A joint Fermilab/SLAC publication

Giant sky-scanning digital camera taking shape

11/11/10

A monster, 570-megapixel camera that will enable the world's largest galaxy survey is quickly developing.

Images of researchers busily linking together the mammoth camera parts like Lego pieces flashed on the screen during a collaboration meeting last month for the Dark Energy Survey. Scientists from Europe, Latin America and the United States working on this host experiment for the Dark Energy Camera have mapped out the final assembly and shipment of the 4-ton camera that will have the largest optical survey power in the world.

Building and assembling the camera is quite a feat. You won't find the parts you need to peer past exploding stars and patches of dark matter on the shelf at Radio Shack. The camera components are either stretching modern know-how, super-sizing manufacturing capabilities, or both.

The camera has the world's largest shutter and filter, both standing nearly 5 feet tall. The light-sensitive photo chips, called CCD's, are souped-up versions of those in conventional digital cameras. These can see red and near-infrared wavelengths to capture the light of distant galaxies 10 million times fainter than can be seen with the naked eye. The camera will enable the collaboration to peer through 300 million galaxies three-quarters of the way back to the time of the big bang.

 Almost all of the major material components of the camera have been shipped to Fermilab. They were fabricated by SLAC National Accelerator Laboratory, Lawerence Berkely National Laboratory, Argonne National Laboratory, Illinois Institute of Technology, the universities of Michigan, Chicago, Illinois and Ohio State and institutions in Germany, Japan, Spain and Italy.

 The five lens still are being polished in France and will be installed into a corrector in London before shipment to Chile.

Fermilab has taken the lead in building the camera, which functions similar to the three-story detectors at the laboratory's flagship Tevatron collider. The collider detectors take snapshots of particle collisions just as DECam takes snapshots of galaxy clusters and supernovae.

"Studying the universe is a way to study the fundamental nature of matter, space and time, which is what the lab is for," says Craig Hogan, head of the Fermilab Center for Particle Astrophysics. "This is also something that people here are pretty good at. Putting together the Dark Energy Camera is like putting together the collider detectors."

Construction is 80 percent done for the camera and a two-story, rotating ring that mimics the top end of the 4-meter Blanco telescope in Chile. The above Fermilab time-lapse video shows the construction progress. By mounting the camera and conducting initial tests at Fermilab, collaborators avoid the risk of having to build or retrofit parts on a remote Chilean mountain top.  It also allows the crew in Chile to shorten the time it takes to install and test the camera.

"The simulator makes commissioning easier and simpler," says Alistair Walker, DES collaborator and former director of the Cerro Tololo Inter-American Observatory, where the Blanco telescope resides.

More than 120 senior-level scientists plus graduate students and postdocs are working on the camera, preparing the Blanco telescope to hold it and building the computer programs that will distribute its pictures to researchers across the globe. The public also will get to study the camera's images a year after they are collected, just as occurred with the Dark Energy Survey's predecessor, the Sloan Digital Sky Survey.

The first support piece, the platform for mounting the secondary mirror on the camera, arrived in Chile in mid-October. The remainder of the camera will be loaded onto boats and trucks for the long journey to Chile once installation and picture quality tests finish at Fermilab within the next few months.

DES collaborators from Germany built the world's largest shutter for DECam. Credit: Argelander-Institut für Astronomie der Universität Bonn.

DES collaborators from Germany built the world's largest shutter for DECam. Credit: Argelander-Institut für Astronomie der Universität Bonn.

The white ring simulates the top-end of the Blanco telescope where the Dark Energy Camera will attach.

The white ring simulates the top-end of the Blanco telescope where the Dark Energy Camera will attach.

Fermilab astrophysicist Tom Diehl inspects the Dark Energy Camera.

Fermilab astrophysicist Tom Diehl inspects the Dark Energy Camera.

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