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The big picture: Bay Area space scientists build world’s largest digital camera

MENLO PARK — The universe is about to get its biggest close-up ever.

The most powerful digital camera ever built, now being assembled at SLAC National Accelerator Laboratory at Stanford University, will create a vast panorama of space by taking snapshots of 20 billion galaxies — more than twice as many as there are people on Earth.

With 7,000 unique parts, it will be paired with a telescope “to survey the heavens, looking at every part of the available sky — not just once, but many times,” said Aaron Roodman, professor of particle physics and astrophysics at SLAC/Stanford and the program lead for the camera project.

Seven years in production, the $168 million camera project is almost finished. Next spring, it will be carefully loaded into a protective frame and tucked into a cargo container, then driven by truck to an awaiting 747 chartered jet at San Francisco International Airport for its trip to Chile’s Rubin Observatory. To prevent any collisions on the Peninsula’s crowded U.S. 101 freeway, the camera will be escorted by a car caravan.

“Right now, we’re trying to bring everything together and make everything work,” said Travis Lange, lead mechanical engineer. “This is when things get hard. It’s a little frenetic.”

The camera’s vision is so sharp that it could spot a golf ball from 15 miles away.

But what really matters is its persistence – and its reach.

Once in place, the camera will shoot photos of the entire southern celestial hemisphere. A joint project of the National Science Foundation and Department of Energy, the Legacy Survey of Space and Time (LSST) project will take photos every 15 seconds — accumulating many images, every night, over 10 years.

Its time-lapsed photos will reveal changes in the sky, helping scientists detect exploding stars, stellar collisions, flying asteroids and galaxies that mysteriously dim and brighten. In real time, it will alert scientists to these startling sights.

The many photos also can be stacked atop one another, brightening objects so dim that they’d normally escape notice.

The camera will also probe our own solar system, spotting an estimated six million objects — 50 times more than we can see today.

With a click of its giant shutter, the LSST camera can help answer even deeper questions: What is the universe made of? How do these ingredients interact with each other? Why is the universe evolving, and accelerating its expansion? Do the lumps of dark matter offer clues? And more.

“The discovery potential is fantastic,” said Steve Ritz, project scientist for the camera and a physics professor at UC Santa Cruz.  “We want to find new things. We want to be surprised.”

Unlike the new James Webb Space Telescope, now drifting in space at a location beyond the moon, this camera will live here on Earth, gazing out from the clear dry skies of Chile’s high Atacama desert.

It differs from Webb in another key respect: It will study the entire sky, not a narrow swath. Each night, it will generate 20 terabytes of data.

And, unlike Webb, its data will be shared with everyone. It’s hard to get access to the Webb telescope; scientists must submit their proposals in a highly competitive process. In contrast, the LSST data “is public to the whole U.S. science community, as well as a certain number of international partners,” said Roodman.

Such data sharing “creates a crossroads where different people who have very different interests all work together, trading ideas,” said Ritz. “Crossroads, historically, are where great new things are made.”

The custom-built camera is a behemoth.  The size of a small car, it weighs three tons.

It rests on its side at SLAC’s high-ceiling cleanroom, where workers wear gloves, Tyvek bunnysuits and booties to avoid introducing dust into the delicate machinery.

The telescope’s three giant mirrors, each 25 feet across, will direct light to the camera.

The image comes into focus on the camera’s giant “focal plane” — which, like any digital camera, has sensors.  The size of a sensor dictates the quality of a camera’s images. The sensor in a smartphone’s camera measures a few millimeters; in a professional DSLR, the sensor is 35 millimeters.  By comparison, each LSST sensor is giant — 28 inches.

And it has lots of sensors — more than 200, all stitched together into one giant mosaic.

The camera also has many more pixels than conventional cameras, further enhancing its images. A smartphone camera has about 20 million pixels. This camera has 3.2 billion.

“The larger it is, the more of the sky we can see,” said Roodman.

But the team faced a practical dilemmna. The electronic “noise” of bouncing electrons creates image distortion, said project scientist Yousuke Utsumi. To calm things down, the camera’s sensors must be chilled to minus-150 degrees Fahrenheit,

The camera’s glass filters are made of fused silica, free of impurities. Its shutter — triggered by entering “enter” on a keyboard — will be automated and computer-controlled.

How big are the images? According to SLAC, they’re so large that showing just one of them would require 378 4K high-definition TVs.

This creates a data tranmission problem. Because of the size of each image file, and the need to send it quickly, the typical Internet isn’t good enough. So SLAC will ship the data via thousands of miles of dedicated fiber optic cable.

During the project, the SLAC team has confronted many surprises. A refrigeration system dangerously misbehaved.  And some screws left tiny metal shavings on the precious sensors — requiring a meticulous cleanup, using tweezers and miniature vaccum cleaners.

“You have to struggle with every piece of it,” said Roodman. “Things don’t work exactly the way you expect them to.  So you have to adapt.”

Before departure, the camera will undergo several months of testing, said Travis Lange, lead mechanical engineer. Its route to Chile is already rehearsed, using a box filled with instruments to measure stress.

Long awaited, “it’s just fantastic to see it all together,” said Ritz. “This is a great milestone.”

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