Masami Yutani

CIAX: Cassegrain instrument auto exchanger for the Subaru telescope

The Cassegrain Instrument Automatic eXchanger (CIAX) system for the 8.2 meter Subaru Telescope moves instruments between the Cassegrain mounting flange and stand-by flanges without manual intervention. Observation efficiency improves not only because of quick exchanges, scheduled or emergency, but also because of increased flexibility in selecting an optimum instrument for weather conditions or observation goals. Reliable and safer instrument exchanges are achieved by the precision mechanical positioning system (less than 0.5 mm) and an automatic connector system for electrical cables, optical fibers and fluid lines. Instrument down time due to connector/cable failure by human error is eliminated. Interfaces to the telescope flange are standardized for all five Cassegrain instruments (approximately 2000 kgf each) currently in use or under preparation.

Control of the Subaru telescope instrument exchanger system

The CIAX system especially CIAX-3 increased observation efficiency for Cassegrain test instruments at the early phase of Subaru telescope test observation. In order to control this system effectively and automatically, a control software for the entire system of the CIAX was developed. The software design goals are (1) redundancy for robust system, (2) the safety of the instrument by interlocking, (3) maximum efficiency by automatic control and (4) easy user interface for operator. In this paper, we describe the software which has been being tested through the telescope and instrument commissioning phase.

Wind deformation of the Subaru primary mirror

I will report on the deformation of the Subaru Telescope primary mirror surface due to wind pressure. The 261 actuators, controlled precisely down to 0.01 N level, together with 3 fixed points maintains the optical figure of the primary mirror. The extra-force exerted by wind pressure, however, pushes the actuator pistons to cause their displacement while not affecting the fixed points. This results in an overall deformation of the primary mirror, which we measured. We first measured the difference in the actuator force of the sensors with and without wind pressure, i.e., with the dome shutter opened and closed. The force were then converted to the displacement of the 261 actuator pistons. The experiment was made under the wind speed of 5m/s with the telescope pointing toward the wind at elevations 30 and 60 degrees. The deformation pattern at EL=30 was triangular with three fixed points protruding, while that at EL=60 was saddle with the left and right pushed back. The value of deformation was ~2um. The patterns were interpreted that the wind pushes the entire mirror surface at EL=30 while it lifts the bottom part up at EL=60.

Cleaning procedure for mirror coating at Subaru Telescope

We would like to present the procedure of how to prepare the primary mirror of Subaru Telescope for the realuminization. The equipment for the coating and its preparation are located at the ground floor of the telescope enclosure. There are two trolleys for carrying the mirror cell and the mirror itself, a mirror lifting jig, a washing facility for the primary mirror (PMWF), the water purification system, the coating chamber and the waste water pit. The PMWF can provide the tap water for initial rinsing, the chemical for stripping the old coating, and the deionized water for final cleaning. It has two pairs of arms that deploy horizontally above the mirror and have nozzles to spray. The arms spin around its center where the rotary joints are connected to the plumbing from storage tanks. Deck above the water arms serve as platform for personnel for the inspection or for scrubbing work. We use hydrochloric acid mixture to remove the old aluminum coating. For rinsing and final cleaning, we use the water through the purification system. The water supply from the nozzles and the rotation of the arms can be controlled from a panel separated from the washing machine itself. After several experiments and improvements in the washing, we have carried out the coating of the 8.3 m primary mirror in September last year. This was the third time, and the reflectivity of the new coating show satisfactory result.

SUBARU top unit exchanger

The SUBARU Telescope has four focal positions to allow different types of instruments. At present, there are four different Top Units; three types of secondary mirrors and one primary focus unit. These units have the weight of about 3 tons, and they need to be installed or changed high above in the air, with the telescope in its rest position, namely, pointed to the zenith. In order to carry out this exchange work safely and securely, in already a difficult working condition of high altitude place like Mauna Kea, we developed an automatic exchanger with remote control, called Top Unit Exchanger (TUE).

Update on the Subaru Cassegrain Instrument Automatic Exchanger Control System

We report on the status of the Cassegrain Instrument Automatic Exchanger (CIAX) control system for the Subaru Telescope. Devices controlled by a shell program in the previous version are now controlled by a macro. It can now be operated safely from remote site. Features of the new system are: 1. New macro. The new macro has two features: (1) Action skip. The macro can skip actions that have been executed earlier. It judges whether to skip by checking the status of devices. Resumption of interrupted macro or reversal from halfway of a process is possible. (2) Macro flexibility: The script has every possible sequential action and chooses actions by checking device status. For instance, it can determine whether the cart is at the telescope or at one of the instrument standby flanges and select a proper hookup command. 2. GUI for macro operation and CGI for rewriting setup files. The new GUI uses a commercial instrument control language. A CGI application accesses setup files. 3. Omni-directional Infrared (IR) LAN. Omni-directional IR LAN is being tested for the cart because radio frequency wireless LAN is prohibited on Mauna Kea to avoid interference to radio telescopes. Conventional IR LAN failed because of its directionality. The CIAX system is now routinely used for instrument exchange. For complete automatic operation, there are still a few tasks left, such as macro-controlled instrument shutdown and restarting, standardizing interfaces and procedure for all instruments and further increasing reliability which is higher already compared to conventional manual exchange.

