Large Synoptic Survey Telescope || 3.2 gigapixels Camera ||

The LSST camera is the largest digital camera. Approximately 5.5 feet (1.65 m) to 9.8 feet (3 meters), this is roughly the size of a small car and weighs about 6200 lb (2800 kg). It is a large-aperture, broad-regional optical imager capable of viewing the light from the nearest ultraviolet near near-infrared (0.3-1 micron) wavelength. The camera is designed to provide a view of the 3.5-degree field, its 10 microns pixel, in which 0.2 pencil sensitivity vs. pixel resolution is capable of sampling 0.2 ARCseconds.

The surface of the image is flat with a diameter of approximately 25.2 inches (64 cm). The detector format works as a mosaic of 18 9-16-megapixel silicon detectors arranged on 21 9 rafts, with a total of 3.2 gigapixels available. The camera includes filter-changing mechanisms and shutters. It is located in the middle of the telescope where the cross-sectional area has been compounded by optical widgeting (depth depth) and should be controlled to limit lens-distorted thermal gradients in the coming light.

The LSST camera will produce extremely high quality data with minimal downtime and maintenance.

Animation shows how the camera’s shutter works (L) and how the filter-changing mechanism can change the camera filter (R) robotically.


LSST Focal Plane

The camera’s focal plane is the area in which the light from the telescope mirrors, fixed by the telescope lens, comes to a focus such as the focal plane is the heart of the camera, be protected from billions of distant galaxies as light. Could.

In the camera’s focal placement, the array of charge-coupled device (CCD) sensor runs at approximately -100 ° C to achieve the desired detector performance. Focal plane array is placed in the empty crystall, which includes the front end electronics and thermal control for the detector array. Cryostat lens acts as a vacuum seal for both light entrance window and cryostat.

Similarly, the camera body lens acts as a gateway and gas seal for the housing of the camera, which is filled with dry nitrogen gas to provide an operating environment for the shutter and the filter conversion mechanism. The filter carousel can accommodate five filters, each 75 centimeter diameter, and the filter can be switched robotic in two minutes or less.

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Detector Design – Rafts and Towers

Charged-coupled device (CCD) sensors that make the focal plane of the LSST camera are called rafts on 21 platforms, in which each fleet has 3×3 square sensors, for a total of 189 ccd. Each CCD is composed of 4096 horizontal and 4097 vertical (4 x 4) imaging elements, and 16 outputs, total 144 channels and 3024 channels in the entire fleet add to the entire focal plane array.

Each similar fleet is placed on a tower, which also holds front-end electronics for mounting data readout in the shadow of 3×3 sensor array to reduce the gap between the sensor. To collect high density, flexible cable data in each tower, convert it to a digital format and transmit data acquisition hardware and software, take data for back end electronics from sensors. Coolant straps connect sensors to cooling planes having a fleet of -100 ° C to help prevent noise from the sensor.

Technical Details

Focal Plane Requirements

  • High QE to 1000nm
  • Thick silicon (> 100 µm)
  • PSF << 0.7 arcseconds
    • High internal field in the sensor
    • High resistivity silicon substrate (> 5 kohm/cm)
    • High applied voltages (40 – 50 Volts)
    • Small pixel size (0.2 arcseconds = 10 µm)
  • Fast f/1.2 focal ratio
    • Sensor flatness < 5µm p-v
    • Package with piston, tip, tilt adj. to ~1µm
  • Wide Field of View
    • ~ 3200 square cm focal plane
    • > 189-sensor mosaic (~16 square cm each)
    • Industrialized production processes
  • High throughput
    • > 90% fill factor. 4-side buttable package, sub-mm gaps
  • Fast readout (2 sec)
    • Segmented sensors (3024 total output ports )
    • 150 connections per sensor
  • Low read noise
    • < 10 electrons

Camera Data Rates

  • Over 3 GBytes/sec peak raw data from camera
  • 1 pixel = 2 Bytes (raw)
  • 3.2 billion pixels read out in 2 sec (15 sec integration)
  • Dynamic Range: 18 bits / pixel
  • > 0.6 GB/sec average in pipeline
  • ∼15 TBytes/night
  • 2 TFlops/s average, 9 TFlops/s peak

Focal Plane Design

  • FPA is 189 4K x 4K CCDs, each with 16 outputs
    • 3024 video channels/FPA total
  • Sensors organized into identical rafts of 3 x 3 sensors
  • Clocking of Science CCDs is synchronous and global throughout the FPA
    • 500 kpix/sec * 16 outputs/CCD * 189 CCDs = 3.2 Gpix/2sec
  • A raft is an autonomous object and can function as a complete camera
    • 144 channels/raft
    • readout electronics fit in “shadow” of sensors
  • Raft functions as a dumb slave to OCS
  • 16-bit dynamic range is handled by a single-gain readout

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