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Building the sensor array for the world’s largest digital camera
Astronomical surveys have been instrumental in providing data about the universe, from within the reaches of our galaxy and beyond. Over the years, technological upgrades to telescopes have enabled us to detect and image fainter, smaller, and more distant objects in space.
Under construction in Chile, Vera C. Rubin Observatory’s Simonyi Survey Telescope will peer into space like never before. Scanning the visible sky each night for 10 years starting in 2023, the telescope will offer the widest, deepest, and fastest survey of our universe to provide insights into dark matter and energy, the Milky Way, transient objects, and potentially dangerous asteroids.
A 3,200-megapixel sensor array will enable the telescope to capture this unprecedented view. For nearly two decades, we have been leaders in the conceptualization, design, construction, and qualification of this sensor array and a complementary electronics readout system.
We began this effort by researching different options for sensor and readout electronic configurations, following an initial set of technical requirements we had drafted in collaboration with government agencies and academic institutions. Under our leadership, a Sensor Working Group produced “strawman” designs for two kinds of sensor implementations: charge-coupled device (CCD) and hybrid complementary metal-oxide semiconductor (CMOS). This early-stage exploration led to the selection of a CCD sensor implementation. We also proposed concepts for optimizing sensor thickness and repurposing science sensors (which take the images) as guide sensors (which help steer the telescope). In collaboration with Harvard University, IN2P3 in Paris, and University of Pennsylvania (UPenn), we advanced the sensor mechanical design and electronics design.
As the technical point of contact for the first round of sensor prototype production, we constructed a cleanroom to evaluate whether vendor prototypes could meet technical specifications. On the readout electronics side, we collaborated with Harvard, IN2P3, and UPenn on an application-specific integrated circuit (ASIC) concept. Together with UPenn and Harvard, we produced prototypes of the readout electronics boards to house this ASIC. Moreover, we provided tailored designs for the detector readout system to enable functions such as digitization, clock and bias generation, and thermal control.
We then devised a plan for integrating a set of nine production-ready sensors with the readout electronics boards into a fully testable, autonomous module. Called the raft tower, this module became the building block for the camera focal plane.
To test the prototype sensors and electronics in an environment close to the expected operating conditions of the final camera, we constructed a laboratory with a specially designed cryostat and optical sources. Here, we performed a “vertical slice test” to characterize the performance of a subscale version of the full system with otherwise final hardware. We also built an optical metrology test station to measure the flatness and coplanarity of the sensors over a range of temperatures (77–200 K). By analyzing the data generated in these test facilities, we validated the mechanical and end-to-end (from incoming photons to outputted digital images) electro-optical performance of the focal plane modules. The equipment, test protocols, and analysis methods served as the basis for Brookhaven’s raft production facility, which was later cloned by SLAC and Rubin Observatory.
Examples from our project portfolio
The Instrumentation Division is part of Brookhaven Laboratory's Advanced Technology Research Office.