Coating experiment with 1.6-m vacuum evaporation chamber

We have conducted a series of coating experiments using the newly installed 1.6 m evaporation chamber at the Advanced Technology Center (ATC) of the National Astronomical Observatory of Japan. The main task of this chamber is to re-aluminize the 1.6 m mirror of the Infrared Simulator at the ATC. The design concept of the 1.6 m chamber is basically the same with the 8.3 m coating facility for Subaru Telescope. Therefore, we could utilize this chamber to evaluate the fundamental performance of the larger chamber. The extensive coating experiments were done in the spring, autumn of 1996, and autumn of 1997. Reduction of the number of the filaments has lead to the increase in their size, which caused difficulty in the annealing process. Attempts are focused on securing the sufficient metal loads on the filaments. Then the filaments are fired to measure the spray pattern of a single filament exposure, or the uniformity pattern resulted from the full setup of filament arrays. Using small slide glasses, the important parameters of the resultant reflecting film that are the thickness, the uniformity of the thickness, and the spectroscopic reflectance are measured. The absolute value of the reflectivity is estimated to be around 91% immediately after opening the chamber. In order to cover a wide range of observing wavelengths for the Infrared Simulator, and eventually for the optical-IR Subaru Telescope, it is necessary to seek after a higher evaporation rate with these chambers.

Status of the coating facility of the Subaru Telescope

One of the major problems to retain the efficiency of a telescope is to achieve and maintain high reflectivity in the wide wavelengths of the coatings of the telescope optics. For coating the large mirrors of Subaru Telescope, we employed the conventional evaporation scheme, in the expectation of uniform coverage of the film. In this paper, we will report the installation and the performance verification of the coating facility. This facility consists of a washing tower for stripping off the old coating, an evaporation coating chamber, two trolleys and a scissors- like lifter for handling the primary mirror. To supply a large number of filaments loaded with uniform quality molten metal, the practical solution is to pre-wet the filaments with the agent metal and keep them in a controlled manner before the evaporation. The aluminum film deposit on the test samples in the 8.3 m coating chamber proved the film thickness uniformity matching with the specification. Reflectivity of the fresh surface was over 90% at visible wavelength. In September 1997, we re-aluminized 1.6 m and 1.3 m mirrors for the first time (at least for ourselves) application to the real astronomical telescopes. The resultant surface reflectivity confirmed the feasibility of using pre-wetted filaments.

Mirror coating 2003 in Subaru Telescope

The SUBARU Telescope has four focal positions to allow different types of astronomical instrument. At present, there are four different Top Units; three types of secondary mirrors and one primary focus unit. IR secondary mirror which is one of the three units, has silver coated surface. Other secondary mirrors are coated by aluminum for observations at visible wavelength. The silver coating for IR secondary mirror was first carried out in 1999 at the medium size (1.6 m) vacuum evaporation chamber in Mitaka campus of NAOJ at Tokyo JAPAN. Since then the reflectivity had deteriorated over the years. Then, we made a plan to recoat IR secondary mirror in 2003 using the SUBARU’s large-size vacuum evaporation chamber at the summit facility on Mauna Kea, Hawaii. Some tests were performed for silver vacuum evaporation at the base facility, and then the IR secondary mirror was recoated at the summit. The reflectivity achieves 97.6% and 99.3% at the wavelength of 500 nm and 2000 nm, respectively. Degradation of the coat has not been seen 8 months after recoating. We also performed the recoating of the aluminum surface of the primary mirror in 2003. This year we made effort to simplify the procedure. The reflectivity is 91.2% and 97.4% at the wavelength of 500 nm and 2000 nm, respectively.

Silver coating of the Subaru telescope IR secondary mirror

We describe the silver coating of 1.3-m secondary nirror being used for infrared observations at Subaru Telescope. This was the first successful in-house runof silve coating on thelarge moern astronimical mirror. Silver was desposited over the chromium bondange layer, using a 1.6-m vacuum coating chamber at the Advanced technology Center of the National Astronomical Obervatoryof Japan in March 1998. The reflectnc eand scatter performnce are measured by micrScan at 670 nm and 1300 nm. Monitor over 17 month shows the silve coated mirror continues to maintain high refleciton.