Accident Damages Mirror on Telescope Slated for Dark Energy Camera


An accident at the Blanco 4m telescope at Chile’s Cerro Tololo Inter-American Observatory has severely damaged a secondary mirror. The telescope is currently shut down for installation of the highly anticipated Dark Energy Survey Camera, and on February 20, 2012, the telescope’s f/8 secondary mirror was dropped during testing, resulting in fractures in the glass in the center of the mirror. Officials at the telescope said they are analyzing the extent of the damage to the mirror, and whether it extends beyond the visible cracks on the surface. They are also reviewing how the accident might affect the installation of the “DECam.”

Two staff members were injured during the incident, but are expected to fully recover. According to a post on the CTIO website, the f/8 had been removed for the installation of the DECam, and the f/8 was on the dome floor to test the focus mechanism. “The mirror and its back end assembly were being transferred to a handling cart to enable the tests. Unfortunately, the mirror was improperly installed on the cart and when the mirror was being rotated on the cart, the entire cart/mirror assembly toppled over injuring two of our technical staff,” said the report.

The mirror itself impacted the dome floor, causing the fractures, pictured above.

At this time, officials say it is not clear if the mirror is repairable or not and are reviewing what needs to be done to stabilize the cracks in the mirror. The accident is being investigated and initially, officials said they didn’t expect the incident delay the installation and commissioning of Dark Energy Camera as the f/8 is not required for the installation or operation of the Dark Energy Camera system. However, a later update said the DECam installation schedule was being modified to allow for the absence of the f/8 mirror.

The Dark Energy Camera will map 300 million galaxies with an extremely red sensitive 500 Megapixel camera, with a 1 meter diameter, 2.2 degree field of view prime focus corrector, and a data acquisition system fast enough to take images in 17 seconds.

The CTIO website said they would be providing future updates on the status of the mirror and the DECam installation.

Our previous article about the DECam.

8 Replies to “Accident Damages Mirror on Telescope Slated for Dark Energy Camera”

  1. This is a question for the folks on this site who have the technical knowledge of telescope mirrors that I sorely lack: Is something like this RELIABLY repairable? I would assume any repair would result in surface imperfections that were not there previously? I would assume a mirror like this would be quite expensive to replace though, so is it feasible?

    1. Things like this are somewhat repairable, and although i do not know exactly how they will attempt to repair it, i can explain to what consequences it can be repaired.

      1. If the cracks are localised to a small area on the mirror, then the simplest measure is to simply ‘blacken’ it. The loss of light is neglectable if it is only a small area that is damaged, and this will not affect the resulting image much. I cant determine if it is indeed just a small area damaged.

      2. If the damage covers a larger area (i.e. the shape is disfigured beyond just the cracks), but the mirror is not cracked through, the surface might be repolish to the required shape (except for the obviously smashed area). This is similar in difficulty to starting from scratch though, except the mirror does not need recasting.

      I dont know if a mirror can easily me remelted only on certain spots, i doubt it though. The accuracy needed is very high.

    2. The 107″ telescope mirror at MacDonald Observatory has 7 (I think) bullet holes in the surface, the legacy of an employee that went bonkers. The figure was not damaged, and the amount of light lost by the surface area of the bullet craters is negligible.

      So it’s *possible* that the mirror is still usable here. But dropping it on its side is not quite the same thing, so it will have to be examined.

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