Terry S. Mast

Control and alignment of segmented-mirror telescopes: matrices, modes, and error propagation

Starting from the successful Keck telescope design, we construct and analyze the control matrix for the active control system of the primary mirror of a generalized segmented-mirror telescope, with up to 1000 segments and including an alternative sensor geometry to the one used at Keck. In particular we examine the noise propagation of the matrix and its consequences for both seeing-limited and diffraction-limited observations. The associated problem of optical alignment of such a primary mirror is also analyzed in terms of the distinct but related matrices that govern this latter problem.

ACTIVE CONTROL ISSUES FOR THE CALIFORNIA EXTREMELY LARGE TELESCOPE

A team of researchers from the University of California and Caltech are investigating the feasibility of building a 30 meter diameter segmented mirror telescope, following the design approach pioneered by the 36segment Keck telescopes. The current design concept for the California Extremely Large Telescope (CELT) has 1080 segments forming the primary mirror, with the piston, tip, and tilt of each segment controlled by three actuators. The control approach must correct for gravity- and temperature-induced deformations of the mirror support structure, and potentially wind and seismic disturbances, with a cost effective design. We discuss some of the active control issues, including requirements (optical and cost), estimates of the disturbances, actuator options, and control analysis. Several candidate actuator technologies appear capable of meeting the technical and cost requirements, and preliminary error propagation analyses indicate that the optical error budget can likely be met. Additional issues being addressed are identified.

W.M. Keck Telescope phasing camera system

The segmented design of the W. M. Keck Telescope primary mirror places several unique demands upon the alignment and adjustment of the telescope optics. These include: (1) careful determination of the optical figures of individual segments (to provide input data for warping harness adjustment), (2) control of the two tilt degrees of freedom for each of the thirty-six primary mirror segments, and (3) phasing or control of the piston degree of freedom for each of these segments. In addition, (4) the proper alignment of the secondary with respect to the primary, although it is a requirement common to monolithic and segmented telescopes alike, is a more subtle and complicated task for the latter because the optic axis of the primary is not readily defined. These four tasks are performed at Keck by the Phasing Camera System.

Phasing the mirror segments of the W.M. Keck Telescope

We present data which illuminates the method and also discuss details of the operation of the Phasing Camera.

DEIMOS camera assembly

DEIMOS is a large multi-object spectrography with an imaging mode that is being built for the W. M. Keck 2 Telescope. The camera contains nine lens elements in five groups. The overall length of the camera and detector assembly is 0.67 meters, and the largest element is 0.33 meters in diameter. Typical centration and spacing tolerances are at the level of 25 microns. We describe the error budget, the design of the lens-supporting structure, and the assembly procedures.

Aspheric lens fabrication and testing at UCO/Lick Observatory

Aspherical surfaces on lenses are difficult to produce and test. There are many innovative approaches used today to address the complexities of this process. The size, quality, and quantity of the lens to be produced dictate the best approach. The UCO/Lick Observatory Optical Lab has fabricated aspheric lenses to diameters over 12 inches using fabrication and testing techniques developed specifically for high quality, one-of-a-kind lenses, with axi-symmetric profiles and significant departures from sphere. This paper describes the manufacturing procedures used at UCO/Lick to fabricate aspheric lenses typical for todays astronomical applications.