World’s Largest Digital Camera Snaps First 3-Gigapixel Images

The SLAC team used a 150-micron pinhole. Left: Schematic of projecting a Romanesco’s detailed texture onto the focal plane. Right: Yousuke Utsumi and Aaron Roodman remove the pinhole projector from the cryostat assembly. (Source: SLAC, G. Stewart, J. Orrell)

Crews at the SLAC National Accelerator Laboratory have taken the first 3,200-megapixel digital photos – the largest ever taken in a single shot – with an extraordinary array of imaging sensors that will become the heart and soul of the future camera of Vera C. Rubin Observatory.

The images are so large that it would take 378 ultra-high-definition 4K TV screens to display one of them in full size, and their resolution is so high that you could see a golf ball from about 15 miles away. These and other properties will soon drive unprecedented astrophysical research.

Next, the sensor array will be integrated into the world’s largest digital camera, currently under construction at SLAC. Once installed at Rubin Observatory in Chile, the camera will produce panoramic images of the complete Southern sky – one panorama every few nights for ten years.

Its data will feed into the Rubin Observatory Legacy Survey of Space and Time (LSST) – a catalog of more galaxies than there are living people on Earth and of the motions of countless astrophysical objects. Using the LSST Camera, the observatory will create the largest astronomical movie of all time and shed light on some of the biggest mysteries of the universe, including dark matter and dark energy.

The LSST Camera’s focal plane has a surface area large enough to capture a portion of the sky about the size of 40 full moons. Its resolution is so high that you could spot a golf ball from 15 miles away. (Source: SLAC, G. Stewart)

The first images taken with the sensors were a test for the camera’s focal plane, whose assembly was completed at SLAC in January. It contains 189 individual charge-coupled devices (CCDs), that each bring sixteen megapixels to the table – about the same number as the imaging sensors of most modern digital cameras.

Sets of nine CCDs and their supporting electronics were assembled into square units, called “science rafts,” at DOE’s Brookhaven National Laboratory and shipped to SLAC. There, the camera team inserted 21 of them, plus an additional four specialty rafts not used for imaging, into a grid that holds them in place.

The focal plane has some truly extraordinary properties. Not only does it contain a whopping 3.2 billion pixels, but its pixels are also very small – about ten microns wide – and the focal plane itself is extremely flat, varying by no more than a tenth of the width of a human hair. This allows the camera to produce sharp images in very high resolution. At more than two feet wide, the focal plane is enormous compared to the 1.4-inch-wide imaging sensor of a full-frame consumer camera and large enough to capture a portion of the sky about the size of forty full moons. Finally, the whole telescope is designed in such a way that the imaging sensors will be able to spot objects a hundred million times dimmer than those visible to the naked eye – a sensitivity that would let you see a candle from thousands of miles away.

“These unique features will enable the Rubin Observatory’s ambitious science program,” said Steven Ritz, project scientist for the LSST Camera at the University of California, Santa Cruz. Over ten years, the camera will collect images of about twenty billion galaxies. “These data will improve our knowledge of how galaxies have evolved over time and will let us test our models of dark matter and dark energy more deeply and precisely than ever,” Ritz said. “The observatory will be a wonderful facility for a broad range of science – from detailed studies of our solar system to studies of faraway objects toward the edge of the visible universe.”

A high-stakes assembly process

The completion of the focal plane earlier this year concluded six nerve-wracking months for the SLAC crew that inserted the 25 rafts into their narrow slots in the grid. To maximize the imaging area, the gaps between sensors on neighboring rafts are less than five human hairs wide. Since the imaging sensors easily crack if they touch each other, this made the whole operation very tricky. The rafts are also costly – up to three million dollars apiece.

Individual imaging sensors and supporting electronics of the LSST Camera’s focal plane are packaged into units, called “rafts.” There are two different types of units: 21 square rafts (center), each containing nine sensors, will produce the images for Rubin Observatory’s science program. An additional four specialty rafts (left) with only three sensors each will be used for camera focusing and synchronizing the telescope with Earth’s rotation. (Source: SLAC, F. Abbott)

The team members spent a year preparing for the raft installation by installing numerous “practice” rafts that did not go into the final focal plane. That allowed them to perfect the procedure of pulling each of the 2-foot-tall, 20-pound rafts into the grid using a specialized gantry.

The focal plane has been placed inside a cryostat, where the sensors are cooled down to negative 150 degrees Fahrenheit, their required operating temperature. After several months without lab access due to the Coronavirus pandemic, the camera team resumed its work in May with limited capacity and following strict social distancing requirements.

Taking the first 3,200-megapixel images of a variety of objects, including a head of Romanesco that was chosen for its very detailed surface structure, was one of these tests. To do so without a fully assembled camera, the SLAC team used a 150-micron pinhole to project images onto the focal plane. “Taking these images is a major accomplishment,” said SLAC’s Aaron Roodman, the scientist responsible for the assembly and testing of the LSST Camera. “With the tight specifications we really pushed the limits of what’s possible to take advantage of every square millimeter of the focal plane and maximize the science we can do with it.”

In the next few months, they will insert the cryostat with the focal plane into the camera body and add the camera’s lenses, including the world’s largest optical lens, a shutter and a filter exchange system for studies of the night sky in different colors. By mid-2021, the SUV-sized camera will be ready for final testing before it begins its journey to Chile. (Source: SLAC)

Link: 10-year Legacy Survey of Space and Time (LSST), Vera C. Rubin Observatory (Cerro Pachón, Chile), LSST Corporation (LSSTC), Tucson, Arizona, USA

Speak Your Mind

*