images created by the
spherical primary mirror are aberrated with 13 arcmin diameter point spread function. The University of Arizona is
developing the 4-mirror wide field corrector to compensate the aberrations from the primary mirror and present seeing
limited imaged to the pickoffs for the fiber-fed spectrographs. The requirements for this system pose several challenges,
including optical fabrication of the aspheric mirrors, system alignment, and operational mechanical stability.
New developments in fabrication and testing techniques at the College of Optical Sciences, University of Arizona have
allowed successful completion of 1.4-m diameter convex off-axis aspherics. The optics with up to 300 μm aspheric
departure were finished using a new method of computer controlled polishing and measured with two new optical tests:
the Swingarm Optical CMM (SOC) and a Fizeau interferometer using a spherical reference surface and CGH correction.
This paper shows the methods and equipment used for manufacturing these surfaces.
The ability to grind and polish steep aspheric surfaces to high quality is limited by the tools used for working the surface. The optician prefers to use large, stiff tools to get good natural smoothing, avoiding small scale surface errors. This is difficult for steep aspheres because the tools must have sufficient compliance to fit the aspheric surface, yet we wish the tools to be stiff so they wear down high regions on the surface. This paper presents a toolkit for designing optimal tools that provide large scale compliance to fit the aspheric surface, yet maintain small scale stiffness for efficient polishing.