The world’s largest digital camera is undergoing final assembly and testing before being shipped to the Vera Rubin Observatory in Chile next year. The camera, dubbed Legacy Survey of Space and Time (LSST), will capture half the southern night sky every three days and has a resolution of 3,200 megapixels.
Just over 14 months ago, the camera’s creators, the Department of Energy’s SLAC National Accelerator Laboratory, successfully tested the camera ahead of its planned installation in Chile in 2022. The camera sensor is an array that contains 189 individual image sensors. The sensors are charge-coupled devices (CCD) that each capture a 16MP image. While SLAC is building the camera, the Department of Energy’s Brookhaven National Laboratory assembles square units of nine sensors, called science rafts, and then sends those to SLAC for final assembly. Each raft costs up to $3M. As you can tell, a lot of different teams and a lot of money have been involved in the project.
Earlier this month, the team experienced a new milestone when both the systems that keep the LSST Camera cool worked together successfully for the time since January. The camera produces about 10 times more heat than other, earlier astronomical cameras. There are two separate cooling systems, the ‘Cold’ system keeps the raft electronics operational and the ‘Cryo’ system cools the camera’s 189 CCDs.
Image credit: LSST / DOE
Following the successful test of cooling systems, the LSST Camera team will now conduct a full suite of Electro-Optical tests to optimize the performance of the focal plane, which includes the CCDs, readout electronics and thermal systems, and then run a series of verification tests which include nearly-final operating conditions. The tests will collect nearly six weeks of data and test for factors like diffusion, read noise, dark or hot pixels or columns, gain, cross-talk, non-linearity, brighter-fatter, and any charge transfer inefficiency.
When photographing half the southern night sky every three days, the camera will record images every 15 seconds. This means that every week, scientists will have a complete, massive, picture of the sky and astronomers, astrophysicists and cosmologists can not only view very distant, dim objects with incredible acuity, but they can also see how the sky changes over time thanks to a regular, consistent image database.
‘We will see dimmer objects than people have looked at before in an area on the sky,’ said astrophysicist Aaron Roodman, lead scientist for camera assembly and testing. ‘People have done things deep, but they’ve been in tiny regions of the sky.’
Image credit: SLAC
The LSST camera has six rotating filters that can be swapped depending upon prevailing sky conditions and the target subject. The filters allow the operator to photograph different wavelengths of light. The camera itself, as we saw last year, is large. It’s 1.65m (5.5′) wide and 3m (9.8′) long. It weighs nearly 2,800kg (6,200 lbs). The camera has a 3.5-degree field of view and its 10 μm pixels can record 0.2 arcsecond sampling. The image area itself has a 64cm (25.2″) diameter. You can read in-depth technical features of the camera here.
The optics attached to the sensor array are equally impressive. The LSST’s lens was delivered in 2019 and includes a huge 1.57m (5.1′) L-1 optical lens and smaller 1.2m (3.9′) L-2 lens. In 2019, the L-1 was described as one of, if not the, largest high-performance lens created.