The camera will explore cosmic mysteries as part of the Rubin Observatory’s Legacy Survey of Space and Time.
Teams from the Department of Energy’s 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 at 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 astrophysics research.
Subsequently, the sensor array will be integrated into the world’s largest digital camera, currently under construction at SLAC. Once installed at the Rubin Observatory in Chile, the camera will produce panoramic images of the entire southern sky – a panorama every few nights for 10 years.
Its data will feed into the Rubin Observatory Legacy Survey of Space and Time (LSST), a catalog of more galaxies than there are people living on Earth and the movements of countless astrophysical objects. Using the LSST camera, the observatory will create the greatest astronomical film of all time and shed light on some of the greatest mysteries in the universe, including dark matter and dark energy.
The first images taken with the sensors were a test for the camera’s focal plane, the assembly of which was completed at the SLAC in January.
“This is a milestone for us,” said Vincent Riot, LSST Camera project manager at DOE’s Lawrence Livermore National Laboratory. “The focal plane will produce the images for the LSST, so it is the capable and sensitive eye of the Rubin Observatory.”
Steven Kahn, director of the SLAC observatory, said: “This achievement is among the most significant of the entire Rubin Observatory project. The completion of the LSST camera focal plane and its successful tests is a huge victory for part of the camera team that will enable Rubin Observatory to deliver next generation astronomical science. “
The Vera C. Rubin Observatory and its LSST camera. Credit: Olivier Bonin / SLAC National Accelerator Laboratory
A technological marvel for the best science
In some ways, the focal plane is similar to the image sensor of a consumer digital camera or the camera of a mobile phone: it captures the light emitted or reflected by an object and converts it into electrical signals which are used to produce a digital image. But the LSST camera’s focal plane is much more sophisticated. In fact, it contains 189 individual sensors, or charge-coupled devices (CCDs), which each bring 16 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 “scientific rafts,” at the DOE’s Brookhaven National Laboratory and shipped to SLAC. There, the camera team placed 21 of them, plus four other special rafts not used for imaging, into a grid that holds them in place.
The focal plane has truly extraordinary properties. Not only does it contain a whopping 3.2 billion pixels, but its pixels are also very small – about 10 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 crisp, ultra-high resolution images. At more than 2 feet wide, the focal plane is huge 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 40 full moons in size. Finally, the entire telescope is designed in such a way that the imaging sensors will be able to detect objects 100 million times fainter than those visible to the naked eye, a sensitivity that would allow you to see a candle from thousands of miles away. .
“These specifications are simply astounding,” said Steven Ritz, project scientist for the LSST Camera at the University of California, Santa Cruz. “These unique features will enable the Rubin Observatory’s ambitious scientific program.”
In 10 years, the camera will collect images of around 20 billion galaxies. “These data will improve our understanding of how galaxies have evolved over time and allow us to test our dark matter and dark energy models more deeply and precisely than ever before,” Ritz said. “The observatory will be a wonderful facility for a wide range of sciences, from detailed studies of our solar system to studies of distant objects towards the edge of the visible universe.”
A high-risk assembly process
The completion of the focal plane earlier this year ended a nerve-wracking six months for the SLAC crew as they inserted the 25 rafts into their narrow grille slots. To maximize the imaging area, the gaps between sensors on neighboring rafts are less than five human hairs wide. Since the imaging sensors break easily if touched, this made the whole operation very complicated.
Rafts are also expensive, up to $ 3 million each.
SLAC mechanical engineer Hannah Pollek, who worked at the forefront of sensor integration, said, “The combination of high challenges and tight tolerances made this project very challenging. But with a versatile team we practically nailed each other. “
Inserting rafts into the focal plane of the LSST camera was a high-risk operation that took about six months. Credit: Olivier Bonin / SLAC National Accelerator Laboratory
Team members spent a year preparing for the raft installation by installing several “practice” rafts that did not fit into the final focal plane. This allowed them to refine the procedure of hauling each of the 2ft 20lb high rafts into the grid using a specialized gantry developed by Travis Lange, chief mechanical engineer of the SLAC’s raft installation.
Tim Bond, head of SLAC’s LSST Camera Integration and Test team, said: “The size of the individual components of the camera is impressive, as is the size of the teams working there. It took a well-trained team to complete the assembly of the focal plane and absolutely everyone who worked on it accepted the challenge. “
Take the first 3,200 megapixel images
The focal plane was placed inside a cryostat, where the sensors are cooled down to negative 150 degrees Fahrenheit, the required operating temperature. After several months without access to the lab due to the coronavirus pandemic, the camera team resumed their work in May with limited capacities and following strict social distancing requirements. Extensive testing is currently underway to ensure that the focal plane meets the technical requirements necessary to support the Rubin Observatory’s scientific program.
Taking the first 3,200-megapixel images of a variety of objects, including a Romanesco head – a type of broccoli – which was chosen for its highly detailed surface texture, was one such test. To do this without a fully assembled camera, the SLAC team used a 150-micron pinhole to project images onto the focal plane. These photos, which can be explored in full resolution online (link at the bottom of the shot), show the extraordinary detail captured by the imaging sensors.
“Taking these images is an important achievement,” said Aaron Roodman of SLAC, the scientist responsible for assembling and testing the LSST camera. “With the rigorous specifications we have really pushed the limits of what is possible to exploit every square millimeter of the focal plane and maximize the science we can do with it.”
Team room in the home straight
As the team completes the camera assembly, more demanding work awaits us.
In the coming months they will insert the cryostat with the focal plane into the camera body and add the camera lenses, including the world’s largest optical lens, a shutter and a filter exchange system for night sky studies in different colors. By mid-2021, the SUV-sized camera will be ready for final testing before starting its trip to Chile.
“The completion of the camera is very exciting and we are proud to play such a central role in building this key component of the Rubin Observatory,” said JoAnne Hewett, SLAC chief research officer and associate laboratory director for fundamental physics. “It’s a milestone that takes us a big step towards exploring fundamental questions about the universe in ways we weren’t able to do before.”
Click the links below to explore images taken with the LSST camera’s full resolution focal plane. Press the “+/-” buttons at the top left of the web viewer to zoom in and out of the images. The characteristics of these images are explained at the bottom of this article
Head of the Romanesco
Photo collage from the LSST Camera team
Detailed features of the pinhole projector images
These are caused by small dust particles or small defects on the intake window. They appear as diffraction rings because the pinhole projector produces a very collimated optical beam, very different from the F # 1.23 beam we have in the Rubin Observatory. The Rubin Observatory images will not have such diffraction rings. The current vacuum window is also a test window. The final window of the cryostat is the third lens of the camera and was made to a higher optical standard than the test window. It will be installed by the end of the year.
These diffraction rings are available in pairs because we applied a simple illumination correction, obtained from a calibration image taken from a white piece of paper. For each image we had to remove and replace the projector hole, so these rings don’t line up perfectly between the two images.
You can also see a lot of cosmic rays in the images; these are small bright spots or short streaks in images from secondary electrons or muons. These occur in all astronomical images and in the Rubin Observatory the images will be detected and masked.
These images were taken with long exposures of 600 seconds, compared to the 15-second exposures planned for our survey, and the longer the exposure the more cosmic rays.
Finally, there is a circular reflection in these images, coming from inside the cryostat. The light from the telescope will be shielded or blurred by the full LSST camera and should not reach this part of the cryostat.