The 3.8 m United Kingdom Infrared Telescope (UKIRT) has recently installed active control of the primary mirror figure, taking advantage of aspects of the original mirror design, which permits the correction of low order aberrations. In this paper, we present results from a campaign of all-sky wavefront sensing carried out UKIRT. As a result of the campaign, a lookup table is being used to correct for attitude dependent astigmatism, while fixed corrections are applied to trefoil and spherical aberrations. Coma is removed by secondary mirror alignment. A continuous, model based, correction of focus for thermal and elastic effects is also applied. Accurate focus is now maintained throughout an observing night.
The 3.8 m UK Infrared Telescope has been the focus of a program of upgrades intended to deliver images which are as close as possible to the diffraction limit at (lambda) equals 2.2 micrometers (FWHM equals 0.'12). This program is almost complete and many benefits are being seen. A high-bandwidth tip-tilt secondary mirror driven by a Fast Guider sampling at <EQ 100 Hz effectively eliminates image movement as long as a guide star with R < 16.m5 is available within +/- 3.'5 of the target. Low-order active control of the primary mirror and precision positioning of the secondary, using simple lookup tables, provide telescope optics which are already almost diffraction limited at (lambda) equals 2 micrometers . To reduce facility seeing the dome has been equipped with sixteen closable apertures to permit natural wind flushing, assisted in low winds by the building ventilation system. The primary mirror will soon be actively cooled and the concrete dome floor may be thermally insulated against daytime heating if fire safety concerns can be resolved. Delivered images in the K band now have FWHM which is usually <EQ 0.'8, frequently <EQ 0.'6 and quite often approximately 0.'3. Examples of the latter are shown: these approximate the resolution achieved by NICMOS on the HST. We estimate that the productivity of the telescope has approximately doubled, while its oversubscription factor has increased to > 4.
The 3.8 m UK infrared telescope (UKIRT) is currently the focus of an upgrades program to improve its imaging performance, ideally to approach its diffraction limit in the near-IR at 2.2 micrometer, with FWHM approximately 0.'12. This program is now in its late stages. All the new systems have been designed, most have been manufacture and many have been installed. A new top end carries an adaptive tip-tilt secondary mirror with active precision alignment, which, with low-order active control of the primary mirror, should provide the desired intrinsic optical performance. The adaptive tip- tilt system will correct image motion from telescope vibrations and drive errors and from atmospheric wavefront tilt; delivered images are expected regularly to be less than 0.'5 over wide fields, and within a factor 2 or so of the diffraction limit, at least inside an isoplanatic patch of order an arcmin radius. To reduce facility seeing the primary mirror has been equipped with a ventilation system and will receive a 5 kW cooling system; the dome is being equipped with sixteen closable apertures to permit natural wind flushing, which can be assisted by the building air handling system in low winds. It is hoped that facility seeing -- excluding boundary layer effects -- will be imperceptible during approximately 85% of observable time. The upgraded UKIRT should be well capable of exploiting fully the very best conditions on Mauna Kea.
The Instituto de Astrofisica de Canarias (IAC) is taking preliminary steps towards the building of an 8-m class optical-infrared telescope to be placed at the Observatorio del Roque de Los Muchachos (ORM) on the island of La Palma in the Canary Islands, Spain. This paper presents a brief description of the preliminary conceptual design of the control system for the telescope and its instrumentation in all planned modes of observation and configurations. An outline of the devices that are to be controlled and the functions that are to be performed is presented, together with a description of the system architecture. The system will be distributed and highly modular, and will allow for an easy and efficient exchange of instruments, focal stations and observing modes. It will also be designed so that technological upgrades can be implemented at low cost and minimum down-time.
In the 1970s the pioneering thin-mirror 3.8 m United Kingdom Infrared Telescope (UKIRT) of the UK Science and Engineering Research Council (SERC) was conceived as a low-cost `light bucket', with an 80% encircled-energy diameter <EQ 3'. However the delivered primary mirror had an 80 encircled- energy diameter of approximately 1' and the telescope has regularly delivered sub-arc-second images. To exploit this quality and to keep UKIRT competitive in a 21st century of 8-meter telescopes, in 1991 the SERC initiated an ambitious Upgrades Program, with the goal of routinely providing near- diffraction limited images at 2.2 microns. The major elements of the program are an adaptive tip-tilt secondary system, an active five-axis secondary collimation system, an upgraded primary mirror support system providing active control of the main optical aberrations, and modifications to the telescope and its enclosure to reduce or eliminate dome and mirror seeing, so as to take advantage of the excellent natural seeing on Mauna Kea. This paper outlines the overall project goals, the proposed strategies for upgrading the telescope and the progress to date.
This paper presents a solution to correct wind induced deformation on a 8.0 m thin meniscus mirror supported by a system of astatic active supports. The correction scheme is based on an active correction using the force actuators which support the mirror, and a passive rate dependent coupling of the mirror to the cell. The paper identifies the fundamental design parameters of the passive correction system and the active controller, and shows its wind attenuation capabilities. A 3D simulation verifies the good performance of the system for wind velocities of about 45 km/h. Furthermore, the influence of cell deflection on the mirror due to the passive coupling system is shown.
This paper presents the IAC (Instituto de Astrofisica de Canaries, Spain) proposal of a distributed control system intended for the active support of a 8 m mirror. The system incorporates a large number of compact `smart' force actuators, six force definers, and a mirror support computer (MSC) for interfacing with the telescope control system and for general housekeeping. We propose the use of a network for the interconnection of the actuators, definers and the MSC, which will minimize the physical complexity of the interface between the mirror support system and the MSC. The force actuator control electronics are described in detail, as is the system software architecture of the actuator and the MSC. As the network is a key point for the system, we also detail the evaluation of three candidates, before electing the CAN bus.