Scopes get repairs after quakes
Hawaiian observatories assess damage and repair telescopes following October 15 earthquakes.
October 30, 2006
When telescopes that can resolve the date stamped on a coin a mile away are bounced up and down, where do you start looking for damage? This is the task scientists, engineers, and technicians have been dealing with since a pair of earthquakes struck Hawaii Sunday, October 15. At magnitudes 6.7 and 6.0, respectively, the quakes were the largest to hit Hawaii in 20 years. While cleanup at Hawaii's observatories will continue for some time, the telescopes escaped with little damage overall.
Mauna Kea, on the island of Hawaii, is the high-altitude home to 13 observatories operated by more than two-dozen agencies around the world. All of the observatories on the 13,796-foot (4.2 kilometers) summit were finished observing for the night when the temblors shook. Most of the telescopes are headquartered in Hilo, on the eastern side of the island, where there was little damage. However, the Canada-France-Hawaii Telescope (CFHT) and the W. M. Keck Observatory operations are based in Kamuela, west of Mauna Kea, where no ceiling tile or bookshelf was left in place.
When the shaking stopped, inspections started. After determining that no one was injured, safety bolts and earthquake restraints were assessed. Most observatories reported loose or broken bolts, and earthquake restraints that did their job. The 300-ton Keck I holds the record, with a horizontal shift of 1 inch (2.5 centimeters), but it is already "back on sky," reports observatory spokeswoman Laura Kinoshita. Drive problems will keep Keck II offline at least until the end of October. The damage to both scopes would have been greater had the quakes hit a few hours earlier, before the equipment's brakes and restraints were locked down for the day.
The James Clerk Maxwell submillimeter telescope (JCMT) was gathering inclonometry data that involves tracking the exact position of the telescope as it moves along the azimuth track. Data from this run showed angle measurements off the recording paper.
Although there were no broken mirrors or charge-coupled devices (CCDs) at the CHFT, technicians found a smashed encoder — a device that tracks the telescope's movement to ensure accurate pointing. Christian Veillet, the observatory's executive director, reported that a new encoder was built within a few days, has been installed, and is working well.
By mid-day Monday, most of the obvious problems had been addressed and technicians could only wait for the weather to clear so telescope pointing and tracking could be assessed. As expected, problems emerged.
Peter Michaud from the Gemini North Telescope explained that once the team corrected for shifting on the scope's alt-azimuth drive, they discovered some problems with the mechanism that controls the secondary mirror. Repairs to this unit should be completed shortly.
When power was interupted, immediate concerns arose about instruments heating up. Some of the telescopes at the summit slumber in air-conditioned temperatures below freezing during the day to keep the equipment near nighttime temperatures. To avoid long cool-down periods and possible damage caused by temperature changes, CCD cameras are kept cool continually when attached to the telescope. CCDs used for infrared photometry are particularly sensitive. Andy Adamson, from the UK Infrared Telescope, reported that the instruments warmed up somewhat but were usable by the time the weather cleared on Wednesday.
CFHT's Veillet reported the system was returning good-quality images with the exception of one set of exposures. These images showed obvious star trails, streaks that indicate tracking problems. Inspection showed a nick on the right ascension drive where the encoder had impacted it. This bump caused the encoder to misread the telescope's location. Until the problem can be fixed mechanically, astronomers will avoid the problem spot.
It appears the most earthquake-hardy instruments on Mauna Kea are the smaller optical telescopes operated by the University of Hawaii and the Very Long Baseline Antenna (VLBA). The latter was able to punch through the cloudy weather and confirm its full operating status early Monday.
Kate Meredith is an astronomy educator in western Wisconsin.