Report 2: Update on the Status of the Subaru Telescope

(July 14, 2011 Hawaii Time)

Subaru crews have made progress toward restoring the telescope’s operation. This report describes the current condition of the telescope and the prospects for resuming its operation.

1. Affected Instruments and Other Equipment

Inspections located coolant on the following: the primary mirror, some of the actuators supporting the primary mirror, part of the primary mirror cell, and both the optical and infrared tertiary mirrors, the telescope floor, and the auxiliary systems (note 1) of the primary and Cassegrain foci (note 2) as well as two instruments (the Subaru Prime Focus Camera or “Suprime-Cam” and the Faint Object Camera and Spectrometer or “FOCAS”). Crews did not find any coolant on the ground outside the telescope enclosure building. The trace amount of coolant that fell to the concrete floor at the center of the enclosure building was completely removed within hours of the incident. No coolant entered into the ground but was completely contained on the concrete floor before it was removed.

An inquiry panel that includes external members has been established to determine the cause of the leak.

2. Restoration Efforts

Subaru crews are working to clean and restore the operation of the telescope. During this restoration process, open use has been suspended until July 21st at the earliest.

The restoration workvis now focusing on the inspection and testing of the instruments and equipment. On July 6th, crews washed both of the tertiary mirrors with water. The successful cleaning of the aluminum-coated tertiary mirror led to the July 7th water-washing of the primary mirror, which also has an aluminum coating. There are no visible effects either from the coolant or from the washing. Monitoring of the surface of the primary mirror will continue. Crews have removed the instruments and auxiliary equipment from prime and Cassegrain foci. Inspection of each piece of equipment as well as the instruments Suprime-Cam and FOCAS continues.

3. Resumption of Operations

The results of the cleanup activities as well as the outcome of various tests and repairs will establish the schedule for resuming open use observations. Different foci may become operational at different times. The first test observations will be at the Nasmyth focus. Resumption of primary and Cassegrain foci operations may take longer.

Primary Mirror

Photo: A July 11th photo of the primary mirror of the Subaru Telescope after water-washing. Coolant pictured in the first report has been removed, and the surface appears normal.


1. The auxiliary optics systems help to ensure precise observations. The auto guider system operates to accurately track a target object. Another system functions to inspect the shape of the primary mirror and provides correction so that the shape of the mirror is always in its ideal configuration.

Most of these auxiliary optics systems as well as the instruments used to obtain astronomical data (e.g., a camera that captures an image of a galaxy) sit on an instrument rotator that compensates for the rotation of the field of view as the telescope tracks a target. An image de-rotation system is used for Nasmyth focus.

2. The Subaru Telescope enables observations at four different foci. The primary focus at the top of the telescope collects light reflected from the primary mirror and provides a very wide field of view. The primary focus instrument can be exchanged with a secondary mirror, which sends the light back down to other foci. Cassegrain focus is straight down from the secondary mirror and below the primary mirror. When a third, flat mirror is inserted into the optical path from the secondary mirror, it sends the light to the side of the telescope, and one of the two Nasmyth foci becomes available for the observation.

Focal Stations

Figure: Subaru Telescope and its four foci

National Astronomical Observatory of Japan

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